Performance Alignment

[DeaconBlue]

Although street, autocross and road racing require different alignment settings, I thought I would throw in a set of road racing alignment specs into this discussion. These are from Eric at Rickety Engineering. They were originally from either Vadim or Doug.

front;

caster +4.5 to +5.0 (move the SF as far forward as possible)
camber -1.50
toe 1/16" out total with stock strut rod bushings
toe 0 with poly or TRP bushings

rear;

camber -0.05
toe 1/16" out with stock strut rod bushings
toe 0 with poly or TRP bushings

Of course total thrust angle must be zero.

On the street you would want less front camber and slightly more rear camber (something like -0.20)

 

[shooff-usa]

Is there a comprehensive source for learning all about bump-steer?I have to replace my rack also,with the Koni/Intrax combo,how much do you pros think I should raise it?

 

[Todd TCE]

Bump steer is easy to describe but hard to repair on a street car.

It's the change in toe setting relative to the height of the spindle center line while moved through both bump and droop. Meaning as the tire goes up and down the arc of the toe setting does or does not stay constant.

While we want constant numbers it does not always stay that way. It becomes harder to do this as the suspension travel increases.

I believe most cars start with some toe in, and as you turn, the outside wheel toes in even more (contributing to the 'push') while the inner may stay constant or even toe out a bit. In any case, as you lower the car the arc of this changes. That's why most SHOs with lowered springs 'hunt' a bit over rolls in the road- every time the suspension goes up a bit it toes out some. As the steering arm goes from its longest point to a shorter one it pulls in, thus the knuckle turns out.

There's not too many ways around this short of some major work. Either you move the rack or you move the tie rod ends to get them properly aligned again. Reverse mounting the tie rods is the way to go in my mind, but you'll need proper angle adjustment of the rod ends to be used, and you'll need good ones at that. Pricey for sure. Not sure how much change this will net you as I looked at it years ago, but it's a healthy change.

More info about bump steer and suspension can be found in Carroll Smith books if you want.

<small>[ August 12, 2002, 09:20 AM: Message edited by: Todd TCE ]</small>

 

[DeaconBlue]

Gary Morrell has suggested raising the steering rack by using 2 or 3, 14mm hardened washers between the rack and the sub-frame. This raise the rack about 0.2" to 0.3" which should bring the links back to a parallel position. The full writeup is in the FAQ at;

www.shotimes.com