Something jumped out at me when I read your post, 555: because of the rear's self-steering design, which is intended normally to increase understeer and thus make the car more stable for typical drivers under typical conditions, I could see that with soft, tall sidewalls, and with lots of torque applied to the rear, that the angle of rear roll, and thus rear steer, could get significantly modulated by the rear's torque input. That is, as torque input is varied (gear shifts mostly,) rear roll gets varied too, and the roll variation is finally reflected as a variation in the car's direction of travel. The result is "weird" steering. Another kind of modulation happens too: with tall, soft sidewalls, sidewall height will vary from one side of the rear to the other, as the rear's torque input is varied. This variation in side-to-side sidewall height alters the effective rolling radius from one side to the other, and this will tend to steer the rear as well.
I would think that stiffening the shocks, and especially the rear suspension roll stiffness, should ameliorate this. Or better still, eliminate the rear's self-steering behavior directly. Stiffer sidewalls would help too in this respect, but this may have other kinds of negative impacts that may preclude this option.
Edited by MAP (05/17/11 04:10 PM)