Night before last, I went to work on the problem of the front shock mounts. I had to figure out where the shocks are going to sit up front, yet allow the needed space for the mounting and motion of the pushrod and bellcrank... AND allow enough room for the rack and pinion and other needed items.

Here's what I came up with, along with some newer photos of what the frontend looks like now. Also got some photos of the new Woodward rack that showed up on my doorstep last week:

The frontend as it sits after the work night before last:


Suspension is starting to take shape. You can see one of the rockers on the right side of the chassis:


Details of the suspension. I have all the brackets tack welded to the chassis now.


Final placement of the lower coilover mounts.


I custom fabricated these brackets with a little beer-box prototyping work and the plasma cutter. Took 1 hour from start to finish for the set. They are different front and rear due to the chassis width changing, so it was a bit of a challenge to get them right.


Looks like it should work. I have room to change the rocker dimensions should I need to alter the motion ratio.


Top down view:


Top down (front of chassis is up in the photo). Lots of room between the shocks!


With new steering rack mocked up in place:


It'll probably sit just a hair lower than this photo:


End of rack looks good for bumpsteer.. I'll be running the steering link off the bottom of the rack end to allow it to drop down. This will let me orient the rack a little higher to clear the nitrogen canisters on the shocks.


Its snug, but I think its entirely doable!


The new rack is a real work of art:


You can see how the unit is opened up to change the steering ratios:


Woodward Precision, indeed..


[Edited on 18/6/06 by datz510]

[Edited on 18/6/06 by datz510]

The front suspension is done and it works!!!

Fabbed up the rocker mount brackets today and got the front suspension pretty much done.

Here are the brackets I made:



This side is actually sitting on its own after I got it all mocked up:


The rocker in place.. perfectly straight shot to the pushrod mount at the wheel.


Here you can see that at ride height (left), the shock is compressed about halfway, which is right where I wanted it.


A couple more views of the rocker assembly:



A shot of the whole frontend.


I have decided to change over to the 2003-2004 Yamaha R6 shocks in the front, which puts the nitrogen canister parallel to the shock body. I decided this after looking at the clearance between the pushrod and my tie rod with the rack and pinion set in place.. it looked way too tight of a fit. I figure that I can move the rack forward if I go with the later shocks, as the only thing in the way is the nitrogen canister, not to mention this will give me springs that are the same, left to right. The r6 shocks I have now have different springs on them for some reason.


Here is one of the 2003-2004 R6 shocks:

Blimey!!!

Very, very nice job!

Thanks for the kind words, guys!

The only thing I will really need to do on the front suspension is alter the rocker pivot to include an oillite bronze bearing. Right now, its just a 1/2" bolt going through the eyes of the rocker triangle, which works, but would probably get a bit sloppy over time.

FWIW, total cost for parts (including the coilovers) for this pushrod setup will come out to about $130. The rockers are from a 2001 Yamaha R6 motorcycle and can be had on ebay for $5-10 a set. The coilovers are second hand 1999-2001 Yamaha R6 shocks off Ebay for $20 each. The most expensive part is probably the heims for the pushrods at 4 @ $15 each and the misc nuts and bolts I needed (about $30 total).

It was a hell of a lot cheaper to go this route than with standard outboard coilovers.

[Edited on 18/6/06 by datz510]

Thats just porn, that is.

looks good! i too noticed that r1 and r6 shocks change over the years, not sure what differences there are besides the angle of the canister. They are closer to £20-£30 in the uk.

[Edited on 18/6/06 by JoelP]

welding looks good on the frame, is that tig on the completed bits?

my only observation would be that where the tie rod on the top wishbones is on the outboard end i'd of sandwiched the rosejoint between two plates, not justed bolted the rod end to one plate.

but nice work.

Ned.

ps looking closer is that rod end i mentioned some sort of clevis? if so disregard the above the contact area on the front top wishbone bracket looks 'ish' with the angle the bracket is aligned at, are you going to just weld round it as is or fillet it or something to strengthen the weld area?

[Edited on 18/6/06 by ned]

I thought that's how those clevis pin type things were supposed to attach? Hence the slot in them? Could be wrong, it's been known to happen....

quote:

---

Originally posted by ned
welding looks good on the frame, is that tig on the completed bits?

my only observation would be that where the tie rod on the top wishbones is on the outboard end i'd of sandwiched the rosejoint between two plates, not justed bolted the rod end to one plate.

but nice work.

Ned.

ps looking closer is that rod end i mentioned some sort of clevis? if so disregard the above the contact area on the front top wishbone bracket looks 'ish' with the angle the bracket is aligned at, are you going to just weld round it as is or fillet it or something to strengthen the weld area?

[Edited on 18/6/06 by ned]

---

istr last time mig welding like that was showcased, it was said to be a really bad idea. was it due to cold spots or something like that?

i could be completely wrong, but i'd probably be happier with a nice seam.
tom

I'm not a pro welder... but I have built quite a few offroad rigs, rock crawler suspensions, and other parts that get abused heavily and none of them have ever broken a weld. Having said that, I'm really not too worried about my welds.

The problem with laying a solid bead on some of these parts is that the intense heat can warp the part fairly badly.. at least thats what I've run into. So, I lay a row of dimes, stop, wait a while, and then continue on.

BTW, I was not showcasing the weld on my upper A arm there.. that was posted in response the question regarding the clevis attachment. I know its not ultra-pretty, but it will work just fine.

IMO, it is just personal preference how the final weld should look:

quote:

---

While moving the gun forward consistently produces a sound weld with decent appearance, some people like the appearance of an overlapping bead profile, which is sometimes referred to as the "stack of dimes" look. This takes practice.

The "stack of dimes" look can be achieved a couple of ways. One is through a forward or push movement of the gun, then a slight back step or hesitation, and then moving forward again. Another method is using an overlapping "C" motion of the gun. This produces the "CCCCC" look of stacked dimes. Remember to make your individual beads close together. If they are too far apart, to the point where the toes of the weld become widely separated, the weld can fracture at any of those indent points (stress risers and/or crater cracking). Note that on 0.120-in.-wall tubing, melt-through and/or warping may occur if you make too long of a weld bead using this technique. To minimize heat input, make several short welds rather than one long one. Also, consider skipping around a frame, making a short, partial weld on one joint and then moving to a different part of the frame. This gives the weld a chance to cool.

---

The shockers are upside down. I don't know if this will affect the damping, but they run the other way up on the bike.

Get ready for some spring swapping as well, the original bike springs are 540lb ish so they will be a bit on the stiff side for the front of a car unless you change the linkage ratio.

Thanks for the info on the shocks. Only problem is that I dont know if they can be turned around right way up, as they only have a bearing on one end.

I seem to remember a discussion over on one of the other locost boards mentioning that they will work either way. They seem to work ok when I jump on the front of the car.

As far as the spring rate goes, it will be a little stiff for now. It will definitely require some fine tuning once I get it on the road, so I'll deal with that aspect when I get there. It is set up now with enough room to allow me to change the rocker out to alter its ratio.

you can just turn the rocker around to improve it somewhat, currently it appears to increase effective spring rate by 1.5 (ie, to 750lbs/inch), switching it round would reduce it to roughly 450ish?

I'll have to take a look at it. I dont think I have enough room to just flip the rocker. I'd have to make new ones from scratch. Not that big of a deal, but there may be other solutions. I believe the current ratio is closer to 1.2:1 than 1.5:1.

One other thing, Keep in mind that I'm running about a 40 degree angle on the pushrod, which gives a much greater reduction in spring rate. If the shocks are currently 540 lb/in, with a 1.2:1 ratio, that gives about 416 lb/in at the wheel.

I've been looking at coilover springs. I can get 8" coils for about $40 each in any spring rate from 200-500 lb/in, so I might go that route. need to pull one of these springs off and see if it is close to 8" free length.

Found a place called Hyperco that sells any coilover spring imaginable:

http://www.hypercoils.com/Catalog.aspx

They carry everything from 1.4" to 3" ID and from 4" to 12" in free length. Prices are around $50 each.

well, on the plus side, with the shock that way up you have minimal unspring weight as its the light end you are moving. And you are right, the push rod is at a fair angle to help the spring rate down.

You could try sticking weights on the front to measure the overall effective rate?

When I let the car down onto the suspension, you can see in the photos that it compressed the shock about 1". The engine and tranny combinaton in the car weighs around 490lb, and mabye half of that weight plus the weight of the chassis for that corner was on that wheel. So, mabye 300lb on that corner, compressed the shock halfway. It is a bit stiff, but since it has compressed the shock and spring so far, the rate at the wheel doesnt appear to be too terribly high.

Once I get the other rocker assembly and get the whole frontend on the ground, it'll be a little easier to measure the wheel rate.

I'm always bemused when I see these cars with 'pushrod' suspension. Why do it? If only to say that you can?

It adds cost, weight, complexity, and stresses that are unnecessary in a car of this type.

Reengineer the front wishbones and damper pickups to be as they should, and the job is done.

Cheers,
Syd.

Noticed that your shock mountings do not look to be parallel, with most shocks this is not a problem, but you will need them parasllel if using the R6 shocks due to the use of a needle roller bearing in one end. The shock is only designed to move in one plane, and by not having the eyes parallel it will be introducing stress into the mountings.


Syd, it's to prevent the paint on the shocker getting chipped.

I don't see how it can add cost. He's said it's cost him pennies so far, but he has made many pf the bits himself. However, much less than a new set of shocks would be. And it does make the front end look a bit 'cleaner'.

Gaza, the shock ends are a slightly off. The end mounted to the chassis has a rubber bushing in it, so it should be fine. If it was a roller bearing on that end, I'd definitely have them in line.

quote:

---

Originally posted by Syd Bridge
I'm always bemused when I see these cars with 'pushrod' suspension. Why do it? If only to say that you can?

It adds cost, weight, complexity, and stresses that are unnecessary in a car of this type.

Reengineer the front wishbones and damper pickups to be as they should, and the job is done.

Cheers,
Syd.

---

datz510
Nice work there But i can't help notice that the dampers are in the spot where you might expect to find that wonderful piece of machinery from Woodward. I fear that moving the rack so far back might cause some unwanted ackerman effects.

Syd Bridge
As most open wheeled race cars take all those drawbacks there must be some advantages too.

leto.. it is going to be tight.. that is for sure. I'll cross that bridge when I get there.

One real advantage of a pushrod suspension is the ability to adjust the ride height of the car without touching the shocks. I'll be able to set damper rebound, spring preload, and ride height independently.

[Edited on 20/6/06 by datz510]

One other thing I wanted to post.. I'll be picking up one of the 2003-2004 R6 shocks tonight. Because of the parallel nitrogen canister, if needed, these will allow me to rotate the lower mount to put the shock eyes parallel to eachother.

If I got this right, moving the rack back will make the inner wheel turn faster and the outer wheel turn slower. When you transfer wight towards the outer wheel, accelerating, braking or turning sharper, the car will under steer. And when you transfer weight back towards the inner wheel, going out of a corner, the car will over steer. Moving the rack forward will have the opposite, and to my ears more desirable, effects.
I have no idea how significant this effect will be or if it can be compensated. So I might be howling “Wolf” here.

Ackerman effect

Yes, moving the rack back helps generate ackerman angle:

http://www.stockcarproducts.com/steer12a.htm

quote:

---

Fig. 3 - The front end has now been improved by altering the spindles so that their steering arms are permanently diverged with the wheels still pointed straight ahead. This will generate positive steering toe (Ackerman) while eliminating the necessity for static toe-out. A further improvement has been made while they were at it: the rack has been moved an inch rearward, which not only helps generate Ackerman but, as a bonus, straightens the push-pull alignment of the tie rods as the steering angle increases. Compared with Figures 1 and 2, this is going to feel like a whole new ball game. Not only will corner entry be more positive, but it will now be easier to control the car in a slide.

---

quote:

---

, it's to prevent the paint on the shocker getting chipped.

---

The gain is that I have something in the end that both works and is unique. I dont WANT a car like everyone elses. If my chassis gains a few pounds doing this, so what?

Building unique personalized vehicles is what I like to do. If I put a dollar value on the time I've spent building things, I could have been a millionaire long ago.

I find it funny that someone can say to another that they shouldnt think outside the box and explore something new, and instead should just can it all and do it the "accepted" way.

Mabye I get a lot of joy out of solving problems? and spending time tinkering in the garage playing with metal? It is relaxing for me to dive in and try to figure out these problems. In the end, I'll have a unique and fun car to putter around in, at which time I'll probably sell it to build something else... and the cycle goes on.

To each his own... This is my car.

[Edited on 20/6/06 by datz510]

yeah, if we cant do things our own way, what's the point in building your own car.

incidentally I was looking at a shiny new cossie powered caterham on a dealer stand at a show, and they have gone to pushrods on that model at least.

i've been toying with doing either push or pullrod suspension for mine. why? well it keeps the shocks clean, looks neater, potentially allows a wider choice of shocks, is more adjustable, and mostly because I feel like doing something different!

STill bemused and amused. Puddin' heads, the lot of ya. If you must you must.

As for Caterham, how much extra do they charge? Plenty of bling and sales hype 'added value'. Not much else.

Cheers,
Syd.

[Edited on 22/6/06 by Syd Bridge]

Pros and Cons of inboard shocks.

PRO

You can get a 1:1 motion ratio. This is good for damping and makes spring swops dead easy.

It keeps your expensive dampers out of the road dirt and wet.

Structurally you can keep all the forces quite central on the chassis without having to cantilever out mountings for the shocks.

It gives a clean front end.

CONS

Extra complication and weight, brackets rockers etc.

The rocker pivot bolt sees double the load compared to the other bolts in the system.

Anti roll bar mounting can be awkward.

It takes up a lot of room in the car.

I have inboard suspension on my car and the biggest attraction to me is the 1:1 motion ratio. However in future if I could get a 1:1 motion ratio with outboard suspension I would probably go that route.

John

[Edited on 23/6/06 by JB]

The big benefit of a pushrod suspension is not reduced drag, it is the possibilities in suspension tuning and setup. If you know what you are doing, keeping the dampers out of the dirt is a great way to make a locost faster.

The biggest attraction of inboard suspension for me is that you get rising rate suspension, which curiously noone has mentioned?

Mark

Standard suspension is rising rate as well, but for the amount of travel used, its not really important.

I have to say this is a rather crazy argument to get into. Actually, the localized aero advantages of replacing a spring over damper with a push/pull rod is pretty good, but when factoring in the rest of the package is does rather dwindle. The reasons regarding suspension tuneability are quite good and true, as long as the time has been put in to optimize the package within reason. There actually are no unsprung weight advantages, an negligable if any moment of inertia advantages. There could be slight CofG perks, but again usually minimal. Actually, the overall mass of the system, if roll bars are to be used, should come out pretty equivilant since the roll bars can be made considerably shorter and thus lighter to make up for the added weight of the rockers and rods. Ultimately though, I have to say I agree that it comes down to building whatever gets your panties in a twist.

Cheers

I do not like changing rate for the following reasons:

I like a balanced, neutral handling car, this means it does what I want without excessive under or over steer. One way of altering the under over steer balance is to adjust the relative front and rear roll rates. A well set up car will be sensitve to this, for example on my car moving the anti roll bar drop link 20mm along the bar will change my car from undrivable under steer to un drivable over steer.

Now a rising or falling spring rate suspension changes the roll resistence. If the change at each end is the same then this is not a problem. However the chances of this happening is very unlikely. So a changing rate suspension just adds another extra complication in this already very complicated and compromised business.

I can understand why people want rising rate and the dead easy way to do this is to use progressive bump rubbers on the coil overs. These will only come into play over the biggest bumps.

John

[Edited on 25/6/06 by JB]

Are you sure standard is not falling rate? The way I see it, as the damper compresses the angle between it and the lower wishbone becomes more acute, ie. falling rate?

As has been said it's probably not a huge deal on a locost but you can't deny the advantages of rising over falling rates.

quote:

---

Originally posted by Mark18
Are you sure standard is not falling rate? The way I see it, as the damper compresses the angle between it and the lower wishbone becomes more acute, ie. falling rate?

---

quote:

---

Originally posted by crbrlfrost
I have to say this is a rather crazy argument to get into. Actually, the localized aero advantages of replacing a spring over damper with a push/pull rod is pretty good, but when factoring in the rest of the package is does rather dwindle. The reasons regarding suspension tuneability are quite good and true, as long as the time has been put in to optimize the package within reason. There actually are no unsprung weight advantages, an negligable if any moment of inertia advantages. There could be slight CofG perks, but again usually minimal. Actually, the overall mass of the system, if roll bars are to be used, should come out pretty equivilant since the roll bars can be made considerably shorter and thus lighter to make up for the added weight of the rockers and rods. Ultimately though, I have to say I agree that it comes down to building whatever gets your panties in a twist.

Cheers

---

quote:

---

Originally posted by gazza285
? The angle gets nearer 90 degrees as the shocker compresses, hence rising rate.

---

Actually Sid, I don't care to revise any of them. My observations are accurate on aero, ie very local improvement with very little overall gain. On unstrung weight I am right again, inboard suspension often adds to unsprung weight, in both locosts and open wheelers. I said that would be small but mostly neglible gains in moment of inertia (most of the time they will still lie along the front axle line, sometimes just behind it, but considering the weight of the dampers in comparison to other components, its a relatively small change), and possible but not likely improvements in CofG (some people use pull rod and mount the dampers low, but usually it is rocker arm or pushrod with them mounted high. Overall weight of the system will probably even out if the often heavy rollbars are shortened and connected inboard. If no rollbars, you'll usually end up slightly heavier. Tuneability is the primary reason to include rockers of any kind, either inboard (most every formula car and many sports racer) or outboard such as the cantilevered Stohr DSR cars. Formula cars are significantly better positioned to take advantage of the aero gains so that is another good reason for their inboards. Seems my ultimate conclusion was to do what they liked as its their car. And taking a strong look back at my reasoning, it is accurate. Cheers.

You keep believing that stuff and my work will be secure for a long time.


Cheers,
Syd.

[Edited on 27/6/06 by Syd Bridge]

Syd,

If you have such a dislike of pushrod suspension, then why do you keep posting in this thread.

Alternatively, if you are interested in the topic but believe you can provide some proper justification as to why you wouldn't use it, then we're all waiting to hear it.

I know from other threads that you have a lot of experience and knowledge which you seem fairly willing to share, but then I keep coming back here and seeing yet another smug dismissive comment. What's the point?

I don't dislike it, quite the opposite in fact, just see it as unnecessary in a 7 type car. It goes against everything a se7en is meant to be.

Cheers,
Syd.

whatever sid. I've worked the numbers several times myself, and if you don't want to supply reasoning, then I guess there's no point in posting. Cheers

quote:

---

Originally posted by crbrlfrost
On unstrung weight I am right again, inboard suspension often adds to unsprung weight, in both locosts and open wheelers.

---

Actually, its quit simple Syd, unsprung weight is defined as all the mass that the coil spring has to react, which in the case of an inboard suspension, also includes the same amount of the coil/damper assembly as normal (although since most dampers on an inboard suspension are monotube, they can be oriented to take advatage of using the lighter, non-reservior end of the damper as unsprung), in addition to the linkage it has to react force through to control the wheel. Is it not the spring that then has to push the bellcrank and in turn the pushrod to react force to the wheel? Effectively you are adding mass between the A-arm and the end of the damper which all has to be controlled by the spring/damper. You can't look at it as what is hanging off the dangly bits of the chassis. When the wheel is forced into bump or droop, the pushrod and bellcrank has a mass that is accelerated just as the control arms and wheel hub assembly are. They are accelerated in direct relation to the spring/damper and not reacted directly to the chassis. Thus, they are unsprung weight. The"Unsprung" weight is all masses that have to be reacted at the spring. The reason for adding this weight is simply that the ends usually justify the means. Such as aero improvements on a race car (not just external,as is the case with a formula car, but more room to flow air to the underfloor and brake/hubs in a sports racer), and better leverages on the damper (typical locost probably see approximately .5-.7'' of travel at the damper of each 1'' of wheel travel rising rate, whereas a linkage can provide 1:1 or even better). The bonus of a greater ratio is the fluid velocity in the damper. The greater the movement, the more fluid moves through the piston causing easier tuning of the damper and less stiction per actuation. The other option to get the same amount of fluid flow on a typical outdoor suspension is to increase the piston area, effectively making the outside of the damper larger and again reducing aero efficiency. As with every other facet of engineering, designing a car is a compromise and the slightly added unsprung weight of an inboard suspension pays for itself in other benefits. And as stated before, the ability to then shorten roll bars to react at the bellcranks or dampers instead out at the wheels will most likely save enough weight that the mass of the overall system will probably be equivilant, the unsprung weight will almost always be higher. Cheers

PS, I may not have been at it for 20 years, but I also happen to make my living in engineering, and specifically automotive. And in all fairness, it is a common misconception that inboard suspension reduces unsprung weight. But, I'm not smug, I'm opinionated but always willing to learn. So if you'd like to get together and work out the physics, I'll bring the easel's. Cheers!


[Edited on 27/6/06 by crbrlfrost]

Oh, and just because I happen to be thinking about it, some very high end formula cars have managed to reduce unsprung weight slightly (although whether it would be below outboard I don't know) by running their pushrod directly to the upright instead of the lower A-arm, which allowed them to take the bending loads out of the A-arm and lighten it slightly, not to mention one less link between the wheel and the damper. Not that I would recommend this to anyone as I haven't analysed the consequences. I would think you'd want it as close to the bottom of the hub as possible to get the best angle, but it should also be inline with the steering axis to that steering movement wouldn't cause suspension binding. Oh well, random ideas.

[Edited on 27/6/06 by crbrlfrost]

Trusty seppo...if you can't understand the simplicity, baffle 'em with bullsh1t.

No dynamics and fancy maths and arguments involved. You're confusing the simple weights involved with the dynamic situation. Two totally different scenarios.

Weight and mass are simple things. Weight is mass under gravity. The weight of the coilover assembly is supported by the chassis and the wishbone, equally, in a standard Locost. So is a (much lighter) pushrod. The spring also has to support the extra weight of the added mechanical linkages as well. Otherwise, you'd be adding components, but not adding weight. Unobtainium, only available in the good ol'.....

When the coilover assembly is put inside the chassis, the weight of the coilover is then supported entirely by the chassis.

Therefore, the sprung weight is increased, and unsprung decreased. I think even the least educated on the forum can understand this.

It's really that simple.

If you have trouble with that, then you better go back to your books.

Cheers,
Syd.



[Edited on 27/6/06 by Syd Bridge]

[Edited on 28/6/06 by Syd Bridge]

what if you hung a 50kgs lump of lead on the end of the shocker syd? It doesnt matter if the shocker is inboard or outboard, for the wheel to move, the lead must move. You could call it increased unsprung mass, but i dislike the term myself as it is an inaccurate description of what it commonly represents. Im afraid that mr frost is correct here.

Unsprung mass in an outboard situation is commonly added up as the hubs, brakes callipers wheels tyres, half the wishbones, half the spring and the mass of the part of the shocker that is moving. You could even pisss about adding up half the brake flexis and some fluid. This isnt quite accurate anyway, as for the wheel to move 1 inch, the shocker might only compress half an inch, depending on angle and leverage ratio, so you cant add it all up as equal. Likewise, its not the literal weight of the wheel as it hangs free, because in an inboard scenario some of the mass of the rocker would be pulling in the opposite direction. Imagine trying to weigh a seesaw as it pivots. Maybe rotational inertia would be more accurate for comparisons, but again, its not quite right. The only perfect way to compare two different setups would be to measure the inertia vertically at the wheel, ie, apply a specific force and measure how fast it accelerates. You could then use this to calculate a mass for comparison, but the calculated mass wouldnt equal the sum of the components exactly.

Anyway, its all a little bullshitty. The fact is, the man wants to build an inboard suspension system.

quote:

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Originally posted by JoelP
what if you hung a 50kgs lump of lead on the end of the shocker syd?

---

Wow, you mean you have actually been served something hot from macdonalds? now THAT is a revelation

well syd, its not that i like having a 'pop' at you, but IMHO, you're wrong, and i do love arguing unfortunately. But then, so do you

It would seem that you accurately describe unsprung mass then, though i might add that if you remove the shocker in an inboard situation and do what you suggest in your post, the rocker too will be pulled down by the wheel. Removing the push/pull rod is like removing the lower bracket in an outboard situation.

However, i still say you are wrong because, when people talk about reducing unsprung mass, they are aiming to make the wheel move easier over bumps. You are describing literal unsprung mass, which is a worthless concept - who cares if the wheel doesnt drop at all (ie zero unsprung mass) if there is a bloody neutron star perfectly balanced on the rocker? The wheel wont move at all whatever you do.

To get the wheel to move easier over bumps, you want a low inertia, as i described on my last post.

Anyway, lets not fall out over this. We might even end up arguing about antisquat!

Love, Joel.

It seems you both have different interpretations of what unsprung weight is.

My understanding is.... all that is controlled by the spring / damper. So this includes the pushrods and rockers (or a proportion of).

In most cases an inboard set up increases unsprung weight due to the extra pushrod and rocker.

Suspension is all about compromise and I am willing to sacrifice extra unsprung weight for a 1:1 motion ratio by using a rocker suspension.

John

I have just done a Google search on inboard suspension unsprung weight.............

Most say that you get a reduction in unsprung weight with an inboard suspension.....even the Porsche website.

HOWEVER I found a posting from a top Formula Student judge who concurs with my thinking.

"Dear Pat,I have been reading your tech introduction paper for beginner Formula SAE teams, and I think Idisagree with something you have said.When you wrote about the virtues of mounting the shock absorbers inboard, one virtue youmentioned was a reduction in unsprung weight.I cannot understand that, as I think that anything that moves when the wheel moves up and down isunsprung weight. In this case, the shocks would be unsprung regardless of being mounted inboardor outboard.Am I wrong, or is there something I have failed to take into the equation. I look forward to yourresponse.Regards(Name withheld by request)


Hi,Thanks for the feedback. You don’t know how good it feels to have proof that someone actually reads the stuff Iwrite.You are correct of course, anything that moves with the wheel is unsprung, or a percentage is depending on thesuspension motion ratio.Having reread the article, I see I was less than clear on that point. What was in my head at the time was thatwhen coil-over suspension units are mounted outboard, usually the damper body end is mounted to thesuspension and therefore is ‘live’, whereas when the coil-over units are mounted inboard, usually the heavy end ismounted to the chassis, and the lighter shaft end is ‘live’. This is why I wrote there is ‘usually a reduction inunsprung weight’.Of course, there is no reason that outboard dampers cannot be mounted with the body end to the chassis, as longas these dampers are suitable for inverted use. I didn’t take into account the unsprung weight of the actuating rodand the bell-crank, so all in all, there is probably very little saving in unsprung weight with inboard mountedsuspension.Again, thanks for the feedback, and next time I revisit that document, I will correct it.RegardsPatTech Q & A – Pat ClarkeFormula SAE-A Newsletter – Page 6August 2003



I have been a chief design judge so know Pat and he has good credentials.

I hope this clears up the argument.

John

Thank You for the kind u2u's, you know who you are. And to the dear gentleman with the suggestion re my head and anus; I would if I could bend that far.

I just love it when people fail to grasp simple things, then resort to those blessed Staniforth books.

The best analogy of what is going on is a piston and conrod in an engine.

They whizz about at great speed exerting great force on the crank.....BUT...they still weigh something. They still have to be supported by something. Otherwise, when the engine was running it would weigh less than when it was not. As the crank turns it has to push the piston up against its own weight. As the piston comes down, it still exerts its own weight on the crank. Doesn't it??????

The confusion here is between simple weight(mass under gravity), and the dynamic forces when it all moves. Two completely separate sets of numbers. Whilst one involves some of the other(and at my age a bit of 'the other' is a non-occurrence. ), the converse does not apply.

These foreigners do so like to get all unnecessary with themselves.

I wonder if Mummy will send him to bed with his boxing gloves on tonight?????

Cheers,
Syd.

[Edited on 28/6/06 by Syd Bridge]

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Originally posted by Syd BridgeThe confusion here is between simple weight(mass), and the dynamic forces when it all moves. Two completely separate sets of numbers.

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These foreigners do so like to get all unnecessary with themselves.

I wonder if Mummy will send him to bed with his boxing gloves on tonight?????

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Thank you Joel, not for agreeing with me, but for not taking things on blind faith. Gecko, I realize mass and weight are not the same thing, but often for these forums they are close enough for banter. Anyway, while driving around today, taking the 325 for a spin through the hills, I figured one of the mental blocks for some might be the fact that in reality, the bellcrank's mass is (when static) completely supported by the chassis. However, the moment it starts to move, and thus develope inertia, that force must now be reacted by the spring/damper and adds the the inertial reaction caused by the acceleration of the unsprung "mass."

Sorry Syd, none of this is BS, but since I don't have a good picture, a 1000 words will have to do. As I said, I would be more than happy to argue this out using math, but it might not go well on the forums. Besides, you don't have to take Stanifoth's or my word for it either, you can gladly check out most engineering texts, VanValkenburg, Rowles or Milliken and Milliken. Cheers!

Ps, I thought you had more things you wanted to argue than just unsprung weight. Or are we to busy with this already?

Oh, sorry to interrupt again, but I had a thought. While we're raising and lowering cars for giggles lets analyse another scenario. We've agreed that if you take the spring damper out of an outboard suspension, then the sprung mass falls to the ground. We've also agreed that if we remove the pushrod from an inboard suspension, the mass again falls to the ground with the spring/damper removed from the system and thus part of the sprung mass. But since we seem to be getting a little more technical these days, lets compare apples to apples. If we take the same inboard suspension, and remove the spring/damper just as we did with the ouboard suspension, and leave the pushrod in place, what happens? The sprung mass falls to the ground. Ooops, thats made to much sense.

[Edited on 28/6/06 by crbrlfrost]

[Edited on 28/6/06 by crbrlfrost]

Ok, I've been mixing mass and weight.

Try this....

Just take the spring out of any of the systems, what happens?

What falls towards the ground under its own 'weight', relies on the spring to hold it up. Sprung 'weight'. 'Weight' because it has gravity acting on it. All things have weight, so it can't be ignored, as you seem to be want to.

What doesn't fall, doesn't rely on the spring, so is 'unsprung weight'.

The bits that don't quite do either, are partially 'sprung weight' and partially 'unsprung weight'.

When it is all moving, we come into the realms of dynamics, where everything attached to the bit that finally pushes on the ground, is dynamic 'mass'. But note, this mass does not include the damper body(unless it moves and is not fixed to the chassis), and this 'mass' still has to be supported statically, so exerts a 'weight' on something.

Just because it starts to move, doesn't mean it loses its 'weight'. eg. The bellcrank...When moving, it is still supported by the pivot, so exerts its 'weight' on the pivot. It doesn't stop having 'weight', just because it starts moving!!! But, it does start to exert more and different forces on the components it is attached to, due its momentum and thereby inertia.

You are failing to separate the static situation from the dynamic. The two are real, and separate, and different.

There, simple enough?

And I am personally well aware of the texts you quote, even one of the writers. None would disagree with what I have just put above.

Now you can go and have another look at your polar stuff.

Cheers,
Syd.






[Edited on 28/6/06 by Syd Bridge]

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My understanding of this subject has always been that it is ONLY about the dynamic situation i.e. it's about the inertial mass of the components NOT the gravitational mass (aka weight).

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Note: a sense of superiority is very often not accompanied by actual superiority.

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Originally posted by Syd BridgeEverything exerts weight, and to ignore it is poor engineering indeed.

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Who is that aimed at? You better watch out that a mirror doesn't suddenly appear in front of you.

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Well, frankly, I'm tired of beating a dead horse. It's gone from simple fact to symantics and without a specific system we can't even argue exact masses. Ignornace must be bliss Syd. Anyway, I have a formula car and a prototype hybrid to attend to. And then, the coolest project of all, a soapboxer for 4th of July. Fireworks, beer and gravity. Will the good life ever cease? Cheers guys!

[Edited on 28/6/06 by crbrlfrost]

All very sad really.

You see, I understand what you fellas are saying, what it's about, and know the subject area.

The sad thing is, you don't understand what I'm saying, don't seem to want to, and just keep saying I'm wrong. Without understanding what I'm saying!

If it's not in the little that's in your books, it just don't exist. Thing is, the fellas that write the books and who are actively working in the industry, rarely publish all they know. You get the rest at seminars and over a beer after a long testing and development session.

I'll leave you lot in your own little blissful worlds.

Cheers,
Syd.

Arrogance knows no bounds. I know exactly what you're saying and thoroughly disagree on the basis that I've done the computations, and testing, and the modelling, and frankly, that has nothing to do with the books. I've also talked to many old race engineers, and the funny thing is, is that even they disagree with each other. The obnoxious thing about your arguments is the lack of basis in the actual science of it and your smugness. Frankly, I wouldn't want a lawn mower based on those priciples. But to each their own. On the matter of moment of inertia, that is actually one topic where you are right. If the rest of the package is already optimized the relocation of the dampers can have a good effect, but primarily in a small package (formule type car). Versus a Locost where the movement of the engine by an inch would have a far more drastic effect. Anyway, go bury your head in the sand. Cheers

just to get one thing straight syd, i have read no books on the subject, nor have i seen this subject on the internet. The stuff I posted, I actually worked out myself, and it is quite simple. One minute you say we are wrong and the next, you agree its about inertia.

Darn Joel, you beat me to it. I was just going to say that if someone wanted to choose for themselves to simply do the sums. The accelerations are easy to figure, the moments of inertia calcs can be found by anyone in a machinist handbook or statics book and the masses are easy to estimate. Happy building/engineering. Cheers

No, No,NO,No,No. I will not continue!!



But this won't be the last post on this, as there's at least one person who can't be seen to be wrong.

Cheers all,
Syd.

You keep believing that stuff and my work will be secure for a long time.

[Edited on 29/6/06 by Syd Bridge]

Rather than dropping either car to the ground to demonstrate, imagine holding the chassis still by bolting it to the floor and jacking up one wheel. All the bits that move despite the chassis being bolted to the ground are unsprung or partially unsprung, all those that stay still are sprung.

Chris

Just an update.. I got both sides of the front suspension together with the new 2005 Yamaha R6 shocks and checked the wheel rates. The wheel rates came out to right at 200lb/in at each wheel.

The suspension appears to work very well. I still have some fit and finish work to do (making spacers for all the heim joints), but for now, the front suspension is good to go.

For all the naysayers: Many in your general direction..

Only kidding...

I know there will always be people that disagree with the way others build their cars. If we all did them only one way, it would make for a very boring hobby, don't you think?

[Edited on 5/7/06 by datz510]

Couple photos of the suspension. The car is sitting on the front suspension in these photos:





[Edited on 6/7/06 by datz510]