Not4off

Folks...

I have a 2009 Carrera S to which I've added (996) GT3 lower control arms from Tarret. Am currently running 2.5 degrees negative camber in the front and neg 2.0 in the rear. Have one 16mm shim on each side and am happy with the way the car handles both street and track...but...with such a large shim, the bolts that connect the two halves of the arm are barely long enough to handle the shim and the attachment nut. My questions are: Should I replace each 16mm shim with say a 10mm width? Can I do this with no effect on the alignment? Can I just jack up the front of the car, loosen two nuts per side, remove the shim and add a smaller one? Any special tool required? Finally, do my camber settings make sense?
...Richard

Carrera GT

You can search here for some comments on this, but I don't know the specifics for the Carrera distinct from the GT3. I think you've exceeded the maximum shim thickness. I know that when camber changes, toe will change, so the car will need to be realigned. The rule is "caster->camber->toe." FWIW 2.5 on the front of a 997 is beyond the limits I've seen, so I'm guessing you've got more like 2.2. I don't know of a 16mm shim (that doesn't mean it doesn't exist, but I think the thick shim is 10mm) so you will probably find two 8mm shims in there and they're just neatly aligned and look like a single piece.

CRex

Personally I wouldn't shim more than 10mm, for no reason other than leaving enough thread for the nuts to bite. If the Tarrett arms are anything like OEM (non-motorsport version with rubber bushings, that is) you'd barely have any thread left at 16mm of shims. Been there done that, and it was too close for my comfort.

My .02: go back to 10mm shims for safety. You will lose some 0.5 degs of camber and need a realignment. But before you realign, drive around and see how you like the handling with less camber. Unless you're a dedicated trackrat (and have the tires to match that) 1.5 degs or less should suffice. All that -ve camber on the street only weighs down your steering and eats up your tires.

NJ-GT

No more than 13mm of shims can be used in the LCA. Beyond that they require longer studs.

Check the top mounts, they should be close to full inboard, if they are not, you're leaving negative camber on the table.

Go to 13mm shims or less, max out the camber at the upper strut mount, then even out camber side to side. Remember to adjust toe first then camber.

Carrera GT

You mean camber first, then toe, no?

NJ-GT

Brain fart!

Correct, Camber first then Toe.

Minor moves on the upper strut mounts (aka camber plates) and/or adding/removing shims to the LCA, move the front toe plenty.

Not4off

Here's what I've learned. The Tarret Engineering 996 GT3 LCAs come with spacers that are needed when using much smaller shims. The bolts that connect the two halves of the control arm have a center section that is not threaded. With a small amount of shim this section might be exposed and would prevent screwing on the lock nuts. The spacer would cover this area after which the nut may be put on the bolt.
With a larger shim this non threaded area is not exposed thus the spacers are not needed and as a result, the length of the bolt is not an issue.

Initially I targeted 2.4 (front) 2.0 (rear) degrees negative camber. This dramatically improved my front end grip but made the car ('09 Carrera S) feel a little loose. Subsequently increased rear camber to -2.3 and the car feels fantastic.
...Richard