Rear Uprights

[Conor]

I've been working on our new rear upright design and this year we're going to be mounting our toe link on the top of our upright in line with the control arm mounting point. This is the first time we've tried this, so I was wondering what the distance between the control arm point and the toe link point is for most teams. I know the suspension design and everything is important and I shouldn't be taking other teams' numbers, yada yada yada, but I'm just looking for a rough estimate. Thanks in advance.

[Conor]

I've been working on our new rear upright design and this year we're going to be mounting our toe link on the top of our upright in line with the control arm mounting point. This is the first time we've tried this, so I was wondering what the distance between the control arm point and the toe link point is for most teams. I know the suspension design and everything is important and I shouldn't be taking other teams' numbers, yada yada yada, but I'm just looking for a rough estimate. Thanks in advance.

[fade]

consider what the toe link does. control toe/steer angle. Look at aligning torque data for the tire you plan to use. Use that torque ( dont forget about any mech trail you might have)Consider the highest normal load (highest Mz) you expext to see. Once youve determined your overall compliance OS/US budget you can decide how stiff you want your upright/toe link to be.

[Conor]

I thought the stiffer the upright the better. Am I wrong with this assumption? I'm not too sure why you would want an upright to flex, but I've been wrong many times before...

[Jersey Tom]

Just make it as wide of a spread as practical.

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Conor:
I thought the stiffer the upright the better. Am I wrong with this assumption? I'm not too sure why you would want an upright to flex, but I've been wrong many times before... </div></BLOCKQUOTE>

Yes. The stiffer the better.

Also, the lighter the better.

So- it is important to know how stiff it needs to be.

[Conor]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
Just make it as wide of a spread as practical. </div></BLOCKQUOTE>

The was the basis I was going by and was hoping somebody would confirm. Thanks for the tip.

[Goran Malmberg]

I would not use the word "flex". I should say that the uppright will break if to weak. Make the distance as wide as will fit in the wheel. I have a 700 hp car that wheights in at 2400p and the distance is 170 mm, which is probabley moore than you need.
Goran Malmberg

[jowen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Goran Malmberg:
I would not use the word "flex". I should say that the uppright will break if to weak. Make the distance as wide as will fit in the wheel. I have a 700 hp car that wheights in at 2400p and the distance is 170 mm, which is probabley moore than you need.
Goran Malmberg </div></BLOCKQUOTE>

I'm not sure that you can have to much toebase. Wider toebase will result on lower force in the tierod and less material is needed to achieve the same stiffness. Our last years uprights did not break but when bending the wheel by hand, it was easy to see the deformation. The judges did not like it and I'm convinced that it is disastrous for the stability. But how much stiffness you need is a very good question. Has anyone of you made any scientific approach to that question?

[Goran Malmberg]

Well, of course an uppright can flex if not properly designed, and any uppright will flex to some degree if measured closley. However,it is not good for an uppright to flex, for two reasons. The wheel should keep its location and the uppright should not break (in this case by the time).
So, the design of the uppright should be such that it eliminate flex to the greatest extent.
Such "flexfree" design will break pretty soon if forced to flex. What we are looking for here is a flexfree design that are also light, and this is sort of walking a tight roop between flex and strength.

Sorry to say, but I have not study uppright flex and strenght, that is one thing I missed. My last rear uppright is 4,4 pound designed for a 2200p 600 hp car (Nordic Supercar Cup). It is made from 2mm chrome molley sheet metal welded in "box" design.
Not very seintific as it is overzised to be on the safe side. But the design is fairly sofisticated(compared to common stuff)and appear rock solid. But from impacts I have learned that this sort of upprights show crackings before the wheel hit surrounding parts,like A-arms and calipers very close to the wheels.
Regards
Goran Malmberg

[adrial]

You can design the upright geometry to minimize load in the toelink under accel/braking.

You should also consider slop within the joints when you chose a toe base.

Essentially...bigger is better and it is easiest to get a big toe base without compromising upright geometry by doing a center toe link (5" for 13" wheels). You have to design with bump steer in mind when you do this, but bump steer of any significance can be designed out of the system.

It's really just a guessing game...best to error on the side of too stiff when there are so many variables. It is easier to figure out how stiff to go when we are talking camber compliance...for those of you that have tire data.

[Chris Allbee]

Things often overlooked or misunderstood in upright design:

Torsional Stiffness. Who wants radically changing slip angles?

Bolted Connections/Joint Preload. When was the last time you saw correctly sized bolts with correctly toleranced holes for the application. Beyond that, how many of you use a torque wrench to install critical suspension fasteners?

And as adrial has mentioned, Tire Data. That will pretty much answer your question of how stiff is stiff enough when you examine the tire's sensitivity in certain areas.

So how stiff? Stiff Enough.

[jowen]

But the tire data does not say how much the grip is affected by normal load variation. Which is the reason why low unsprung mass is more important then sprung mass.

What is a correctly toleranced hole for a rodend joint? I always thought that you make sure that you have enough preload so that you have enough friction to hold the ball in place.

[fade]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> But the tire data does not say how much the grip is affected by normal load variation. </div></BLOCKQUOTE>
actually it does. the tires were tested at different normal loads. plot Mz vs SA for different Fz for aligning torques. similar for Fy ,Fx for cornering stiffness and slip ratio stiffness. Or use a peak SA for a Fz and look at the effects of grip (Mu) vs Fz.

[Goran Malmberg]

I have a philosophy I call the "Zero-car". It is simpley a car one advanced step ahead of the "flintstone car". Some of its feature is that it has no scrub distance, 0 dgr SAI angle, no caster, parallel equal lenght A-arms etc.

Applied to the uppright it will put acc and braking forces right in the middle of the SAI axle, (even if it in this case is a rear uppright without "steering axis"), eliminating twisting of the upright. Even vertical forces will very much be located in the centre of the uppright.

Goran Malmberg

[jowen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by fade:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> But the tire data does not say how much the grip is affected by normal load variation. </div></BLOCKQUOTE>
actually it does. the tires were tested at different normal loads. plot Mz vs SA for different Fz for aligning torques. similar for Fy ,Fx for cornering stiffness and slip ratio stiffness. Or use a peak SA for a Fz and look at the effects of grip (Mu) vs Fz. </div></BLOCKQUOTE>

I guess I wasn't clear enough with my question. The tire data is logged during nearly steady state conditions. What happends with Fy if Fz varies fast - like of you were driving on a rough road. Can you look at what average Fz you have, and than estimate Fy from tire data? Or maybe it is more correct to look at what minimum Fz you had during the cycle and see what cornering force that corresponds to. Is it that type of phenomenons you can see in transient tire data?

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Bolted Connections/Joint Preload. When was the last time you saw correctly sized bolts with correctly toleranced holes for the application. Beyond that, how many of you use a torque wrench to install critical suspension fasteners? </div></BLOCKQUOTE>

I'll admit I f'd up on bolted connection design on my upright design. Costs you a heap of grip. Take the extra quarter pound of weight..

I did install every upright fastener with a torque wrench though.

As for grip sensitivity with high frequency load variation.. no. You wont get that from the tire data. The flat trac had a hard enough time with quasi steady state control of load on these tires.. much less rapid variation. Plus the frequency at which that's gonna happen is track and vehicle dependent, and this competition has a lot of variation there! I wouldn't worry about it too much. Suffice to say every tire is gonna lose grip like that.

[Christopher Catto]

again, my bad habit of briging back the dead (old posts)

guys, every single time i read rants about how stiff components are, it always brings up the same problems. the whole system has not been completely defined. all who posted have COMPLETELY forgotten the bearings!

now, if anyone tells me that two bearings which are say 80-120mm dia and spaced apart say 40mm are stiffer than your upright and toe link I am not gonna believe it.

basically, your bearings are your weakest point in the system. you can have super stiff uprights and it wont help. look at the assembly:

1) rod-ends or spherical bearings. linear deflection maybe 0,2mm max due to compression of the teflon lining and due to tolerances

2) toe link. deflection practically zero. even if you had a 1/2 inch tube with thin wall I doubt you could measure it

3) upright bracket. linear deflection along its span due to torsion probably 0.1 mm if you use some thin steel box section or aluminium. it is quite easy to check the deflection of a box section.

4) rear bearings. check the deflection by mounting a big bar on your wheel or on the brake rotor. You will be VERY surprised.

As for having a central toe link like F1. This may help if you want to have your upright so shaped as to put the brake calliper low-slung. otherwise I would not both bother with the need to setup your toe everytime you change the camber.