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Author: Subject: Roadrunner Racing SR2 Poor front suspension design
Rocket_Rabbit

posted on 28/8/18 at 10:36 PM Reply With Quote
Roadrunner Racing SR2 Poor front suspension design

Some of you may remember that I had to redesign and rebuild the rear end of the SR2 after it snapped the diff within about 2 miles of driving.

http://www.locostbuilders.co.uk/viewthread.php?tid=203077

Finally got around to looking at the front and, after we noticed the front suspension collapsing, we found this:

https://www.youtube.com/watch?v=CZnkCkNunMk&feature=youtu.be

So now the front end needs the redesign and restructure.

Roadrunner have banned me from their facebook page and not once have they offered any help for a chassis they built and has done about 5 miles including tuning on the rolling road.

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number-1

posted on 28/8/18 at 11:18 PM Reply With Quote
Wow! Did they fit that front suspension? Have any SR2 owner had the same issue? Ive had nothing but good service from RRR so far.
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Rocket_Rabbit

posted on 28/8/18 at 11:32 PM Reply With Quote
quote:
Originally posted by number-1
Wow! Did they fit that front suspension? Have any SR2 owner had the same issue? Ive had nothing but good service from RRR so far.

It's not the fitting, it's the design of the chassis. But yes, they built the car.

Their service has been woeful - they weren't interested in acknowledging their mistakes nor offering a way to rectify them.

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russbost

posted on 29/8/18 at 07:05 AM Reply With Quote
Difficult to see from the video exactly what is moving, is it simply that the pivot end of the front wishbone is too short, hence there's not enough triangulation to stop everything moving/distorting? On top of that at the outer end of the wishbone, they are asking two small circular welds to take all the vertical & horizontal forces during cornering/braking - I'm surprised that would pass IVA!

Edited to add, the first time I saw a kitcar in the brake rollers I was quite shocked at the amount of "wind up" there was between the two wishbones under hard braking, having seen many more kits in the rollers since it would appear that some considerable movement is normal, however with the setup shown here I would imagine what you'd see in the rollers would be horrific, & that's not just the outer end that's wrong, it's the whole concept of such a narrow angle - the pickup points on the chassis need to be moved

[Edited on 29/8/18 by russbost]





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Doctor Derek Doctors

posted on 29/8/18 at 07:41 AM Reply With Quote
It looks like that the very acute angle between the upper wish bone legs and the rod ends on the inner ends not providing any rotational resistance the two top wishbone legs are acting as torsion springs.





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Rocket_Rabbit

posted on 29/8/18 at 09:00 AM Reply With Quote
quote:
Originally posted by Doctor Derek Doctors
It looks like that the very acute angle between the upper wish bone legs and the rod ends on the inner ends not providing any rotational resistance the two top wishbone legs are acting as torsion springs.

I thought, like you, that it was the lack of bracing on that upper arm, but worse than that

If you look toward the bottom, it's actually the lug mount for the upper arm that flexes along with the chassis - it all bends slightly and as the arm is spherical bearing'ed it rotates about it.

It's worrying to see and there is no way that design would last more than a couple of track days before simply failing.



[Edited on 29/8/18 by Rocket_Rabbit]

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Sam_68

posted on 29/8/18 at 09:06 AM Reply With Quote
quote:
Originally posted by russbost
Difficult to see from the video exactly what is moving, is it simply that the pivot end of the front wishbone is too short, hence there's not enough triangulation to stop everything moving/distorting?


It's perfectly simple; and coincidentally is exactly the problem we were discussing on this thread: the arrangement of the outer end of the wishbone turns it into a trapezium instead of a triangle.

Triangles are stiff (because they resolve all forces into pure tension/compression); untriangulated quadrilaterals are not (because they allow bending, which is very inefficient, structurally).

Simples.

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Tazzzzman1

posted on 29/8/18 at 02:32 PM Reply With Quote
Got to say, that I am one of many really happy with Roadrunner. Mine was one of the first chassis's for the SR2, and I did 10+ track days and over 15K (very hard) road miles on mine before tearfully waving goodbye as it departed to Italy, after over 3 years of build/ ownership.

I had a couple of issues with cracked diff/ mount as you described. This was promptly fixed by Roadrunner (they collected my car from 60 miles away and had it sorted within 2 days).
Also had the front crack where you have shown a weakness which again was fixed by adding in some additional bracing/ gussets.

Car, build and dealing with Roadrunner made it a fantastic build and one I would recommend to anyone.

I guess every company will get it wrong occasionally and in my case was dealt with by them going above an beyond. The car is evolving and being improved all the time and they like most are learning by mistakes to improve and move forward with what was already an excellent product.

Seems strange that you are the only one I know of who has been ex-communicated? I dont know reasons why etc but believe that there is always 2 sides to a coin...

Hope you get it sorted as the car is IMHO one of the best for the £ out there

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Sam_68

posted on 29/8/18 at 03:38 PM Reply With Quote
It has to be said that if you apply a big enough lever to anything you will be able to make it deflect.

As Archimedes reputedly said (presumably in Greek): "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world".

...but it also has to be said that that's a crap wishbone design, and is asking for trouble.

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russbost

posted on 29/8/18 at 04:47 PM Reply With Quote
Sam - I am in shock - we agree about something!





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Rocket_Rabbit

posted on 29/8/18 at 08:28 PM Reply With Quote
quote:
Originally posted by Tazzzzman1
Got to say, that I am one of many really happy with Roadrunner. Mine was one of the first chassis's for the SR2, and I did 10+ track days and over 15K (very hard) road miles on mine before tearfully waving goodbye as it departed to Italy, after over 3 years of build/ ownership.

I had a couple of issues with cracked diff/ mount as you described. This was promptly fixed by Roadrunner (they collected my car from 60 miles away and had it sorted within 2 days).
Also had the front crack where you have shown a weakness which again was fixed by adding in some additional bracing/ gussets.

Car, build and dealing with Roadrunner made it a fantastic build and one I would recommend to anyone.

I guess every company will get it wrong occasionally and in my case was dealt with by them going above an beyond. The car is evolving and being improved all the time and they like most are learning by mistakes to improve and move forward with what was already an excellent product.

Seems strange that you are the only one I know of who has been ex-communicated? I dont know reasons why etc but believe that there is always 2 sides to a coin...

Hope you get it sorted as the car is IMHO one of the best for the £ out there


I followed your build/trackdays Terry and, without offering offence to you, compared to how I'll be driving mine I think it's not quite the same. Bearing in mind, we noticed the brake torque reaction issue just doing moderate braking on a test drive and it was horrific, not to mention the rear diff exploding.

Two sides to every coin indeed. Every single piece of communication I had with RRR is on that other thread. Here it is for you:

Me: Hi, here is what happened to my SR2000 (Rear diff break) after about 3 miles of use (including rolling road tuning). The diff and car was built by yourselfs too. Have you had it happen before?


RRR: 02/29/2016 8:45PM

Hi we have had a few broken casings (only after serious use ie slalom/drifting etc) Mazda deliberately weaken the casting (half round hole on top and bottom edge) we now plate factory built higher powered cars with 2mm alloy on either side of the alloy differential casing. We also have added an extra top front mounting on some cars. Also polybushes seem to be more forgiving than the solid bushes allowing small movement of the differential under extreme loadings.

Me: 03/01/2016 12:27PM
Hi, Thanks for you reply. Is there anything else that breaks under 'extreme' loadings as this broke whilst driving up the trailer ramp! I don't know whether or not it was the same diff casing for when you had the V8 in it or not. Could you provide an pictures for the front mount modification? Thanks. Ron

RRR: 03/10/2016 7:34PM

Spoken to Norman about this, from speaking to him it looks like someone has not fitted the front mounting bolts 2 x 14mm. If that is the case I am not surprised the rear casing broke. I recommend on higher power cars the rear casing is plated with 2mm alloy. Mazda weaken the casing for collision compliance.


Me: 03/10/2016 9:58PM
Hi, Thanks for the reply. I have spoken to Norm, the bolts were installed (They are 12mm cap head bolts, not 14mm and they would have been installed by you when you put the reconned diff in) and the mount has twisted. What he said to you was that he couldn't see the bolts because they were obscured by the diff. Regardless, I have been speaking with Stuart and his diff has broken despite Poly bushes and the latest design for the front mount. Please bear in mind, that I have already replaced a prop you supplied that was completely inappropriate for the car by being a CV/UV joint combination. Please also note that the diff was supplied and installed by yourselves. I have found other users running turboed MX5 engines that are also having their differentials snapping. Looking at the MX5, the diff is NOT solid mounted at all. The front mount is fully floating as it is supported by the PPF connected to the gearbox. This is why your front mount continually fails - it's rigidity is not allowing movement until it bends and puts full load on the oxbow of the diff. In the OEM car these diffs handle 400bhp after all! Finally, it is all very well quoting the 285bhp supercharged one, however you have now had two failures of exactly the same nature on cars with the same engine - there is a problem. I'm sure Stuart would say the same in that we'd be willing to work with you - hence why I told you about the mistake you made with the prop that I paid for to rectify. Please see it from a customer point of view. I am now over £20k into a car that doesn't work.. I have had to replace the prop, had to have sections of the rollcage welded that had been missed, had to have the seat mounts welded where they had come off, will have to fit new springs to get some compliance in the suspension, and now I'm having to redesign the rear end to accept a different differential and mounting solution. How can I recommend you to others? I even sent a request for a quote on a new rear boot panel through your website and got nothing back!! So that is my current stance on the vehicle and the customer service. I look forward to your reply. Thanks. Ron

RRR: 'thumbup'

Chat Conversation End


And that is the FULL extent of the conversation so all sides of coin on display.

I'd be interested in your view on this Terry as you have been an advocate of RRR for quite some time.

But the only reason I can think of for this type of service is that they knew the chassis was a dog, sold it me and washed their hands of it.

It's never too late to do the right thing of course, but I'm not expecting any offers from RRR.

Sam_68 - I agree. However there is a 600kg car braking from 150mph at 1.5g on that arm. It was foulding the damper at about 0.5g from 30mph. The lever shows where the deflection is coming from - the front upper arm lug.

[Edited on 29/8/18 by Rocket_Rabbit]

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Mr Whippy

posted on 30/8/18 at 11:41 AM Reply With Quote
you've done 5 miles in 2 1/2 years?
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Sam_68

posted on 30/8/18 at 12:16 PM Reply With Quote
quote:
Originally posted by Rocket_RabbitThe lever shows where the deflection is coming from - the front upper arm lug.


Looking carefully at the video, I'm not at all convinced it is. There may be a tiny amount of deflection in the lug (certainly less than you'd get with a rubber or polybushed wishbone though), but most of the flex seems to be in the actual wishbone, due to its poor - very imperfectly triangulated - design.

You do seem to have a very large axe that you're desperate to grind, though.

Redesigning that wishbone is not a major job (yes, I know it's RR's job, really, but if you run a high-powered variant of a kitcar, you have to face doing a bit of development work yourself from time to time). If you'd expended half the time and effort that you've spent bitching about it on actually fixing the problem (and maybe sharing the solution with the factory and fellow owners), you might be a happier man?

[Edited on 30/8/18 by Sam_68]

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MikeRJ

posted on 30/8/18 at 12:37 PM Reply With Quote
quote:
Originally posted by Tazzzzman1
Hope you get it sorted as the car is IMHO one of the best for the £ out there


It quite clearly isn't. A long, narrow, trapezium shaped wishbone is an inherently useless design for resisting braking forces.

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russbost

posted on 30/8/18 at 12:43 PM Reply With Quote
Looking carefully at the video, I'm not at all convinced it is. There my be a tiny amount of deflection in the lug (certainly less than you'd get with a rubber or polybushed wishbone though), but most of the flex seems to be in the actual wishbone, due to its poor - very imperfectly triangulated - design.

You do seem to have a very large axe that you're desperate to grind, though.

Redesigning that wishbone is not a major job (yes, I know it's RR's job, really, but if you run a high-powered variant of a kitcar, you have to face doing a bit of development work yourself from time to time). If you'd expended half the time and effort that you've spent bitching about it on actually fixing the problem (and maybe sharing the solution with the factory and fellow owners), you might be a happier man?


Again I'm inclined to agree with Sam, as I said b4 the amount of movement in any double wishbone system on a 7 type vehicle looks quite shocking when you load it up in the brake rollers, but is , nevertheless, normal. Would you expect to get as much movement as you are if you load it up with a bar as shown - well, no, but I think the movement is largely not where you've said, but within the actual wishbone itself.

Have they updated the design or is that wishbone still what they are selling? It looks like the sort of thing a bloke who could use a welder but didn't know too much about engineering or how forces are transmitted might knock up in a shed &, as said, it wouldn't surprise me if an IVA inspector wasn't satisfied it could safely do the job required - the base of the pivot end is far too narrow & the outer end should have the two tubes joined together at the tube for the top ball joint, I'm guessing that would cause the tube to foul the shock, hence why they've done what they've done - that said, presumably there are dozens of these running around without problems as I can't find loads of stuff on the web referring to issues others have had

I do have some sympathy with the company as I frequently get people ask me can I put a "Blah 123xyz" motor in it - it'll make 400bhp - to which I answer that the main chassis will take it, but that I can't answer for the suspension as it was never designed for significantly over 200bhp & certainly would not do it without beefing up suspension, pickup points, possibly adding further triangulation or some form of load spreader at stress points etc etc - I also point out that perhaps a brake upgrade & some bigger wheels & tyres might be in order - Oh! look, we've just spent loads more money on one "simple" upgrade which maybe wasn't needed in the first place. I am always happy to help a customer achieve what they want, but do sometimes need to bring peeps back to reality (& within their budget!) - on the other side of the coin even with a bog standard Mazda setup I don't think I'd ever feel confident in stamping on the brakes from any significant speed with a wishbone like that ...............





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Angel Acevedo

posted on 30/8/18 at 01:02 PM Reply With Quote
I seem to recall that either Australia or New Zeland have in their version of the IVa the resistance of the chassis to twisting, therefore the Cymtrics mods to book chassis.
I wonder how this chassis would fare to this test, and what will need to be done to approach this requirement -even if you don´t have to comply on UK.
Wether to be carried by the car owner or the factory, that is another completely different matter.





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Sam_68

posted on 30/8/18 at 01:06 PM Reply With Quote
quote:
Originally posted by Angel Acevedo
I seem to recall that either Australia or New Zeland have in their version of the IVa the resistance of the chassis to twisting...

I wonder how this chassis would fare to this test...

It's Australia... and possibly quite well: their test measures torsional and beam stiffness of the chassis. It makes no attempt to measure fore-aft deflection of the suspension under braking.

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Mr Whippy

posted on 30/8/18 at 03:22 PM Reply With Quote
quote:
Originally posted by Angel Acevedo
I seem to recall that either Australia or New Zeland have in their version of the IVa the resistance of the chassis to twisting, therefore the Cymtrics mods to book chassis.
I wonder how this chassis would fare to this test, and what will need to be done to approach this requirement -even if you don´t have to comply on UK.
Wether to be carried by the car owner or the factory, that is another completely different matter.


I think torsional strength may be the least of the concerns

Saying that good old Landrovers twisted like crazy to the point the doors often pop open, doesn't mean their weak or think of a truck, most of them are like jelly over rough roads, still very strong... Probably the biggest issue with 7's is the lack of a box truss on the sides but that would be difficult to get round style wise unless they had a proper body shell like a Fury. As for the front wishbones just a rubbish design

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Angel Acevedo

posted on 30/8/18 at 03:30 PM Reply With Quote
quote:
Originally posted by Mr Whippy
quote:
Originally posted by Angel Acevedo
I seem to recall that either Australia or New Zeland have in their version of the IVa the resistance of the chassis to twisting, therefore the Cymtrics mods to book chassis.
I wonder how this chassis would fare to this test, and what will need to be done to approach this requirement -even if you don´t have to comply on UK.
Wether to be carried by the car owner or the factory, that is another completely different matter.


I think torsional strength may be the least of the concerns
...


May be, but I´m quite sure the diff broke because it was taking more twisting loads than it was designed for.
Most likely due to low torsional stiffnes of chassis in one or more axis.....
Strictly my opinion of course....





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mechanic

posted on 30/8/18 at 07:43 PM Reply With Quote
It's not my thing to criticise other peoples designs, but I see this as a safety issue.

This upper wishbone really is a poor design, for reasons other people already mentioned above.

I'm really worried about fatigue here. Everytime you apply the brakes, these welds will see high stresses. In a proper wishbone design the tubes hardly see any bending moments, only normal force, hence stresses in the welds are low. In this case the tubes see a lot of bending moments, and stresses in the welds will be high. If you double the stress in a weld, it will fail 8 times sooner.

Additionally the welds don't seem very well executed as well.

I really really would consider replacing these wishbones with a better design. Especially if you've done some mileage with them already. The cracks start from the inside out (root of the weld), so you wont'see it coming. They may be fine now, but it might just snap at some point.

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motorcycle_mayhem

posted on 31/8/18 at 08:43 AM Reply With Quote
I'm going to criticise, sorry. Not something I do often, I tend to simply get on and do things.

That top wishbone assembly requires disposal.
I can't see the bottom clearly, so I can't make a visual assessment, but would ask you looked at that too. The leverage (for example) that I 'think' I can see on the bottom shock location to the upright would concern me.

I would not want to get that car on a track, the thought of those wishbones going over Avon Rise into Quarry at full chat... perhaps on slicks...

What my Westfield chassis (and components) took is incredible, given the absolute simplicity. Yes, things cracked and broke, but the old design (1" square) was easy to inspect, easy to repair, proven.

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Rocket_Rabbit

posted on 31/8/18 at 09:14 AM Reply With Quote
quote:
Originally posted by Mr Whippy
you've done 5 miles in 2 1/2 years?

Pretty much. I paid MK to do some work on the car. I paid them £3k to fit an oil cooler, fit a gearbox I lent them for some dev work, design and build a manifold/exhaust, and paid for a new prop that was UV joints at both ends. They didn't fit the clutch properly, so ended up doing that myself and the exhaust they designed, despite me saying, and giving them, a 4-1 collector is what I wanted, came back with a 4-2-1 that caused reversion and cost me 30bhp so I needed another exhaust. Obviously life gets in the way too and I also moved house and job twice.

quote:
Originally posted by Sam_68
quote:
Originally posted by Rocket_RabbitThe lever shows where the deflection is coming from - the front upper arm lug.


Looking carefully at the video, I'm not at all convinced it is. There may be a tiny amount of deflection in the lug (certainly less than you'd get with a rubber or polybushed wishbone though), but most of the flex seems to be in the actual wishbone, due to its poor - very imperfectly triangulated - design.

You do seem to have a very large axe that you're desperate to grind, though.

Redesigning that wishbone is not a major job (yes, I know it's RR's job, really, but if you run a high-powered variant of a kitcar, you have to face doing a bit of development work yourself from time to time). If you'd expended half the time and effort that you've spent bitching about it on actually fixing the problem (and maybe sharing the solution with the factory and fellow owners), you might be a happier man?

[Edited on 30/8/18 by Sam_68]

Axe to grind...well I'm not impressed with RRR I think it's fair to say that. I tried all avenues of communication to get assistance but received non. You have to remember that this car was sold to me factory built and originally had a 400bhp LS V8 in it. I paid £9000 for the chassis and I was expecting something reasonably decent. The seat mounts weren't welded in properly, the powdercoating was awful, some of the welds on the cage were missing, then they criticised the fact M12 bolts, instead of M14, were used in the diff...when they installed them there (so they have admitted to their own negligence). The prop they sent me was a UV joint and CV joint combination and I let that slide but £300 for something they should have known is poor engineering, I even got back in touch to tell them to change it for future customer. Didn't even get a thank you. I just think that's unacceptable. Shit happens and everyone bleeps up (I am certainly no exception), but it's how you deal with that which sorts the wheat from the chaff.

I know the wishbone looks like it's bending, but it is the lug mount. I thought it was the wishbone too until we did that test. Still, I'll add some guessting to the wishbone. I was looking at making new ones as you said, but making a new mounting point further back would be extremely difficult and involve significant cutting to the chassis which I'd rather not do.

quote:
Originally posted by russbost
Again I'm inclined to agree with Sam, as I said b4 the amount of movement in any double wishbone system on a 7 type vehicle looks quite shocking when you load it up in the brake rollers, but is , nevertheless, normal. Would you expect to get as much movement as you are if you load it up with a bar as shown - well, no, but I think the movement is largely not where you've said, but within the actual wishbone itself.

Have they updated the design or is that wishbone still what they are selling? It looks like the sort of thing a bloke who could use a welder but didn't know too much about engineering or how forces are transmitted might knock up in a shed &, as said, it wouldn't surprise me if an IVA inspector wasn't satisfied it could safely do the job required - the base of the pivot end is far too narrow & the outer end should have the two tubes joined together at the tube for the top ball joint, I'm guessing that would cause the tube to foul the shock, hence why they've done what they've done - that said, presumably there are dozens of these running around without problems as I can't find loads of stuff on the web referring to issues others have had

I do have some sympathy with the company as I frequently get people ask me can I put a "Blah 123xyz" motor in it - it'll make 400bhp - to which I answer that the main chassis will take it, but that I can't answer for the suspension as it was never designed for significantly over 200bhp & certainly would not do it without beefing up suspension, pickup points, possibly adding further triangulation or some form of load spreader at stress points etc etc - I also point out that perhaps a brake upgrade & some bigger wheels & tyres might be in order - Oh! look, we've just spent loads more money on one "simple" upgrade which maybe wasn't needed in the first place. I am always happy to help a customer achieve what they want, but do sometimes need to bring peeps back to reality (& within their budget!) - on the other side of the coin even with a bog standard Mazda setup I don't think I'd ever feel confident in stamping on the brakes from any significant speed with a wishbone like that ...............

Yeah, as with the comment for Sam, it really is the lug that moves, just that the video doesn't show it quite as well as I'd hoped. Remember, this car was factory built and originally had a 400bhp LS V8 in it so I thought my 250bhp F20C inline 4 wouldn't present any issue. Initially, before the diff broke and I redesigned the rear end with the RX8 solution, I made no modifications to what RRR had given me and that was the whole point - I wanted something I could get in and happily fettle, but not be required to perform large scale modifications to as I don;t have the time any more.

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Sam_68

posted on 31/8/18 at 10:13 AM Reply With Quote
quote:
Originally posted by Rocket_Rabbit
Still, I'll add some guessting to the wishbone. I was looking at making new ones as you said, but making a new mounting point further back would be extremely difficult and involve significant cutting to the chassis which I'd rather not do.

Don't just gusset the wishbone - that's a half-arsed solution applied by people who don't understand structures. It merely moves the stress raiser from one position to another.

If you're going to fix it, fix it properly. You don't need to move mounting positions or cut the chassis, you just need to design and fabricate a wishbone that is triangular rather trapezoidal!

Upper wishbones aren't all that heavily loaded, hence the distance between fore and aft chassis pickups isn't that critical. If you don't believe me, look at the upper rocker arm on something like a Lotus 79 F1 car, then ask yourself whether you think you'll be generating higher braking loads than a ground effect F1 car on slicks...

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Rocket_Rabbit

posted on 31/8/18 at 10:28 AM Reply With Quote
quote:
Originally posted by Sam_68
quote:
Originally posted by Rocket_Rabbit
Still, I'll add some guessting to the wishbone. I was looking at making new ones as you said, but making a new mounting point further back would be extremely difficult and involve significant cutting to the chassis which I'd rather not do.

Don't just gusset the wishbone - that's a half-arsed solution applied by people who don't understand structures. It merely moves the stress raiser from one position to another.

If you're going to fix it, fix it properly. You don't need to move mounting positions or cut the chassis, you just need to design and fabricate a wishbone that is triangular rather trapezoidal!

Upper wishbones aren't all that heavily loaded, hence the distance between fore and aft chassis pickups isn't that critical. If you don't believe me, look at the upper rocker arm on something like a Lotus 79 F1 car, then ask yourself whether you think you'll be generating higher braking loads than a ground effect F1 car on slicks...

Much appreciated. The issue now becomes one of clearance with the damper. In order to retain the same geometry and get clearance on the rear non angled arm, I will have to either move the damper mount or move the upper arm mount.

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Sam_68

posted on 31/8/18 at 10:54 AM Reply With Quote
quote:
Originally posted by Rocket_RabbitThe issue now becomes one of clearance with the damper. In order to retain the same geometry and get clearance on the rear non angled arm, I will have to either move the damper mount or move the upper arm mount.


There are other solutions that avoid that need: for instance, if you use a housed spherical bearing (as opposed to a rod end or ball joint) at the outboard end of the wishbone (with shimmed adjustment of camber, if you like) the arms would triangulate properly on pretty much their existing alignment, without any buggering about with the location of the damper.

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