I am actually posting this on behalf of my mate who has a V8 locost. Last year whilst hammering round Castle Coombe he managed to bend the nearside lower wishbone. Now the thinking was that the car had been built by someone else and the wishbones were of unknown quality so both lower wishbones were replaced with items purchased from an engineering company up north (can't remmember the name). To help with any potential problems the wheels/tyres were replaced with 14" lighter items and Yoko 539's and the damper settings were also softened as these were deemed to be set much too firm. However yesterday after a Blat it was noticed that the offside lower wishbone has now gone the same way (although not quite as bad). Does anyone have any ideas as to why this should now be happening?
Rescued attachment Nicks wishbone.jpg

i would contact the company that supplied them myself, im sure they will want to see the part themselves. they would probably be as gutted as your friend.

no idea why it has bent myself, unless they werent designed for v8 use?!

probably not the cause but maybe it has "bumped" on full travel and the wall of the tube had been creased on the edge of the hole in the side panel and therefore allowed it to then bend? Just a guess.

or there is something inherantly wrong with the geometry, ie lengths of bones etc. I would remove the coilover and see if you have free travel to full bump and full droop, compare to the other side too.

Hope you iron it out cos it cant be much fun knowing its going to do that every time your out in it.

[Edited on 13/4/04 by colmaccoll]

Bottom line...

Uncle Rons "design" loads the lower wishbone in bending more than is healthy....usually everyone gets away with it....

Joel

quote:

---

unless they werent designed for v8 use?!

---

I agree with mr meerkat, the lowers arent position perfectly to compensate for the loads, but with the lighter engines, it really isnt a proble, my guess is that the V8's extra weigh is the contributing factor. Next time you build a set of arms, make them thicker walled, or have a double tube (2 side by side or on top) for extra strength.

The recommended diameter can be bought in 3mm wall thickness and should stand up to anything. I think MK have it. You could invest in some oval DOM tube which is supposed to be stronger. It looks like the suspension bracket support plate is the weak point, it is a long way back towards the body and might be somehow levering against the shock mount or weakened by the weld.

with something with the weight of a v8 upfront i would say that the tube is too small in diameter and is not thick enough wall size, would definately recommend 30 x 15 x 2mm as a suitable replacement

RV8 weighs less than a pinto or thereabouts, maybe weak but i would suspect/check for some stiffness, binding, lack of travel locking up solid ect too....

Very very interesting! I was going to use oval for the lower (just using stock ERW for the upper 'bone). I note MK uses oval on the lowers but "alongways" rather than up/down so I'm not sure about getting extra beam strength from it, but should be better aerodynamics! I would not have expected the bend to happen there, I'd have expected it near the shock bottom mounting. And why the back & not the front? Maybe a fat bloke used it as a step??? Perhaps that long weld has "tempered" he tube up to the bending point? I think I'll use inch CDS now i've seen that! It's true the RV8 is very light - IIRC the corner weights for the MGBV8 were within 3lbs of the 1800!
Bob C

Looking at the pic - that wishbone's not the "book" design is it?

The plates much bigger, and not shaped.

Could be important.

Cheers

Chris

Wishbone

Alan,
I am with chrig on this one, I think he has hit the nail on the head. The curve of the reinforcement plate will extend the area of maximum bending, an this will lessen the load on a very specific are of the tube by speading it over a larger area.

I am relying on this as I have a heavy pinto and 19mmx2mm seamless lower tubes!

...........on rejoining the thread after posting, I looked at the picture again, the spring on the coil over looks like it is wound right up, there cannot be much travel or springing action, ALL the load must be on the lower wishbone?

I agree with Mark Allanson. The plate looks bent, as if the suspension has travelled further than the spring would allow. In this case the wishbone would turn into a see-saw and all the stresses generated would concentrate at that point in the tube where it has bent, exactly as detailed in Alan B's sketch.

Would suggest hitting a high curb on an apex or similar would do it, or even the same curb several times.

What I meant was that the area susceptible to bending is larger with the reinforcement with a curve in it than a straight reinforcement, just like alanb's diagram
Rescued attachment Wish Bend.jpg

Guys,

This has obviously rattled a few cages!

To clear some points up.

Our thoughts on the plates being straight edged and not curved were the same, ie with the curve you spread the load a bit more, however the replacements were exactly as per the book and supplied by a Locost part maunfacturer, not home made jobbies. These have the curved edge and yet the tube is still bending. You are right in noticing the plate had also 'dished' due to the load from the shocker but again it was found that the plate used seemed thinner than that suggested by the book and we realised that the shocks were set far too hard. The wheels in use when the attached picture was taken were also 17" fox alloys which weighed about 20kg each with tyres but as said earlier these have been swapped for 14" jobbies weighing around 15kg.

I think the only way forward in this case is to 'beef-up' the tubes and see what happens!

I'll try and get a picture of the latest wishbone failure for you guys to mull-over!

Chris

All good points but still alarming! Al's theory looks plausible but he's had to half the bending strength where the 2mm plate ends to make it work. On the picture the plate extends a good way towards the chassis. And most folk have 275lb springs on there, plus the dampers wound right up. Could it be that a lot of us actually have undamped springing supplied by bending wishbones, not the coilover damper units!!
What a good thread! This is where this kind of forum is worth its weight in gold. However did we manage in the olden days before the internet.......
cheers
Bob C

Is it my imagination or are the front coilovers much more vertical than in the "book"? If the mounting point on the lower wishbone is correct then is the upper mounting too far outboard? looks to me like the shocker is more upright anyway and this will dramatically increase the effective spring rate for a given spring fitted. Very heavy spring rate combined with hitting curbs could have done this. Before we all start worrying, sevens have used this type of wishbone for many years, and other considerably heavier kit cars have used similar designs, so let's not all criticise until we know what we are doing!

With the lower arm folded like that it would bring in the outer side of the arm/shock mount making the shock look like it was mounted more vertically.
I am just at the point of installing rockers for inboard shocks and find all this info great even if my setup is different the same worries carry over to different parts.
Dale

I know what Alan B's talking about and I also take on what Mark Allanson refers to, but I think this particular problem lies elsewhere.
It's of little consequence if the shock bottoms out, so long as the top and bottom shock mounts stay put. I've seen similar cases to this with poorly built home-made off-road cars where the extreme punishment of jumping and general off-road conditions will soon highlight any weaknesses.
I reckon the front wishbone pivot is the trouble. It may be seized, in need of lubrication, or the actual wishbone bracket on the chassis may be off-axis, which combined with a less-than-perfect Metalastic type bush can duplicate the effects of a seized bush.
If the pivot doesen't pivot (properly), then something along the way must bend. Making another new wishbone out of thicker wall tube still may not cure the problem.
If everything is well designed and works properly, 22.2mm or 25.4mm tube with a wall thickness of 1.6mm should be sufficient. I really do think Ron's choice of 19mm x 1.6mm is a little optimistic. Far more strength can be obtained by increasing OD rather than wall thickness.
Forget oval and teardrop tube, it's a wank. It may offer increased resistance if you intending doing lots of nose-first landings off a humped-back bridge, but apart from that, in these circles at least, it's just for poseures.

Guys, just to re-iterate my point....I'm only trying to explain why it bent at THAT location rather the circumstances under which it occured......

What I'm saying graphically is the un re-inforced section is the weakest (obviously) and the the point that it bent was the highest loaded location of the weakest section.....again pretty obvious.

The real question...which everyone is trying to answer, is what caused that loading to by high enough to cause the bending?

While I don't necessarily agree with Rorty's diagnosis it this case, it is true that this is a common cause of part failure....parts which should rotate being subjected to bending loads they weren't designed for.....a famous mining accident was found to caused by this phenomenon, a brake shaft pivot was siezed and was flexing a tensioner rod which should have been pivoting like a rod end...so although the tensile loading on the brake rod was quite low it had bending loads to deal with which were not designed for and hence failed due to fatigue and several lives were lost.

Just to clear up another point......

NO CURBS WERE HIT IN THE MAKING OF THIS WISHBONE

But seriously, the wishbone was fine when Nick (the car's owner) went out of the pits and he felt it go as he turned through Quarry corner at Castle Coombe. The car was 2 up at the time but there was no jumping or curb hitting!

I guess the stiffness of pivots is something that needs checking but remember that the one that went this Monday has only been on there for a couple of months and only done about 50 miles or so since being built!

Chris

The reason why the the wishbone failed where it did is that the end weld to the plate acts as a stress raiser --- a this point the plate weakens the wishbone more than it strengthens it. The grain structure of the steel at this point due to the heat of welding would also reduce the strength of the steel at this point. The plate also ends very close to the point of peak bending moment on the lower wishbone -- all of which is not good design.

The failure probably occured when the suspension hit a minnor bump under braking.

The lower wishbone tube buckled at the corner of the weld to the plate where stress is highest and as a result lost its structural stiffnes and kinked.

Tiger had to recall wishbones after suffering similar faillures

The book wishbones aren't a good design a better design of lower wishbone is sold by GTS -- on Gts wishbones the reiforcing plate dosent end in a sharp right angle at the point of max bending moment.

[Edited on 14/4/04 by britishtrident]

[Edited on 14/4/04 by britishtrident]

I have an RV8 car, and the engine weight is not an issue. Even the vehicle weight should not be a problem, as in a correctly designed wishbone suspension, with the spring mounted so far out, there is very little of the vehicles weight acting directly on the inner bushes or the lower arm itself. The main stresses are lateral loads from cornering and braking. It looks a bit flimsy to me, a combination of heavy braking and cornering would load it up heavily, and as others have said, it is logical that it would bend where the reinforcing plate stops.

Lightweight tubular wishbones are only really suitable when spread further apart at the chassis mount points, making an angle of 90 deg. to each other at the outer ball joint, the loads are then acting directly along the tube rather than trying to bend it. My front suspension is built quite heavily, the unsprung weight penalty is not that significant in a road car, and we certainly have more than enough power to push it along.

Sorry for the long winded post.

Cheers
Bigfoot

I'm not a suspension whizz kid, the following are just my 'feelings' about what may have caused the failures.

In my opinion the loads that have caused the tube to bend are more likely to be in the direction of trying to push the wheel backwards, (hitting kerb, heavy braking ?).

My thinking behind this is as follows:
For the failure to be caused solely by the weight of the car, the vertical force required to bend the wishbone in this manner would be using the suspension lower mount as it's fulcrum. Therefore unless something has siezed / bottomed the suspension would move to relieve the load.
If however the wishbone was to receive a force trying to push it backwards the natural tendancy would be for it to bend at it's weakest point, and away from the vertical force being applied by the weight of the car. This seems to be what has happened.

Or am I just talking B******s ?

Mick

My suspicion is that the damage was caused by a ball joint reaching the end of its travel - I'd check the maximum travel by removing the coil over and lifting the whole assembly manually and seeing what locks up first and where.

I would suggest that's it's not braking - the damage is not what I would expect given the forces applied during braking.

Kingr

I don't buy pivot stiffness - it would bend near the stiff end (!) and you'd never get the bolt in & how can a metalastic joint be stiff - it's just rubber flexing. Ball joint limit could be it but that looks unlikely too, the bending moment would be at least double near the bottom ball joint, also it's traditionally the uppers that bind. From what Chris said about the actual incindent the tube faied in compression! If the brakes are on 1) caliper torque reactiion on front upright is compressing this tube; 2)braking force is compressing this tube; 3) a right hand bend is compressing this tube. A buckling in compression would occur in the middle of the tube and it would buckle downwards because 1) the spring is pushing it that way and 2) that long weld where the plate joins will have warped the tube to have a "belly down " bend anyway.
OK I guess it was a combination of the compression and bending due to beam stress.
I'm right at the point of making my own lower front wishbones & this has been such a valuable "wake up call"
Cheers dudes
BobC

dare I be the one to suggest that these wishbones "supplied by a locost parts specialist " are possibly from Lolocost ??

I think we all have opinions on their products........

I also do not 'buy' the pivot point as being the cause - for the similair reasons.

I think a lot of insight could be gained from jacking the car up and removing the springs/dampers completely and then examing the full range of movement ( not forgetting to check throughout the range of travel of the steering as well!)

My best guess (reasonably pointless based on a single photo) would be that it is a combination of the various attributes of the geometry that are causing a ball joint to reach its maximum angle.

Just an after thought... You say he was going into a bend? was by any chance braking heavily ? the difference in the bend in the 2 sides of the wishbones imply a twisting moment. A combination a big brakes/sticky rubber/heavy car would put some abnormal twisting loads on the wishbones which would add to a basic weakness in the design could lead to this failure ? - just a thought..

HTH

[Edited on 14/4/04 by protofj]

quote:

---

dare I be the one to suggest that these wishbones "supplied by a locost parts specialist " are possibly from Lolocost ??

---

was it daniels engineering?

Ned.

That's it Ned, Daniels Engineering as seen here:

http://web.ukonline.co.uk/members/p.dunn2/new%20web%20page/Locost%20Parts/pictures/depics/traillingset.jpg

Remember though, this wishbone has not failed anywhere near as badly as the one allready shown, but then the car has only been driven on public roads with lighter wheels etc and no track work at all!

Chris

To summerise:
(1) The primary mode of failure was bending from vertical load with additional compressive loads from cornering.
(2) Inital failure initiated by buckling of tube wall.
(3) Failure occured at stress raiser formed by right angle corner formed between plate and tube.
(4) This stress raiser was very close to point of max bending moment


Course of action to avoid future failures
(1) Use tube of slightly larger diameter to increase stiffness and strength in bending.
(2) Use slightly thicker tube to increase ressistance to localised buckling and give a small increase in stiffness and strength in bending.
(3) Re-design plate to reduce angle at which plate meets the tube to reduce the stress concentratio factor and move the corner away from point where max bending moment occurs.
(4) Carefully dress the ends of the welds between the plate and tubes to reduce the stress raising effect.

Notes
(1) If desired DOM tube will give some addional strength but not any increase in stiffness.
(2) Use of oval tube will give little or no structural benefit.

[Edited on 14/4/04 by britishtrident]

[Edited on 14/4/04 by britishtrident]

Hi all,
Looking at how compressed the spring is, I'm wondering what it looked like when the wishbone failed. Must have been almost closed. A shock adsorber without the ability to adsorb shocks?

I'd also like to pick up on a point made by Bob C in that welding a plate on top of a tube tries to bend it upwards.
Is it not better to join onto a tube on it's centre line & fillet weld both sides.
(see pic). Just good engineering practice IMHO.

By the way, tube is 22.2mm dia, 2.5 wall, plate is 4mm thick, stainless.

Paul G
Rescued attachment w-bones s.jpg

Just to expand on the bending vs strength posts I reckon the bending moment at that point is around 960 inch lbs. This gives the following safety margins assuming a 3g bump and that the load is shared by two tubes:-

3/4 - 16g gives 0.75
3/4 - 14g gives 0.88
1.0 - 16g gives 1.42
1.0 - 14g gives 1.70

Less than 1.0 = bent wishbone

The solution appears to be to use 1 inch tube for the lower wishbones.

BUGGER!!

Well, that's about covered it!
Chris_G states the bushes were new and that lubrication wasn't an issue, but doesn't mention the accuracy of the chassis brackets, and Bob C states:

quote:

---

I don't buy pivot stiffness - it would bend near the stiff end (!) and you'd never get the bolt in & how can a metalastic joint be stiff - it's just rubber flexing.

---

Failure in picture is nothing what so ever to do with pivots binding.

As has already been pointed out If binding was the cause the failure would occur where the tube is welded to bush eye as this is where the peak bending moment would occur in this scenario.

In any case if a pivot was sezied I suspect the chassis bracket would be more likely to rip out.

[Edited on 14/4/04 by britishtrident]

OK, here is a picture taken tonight of the new Daniels Engineering wishbone which has failed in a similar way but on the opposite side of the car. We are sure that bottoming out is not occurring and something ammis in the geometry is the current favourite. We will have a look at the measurements against the book at the weekend.

Chris
Rescued attachment New wishbone gone.jpg

GTS wishbone
Rescued attachment bottombone.jpg

I stick to the comments in my first post. This has nothing to do with weight, binding or geometry. The second picture confirms that braking loads are bending the tube. The part simply isn't strong enough. Britishtrident's comments on the design of the reinforcing plate seem reasonable, why not just build a bigger stronger one?

I don't mean to critical of the SVA system in the UK, but we just wouldn't get certification for such a lightweight part over here.

Cheers
Bigfoot

This thread is the first I had heard of bending lower wishbones, is it a recurring problem or just an isolated case?

Quit right Mark! Caterham have used 3/4" tube for 30 years with few failures, yet further up the thread a "calculation" showed that these would bend at 3g accel on the wishbone, I just don't buy this. If it were right then all westfields, Caterhams plus all the locosts would have broken!!!!!!!!!!

If you consider the lower shockabsorber mounting position for a moment, if it were positioned at the lower balljoint position then the lower wishbone would have zero bending stress on it, it would be purely tension/compression. The shocker is mounted very close to the lower balljoint, the stress in bending is not that great, the stress under braking however, is very great! Curbs on must tracks have the ability to bend even tough suspension components if you clip them with the wheels loaded up (rather than unloaded as is the case with the inside wheels when "curb-hopping"

Anyhow, can't be bothered to write anym more, fingers are wearing away!

There is nothing wrong with using 3/4" tube, it just depends how you use it. It's not just a matter of welding up a few bits and pieces, these parts need to be engineered correctly. The failed part in the picture may appear, to the layman, to be the same as a factory part, but the original designer would probably not approve.

Bigfoot.

My locost will be the 4th car that I have built from scratch (well, the locost won't be from scratch), the others having been for rallying and grass oval racing where the stresses involved are much greater, and I Have designed my own suspension each time, and never had a failure. I realise how to engineer suspension but the locost suspension is engineered plenty strong enough for a rover V8 in the front, as was said elsewhere, the Rover V8 is actually about the same weight (110kgs approx) as a pinto.

It was all summed up in Alan B initial post in the the thread.
quote
___________________________________
"Bottom line...

Uncle Rons "design" loads the lower wishbone in bending more than is healthy....usually everyone gets away with it..."
---------------------------------------------------

A Caterham wishbone is VERY different from a Locost one, the position of the coil spring damper monting on the Locost wishbone puts large bending loads on the wishbone, the only way to counter this is to increase the bending strength and stiffness of the wishbone by increasing both tube diameter and wall thickness.

On many Locosts I suspect the front lower wishbone bending gives as much front suspension movement a the spring compressing, this would go a long to explaining why some people are running very high front spring rates without colossal understeer.

An ideal wishbone design will have the lower end of the damper very close to the lower ball joint centre, this removes almost completely bending loads on the lower wishbone tubes allowing them to act an almost pure strut and tie framed structure..

A round tube loaded in bending is not a very efficient structural member compared to square RHS of the same dimensions --- as a rule of thumb 0.75" round tube will fail in bending at 2/3 the load a 0.75" sq RHS will take.
To make a lower wishbone strong and stiff enough in bending both diameter and wall thickness must be increased.


For those who "feel" the failure was due to brake reaction forces may I point out that the front tube of the lower wishbone is under tension when the brakes are applied and the failure is clearly not a tensile failure.
In addition a tensile failure would be more likely to occur on the lower wishbone in the weld between the front tube and the pivot bush tube.

As for theories about ball joints running out of articulation the lower balljoint on Locosts is from a road car a Cortina or Maxi both of which have much greater suspension movement than the Locost.

The upper balljoint (transit drag link) has much less articulation but if it bound up under suspension dive it wouldn't cause a faliure of the lower wishbone.

The most likely scenario is the wishbone started to bend at initial turn in for a corner just after the brakes were released the springs were still compressed after braking and a minor undulation caused the suspension at that side to hit the bump stop. The cornering load placed an additional compressive load on the front tube of the wishbone and together with the spring/damper/bump stop load caused the tube to buckle.

As for the contribution of engine weight the Rover V8 is a very light V8 -- compared to a small block Chevy or even a a 289 Ford BUT it is a heavy engine compared to what the Locost was designed for.

[Edited on 15/4/04 by britishtrident]

Only decent picture I could find of a Caterham wishbone see note how close the lower mount for the spring/damper unit is to the trunnion end of the wishbone.
http://www.carenthusiast.com/caterham/caterham_7_2003_aj_15_250.jpg

I agree with most of your comments B.T. and would agree that it needs a more generous reinforcing plate, which tapers towards the inner bush, but the photo appears to show that it is the rear tube which is bent, not the front. The rear is under compression under braking, not tension. I'll stick with braking forces.

One thing I'm sure we all agree on, the wishbone is not strong enough.

If the RV8 is too heavy for the locost chassis design, then so are many of the other (smaller?) engines in use.

Bigfoot.

The plate isn't a reinforcing plate it actually weakens the wishbone, making it more generous may weaken the wishbone more making it more likely to fail.

The plate should taper off very graually as on the GTS example. As someone pointed out way back ideally it should be welded on to the wishbone tube centre lines not forming a lump the top again in this respect the GTS wishbone follows best practice.

The finish of the weld ends is particularly important -- ideally they should be ground as smooth as possible using a "Dremmel" or Die Grinder to a void causing a sharp edged stress raising feature.

[Edited on 15/4/04 by britishtrident]

[Edited on 15/4/04 by britishtrident]

some more fuel for the fire...
my thoughts on the topic agree with those of BT.

firstly consider the "locost" design, we have a large offset between the outer balljoint and the shock mount and an offset also occurs in a vertical sense between the centre of the outer bj and the centreline of the wishone tubes. Both of these features will introduce undesired bending moments in the wishbones.

Take a look at the SBD wishbones fitted on hillclimb westfields and you will find spherical bearings are used to remove the latter offset and the shock mount is almost coincident with the spherical bearing centre interms of line of action. (i.e. imaginary line the load acts through)

All that as given lets consider the design we have to deal with. Imagine a car taking a corner.

a) brake before the bend.
The reaction of the braking force induces tension load in the forward tube and compression in the reward tube. The bj/tube offset introduced an anount of torsion in both tubes.

b) turn in, and through the bend
The outside front wheel picks up the most weight transfer, thus must react the most force in terms of compression in both tubes. Due to the bj/tube offset a bending moment will also be present tending to bend the wishbone middle toward the ground, this will increase the level of compression in the upper parts of the tubes and decrease it in the lower part.

c) imagine also catching a bump,
we now get a bending moment proporsional to the shock to joints offset again causing the arm to bend toward the ground, so compression in the upper side of the tube and tension in the lower.

Taking a look at the photo at the top of this topic it looks very much like a classical buckle in the upper rear tube, which as described above is the region of the structure carring the most compressive load, eureka. If its gonna buckle then it gonna be the top suface of the rear arm.

Add now BT 'scomments which are spot on. Where you have a weld the material has modified strength and stiffness properties, i.e potentially degraded structural performance.

Where a structure is stiff, load will be attracted. for example a fatter plate welded onto the wishbone will "pickup" more load. This presents a worse problem at the transition to the plain tube as you have more localised loading to distribute.

stress raisers!!!!

Hopefully this makes sense or ive just wasted alot of typing energy!!

Cheers Chaps.

C

p.s i didntmention that because of the offsets hand analysis may be inaccurate, fatigue of vibration..........

p.p.s I do know of people who have had issues of balljoints "bottoming out" and damaging wishbones, it was maily on the upper arm tho. Have a look at the procomp locost racecar upper arm design and the LA Gold.

The bigger=better idea seems to have caught hold of too many Locost builders who apply it to everything in sight. The original Lotus 7 chassis was mainly designed around two very different different engines the Ford 100e sidevalve with a 3 speed Ford gearbox and the 1220cc Coventry-Climax with a BMC A series gearbox. The side valve produced 37 hp and the Climax in race tune about 100 bhp on a good day.
Both engine gearbox combinations weighed a lot less than a Pinto or even an Xflo the Climax with BMC gearbox was about half the weight of a 2 litre Pinto engine with type 9 box..

What made the original 7 fun to drive was good reponsive handling and very light weight

In some areas the Locost/Westfield chassis is better than the Lotus one but in others poor detailing lets it down the wishbones being a prime example. Another is the ridiculous ammount of bumpsteer that dictates the suspension be bone hard rather than the relatively soft ride of the original Lotus built 7.
It is quite interesting to read comparative road test of various Lotus and Caterham Sevens one thing that comes out is that once they get past the sheer blast power of the latest top of the range big engined Caterhams most road tester s seem to preffer the more nimble handling smaller engined models and rate the narrow tyred softer sprung original Lotus models as more rewarding to drive than the latest Caterhams.

The problem these days is lack of suitable engines and gearboxes which are cheap to buy and install as a result the average Locost builder is dropping oversized over weight engines into the chassis without regard to any of the implications..

Taking a leaf from the book of the 750MC racers of old Chapman, Broadley, Terry and Mallock who found that once power and weight started to increase beyond about 140 bhp the simple 7 style spaceframe needed a rethink -- just look at the evolution of the chassis of the Mallock U2 class cars between the first and the last A class car.

My personal solution is a cop out -- My car has relative low power small engine (a 1600 CVH) and fairly minor chassis and suspension mods along the lines of those used by builders in Australia.
Other improvement like getting rid of bump steer and reducing the unsprung weight will give me winter lay up jobs in future years.

[Edited on 15/4/04 by britishtrident]

I agree with you completely, you need a bloody good chassis to fully exploit 150 bhp on either road or track.

Ive been a passenger in a superlight r300 (160 bhp) around a track and it was awesome. Having tried a couple of 140bhp caterham there superb (and i have driven a couple of 190(claimed)hp westfields and alike as comparison.

K series, 4age, thats what you want. modern, light, 140bhp reliably...

Just add to stressy's description of wishbone strut compression - consider the wheel end as a lever with the braking force acting at the contact patch pivots at bottom BJ and top BJ. If bottom BJ is 8" up and top BJ 16" up (guesses) and 1000N braking force applied to the contact patch - leverage says that will be 1000N pushing forwards on top BJ. So there MUST be 2000N pushingbackwards on bottom BJ. It's because the brakes are trying to spin the upright forwards with the wheel. THAT's why I brought up compression loading on the back tube.
I also agree the 7 is supposed to be a light simple car- but I fully understand the lure of a big V8 engine!
Cheers
Bob C
PS 1000N braking force is NOTHING..... say 0.2G..

Quote:

For those who "feel" the failure was due to brake reaction forces may I point out that the front tube of the lower wishbone is under tension when the brakes are applied and the failure is clearly not a tensile failure.
In addition a tensile failure would be more likely to occur on the lower wishbone in the weld between the front tube and the pivot bush tube.

[Edited on 15/4/04 by britishtrident]

quote:

---

Originally posted by britishtrident
The plate isn't a reinforcing plate it actually weakens the wishbone, making it more generous may weaken the wishbone more making it more likely to fail.

The plate should taper off very graually as on the GTS example. As someone pointed out way back ideally it should be welded on to the wishbone tube centre lines not forming a lump the top again in this respect the GTS wishbone follows best practice.

The finish of the weld ends is particularly important -- ideally they should be ground as smooth as possible using a "Dremmel" or Die Grinder to a void causing a sharp edged stress raising feature.

[Edited on 15/4/04 by britishtrident]

[Edited on 15/4/04 by britishtrident]

---

Quote from earlier post
"Caterham have used 3/4" tube for 30 years with few failures, yet further up the thread a "calculation" showed that these would bend at 3g accel on the wishbone, I just don't buy this. If it were right then all westfields, Caterhams plus all the locosts would have broken!!!!!!!!!!"

And if they had been designed along the lines of the Lowcost wishbone a lot of them WOULD have broken. A 3g bump is roughly the upper limit for normal road use. The calculation is telling the truth. The Lowcost book wishbone isn't up to the job, especially if you're going to give it some serious use.

If you look at a Caterham wishbone you'll see that the spring is mounted much closer to the wheel upright which greatly reduces the bending forces on the wishbone.

Another quote
"If you consider the lower shockabsorber mounting position for a moment, if it were positioned at the lower balljoint position then the lower wishbone would have zero bending stress on it, it would be purely tension/compression."

Correct. Do I detect a basic knowledge of beam theory here???

"The shocker is mounted very close to the lower balljoint, the stress in bending is not that great..."

It isn't. It's mounted much further from the lower ball joint than a Caterham.

"the stress under braking however, is very great! Curbs on most tracks have the ability to bend even tough suspension components if you clip them with the wheels loaded up (rather than unloaded as is the case with the inside wheels when "curb-hopping" "

....Maybe. The rear arm of the lower front wishbone is often the most highly stressed part of a car suspension.

I take the point that longitudinal, as opposed to vertical, forces may be the culprit. My calculations still show the relative strengths of the common tube sizes. I'd recommend using 1 inch diameter tube for a Lowcost book wishbone.

Yes, you do "detect a basic knowledge of beam theory"!!!! I do have a little, having designed and built from scratch a few vehicles over the past few years.

quote:

---

Originally posted by jcduroc

quote:

---

Originally posted by jcduroc
OK guys don't laugh because I'm really not gifted for drawing on PaintShop.
This is how I'm making my lower wishbones (Should be completed next saturday).
These are made for the Austin Maxi balljoints (Quinton Hazel QSJ602BLU) and the "things" to the left are the coilover mountings, going down at 45ŗ from the plane of the wishbone; these are intended to be as close as possible to the balljoint "action" point.
The tubes (that thing in red) come as convergent as possible to the same point and are made of 25 mm w/ 2 mm wall thickness (instead of the available 20 x 2.6); as someone said increase the diam. not the wall (moment of inertia).
I'd appreciate your (ponderate) comments on this design.
It would also be very pleasant to see some real calculations on all those bending, torsion, tension and compression loads (strains?) in the "shi...est" situation described: braking (at 1G), taking the bend (1.2 G cornering, please) and hitting a bump (3G vertical?); come on guys, share your skills!...

Joćo

[Edited on 15/4/04 by jcduroc]

---

---

Rescued attachment Img_0067A.jpg

I'm not trying to start an arguement here, but it is a forum.

Nsdev: The pictures would suggest that it is the rear tube which is failing, this is under compression, not tension. This has been established earlier in the thread

Cymtriks: The size of the tube is not the issue, subtle changes in the angles of the tube relative to each other, rienforcing, and the applied loads make a huge difference, if you were to copy the 3/4" Caterham part you mentioned, exactly, it would be fine on the V8 powered car.

Bobc : The alloy RV8 is no heavier that the pinto and other cast iron engines.

There is a lot of phseudo-engineering going on here, there is no mystery, it is just a badly designed wishbone.

Bigfoot (Bigmouth??) :-))

Nicely summarised Bigfoot!!

Thanks mate, I might leave it alone now before I offend someone.

Cheers

Think I better had leave it now too!!

I don't see an argument brewing, just a reasonably informed set of opinions on an important topic. That bottom wishbone always looked like the dodgiest bit of the whole car & I'm pleased as punch that the debate is happening just before I make mine! FWIW I only remember agreeing that the RV8 is very light (approx 150lbs lighter than a 5litre mustang engine!) & I believe anything cymtriks says!
JCduroc that looks like a very nice peice of construction; putting the spring/damper bolt in line with the balljoint will remove the beam/bending stress from the wishbone tubes, but will probably increase the angle of the suspension unit from the vertical leading to a worse "reducing rate" issue under bump. Design is all about compromise..!
Your design is clearly quite different from the book design in this respect so cymtriks analysis won't apply. Unfortunately my mechanical engineering is qualitative beased on experience rather than quantitative based on thorough knowledge of the application of structural analysis so I'm just glad cymtriks is on hand to give authoritative nuggets of wisdom when he does!
Wow long post, all b******t - ain't boddies good stuff! Use inch diam - you know it makes sense......
Bob C

Hi,
I'm coming into this a bit late and I agree with the vast majority of what has already been said. However, for what it's worth I reckon that having the spring wound up so far on the platform must put it close to bind-up under heavy braking/cornering. Could the spring be binding up before the bump stop gets a chance to absord some energy? This would cause a big "spike" in the aforementioned bending loads and could easily cause such a failure.

I'd strongly recommend that you get springs of a higher rating so that you can achieve the same ride height without needing the platforms wound up so far.

Just my thoughts...

By the way, I have a set of Lolocost wishbones and I must say that they are very sturdy indeed and the welding is excellent. The level of "finish" is poor granted and there are other issues which I won't bore you with here but I'd say they are structurally very sound. IIRC they use 22 or 25mm x 2 or 2.5mm wall tubing. I'll check tomorrow.

Cheers,
Craig.

Surely it is better to bugger a wishbone than bugger a chassis. In racing wishbones are expendable items that break/bend rather than bugger an expensive chassis.
Does make you wonder though i must admit as regards what we are actually buying from some places.

I just couldn't stay away, could I? :-)

You are quite right BobC, it is an important issue, and should be discussed, I didn't really see it as an arguement, it's just that I am fairly new around here and I didn't want to get off on the wrong foot. My typing style doesn't always come off as friendly as I would like.

These safety issues worry me a bit though, I am a development engineer these days, but years ago I worked in the motor trade and have advanced trade qualifications. I was also a vehicle inspector, you see some frightening things inspecting cars, and no-one ever thanks you for refusing to sign off an unsafe vehicle. I couldn't help thinking of the consequenses of it letting go at 70+mph in heavy traffic.

Time to go, I am starting to sound a bit too establishment here.

Cheers

ah Bigfoot, another development engineer, me too!!

quote:

---

Originally posted by craig1410
Hi,
snip

I'd strongly recommend that you get springs of a higher rating so that you can achieve the same ride height without needing the platforms wound up so far.

snip



Trouble with fitting harder springs to the front it will or at least should cause gross understeer, using longer springs and adding more bump stop rubbers may be another approach.

However consider the fact that most builders already use springs that are much higher a rate than normally sensible for the weight of the vehicle and the handling balance of the Locost appears from reports to be quite unresponsive to large changes in spring rate at one end --- in one Locost build diary I came across a builder who had change the fronts from 180lbs/i to 380lbs/i to (I quote) "cure bad understeer" !!!??

The extreme angle at which the front springs are mounted dosen't help but I suspect a lot is down to flexing of the front wishbones and spring attachment points.

Yonks+ages ago I used to race Imps and Davrians cars of a similar weight range to the Locost, I found that even a 10lb/in change in the spring rate at either end would alter the handling balance --- good evidence the chassis and wishbones were more than stiff enough. For race springs on the Davrian we ran 190 lb/i on the front 240 lb/in on the rear.

[Edited on 16/4/04 by britishtrident]

[Edited on 16/4/04 by britishtrident]

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britishtrident - 16/4/04 at 08:09 AM

jcduroc --

I like where the bottom of the damper mounts it brings the line of action of the force close to the ball joints centre line.

You could cut/grind away quite a bit of metal as the vertical plates approach the ball joint centre line without affecting the the strength/stiffness.

Add a couple of nicely chamfer webs down from the wisbone tube to the damper mount and it looks good.

(also nice welding !)

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JoelP - 16/4/04 at 08:12 AM

that is one benefit of the maxi ball joint over the cortina one, due to it being smaller you can get the shocker closer to it. I made mine so close that the spring nearly hits the upper wishbone in droop! but i think thats because my top mounting point is quite far out. With a maxi ball joint you could have the points in line nearly, if you follow my drift.

BTW, how many of you dreamed about failing wishbones last night!?!?!? i certainly was pushing the car home in a dream...

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craig1410 - 16/4/04 at 05:12 PM

I suppose what this goes to show is that perhaps we should all consider a track day, and subsequent inspection, as an essential post-SVA (or even pre-SVA if allowed?) test of the car and its integrity. It's also perhaps a good test of our own driving skills too as many/most folk probably haven't ever driven a powerful rear wheel drive vehicle and as we who have know, it's a bit different from your average 100BHP FWD car...

If nothing fails or bends after a hard blast around the track then it should handle anything that the road throws at it, and if anything does fail on the track then it's bound to be safer than a similar failure on the road. Obviously a progressive approach to testing would be wise before very high speeds are involved...

Cheers,
Craig.

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blueshift - 16/4/04 at 06:03 PM

mackie and I plan to take ours on a track day as soon as we get it finished, as much because of fear of the handling and 200bhp going through the back wheels, as mechanical worries.

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craig1410 - 16/4/04 at 07:24 PM

Blueshift,
The only thing I'd perhaps get checked before any serious mileage is the wheel alignment as otherwise it might tend to eat the tyres... Obviously with the de-dion rear end the alignment is fixed but mine is fitted with adjustable length trailing arms so I need to make sure that the footprint is square.

Apart from that, hit the track and see what falls off...

Have you guys started building your chassis yet then?
Cheers,
Craig.

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NS Dev - 16/4/04 at 09:59 PM

Just to throw yet more petrol on the bonfire!! Just been looking at some Westfield wishbones and the shocker mounting point looks the same as the "book" locost one (without the benefit of a ruler)

Also just put the deposit on my Stuart Taylor IRS chassis/body set.

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blueshift - 16/4/04 at 11:20 PM

craig, not quite.. but I have gathered the materials for the build table and starting the chassis is the next thing on the todo list. I've been busy the last couple of weeks, and bashing my road car in the spare time (see thread in "anything else" - it's buggered)

one day

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britishtrident - 17/4/04 at 06:30 AM

quote:

---

Originally posted by NS Dev
Just to throw yet more petrol on the bonfire!! Just been looking at some Westfield wishbones and the shocker mounting point looks the same as the "book" locost one (without the benefit of a ruler)

Also just put the deposit on my Stuart Taylor IRS chassis/body set.

---

Locost chassis =original prelit narrow body Westfield in all but a couple of very minor details

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NS Dev - 17/4/04 at 09:13 AM

sorry to keep the bonfire going then but does that not contradict this????

quote:

---

Originally posted by cymtriks
Quote from earlier post
"Caterham have used 3/4" tube for 30 years with few failures, yet further up the thread a "calculation" showed that these would bend at 3g accel on the wishbone, I just don't buy this. If it were right then all westfields, Caterhams plus all the locosts would have broken!!!!!!!!!!"

And if they had been designed along the lines of the Lowcost wishbone a lot of them WOULD have broken. A 3g bump is roughly the upper limit for normal road use. The calculation is telling the truth. The Lowcost book wishbone isn't up to the job, especially if you're going to give it some serious use.

If you look at a Caterham wishbone you'll see that the spring is mounted much closer to the wheel upright which greatly reduces the bending forces on the wishbone.

Another quote
"If you consider the lower shockabsorber mounting position for a moment, if it were positioned at the lower balljoint position then the lower wishbone would have zero bending stress on it, it would be purely tension/compression."

Correct. Do I detect a basic knowledge of beam theory here???

"The shocker is mounted very close to the lower balljoint, the stress in bending is not that great..."

It isn't. It's mounted much further from the lower ball joint than a Caterham.

"the stress under braking however, is very great! Curbs on most tracks have the ability to bend even tough suspension components if you clip them with the wheels loaded up (rather than unloaded as is the case with the inside wheels when "curb-hopping" "

....Maybe. The rear arm of the lower front wishbone is often the most highly stressed part of a car suspension.

I take the point that longitudinal, as opposed to vertical, forces may be the culprit. My calculations still show the relative strengths of the common tube sizes. I'd recommend using 1 inch diameter tube for a Lowcost book wishbone.

---

If (as BritishTrident correctly says) the westfield prelit wishbones are the same as the locost (as good as anyway) and therefore the Caterham too (as they were a copy, hence the litigation!) then surely my point about the design holds?!

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craig1410 - 17/4/04 at 09:43 AM

Hi,
Here's a sire showing some nice pics of a Westfield chassis for comparison. It certainly does look very similar to the Locost...

http://home.iprimus.com.au/flaherty/westfield/index.htm

Cheers,
Craig.

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britishtrident - 17/4/04 at 09:49 AM

quote:

---

snip
If (as BritishTrident correctly says) the westfield prelit wishbones are the same as the locost (as good as anyway) and therefore the Caterham too (as they were a copy, hence the litigation!) then surely my point about the design holds?!

---

errr no I did imply Locost wishbone were copies of Westfield -- I dont know if extent of the copy the extended to tube wall thickness.

Westfield wishbones are totally diferent from any used by Cateham or Lotus.

The history behind this
Original Seven S1 used Hillman Minx king pin style uprights (as on original Elite) which were quickly changed for smaller lighter Triump Alford & Adler units.. The Triumph upright has a ball joint at the top but a threaded bronze trunnion with delrin bushes at the bottom.


S1 Lotus started out with a steering box but modified to use a steering rack mounted behind the axle centre line. Together with the positioning of steering arms used this gaves toe-in in turns as used on the Lotus 18 racing car.

S2 Moves steering rack to where it is on current Cateham (and Locost) ahead of axle centre giving more conventional semi-akerman geometry..The suspension was tidy up a bit but remained much the same through the S3 and first 20 years of Caterhams.

S4 Used Triumph uprights but with Europa lower wishbone and I think baby Elan upper wishbones.

Caterham later models -- anti-roll bar now seperate from upper wishbone, lower wishbone redesigned.

Westfied -- Original cars (7 & 11) based on MG Midget/A-H Sprite used king pin suspension, with very nicely designed fabricated wishbones.
Due to shortage of donors this was adapted to Cortina ball joint suspension, the adaption was not so carefully thought out or detailed as the original Sprite based Westfield suspension -- hence massive bump steer. This later Westfield suspension is very similar to the book Locost but as I said I don't know if this extended to checking the tube thickness -- I suspect not.

Also the pre-lit Westfield/Locost chassis is not anything like a Caterham chassis. Caterhams law suit was based on the ancient offence of "Passing Off" .

[Edited on 17/4/04 by britishtrident]

[Edited on 17/4/04 by britishtrident]

[Edited on 17/4/04 by britishtrident]

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NS Dev - 17/4/04 at 09:59 AM

Ahhh, it's all becoming clear!

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Peteff - 17/4/04 at 11:18 AM

That's why they were sued for making it as Caterham had paid for the design from Lotus. I think the original case was amended to stop them using the '7' as it was copyrighted. It was smaller than the present chassis which is almost a Locost chassis. A friend down the road has a live axle Westy and without the bodywork on you could not tell it from a Locost and the suspension parts are very similar. The bar across behind the seats where the roll bar and rear shock top mounts is 2"x1" and is a solid bar not a tube, that's about the only difference. The front wishbones on a Caterham are totally different and look spindly compared to locost with only a tube joining the two sides but the shock mount is at the very end near the joint and bolts through the sides with a strengthening spacer tube.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2473427458&category=9886
Look at these before they go.

[Edited on 17/4/04 by Peteff]

[Edited on 17/4/04 by Peteff]

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eddymcclements - 17/4/04 at 12:19 PM

In reply to the original question, here's my tuppence worth....

Both the original wishbone of unknown origin and its replacement have failed in similar ways - this reduces the possibility of a faulty component.

Components common to both failures are:- hub, upright, damper/spring, top wishbone and chassis. The wheel/tyre combination was changed and the dampers were softened.

Under braking the lower wishbone rear tube is in compression, but if the tube is perfectly straight it ought to be able to withstand high forces without bending.

Chris_G says that the damper isn't bottoming out - I assume this has been checked with a tie-wrap round the damper rod, a brisk drive round a challenging route and a subsequent check of the position of the tie-wrap to make sure it's not been pushed right up against the top bump-stop. If it hasn't, then the damper isn't bottoming out, however (and this has already been mentioned) this doesn't prove that the spring isn't going coilbound.

Roll a piece of blutak into a fat snake, wrap it round one of the spring coils and go for the brisk drive again. On your return check to see if the "snake" has been nipped in two by the coils touching each other - although the damper has been softened you don't say if the springs have been changed, nor what their rate and free length is. From the photo I have to say that it looks like a 6" spring has been fitted where a 7" or 8" spring might be better.

When a spring goes coilbound the damper/spring becomes totally solid, and you've just hit a bump then something else has to give. On the book design the shock mount on the lower wishbone is a lot further from the bottom balljoint than on, say, a Caterham. A high instantaneous loading (big bump) coupled with a solid (coilbound) shock might be enough to cause a bent wishbone in exactly the place that this has occurred. Even if only a slight bend appears initially, each time you brake you are feeding quite a large load into a tube which is no longer straight and whose resistance to compression forces is drastically reduced.

Eddy

Edited to remove typos!

[Edited on 17/4/04 by eddymcclements]

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britishtrident - 17/4/04 at 12:25 PM

quote:

---

Originally posted by Peteff
That's why they were sued for making it as Caterham had paid for the design from Lotus. I think the original case was amended to stop them using the '7' as it was copyrighted. It was smaller than the present chassis which is almost a Locost chassis.

snip

---

Westfield started building a Lotus Eleven replica to which nobody had any objections.
It then gave birth to the Lotus 7 S1/S2 replica, the chassis was almost identical to the Eleven replica and had all the features present in the book Lowcost chassis but slightly narrower to suit the MG Midget axle..

The Lotus S3 chassis as made for Caterham at the time was a very sparse spaceframe, it was mainly made of 1.8 swg round tube with brazed joints.

Working from the front of the chassis the front bay of the spaceframe was very different from any Westfield because the suspension design was completely different.

Apart from the different type of tube used the engine bay areas were similar on the Lotus/Caterham chassis and the Westie/Locost, however the big difference starts from the front footwells back, the Lotus S3 chassis lacks any centre backbone structure --- I seem to remember the floor was supported by 0.5" angle iron and the propshaft covered by a minimilist bit of bent 1.2mm alloy sheet with a curved steel plate where the diff nose pokes into the passenger compartment.

The area to the rear of the passenger bulkhead is superficially similar on the Lotus chassis but because the Lotus/Caterham suspension dosen't use a panhard rod the load bearing structure stops at the rear bulkhead and there is no triangulation.

Why Caterham had any case at all was because Chris Smith was selling the original Westfields as "a Lotus 7 S1 Replica" on the grounds that Caterham had the rights to the S3 and S4 models but not the S1. I had a copy of the brochure and it actually stated in this . Gradually the Westie became less 7 S1 like and more like a 7 S3 until Caterham sent for "lawyers guns and money". Caterham had a very shakey case on copyright grounds because the two chassis were different and other spaceframe clubman cars had existed before and after the Lotus 7 was built, but they had much better case on the lesser offence of "passing off".

When the matter was settled out of court the main terms were that original Westie chassis jigs brocken up and Westfield could no longer sell as a 7 replica and had to create thier own identity --- hence the new body work. However the new Westie SE chassis was essentialy just a very slightly wider version of te original Westie 7 S1 chassis.
Looking back Westie came out the litigation significanly better than Caterham, the litigation put Westfield on the map, gave them street cred and forced them to move more up market.
Interestingly post ligation Caterham chassis has changed significantly and has borrowed features found in other 7 style cars :-)

One other thing Caterham isn't the sole holder of rights to the 7 design, somebody in NZ has was producing S4 chassis powered by 907 engines with a Lotus stamp of approval but the project stalled, and I suspect there may be others.
A question has also be raised as to wether Chapman had the personal ownership of the rights which sold to Caterham or if in fact they belong to the Lotus Group. The complex business deals of "Chunky" and his mate Fred Bushell are a mystery of the grave however Caterham apparently paid Chapman personally not Lotus Group, Lotus Cars, Lotus Components or Team Lotus.


[Edited on 17/4/04 by britishtrident]

[Edited on 17/4/04 by britishtrident]

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craig1410 - 17/4/04 at 02:12 PM

Eddy,
I'm glad someone else agrees with my analysis...

It seems the most likely explanation (coil binding that is) given the reasons you stated above. I never agree with second guessing an established design, however marginal, when there is little history of failure of that part. Certainly you can get a one-off failure due to material defects or poor workmanship but two in a row in exactly the same place seems unlikely to be caused by the item which is failing.

Good advice with the bluetak fat snake technique by the way. I think this would be very worthwhile trying and in any event a more appropriate set of springs should be fitted whatever the outcome as these springs must be getting close to coil bind even if they prove not to be binding completely at present.

Coil bind is most likely to happen under "continuous" force such as extended braking or cornering where the damper has time to move. If you then had a bump of, say, 1 inch which would normally be absorbed without any trouble, all of this energy will go into bending something and due to the design issues discussed earlier, the most likely place to bend is exactly where the failure is taking place.

If the car has been coilbound then you should carefully examine all of the other suspension components for bending and/or fatigue cracks. Also check the mountings for same.

Cheers,
Craig.

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NS Dev - 18/4/04 at 09:31 AM

quote:

---

Originally posted by craig1410
Eddy,
I'm glad someone else agrees with my analysis...

It seems the most likely explanation (coil binding that is) given the reasons you stated above. I never agree with second guessing an established design, however marginal, when there is little history of failure of that part. Certainly you can get a one-off failure due to material defects or poor workmanship but two in a row in exactly the same place seems unlikely to be caused by the item which is failing.

Good advice with the bluetak fat snake technique by the way. I think this would be very worthwhile trying and in any event a more appropriate set of springs should be fitted whatever the outcome as these springs must be getting close to coil bind even if they prove not to be binding completely at present.

Coil bind is most likely to happen under "continuous" force such as extended braking or cornering where the damper has time to move. If you then had a bump of, say, 1 inch which would normally be absorbed without any trouble, all of this energy will go into bending something and due to the design issues discussed earlier, the most likely place to bend is exactly where the failure is taking place.

If the car has been coilbound then you should carefully examine all of the other suspension components for bending and/or fatigue cracks. Also check the mountings for same.

Cheers,
Craig.

---

Couldn't agree more craig! you have pretty much hit the nail on the head that I have been trying to get over but getting shot down all the time! As you say, the continuous loading of a corner and then running over a kerb at the exit perhaps would be the sort of situation where the spring might go coilbound and bend something, possibly, maybe.......

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craig1410 - 18/4/04 at 12:10 PM

Anyone fancy estimating the peak force exerted on the end of the wishbone assuming the spring has gone coilbound and assuming a 50mm bump is hit at 60MPH. Assume the bump is a saw tooth kerb with, say, a 50mm linear rise for 300mm travelled. Assume a static corner weight of 175Kg's and obviously when coilbound there are no spring or damper effects to worry about.

The static loading would be about 1750 Newtons but under braking the weight transfer would increase this. I don't know how much weight transfer you would get with a Locost but lets say the corner weight would increase to 200Kg's and use that figure for the bump impulse calculations.

If we figure out the force and then measure the distance between the tyre contact patch and shock absorber mounting this should give us the torque being applied to the wishbone and from this we should be able to figure out the stress on the wishbone tube.

I'll have a go at estimating it later but duty calls (aka the wife)...
Cheers,
Craig.

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Chippy - 18/4/04 at 10:53 PM

As a new, read old, member of the Locost builders forum I would very much like to know if other builders have suffered the problem of the fron wishbones bending. I have just attained my donor, a 1990 Sierrs 4x4 2.9i, and with that weight in the front would like to be sure that the front isn't going to fold up.

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NS Dev - 18/4/04 at 11:21 PM

Don't know, but good point, I'm sure others have used this engine and it'll be about the heaviest you could put in there!

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Chris_G - 28/4/04 at 10:25 PM

Update time......

We tried the bluetack sausage experiment and found that there was no evidence of the coils even getting close to binding!

With the shock disconnected the wishbone/upright assembly moves freely throughout its travel!

So, onto some reinforcements. It was quite scary just how easy the original tube was to bend back straight again! (maybe this tells us what the problem is!)Nick had some 1/4 inch thick steel angle iron seam welded to both bottom tubes and also across the plate below the shock mount. So far, so good! We've been out on a few good blats together (me in my Westy as back-up!) and we were even prepared to go around Castle Combe on Saturday but it was a bit busy there for our liking so with some fast road fun everything seems to be holding up.

Time will tell, but confidence is building once again
Rescued attachment wishbone mod1.jpg

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Chris_G - 28/4/04 at 10:25 PM

view from the front.....
Rescued attachment wishbone mod2.jpg

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skinny - 29/4/04 at 04:02 PM

just thought i'd add my 2p, sorry if i am just re-hashing what has already been said, esp by trident, i am not trying to steal anyones thunder...

the way i see it, the original failure could have been caused simply by hard cornering and an insufficient wishbone diameter.

i don't think braking, bumps, binding bushes, high sprung mass etc are at all to blame, it's a simple matter of geometry.

Talking about the outer (loaded) wheel here, under reasonable cornering, the wheel will be forced upwards relative to the rolling body, and this will be resisted (with no roll bar) purely by the spring pushing it back down again. With this design, the wheel forces operate at the very end of the wishbone, and the opposing spring forces are spread over the wishbone thru the plate.

so you have the inboard mount as your datum, approx 2/3 of the way along you have a significant component of spring force pushing downwards, and at the other end you have the wheel forces pushing upwards. it seems fairly obvious that there are going to be large stresses doesn't it? the only way to completely eliminate or cancel these moments is to have the suspension mounting point and the upright mounting point at the same location as trident has said.

as far as i can see, with that design, it's perfectly sufficient any of only
1) excessive spring rate (not necesarily reaching full spring travel but of course this would accelerate the problem)
2)high mass and heavy cornering leading to a high roll angle
3) insufficient strength of wishbones
in various degrees would cause this to happen.

sorry if i am just stating the obvious or if i have made any glaring errors (just trying to collate my thoughts & finish this before i get off work).

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drmike54 - 29/4/04 at 04:19 PM

One thing that I have been wondering is what is the condition of the top shock mount? With all of this stress on the wishbone isn't the top shock mount the fulcrum? Apparently the forces are high enough to bend the wishbone, yet not enough to rip the top shock mount off the chassis.

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Alan B - 29/4/04 at 04:29 PM

Skinny....yeah that's pretty much what I said early in the thread....

No need to look for mysterious scenarios...the basic design is flawed...too much bending (yes I know it largely can't be helped)

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skinny - 30/4/04 at 08:37 AM

yeah, sorry alan, you did say that too, as did a few others, just thought i'd agree with you all

under cornering there would also be the lateral component adding (in a way - when the wishbone has deflected) to the bending moment which probably wouldn't much help the wishbones.

just wondering, the bending stresses within the wishbone (due to cornering at least, tho of course not and dive under braking etc.) would be significantly reduced with an anti roll bar mounted as close to the ends of the wishbones as possible. maybe you could get away with lower spring rates then too?

[Edited on 30/4/04 by skinny]

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NS Dev - 30/4/04 at 10:36 PM

quote:

---

Originally posted by Alan B
Skinny....yeah that's pretty much what I said early in the thread....

No need to look for mysterious scenarios...the basic design is flawed...too much bending (yes I know it largely can't be helped)

---

I know we are going round in circles again but if this is right, why haven't everybody's wishbones bent? There are a hell of a lot of these cars about now!!!

Why the one off??

I can see the design problems (anybody with 1/2 an ounce of mechanical sense can) but if they are the sole cause then there would be many failures!!!!

---

Bigfoot - 1/5/04 at 02:06 PM

Going round in circles is not necesarily a bad thing, it has been an interesting debate. Some good points have been made, but I am sticking to my original opinion.

Way back in the thread my suggestion was that the part was simply not strong enough. I accept that it is made from the same materials as a successful production part, but that does not make it as durable. Engineering is more subtle than that, if it wasn't, people like me would not make a living.

With the benefit of experience, at first glance it does not look strong enough, even before you start to analyse it. If it holds together with the extra bits welded on, that would surely confirm that it was simply not strong enough.

If that is the case you have two options, either make it from more robust materials, or design it better. Given that most locost builders do not have the facilities to refine their designs to perfection, The sensible option is to build it stronger. there seems to be an unhealthly desire to make these things too light, this isn't Formula 1, you really won't notice the difference of a few pounds in the type of driving you will be doing. Does it handle any different since you welded the extra bracing on?

Cheers
Bigfoot

---

Alan B - 1/5/04 at 02:48 PM

quote:

---

Originally posted by NS Dev
I know we are going round in circles again but if this is right, why haven't everybody's wishbones bent? There are a hell of a lot of these cars about now!!!

Why the one off??

I can see the design problems (anybody with 1/2 an ounce of mechanical sense can) but if they are the sole cause then there would be many failures!!!!

---

Yes, good point. The lack of other failures is hard to explain.

---

Terrapin_racing - 4/5/04 at 02:10 PM

You can also increase the strength of the standard dimension wishbones considerably by having them Nitrotec'd.
It's a fantastic process - I tried to destruction test a Terrapin wishbone post treatment - no chance. Also burnt out three TN treated drills drilling a hole oversize!
Mine were done by Nitrotec in Birmingham (Steve Plum was the contact)

NITROTEC SERVICES
UNITS 5-8
WITTON INDUSTRIAL ESTATE
BICKFORD ROAD
BIRMINGHAM B6 7EF

TEL:0121 322 2280

http://www.nitrotec.co.uk/properties/properties_frames.htm

see chart:

When non-alloyed steels are rapidly cooled after Nitrotec treatment, strengthening of thin sections occurs. This results in an increase in both the yield strength of the base material and its fatigue strength.



Yield Strength
The nitrogen enriched substrate that results after Nitrotec treatment enhances the yield strength of thin section component. With thin sheet metal components this can be increased by up to 4 times for mild steel sheet materials. Parts produced in 3mm and 2mm thick materials can be reduced to 1.5mm and 1.mm thick material and in some instances as low as 0.5mm thick.

[Edited on 4/5/04 by Terrapin_racing]
Rescued attachment sprofiles_graph.gif

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crbrlfrost - 4/5/04 at 04:21 PM

Wouldn't that be the same as the older nitriding process used for crankshafts and such, with the exception that with thin sections you would be hardening a greater percentage of the component (in thick sections it usually only penetrated 20thou or so). My concern would be the trade off between strength and toughness as I'm sure some of these track cars could be subjected to relatively large impact loads. When the wishbone is used under the fatigue limit with only a few mild strikes I wouldn't see an issue, but since we've generally come to the conclusion that its underdesigned and probably flexing significantly, a hardened surface with increased brittleness would cause me some concern. But do keeps us posted, I'm very curious.

---

britishtrident - 4/5/04 at 05:00 PM

Re Nitrotec process looks like Tuffriding ie nitriding forn normal mild steel, personally I would be very reluctant to use it on a welded component.

---

craig1410 - 4/5/04 at 10:25 PM

Yeah, does that mean it will snap instead of just bending? That could be seriously scary!

Interested to learn more though so don't mistake my comment for cynicism...
Cheers,
Craig.

---

Terrapin_racing - 5/5/04 at 11:00 AM

Well, the F1 teams have used it and now a number of the university teams competing in Formula Student are doing so also. No failures reported.


Car 12
May 1st 2002

Car 12 marks the fifth generation of UBRacing car and is based strongly on evolution not revolution. The team is made up of 14 Mechanical Engineers in their final year of BEng and MEng courses. The small team was divided into four design groups, Engine, Suspension, Chassis and driver environment and Drive train. These design groups along with regular whole team meetings have enabled the team to produce the most integrated and well-developed car to date.

The design philosophy was centred around the use of CATIA for the purpose of design integration, design analysis and parts management. The main vehicle concepts that have been designed in from day one are, reliability, innovation, manufacturability, driveability and easy of maintenance and of course performance.

Key design features include in house magnesium cast wheels, an evolution of the rear load transfer device first seen on last year's UBRacing car, integrated uprights and callipers and MMC brake disk with a Keronite coating. The drivetrain has also received considerable attention with an in-house miniaturised differential housing and lightweight CV housings. Engine developments include a vortex induction plenum, rapid prototype injector housings and a carbon fibre restrictor.

The team completed their goal of early car completion, with the car being launched on the 20th of March. The early launch was achieved due to the team's philosophy of design for manufacture, extensive use of in-house facilities and manufacturing planning. This has given the team sufficient time to fully test and develop the car.

The team feels that as a consequence of its integrated design approach, extensive use of CATIA for the purpose of drafting and finite element analysis and design for manufacture philosophy, a car has been produced that has both very high performance, but is innovative and reliable.

Chassis
- Lightweight T45 / mild steel space frame
- Aluminium bonded and fully stressed honeycomb floor

Engine
- Honda CBR600 FX
- Fuel injection with MBE custom mapped engine management system
- Power @ 12000rpm 80 bhp
- Torque @ 8500rpm 61 lb/ft
- Modified valve timing
- Suzuki GSXR750 injectors
- 35mm throttle body for increased throttle response
- Tuned aluminium intake for maximum torque at 10000rpm
- 4-2-1 stainless steel exhaust tuned for top end power
- Hydroflow quick release coolant system
- Electric water pump supplying more efficient and reliable cooling
- Dual pass high density core radiator with high laminar flow ducting

Drivetrain
- In house differential
- In-house cv housings
- 520VM chain driven final drive with ratios from 3.0:1 to 4.0:1

Suspension
- Unequal length non-parallel double wishbones
- In-plane pull rod front push rod rear
- Front anti roll bar
- Rear load transfer device
- Fully adjustable camber, castor and squat
- 2 way adjustable Risse racing shocks
- Stiction reduction by incorporation of bearings throughout system
- Lightened aluminium rockers and uprights
- Nitrotec Treated wishbones

Steering
- Bepsoke in-hose rack
- 150% Ackerman
- 5.5m turning circle
- 270 degree lock to lock steering wheel movement

Brakes
- MMC plasma coated disks
- AP racing 2-pot rear calliper
- Front callipers integrated into front uprights
- Dual circuit with cockpit adjustable bias control

Pedal box and Gear Shift
- Two Pedal tubular Steel Construction
- Quick release with adjustable reach
- Shifter Single action Clutch and gear shift mechanism
- Full throttle gear changes

Additional
- Wheels 13 x 6 In-house magnesium wheels Houssier tyres
- Body 3-piece fibreglass aerodynamically modelled stylish shell
- Quick release fasteners for easy access requiring one person only
- Electrical Completely insulated boxed system, completely weather proof
- Labelled loom and map with easy upgrade options
- Pi Research used for testing and car setup

---

Terrapin_racing - 5/5/04 at 11:05 AM

Oh...and also ...

The amazing new process is Nitrotec. The process can increase the physical properties of the material considerably. The result is a wear surface that is extremely tough and betters the frictional and corrosion properties of many chrome plating processes with NO chance of hydrogen embrittlement.


[Edited on 5/5/04 by Terrapin_racing]

---

crbrlfrost - 6/5/04 at 04:01 PM

I was curious if you have done any hardness testing, know the thickness of the hardened surface or done any tensile stress to failure testing. I've looked at the site, and don't really question the information they supply, my question is the information they don't supply. They don't have any material properties data. F1 gets away with a lot due to lifing of components and data logging <driver go curb hopping off camera?>. We could life components, but I don't think many of us want to. However, I'm be very interested t hear your results if you want to keep us posted, and good luck with the season.

---

cymtriks - 6/5/04 at 09:31 PM

So to summarise a long and interesting thread-

If you copy the book design use a bigger tube to compensate for the design shortcommings.

If you want a good design in the first place lean towards the Caterham design with tubes converging on the centre of the lower ball joint and the spring mounted as close as possible to it.

I have had a quick look at a Caterham in the carpark. I reckon the distance from the ball joint centre to the spring mount centre is just under 2 inches. On the Lowcost it seams to be 4.2 inches. This offset creates a bending moment in the tubes. So the Lowcost wishbone has more than double the bending forces on a Caterham wishbone.

Does anyone know what kind of ball joint is used on a Caterham wishbone and how it is fixed in place?

---

Alan B - 6/5/04 at 11:12 PM

Mr Cym.....just curious why do you always call locosts "lowcosts"?

Not some freudian disrepect to the beloved Mr Champion by any chance?

---

MikeRJ - 7/5/04 at 07:50 AM

Everything I have read here suggests that wishbones made to book design but with oval tubing should be avoided. Fair comment?

[Edited on 7/5/04 by MikeRJ]

---

James - 7/5/04 at 08:21 AM

quote:

---

Originally posted by MikeRJ
Everything I have read here suggests that wishbones made to book design but with oval tubing should be avoided. Fair comment?

---

I don't think so at all- bear in mind MK's wishbones are also oval- as are several other manufacturers.
Other than the example shown above (which started this thread), in 2/3 years of reading this site I don't recall anyone saying their wishbones had bent!

Cheers,

James

[Edited on 10/5/04 by James]

---

MikeRJ - 7/5/04 at 09:05 AM

If the stock design is marginal with tubular steel, then surely oval is only going to make it weaker in bending?

---

Terrapin_racing - 7/5/04 at 02:18 PM

Regarding testing of Nitotec'd wishbones. I was lazy here. I am a judge at FSE and got some test results from the universities whilst at Bruntingthorpe last year. Their materials and results would have been fine for the Terrapin
However, my material far exceed their spec on diameter and wall thickness etc.

I'll let you know if any break

PS: Can any of you american buds help me- see wanted section

---

jcduroc - 7/5/04 at 02:39 PM

quote:

---

Originally posted by cymtriks
If you want a good design in the first place lean towards the Caterham design with tubes converging on the centre of the lower ball joint and the spring mounted as close as possible to it.

I have had a quick look at a Caterham in the carpark. I reckon the distance from the ball joint centre to the spring mount centre is just under 2 inches. On the Lowcost it seams to be 4.2 inches. This offset creates a bending moment in the tubes. So the Lowcost wishbone has more than double the bending forces on a Caterham wishbone.

---

Like these, pe (?)

quote:

---

Originally posted by cymtriks
Does anyone know what kind of ball joint is used on a Caterham wishbone and how it is fixed in place?

---

I'd guess it is still a trunion!... (see pic 2)

Joćo
Rescued attachment EuropaFrtSm.jpg

---

jcduroc - 7/5/04 at 02:47 PM

quote:

---

Originally posted by jcduroc
Like these, pe (?)

HOW DO WE ATTACH TWO PICS IN THE SAME POST???

Joćo

---

Rescued attachment Img_0070small.jpg

---

dozracing - 7/5/04 at 07:23 PM

Is this possibly the craziest and pointless thread ever posted on this forum?

Like James said the proof of the pudding is in the eating, and in all the years that cars have been made in this style with oval tubes why has there never been mention of actual problems encountered with them?

I didn't get my mechanical engineering degree, or my job with the most influencial F1 designer of the past 20 years or my reputation for quality locost parts because i'm an idiot.

I'm a professional engineer with an approriate background and experience, so i'm hardly likely to supply oval tube wishbones just for the sake of it if there was a fundamental flaw and that they were likely to have problems.

Its nice of you all to mention my companies name as it must mean its at the front of your minds, but please understand that misleading comments saying that they should be avoided like the plague does me and the whole locost community no favours at all.

Can we please stick to facts here and not dream up ridiculous statements that have no factual base at all.

Kind regards,

Darren

---

Jon Ison - 7/5/04 at 07:32 PM

spot on i seem to remember the little disscussion about my "oval" wishbones been too strong, thus the chassis got wrote off..........

Remember ??

---

MikeRJ - 7/5/04 at 08:10 PM

Darren,

I apologise for my comments. I certainly shouldn't have mentioned your company in that context, it was thoughtless of me. However, I had just been looking at your web site with a view to purchasing your De Dion conversion, so as you say your company was at the front of my mind. I have edited my post accordingly.

However, I don't consider this thread crazy or pointless. No-one builds a locost in order to drive an inherently "safe" car around, but wishbone failure could easily lead to a fatal accident either on road or track. I certainly would like to be fully confident that this isn't going to happen.

Despite the lack of other reported incidents it has been suggested that the book wishbones are of marginal design. Although I understand the reasoning behind this, I am not a mechanical engineer and obviously I am not qualified to confirm or deny these suggestions.

Could you extend us the benefit of your experience as to wether you feel the book design (including book materials) is marginal and any possible failure mechanisms for the two sets of wishbones shown in this thread that have been missed?

---

britishtrident - 7/5/04 at 08:46 PM

Perhaps time to close this thread ?

Going in to Fred Dinah mode -- Nowt wrong with oval tubes provided the size and thickness is adequate--- as I said earlier the thread both both GTS and MK wishbones are models of good designs unlike the book "thing".

The wishbone in the original picture was a bad interpretation of the book design with poor attention to the details of the shape and postioning of the mounting plate. The book design causes large bending moments in the wishbone it is so marginal that poor attention to the details of the shape and position of the mounting plate will push it over the edge especially if the quality and finish of he welding is rough.

Also as I said earlier in the thread Tiger have had to modify the design of wishbone they used because of customers experiencing failures.

The major problem with the wishbone in the picture was a stress raising feature, only mechanical engineers tend to appreciate the importance of avoiding sharp changes in section. A sharp 90 degree corner is generally taken to increase the local stress by a factor of 3. On the wishbone that failed under what ever combination of loads occured the increase in stress was enough to initiate local buckling and resulting in buckling of the whole tube.

---

craig1410 - 7/5/04 at 08:59 PM

BritishTrident,
Can you give me your honest opinion on these if you don't mind. I bought these from Lolocost over a year ago (this is an old picture taken just after I bought them) and they are made from 22mm o/d 2.64mm wall ERW tubing with 3mm thick plate and as you can see the Cortina ball joint.

The welding seems to have very good penetration all round but I am concerned that maybe the top plate has too abrupt an edge where it might tend to bend like the one at the beginning of this thread. Should I be worried enough to take to it with an angle grinder?

Cheers,
Craig.

---

britishtrident - 7/5/04 at 09:15 PM

quote:

---

Originally posted by craig1410
BritishTrident,
Can you give me your honest opinion on these if you don't mind. I bought these from Lolocost over a year ago (this is an old picture taken just after I bought them) and they are made from 22mm o/d 2.64mm wall ERW tubing with 3mm thick plate and as you can see the Cortina ball joint.

The welding seems to have very good penetration all round but I am concerned that maybe the top plate has too abrupt an edge where it might tend to bend like the one at the beginning of this thread. Should I be worried enough to take to it with an angle grinder?
Cheers,
Craig.

---

The welding is first class and the tube thickness should be sufficent, I had bought them I would be quite pleased but tempted to chamfer the ends of the plate -- I would probably use some less agressive than an angle grinder.

---

MikeRJ - 7/5/04 at 09:18 PM

quote:

---

Originally posted by britishtridentThe major problem with the wishbone in the picture was a stress raising feature, only mechanical engineers tend to appreciate the importance of avoiding sharp changes in section. A sharp 90 degree corner is generally taken to increase the local stress by a factor of 3. On the wishbone that failed under what ever combination of loads occured the increase in stress was enough to initiate local buckling and resulting in buckling of the whole tube.

---

I understand this completetly. However, one thing that bothers me which you can probably clear up.

Both wishbones we saw failed by bending in a horizontal plane i.e. the tube bent towards the ground in the middle. In this plane, wouldn't the reinforcing plate have only a very minor effect on stiffness as it is so much thinner than the wishbone tubing? (i.e. plate offers very little resistance to bending accross the flat sides).

If the failure had been in the opposite plane, I could quite see how this would be a point of very high stress.

---

dozracing - 7/5/04 at 10:37 PM

Looking at the original picture its hard to give an accurate reason why its bent. But, my i would want to look at the angle its bent at, because the picture looks as though the tube has bent forward (or backward) and upward.

When we design a wishbone on a Grand Prix car, we first analyse all the loads and we get a worst case loading for each leg of the wishbone, for each load case.

It maybe of some surprise, but, actually the highest leg loads come from braking on the front and from braking or accelerating on the rear. Usually the highest leg loads are a combination of loadings like a high speed bump at the same time as hard braking.

It occurs to me that looking at the picture, its failed in the obvious place (change in section) but because of the angle of failure and the fact that the rear leg is intact, that braking force may have played a large part in its failure.

Obviously oval wishbones are very much stiffer in this load case than round section tubes.

If you use ERW tubing then you should give careful consideration to how you orientate the welded joint (ie put it on the neutral axis) so that you put the least stress in that weak area.

Darren

---

blueshift - 8/5/04 at 12:28 AM

If bumps put up/down stress on the bones, and braking puts forward/back stress on them.. how should the ERW be aligned?

I might try and get some CDS or just get scared and rich enough to buy GTS bones

---

NS Dev - 8/5/04 at 08:57 AM

I would use CDS anyway, made mine on my original car from 3/4" OD CDS hydraulic tubing.

---

NS Dev - 8/5/04 at 11:07 AM

Gosh, I have found somebody on the forum that I don't feel compelled to argue with!!

I agree once more Syd! Just as an aside, have a look at www.beardmorebros.co.uk, and take a look at the suspension design, chassis design etc on the "New Project"

John Beardmore is one of the few people who designs things which I have great difficulty in criticising!! He should be at Curborough with it tomorrow so I should be popping over for a look. Incidentally, Allan Staniforth has been looking at this car and has just done an article on the design etc of it!

---

Bigfoot - 8/5/04 at 04:22 PM

From the beginning of the thread, I have been pushing the theory that it is just a badly designed wishbone, that failed ,mostly due to braking loads. The other engineers on this forum with real experience in this field, appear to have a similar opinion. The problem lies more with the design than the materials.

Cheers
Bigfoot.

---

britishtrident - 8/5/04 at 05:19 PM

quote:

---

Originally posted by Syd Bridge
snip

snip
Given tubes of similar Moment of Inertia, both oval or round would be of similar suitability, with the round being preferable when buckling loads due to compression are considered.

snip

Cheers,
Syd.

---

Since when did steel stock holders accept orders of tube in terms of "moment of inertia" ?
The tube is stocked by diameter or for oval tube major and minor dimensions.

An "oval" tube with minor dimension of 22 mm will have greater Second Moment of area than a 22 dia round tube.

It will be less efficient in terms of load carriying ability and stiffness to weight ratio but that is not the sole object. The use of oval tube of say 22mm minor dimension is more acceptable when appearance is considered than 25 mm round tube which would look clumsy and out of place.

---

Alan B - 8/5/04 at 06:08 PM

quote:

---

Originally posted by britishtrident
Since when did steel stock holders accept orders of tube in terms of "moment of inertia" ?........

---

Never, and you know it...or ought to...

You also know it's the designers job to specify a material with appropriate "I" value for the intended application...

So, what was the point of that remark?

---

Noodle - 8/5/04 at 07:01 PM

quote:

---

Originally posted by NS Dev
Gosh, I have found somebody on the forum that I don't feel compelled to argue with!!

I agree once more Syd! Just as an aside, have a look at www.beardmorebros.co.uk, and take a look at the suspension design, chassis design etc on the "New Project"

John Beardmore is one of the few people who designs things which I have great difficulty in criticising!! He should be at Curborough with it tomorrow so I should be popping over for a look. Incidentally, Allan Staniforth has been looking at this car and has just done an article on the design etc of it!

---

He's taking the Moggy? I might just drag the kids over to see it. Do you what tomorrow's events are? I couldn't see it on the Curborough site.

Cheers,

Neil.

---

NS Dev - 9/5/04 at 08:44 PM

Noodle, did you get to Curborough?

It was a Nott's club event, and John Beardmore + moggy were there! Had a good chat with him over one thing and another.

His car is stunningly well presented and every detail is done because it was thought out that way (by him not on other advice!!) and it went extremely well!

He could do with some more power/less weight but a time at Curborough of 39.32 on his first timed run (first time out in car and first time at Curborough) was not bad at all. Didn't see his last run so may have been quicker again (would think so, his paractice times were falling and the first timed was the quickest until I left!)

To anybody that hasn't seen it have a look at his website. (anybody easily upset please stop reading now)

His engineering as simple and carefully thought out and is not diverted by the bull byproduct that seems to flow on this forum from time to time! His car just goes to prove that sound engineering is no black art, if something is right in principle then it will work, and well!!!

A good day was had, the rain kept off nicely!(and my XR4x4 got the chance to "stretch it's legs" on some dry roads for a change......doh....need new tyres now....wish it was a bit lighter, might not kill them so fast!!....doh again....new brake pads needed too!!! ah well, best get on with the locost then!)

---

cymtriks - 9/5/04 at 09:51 PM

Come on Darren/Dozracing

Tell us if you have any guidelines for what the loads on the suspension might be. Do you know how these numbers would be estimated for a race car?

I've assumed a 3g bump with a factor of 2 in my calculations but I suspect this is high for a locost.

---

Bob C - 9/5/04 at 10:58 PM

OK ERW tube - there's a seam in it. Now lets say you want to put a bending stress on the tube- Where would you ideally put the seam?
Top? (OK I'm thinking of a book lower front wishbone here...) No shear stress across the weld but weld could act as trigger point for crumplage.
Side? wouldn't have thought so - max shear AND excuse to fold for aforesaid crumplage.
Bottom? looks favourite to me.
Anyone got test results (preferred) or old wives tales to pass on?

Oval ERW tube - where's the seam on that then?

And I want to know what stresses are used professionally for suspension designs too. I've heard a blithe "stressed to 3g" comment from long ago - fair enough - but how do you calculate the effect of running into a pothole?? This looks to me like hitting your suspension with a 1/2 ton sledgehammer doing 40mph!!!
Cheers
Bob C

---

dozracing - 10/5/04 at 09:11 AM

Wishbone loads?

Anyones guess! F1 cars are strain guaged so we know what they see, but, as they generate 4g in cornering and braking they are well over what you would get close to even with a fat boy 7.

Rally cars are usually designed to take 5g bump loads, and Safari rally cars usually 7g bump. In my opinion the bump loads are not the major concern in a Locost, i think you'd have a hard time bending them due to bump alone. All the stories i've heard previously have related to hitting kerbs etc, where you get a horizontal load into the tyre and wheel.

I still believe you want the wishbone to fail if you hit kerbs hard etc, as otherwise the chassis and brackets will get damaged and they are harder and more expensive to replace. Race cars and modern road cars are expected to loose their suspension members before the chassis is damaged.

3g bump is probably a fair loading, but, you should consider what braking loads you get and what a pothole might reasonably do to you as well.

Nice little project for you cymtricks.

I might get round to FE'ing for a laugh and see what happens.

I think you want the seam on the minimum bending stress line, so the tube has the best structure at the max stress and max displacement. Shear stress i'm not sure i'm so worried about it in comparison, considering the way its then likely to fail.

Darren

---

stephen_gusterson - 10/5/04 at 09:48 AM

I whacked a rover 600 into the kerb at 50 drifting out of a roundabout I took too fast in 1996.

It caused 2,500 of damage to the car. The front suspension bent, and the front subframe was also shagged. Nothing atually broke away, but the wheel ended up with about 30 degrees negative camber.

The 'something should break' requirment didnt seem part of that rover / honda design!


atb

steve

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Bob C - 10/5/04 at 11:29 AM

<I think you want the seam on the minimum bending stress line, so the tube has the best structure at the max stress and max displacement.>

cheers - but would that be top, side, bottom or somewhere in between?

I feel a home made test coming on(!), ain't worked out how to do it yet though...

Bob

---

Dougw - 10/5/04 at 02:13 PM

maybe it is a combination of things
1 Is the tube thick/heavy enough
2 Has the weld nearby altered the structral strength of the tube??
3 I cant believe it is anything to do with the engine weight as the rover V8 is light for its size therefore must be either inherent to the tube OR design issue
3mm walled tube at that length should withstand about 4 ton of force ? is it coincidence that it has done the same thing twice
4 Has the manufacturer offered to replace the wishbone?

---

cymtriks - 10/5/04 at 08:46 PM

Check out this site. Very nice suspension on the front of the silver car.

Note how close the spring is to the hub (low bending moment to reduce stresses).

Note how the tubes form a V with the lower hub joint at the point, no offset as on the book locost design (just like Caterham, lowers stresses).

Note the aero tubing and the detailing. (looks good and works if the bending loads are reduced this much).

http://www.elfin.com.au/index.html

Darren/dozracing
What kind of upright does your choice of lower ball joint fit? Your wishbones look like a pure V shape.

---

Dave Gilling - 22/5/04 at 10:55 AM

Tiger have put a recall on kits using oval wishbone tube, finished cars will be collected and new (round tube?) wishbones fitted for free! 22mm dia.X 3mm CDS tubing for me thanks.

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MikeR - 22/5/04 at 11:44 AM

Hmmm, interesting, do we know what the oval where made of and why they are being recalled?

---

britishtrident - 22/5/04 at 12:52 PM

quote:

---

Originally posted by Dave Gilling
Tiger have put a recall on kits using oval wishbone tube, finished cars will be collected and new (round tube?) wishbones fitted for free! 22mm dia.X 3mm CDS tubing for me thanks.

---

Is this another recall ? from memory there was one about 2 years ago ?

---

Dave Gilling - 22/5/04 at 01:37 PM

Very little info, only what is in WK & KC mags (KC page 9,WK page 11 above the article about Richard Stewart wanting £1.5mill for Robin Hood ) only lower wishbone affected, but that makes sense.

[Edited on 22/5/04 by Dave Gilling]

---

SR2 - 27/6/04 at 11:34 AM

Hate to point out the obvious but I think we have a basic design flaw here folks. Surley the gusset plate needs a curved as opposed straight edge to avoid the stress point that caused the failure.

---

JoelP - 27/6/04 at 12:02 PM

thats been pointed out a few times up the thread, but its worth mentioning again.

---

Chris_G - 27/6/04 at 01:16 PM

This is a long thread now, but if you read right the way through you will see that the first images were of a 'home made design' without the curve in the plate, however that was replaced with a commercial part of 'book' design ie with the curved plate...BUT, this also failed!!!


Since it has been 'beefed-up' all seems well, touch wood.

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Rob Lane - 29/6/04 at 12:50 PM

Don't know if this was mentioned in long thread.

MK had a problem with a batch of wishbones he made up at very start.
They were CDS tube BUT were of a soft steel. He withdrew ALL the wishbones, non going to customers but some to two resellers who returned them.

Martin then did a redesign and used thicker wall CDS tube and then eventually oval tube with much thicker wall.

He and I were well aware of the weld stress riser point.

In fact I posted about this very problem in relation to wing stay failures.
So much so I recommended at least 12mm solid bar as uprights and 25x3mm flat for wing mount.
Interestingly my wing stays have stayed intact since I over built them BUT the triangular mounting plate on one has started to fracture now! On a weld stress point!!

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geezer - 4/10/04 at 08:16 PM

looks fairly obvious to me - not enough length ( oh er missus ) in your coil springs , spring are binding up when suspension is loaded up hence running out of suspension movement but car continues to load up suspension and somethings got to give, forces, reactions, opposites, angle of the dangle, blah blah blah.

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JoelP - 4/10/04 at 09:56 PM

not guarenteed though. 300 pounds per inch springs that can compress 4 inches will obviously take around 1200 pounds, This could bend a bad bone before it runs out of travel.

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Chris_G - 4/10/04 at 11:03 PM

quote:

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Originally posted by geezer
looks fairly obvious to me - not enough length ( oh er missus ) in your coil springs , spring are binding up when suspension is loaded up hence running out of suspension movement but car continues to load up suspension and somethings got to give, forces, reactions, opposites, angle of the dangle, blah blah
blah.

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Geezer,

That wasn't the case here, it was tested by wrapping a blue-tac 'sausage' around a coil and monitoring it. It did not get anywhere near pinched to the point the coils would have been bound!

Anyway the problem now seems to have been solved by beefing the wishbones up.

Chris

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Peteff - 5/10/04 at 09:13 AM

Sausages, mmmmmmmm!!!!!! If it bends make it stronger, seems obvious. We had to do the same with a panhard rod which had been made from pipe and did a banana impression. Remade in bigger seamless tube cured it.

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Tigers - 5/10/04 at 05:12 PM

He, he...
I'm making my wishbones out of 25x3mm seamless tube. Was hell to bend them in tube bender (don't know how this this is called correctly) with 1 meter extension tube.
My wishbones will be the last thing that bends. Of coure they weight a lot, but I couldn't get better tube. And saftey first

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stantheman - 18/10/04 at 10:26 PM

its like groundhog day

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erbieb02 - 3/8/05 at 01:34 AM

In my student engineering opinion there was just to much bending going on. One wants their A-arms to be loaded only in tension and compression, no bending. Having the shock mounted so far from the upright's lower ball joint makes the A-arm bend downwards in the middle due to the shock's loading. That coupled with the bend placed into the A-arm just inboard of the mounting plate creates a stress raiser.

Baisically I chalk it up to it being under engineered, I suggest triangulating the Arm vertically, in a sort of pyramid shape if you want to keep the shock in its current mouted location.

Eric B.

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blueshift - 5/8/05 at 09:00 AM

way to unearth an ancient topic!

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locostv8 - 26/5/06 at 05:07 PM

Adding fuel. This happened to someone elses car.


Construction pic.

These front control arms bent under heavy braking on the rear tubes only, causing the wheels to toe out, 13/16" each side! Not good!


I'll need to redesign and build new.

I have a couple theories why that happened. The most prominent: The
original arms had a shorter plate that the shock mount was welded to, and
it's profile was completely straight. The swaybar attachment bracket was
welded just inboard of that plate, directly on the tube, causing a
point-load on the arm under cornering. Bad idea. I underestimated the
force the swaybar would impart on the arm, and I'm pretty sure that's what
started a small amount of the bending. Add sticky tires, track pads that
finally got up to temperature one day, and under heavy braking (no cornering
involved whatsoever) the remainder and majority of the bending occured. As
that rear tube bent, it caused a severe toe out condition, which only helped
the bending along, as you might imagine.

The fix:

I made the new LCA's out of 1" DOM again, but with a .100" wall instead of
.065", I lengthened the "shock plate" such that the sway bar attachment
braket would weld to it instead of directly to the tube, and I made a gentle
curve in the plate between the tubes this time. I also added a 1" 16GA
square tube brace under the plate as far inboard as I could, which is also
directly under the swaybar bracket. No problems so far, and I think I've
pushed the car plenty hard enough since then with no issues.

My car weighs 1500lbs. and I think the arms were just not beefy enough, and
I had some bad design in there as well.

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Liam - 26/5/06 at 05:36 PM

Blimey!! Create a stress concentration with the straight cut piece of plate, then weld an anti roll bar mount to it!! Scary engineering decision. The plate is way too thin too - look how it's bent under the suspension loads. Nice looking design but rather minimalist on the material. I'd worry about that bellcrank mount too.

Liam

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t.j. - 26/5/06 at 06:44 PM

Reading all this i concluded that the Avon-book ain't that bad.

My arms will be made of 25mmx3 seamless pipe with a plate of 10 mm between them.

I don't want any ......whatever with my suspensions.

[Edited on 26/5/06 by t.j.]

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craig1410 - 26/5/06 at 07:22 PM

TJ,
I'm not sure that using 10mm plate is actually a good idea because you need the plate to flex a bit to avoid creating a stress concentration on the wishbone tube at the end of the plate. The best designs available today try to get the shocker lower mount as close as possible to the lower balljoint and incorporate a curve along the inboard edge of the plate to allow a bit of flex and spread out the stress along the wishbone tube. I think they usually use 3mm plate.

I'd recommend copying the design of the likes of the GTS Tuning wishbones which seem to be highly regarded. They use oval tubing as well which is prettier.

Cheers,
Craig.

[Edited on 26/5/2006 by craig1410]

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DIY Si - 26/5/06 at 07:27 PM

One of the best ideas I've seen recently was at stoneleigh. Damned if I can remeber who it was, but someone had a special mount for the shocker which bolted in the same place as the bottom ball joint. That should basically remove most of the bending moment. Just then need arms strong enough to take the load. It would also help to have nice light little wheels, light brakes + calipers etc..

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t.j. - 26/5/06 at 07:34 PM

quote:

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Originally posted by craig1410
TJ,
I'm not sure that using 10mm plate is actually a good idea because you need the plate to flex a bit to avoid creating a stress concentration on the wishbone tube at the end of the plate. The best designs available today try to get the shocker lower mount as close as possible to the lower balljoint and incorporate a curve along the inboard edge of the plate to allow a bit of flex and spread out the stress along the wishbone tube. I think they usually use 3mm plate.

I'd recommend copying the design of the likes of the GTS Tuning wishbones which seem to be highly regarded. They use oval tubing as well which is prettier.

Cheers,
Craig.

[Edited on 26/5/2006 by craig1410]

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I'm confused here. The book say 10 mm.
I'm planning to laser-cut the plate so that the pipe does actually fits over the plate.

The balljoint wil as close as possible to the lower mounting of shockabsorber.

So you think it's better to make a plate for the ball-joint and one for the absorber mount?

my idea was cut everything out of one plate. Hmmm

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DIY Si - 26/5/06 at 07:44 PM

One plate is ok, but don't fit it to the top of the tubes as per the book. This will weaken the top edge of the tube. Try to put the plate in between the tubes as this gives the most extra strength for the least weaken by heat. Sorry if that makes little sense for the reason, but I know what I'm trying to say.

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t.j. - 26/5/06 at 07:53 PM

quote:

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Originally posted by DIY Si
One plate is ok, but don't fit it to the top of the tubes as per the book. This will weaken the top edge of the tube. Try to put the plate in between the tubes as this gives the most extra strength for the least weaken by heat. Sorry if that makes little sense for the reason, but I know what I'm trying to say.

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Damn, wish i have my stuff around.
I want to make one plate which is holding the balljoint and the lower mount. where the pipes hit the plate i wanted to make a sticky thing about 25 mm which goes inside the pipe. Then take the welder an welded all around. Cause the plate goes inside the pipe the whole plate will be in te middle of the two pipe. I'm planning to make the edge of te plate 45 degr. so that the weld is flatted.

So 10 mm plate isn't a problem or schould i go back to the drawing-table?

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DIY Si - 26/5/06 at 07:53 PM

Like this:
Rescued attachment Untitled-1.jpg

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DIY Si - 26/5/06 at 07:58 PM

Arse it's not working, The plate needs to be central to the two tubes, ie in the middle vertically. The edges want to be square, but shaped to fit the tubes.
Rescued attachment 121.jpg

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flak monkey - 26/5/06 at 08:03 PM

GTS lower wishbone:

http://gtslocost.locostsites.co.uk/images/31.jpg

Sorry about pic quality. Pre digicam!

Now this is from memory: 6mm lasercut plate welded along the neutral axis of the arms. Very simple design. The plates are available from GTS to make your own bones from.

David

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t.j. - 26/5/06 at 08:13 PM

quote:

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Originally posted by DIY Si
Arse it's not working, The plate needs to be central to the two tubes, ie in the middle vertically. The edges want to be square, but shaped to fit the tubes.

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Ok, that's my idea also.
Where the edges make contact i wanted to cut under 45 degr so there is room to weld. Also at the bottom.

@ david: Is 6 mm better then using the 10mm?

[Edited on 26/5/06 by t.j.]

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flak monkey - 26/5/06 at 08:19 PM

The plates may be 8mm. I dont have them to hand to measure them. I am 95% sure they are 6mm though. I would say 10mm is seriously overkill. Theres no harm in using it, your main problem will be getting decent pentration on a weld on 10mm plate to 2 or 3mm tube...

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craig1410 - 26/5/06 at 09:03 PM

Hi,
Sorry t.j. I don't mean to confuse you...

I would say that 10mm is too thick for a few reasons (weld penetration & too stiff compared to the wishbone tubing being the main ones). I'd say that you wouldn't want to use plate any thicker than twice the thickness of your wishbone tubing to ensure effective welding and to prevent a stress concentration appearing in the tubes.

In general, a structure is only as strong as the weakest link. However, it is possible to make a weak link even weaker by making an adjacent link unnecessarily strong. Ideally you want the entire wishbone to bend along its entire length rather than bend at one particular point to avoid fatigue and early life failure.

I hope this helps,
Craig.

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locostv8 - 26/5/06 at 09:14 PM

Here is maybe a bit more fuel. Anyone familiar with DAX Camber compensation & antiroll suspension? http://www.daxcars.co.uk/start.htm

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MikeRJ - 26/5/06 at 10:50 PM

quote:

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Originally posted by locostv8
Here is maybe a bit more fuel. Anyone familiar with DAX Camber compensation & antiroll suspension?

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Fairly, but it has little to do with the strength and design of the Locost bottom wishbones. Whilst a clever system, the DAX camber compensation system does not fair so well with one wheel in bump. Look at the picture of the body in roll and then tilt it so the body is level and notice the effect on the camber...

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kb58 - 26/5/06 at 11:51 PM

Yup, what he said ^. For all that effort it doesn't work on a one-wheel bump. I also remember reading it was really hard to set up, in fact the factory wouldn't sell it as a kit - they have to set it up (as far as I remember.)

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locostv8 - 27/5/06 at 03:53 AM

I had wondered if bumps might upset it. If it works it would be great but seems like a lot of trouble to eliminate a sway bar.

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Syd Bridge - 27/5/06 at 09:06 AM

Anyone ever wondered why you don't see that Dax system on topend racecars other than a few Dax's? Patents aside, as top teams would pay the licence fee if it was worthwhile.

Cheers,
Syd.

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andyps - 27/5/06 at 11:13 AM

Relative to the Dax system, I have always felt that a well designed unequal length wishone set up should provide most of the benefits all the time and does not have the problem of a one side bump.

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Uphill Racer - 1/11/06 at 01:09 AM

When they can make the front end react to it, it may work

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onzarob - 25/11/07 at 11:01 PM

Wow what a long thread ( and over a long period of time!!!) and allot of technical details from knowledgeable people.

To summarise the solid points

If using a heavy engine beef up the standard locost design tube wall thickness/size.

With all lower wishbones weld the plate to the side of the tubes and NOT on top.

The Dax suspension is really a different topic and also at the other end of the car!!!

I must add that this is the sort of topic I wanted to find...I want to build something that doesn't break my neck...great stuff

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britishtrident - 26/11/07 at 07:48 PM

Also the other main conclusion is you need a generous fillet radius on the plate.

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MikeRJ - 26/11/07 at 10:23 PM

quote:

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Originally posted by onzarob
The Dax suspension is really a different topic and also at the other end of the car!!!

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The Dax system is used on the front suspension, though it could be used on the rear I suppose if you can get all the linkages to clear the diff and driveshafts etc.

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onzarob - 26/11/07 at 10:46 PM

whoops, I missed read the diagrams....<walks away in shame!>

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austin man - 8/4/08 at 09:05 PM

I had the very same problem of the tube begining to bend I was using MK items I think the problem is that the initial design was for the Kent engine and possibly the old A series this was a considerably lighter engine than the pinto and V8 you must also remember the weight of the gearbox. The heavier engine requires heavier springs therefore increased pressure on the wishbone. Above all else there will also be softening in the tube at the point where the weld ends due to the heat inflicted. MK now supply stronger versions of the lower wishbone to over come this. I added additional 3mm plate to nin to further strengthen. Never heard of this problem with a BEC

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druid - 15/4/08 at 12:49 PM

on looking at photo the lower tube is about 19 mm on later models lower tube dia was 25mm by 2.5mm wall hope this helps

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StuartBJ - 16/4/08 at 09:29 PM

Did you notice how the roll centre raises until its inside the car? That`s not a performance increase now is it! Who thought that would be better, take him outside and shoot him.

The lower the roll centre the better.... imho

Where the roll centre has moved too is similar to a saxo, pug or other hatchback! Lets go to halfords a buy some speakers, innit!

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