Cogito_Ergo_Zoom

hey Brandon, thanks for the advice. I'll probably stay on a DOT tire if I decide to run NASA as you have to take a power/weight ratio penalty if you run a full-on slick. Right now I'm more or less right on the money for GTS3 at my current HP/weight so I'll probably stick with a DOT tire for now. Either way the R7 will be a major upgrade over the spec BFG R1 I've been running.

On the geometry, are you still running the stock C2 uprights? The GT3/Cup uprights differ in that their attachment points for the outer ball joints for the LCA and tie rod end are dropped lower in relation to the ground and with the inner points staying equal corrects the geometry and allows the lower ride heights indicated for the GT3 and Cup. Going too low with the body on the C2 uprights and thus dropping the inboard pivots increases the angularity in the wrong way and basically puts the roll center too far underground which can actually increase weight transfer even at the lower ride heights which can increase bump steer and understeer and make everything generally less predictable, on paper at least. Consider that the factory ride height measurement reference points are basically the low points for the inboard pivots, both at the front and rear.

If you go out and look at your car (as is mine currently) you will see that your LCAs (and tie rod ends) are probably sloping pretty steeply downward from the outside in with the inner pivots much closer to the ground. Notice how the lower control arm in this diagram is parallel to the ground. Given that the angle at the top mount is fixed on a MacPherson strut design and that makes your effective "virtual upper wishbone" angle, that means your roll center is underground. Dropping the outer pivot points with the Cup/RS uprights, using lower control arms with shimmable ball joints, raising the ride heights or some combination of all three will restore the geometry where it theoretically needs to be.



Also have to keep in mind that changing the total diameter of the wheel/tire combo larger or smaller also changes the overall effective ride heights and roll centers. Just for reference I've got my front heights set at about GT3 "street" settings at ~113mm at the front on the 245/40 series tire and just by putting the 245/35 Hoosier rain tire on it drops the front ride height to about 99mm! I'm definitely in agreement with you that using the lowest possible ride heights for best cornering within practical limitations helps. Everything is a trade off at the end of the day and if you are more comfortable and the car is going faster, it's a good setup for you.

That's a good point about the ease of alignment with the adjustable caster arms vs. the center pucks. I'll PM you about them.