TheOtherEric

Keep in mind that there are two kinematic effects:
(1) change in toe due to deflection of the wheel (e.g. compression or sag, like when cornering); and
(2) change in toe due to the radially soft bushing in the lower a-arm (arm 5 in Bill's picture).

As an example, when you brake in a straight line, the rear suspension droops, and wheels toe out. This would be bad. But the lower a-arm compresses due to the soft bushing, causing toe-in to offset to kinematic toe change.

"Adjusting your KT" deals with Effect #1. Effect #2 (soft bushing) is more of a "dynamic" toe instead of a "kinematic" toe, and you can't adjust it.

k722070

I had used the method garth describes in post #1 to set the kinematic on my coupe, the differential between sides was 2.4 degrees and I adjusted it to zero, that is the difference between the angles of arms #2 and #5 was adjusted to 1 degree on both the L and R sides.
but I didn't know if this was actually correct, as garth writes 'if the method has any validity.'

lately I bought a kinematic gauge from gert but it doesn't fit the coupe. today I got a chance to test it out on my cab. the bubble showed around 3.3L vs 4.6R, I adjusted both sides to 3.5 at the same time adjusting camber.
I haven't set the toe yet but I did crawl under and measure the angles of #2 and #5 and compared L to R, it ended up as almost exactly the same differential between arm angles.
so I'm going to say that garth's method has validity and can be used to set the kinematic without spending $300 for the gauge.

M. Schneider

Back to the learning curve and the 993 chassis alignment ... Signed, Grasshopper ...

A good read of the alignment features btw the 964 and 993 vehicles .. +1... to Bill Verburg

http://forums.pelicanparts.com/porsc...-analysis.html

pp000830

What is WSM, the factory shop manual?

Bill Verburg

That's exactly what KT is, you adjust the rear caster to speed up/enhance rear roll steer or to slow down/dampen rear roll steer. Roll steer is the result of toe changes, one wheel goes up the other goes down, the result is toe changes in opposite directions. You can have varying degrees of roll over steer where the rear tires steer away from the turn(outer turns out inner turns in) or roll under steeer where the tires steer into the turn(outer turns in inner turns out) . The driving mechanism is caster, more caster enhances toe change w/ suspension travel, this slows the reaction at the rear, less caster dampens toe change w/ suspension travel this speeds up the rear reactions and cause the car to become increasingly twitchy. The further forward in the wheel well the less caster and less toe change w/ travel the further back the more caster and more toe change w/ travel.

Another way to describe it is w/ the idea of bump steer which is more usually used to describe the front suspension, caster at either end puts more toe change aka bump steer into that end.

The rear is a bit more complicated due to the articulation of the 5 arms and the unique joints in the rear A-arm, where there is a rigid pivoting ball joint on the leading arm and a fairly soft in the lateral direction, enhancing any toe change that the basic geometry provides. It's been my experience that both rear A-arm joints get loose w/ time and use muddying the water so to speak, the best rear for street use is the stiffer RS which damps KT effects a lot, the best for track use is the all mono-ball RSR which has zero play so the only toe changes are those inherent in the geometry used to set the suspension.

At the front the A-arm is set the opposite the leading arm has a softer bush allowing more lateral movement than the trailing arm. Again the can be improved by using RS bushes which tightens the leading leg bush or aftermarket harder bushes on both legs to tighten the front even more, or again the ultimate all mono-ball as used on the RSRs for zero play. The front is also complicated by the actual steering mechanism so you have the additional headache of worrying about the steering arm geometry, here you have 2 basic choices stock wheel carriers and outer steering arms or RS wheel carriers and outer steering arms.