reducing bump steer on lowered racecar

[rmicroys]

This question may be outside the scope of IT rules, but hear me out. I'm looking to reduce bump steer on my lowered Jetta. The A-arms and steering arms all point up, and are no longer parallel. So I want to flip the tie rod end over to the other side of the steering knuckle - using a rod end. Then what do most people use to relocate the lower control arm so that the pivot point is lowered as well - to make the arms and rods parallel for the lowered stance?

[Greg Amy]

R, thee types of mods are WELL outside the IT rules, and in most cases outside the capabilities of most hobbyists.

In "real" tin-top racing, like World Challenge and BTCC cars, and actual pickup points for the a-arms on the chassis are removed and rewelded into optimal locations. The bushings are then replaced with spherical or Heim Joints and the control arms are strengthened or replaced with adjustable links. The closest you're going to get to a bolt-on solution for your car is to seek out (or fabricate) bushings with an offset hole that can be biased as far "down" as possible. The result will not be significant enough to justify the expense however.

Your idea of flipping the tie rod ends is a good one, and will certainly help - but not resolve - your bump steer problem, but note that your tie rod ends are tapered. To flip the end will require your redrilling and retapering the knuckles, or drilling them to a straight through-hole and replacing the ends with a Heim join type affair. Another solution could be to fabricate mounts to raise your steering rack to compensate for the knuckle displacement.

"Real race cars" usually drill out the knuckles and use replacement adjustable steering links and Heim joint tie rod ends, plus they relocate the rack.

Bottom line, there's no easy "bolt it on" solution, other than simply not lowering your car too much... GA

[rmicroys]

Yes, knowing that there is no 'easy' solution is the first step.

Changing the pickup points of the lower arms on the VW is near impossible with the design of the subframe and how they hold the a-arms without reworking the whole subframe.

The solution I've seen require a rod end instead of a tie rod end on the steering arm. requries a longer steering rod, and then just bolt the rod end in single shear on to the steering knuckle on the underside.

Agreed, that in of itself solves nothing. Then the lower arm pivot needs to be lowered. A number of people I've seen make an adapter than then bolts in to the lower pinch point of the knuckle, and then provides a threaded boss for a bolt to go in it from the underside. Then one replaces the LCA ball joint with a bearing. The bolt goes up through the bearing in to the spacer bolting it tight. The spacer then goes in to the bottom of the knuckle. Then the steering rods and a-arms are level.

Redesigning the subframe to hold the a-arms in a different fashion would be a lot of work - but offers the most structurally sound solution.

[racer_tim]

Greg is right, but there is also another tweak that might work. Raise the ball joint up and keep the control arm level. Then reverse the tie rod to attach to the bottom.

That might gain you an inch or so, but bottom line, you want to keep the a-arms as parallel with the ground as possible, right Greg?

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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit
http://linerud.myvnc.com/racing/index.html

[rmicroys]

Did some research.

VW Motorsport designs from a Mk3 rally kit car. The leave the subframe OEM... but do this.

The simple system:

http://members.rogers.com/rmicroys/images/simple.jpg

Part #9/10 are the variable length spacer and bolt for the LCA. They have different parts depending on ride height for gravel/tarmac.

Then they have the fancy knuckle for complete adjustment of suspension geometry, caster, etc.:

http://members.rogers.com/rmicroys/images/fancy.jpg

[racer14itc]

Simply moving the ball joint up on a stock control arm just to level the "arm" part will not work. The effective arm is the line between the center of the inner pivot and the center of the ball joint pivot. You could have curley cue lower control arms, but it won't matter...only the inner and outer pivots matter. The only thing that works is spacing the ball joint downward relative to the hub carrier. You can either weld extensions to the bottom of the hub carrier, or install spacers similar to the VW Motorsports diagrams shown above.

Walt Puckett makes some great bolt on ball joint spacers but they require a heim joint at the outer pivot of the stock control arm. I've done this on my GP Sciroccos, and the first one I used stock lower control arms and 100% bolt on stuff. My current GP car now has custom tubular control arms (built by Walt...awesome stuff!) with all heim ends at the inner and outer pivots. This helped bumpsteer it and put the roll center where it needed to be. He also made me some cool tie-rod adapters so I could use stock tie rods and use rod ends at the outer end where they attach to the steering arms. They (the adapters) are drilled/tapped metric on one side and UNF for the rod ends on the other.

If you want the details on the hardware required, just e-mail me.

MC

Scirocco14gp (at) prodigy.net



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Mark Coffin
#14 GP BSI Racing/Airborn Coatings/Krispy Kreme/Tristram's Garage VW Scirocco
http://pages.prodigy.net/Scirocco14gp

[This message has been edited by racer14itc (edited February 02, 2005).]

[rmicroys]

Originally posted by racer14itc:
Walt Puckett makes some great bolt on ball joint spacers but they require a heim joint at the outer pivot of the stock control arm. I've done this on my GP Sciroccos, and the first one I used stock lower control arms and 100% bolt on stuff. My current GP car now has custom tubular control arms (built by Walt...awesome stuff!) with all heim ends at the inner and outer pivots. This helped bumpsteer it and put the roll center where it needed to be. He also made me some cool tie-rod adapters so I could use stock tie rods and use rod ends at the outer end where they attach to the steering arms. They (the adapters) are drilled/tapped metric on one side and UNF for the rod ends on the other.
Bingo. That's what I'm talking about. I'll pass that on to the guys that do a lot of the work on my car. They also race a VW, so we're looking for the right solution. He thinks he can find a longer inner tie rod so that there is no need for an adapter, and one can just get a female metric rod end. The LCA is pretty much a known. Need a bearing in a plate to replace the ball joint, and a spacer to the knuckle.

[joeg]

I still like Greg's mentioning moving the steering rack upwards as a bump steer solution.

Anyone try that in prod racing?

[rmicroys]

Originally posted by joeg:
I still like Greg's mentioning moving the steering rack upwards as a bump steer solution.

Anyone try that in prod racing?

It certainly offers a solution. I figure looking at Volkswagen's solution - it's a much more tunable configuration - because at least in a rally car one is going to change the ride height significantly for tarmac vs. gravel. So it doesn't make much sense to adjust the rack height between events - certainly more work and difficult access involved. To raise the rack you also would likely have to modify the steering column linkages to fit - so for tunability - that creates issues.

Now on a dry track car, in which the setting is not likely to be changed - then that does offer a bit more a solution. The next question is, is there enough room above the steering arms in full compression not to contact on the body?

Based on all the comments, things I've seen from the factory, and other people I've spoken to today. I'm going to investigate the following:

a - see if I can get a set of inner joints and sterring rods that are the right length to elimate the requirement of an adapter when using the OE steering rods

b - if not, get some adapters made, and look for some nice rod ends

c - get a bearing for the LCA made up

d - get an adapter made for between the bearing and the knuckle.

the rest is all nuts and bolts!

Thanks for all the insight guys!

[Fastfred92]

Care to guess how many bent ( heated up ) steering arms are out there... even in IT ?

[pfcs]

A2 power steering tierods are shorter (25mm?) than A3 tierods. A2 manual rack tierods are completely different.


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phil hunt

[racer14itc]

Originally posted by Fastfred92:
Care to guess how many bent ( heated up ) steering arms are out there... even in IT ?

No one would do that! That would be illegal...and nobody in IT racing cheats!!

http://Forum.ImprovedTouring.com/it/wink.gif

I've seen arms that were cut, flipped upside down and re-welded so that the stock tie-rod could be used (inserted from the bottom instead from the top as delivered from the factory). If you weren't paying close attention you wouldn't notice.

Re: moving the rack. I didn't have to move it to bumpsteer my GP car so I didn't bother.

MC

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Mark Coffin
#14 GP BSI Racing/Action Digital/Airborn Coatings/Krispy Kreme VW Scirocco
http://pages.prodigy.net/Scirocco14gp