BTERRY1

gtred

Mike A: Didn't mean to bore you with the kinematics 101. But, hey... if you understand the Porsche IRS then I've got a Q for you: I spent some time with the shocks out, a toe-plate attached to the hub and string-line to measure the rear toe change with bump/compression. On other cars, the setup was easy to understand and you'd usually just need to correct the toe change at +/- 2" travel to as close to zero as you can get it by shimming the toe-rod attachment points. On the Porsche, it seems different. The two upper links oppose fore and aft movement/rotation of the spindle as well as decamber with compression. However, they attach to the upper hub in an asymmetrical fashion. It's almost as if Porsche designed in some sort of rear steering(?). Is that so? If so, has anyone shared specific numbers of what to try to achieve when correcting rear suspension travel on a lowered car?

Mike_A

Some one with more attention to detail may have a better answer but I suspect the design (selection of attachment points) addresses anti-squat under acceleration. Rear drive cars benefit from rear lift (anti-squat), this raises the rear CG and increases weight transfer to the rear wheels under acceleration. The effect is created by selecting link attachment points such that the reaction to the applied torque from the drive wheels actually tends to lift the car. See Millikin and Millikin, page 395. As far as selecting the right alignment adjustment, the GT3 forum guys have bantered this in a number of threads.

Mike_A

The parts don't come up on the site search for a 99 C2...and when I checked for fitment on the ebay listing the word was "will not fit"....I would have sprung at that price. I'll probably go for the Tarretts, including the boots.