Originally Posted by
Jnovak
Rear caster is the simple way to adjust bumpsteer. However there are a couple of other factors.
In the rear (or the front) there are 2 kinds of wheel steer in the car (not counting driver input).
1. Bump steer or roll steer as some call it.
2. Compliance steer. Compliance steer is the steer effect caused by the compliance (bending, deflection etc) of the mechanical components of the suspension and the chassis. If the chassis and the suspension is exceptionally rigid then compliance steer is a mnor effect. If not it will drive you nuts to try to solve the problem. All cars have some level of compliance steer and the questions are:
1. How much
2. Is the compliance steer understeer or oversteer.
If (on the rear suspension) the center of the contact patch is in front of the compliance axis of rotation then the compliance steer will be understeer. If the center of the contact patch is behind the compliance axis of rotation then the compliance steer will be oversteer.
Do not think that this is a minor issue. I have tested many race cars all the way from NASCAR to F1 in our compliance lab at Ford. It can be a very dominant effect on a race cars transient handling.
Thanks ... Jay Novak