TTurbine

I went to the workshop this morning to have a more track oriented setup on my Gt2,

I was amazed how my current alignment specs were all over the place ... left front 2.45 negative camber , right front .25 negative camber.. rear right -1 negative camber rear left -2.30... not to mention the toe ....

No wonder the front right tire was bouncing whenever i want to do a sharp right...

Now we adjusted the rear to -2 negative camber and a total of .40 toe in...

But the dealer said that i need shims according to porsche in order to have 2.5 negative camber..

Is 2.5 negative camber possible by just rotating the front strut tower?

NJ-GT

yes you can get -2.5 rotating the tops, I prefer that to camber shims for track use. I prefer camber shims (wider track) for autoX use.

80shilling

I used shims to get to -2.5 degrees camber on the front. My rear went to -2.0 without issues.

Bob Rouleau

TT - my experience is as follows:

1) Rotate the struts and this gives you about neg 2 degrees with the adjusters in the minimum position. This varies from car to car so don't be surprised if your car is a bit different.

2) Use shims to get the desired 2.5 negative. If you don't you will end up with too little caster which is a bad thing.

3) If you use shims alone to get 2.5 negative you will have way too much caster and your tires will rub.

Best,

cgomez

Why? You also get more caster with the shims, which is good for high speed handling.
I would have imagined the opposite preference (Rotting the tops decreases caster, makes the steering faster/lighter for the AX acrobatics)

NJ-GT

Actually for autoX the 996/997 push so the increased front track (due to the longer lower arm) helps turning. But once you run wider front tires (in the modified acrobatic autoX classes), moving the struts fully inboard (rotating the top and maxing out the camber holes) help clear big tires.

Adding shims add caster (good) and increases front track (good), but for track use the tires start to stick out of the bodywork, increasing lift at drag, I prefer the tires hidden by the bodywork for track use. I recently experimented this with 295 front tires and 235 front tires, at a track section, my speed (Traqmate verified) was higher on the skinny tires, despite of getting a lot more speed from the previous turn on the fat tires. The section time was better on the skinny tires, but just that section, everywhere else the fat tires dominated.

Here is a video from my friend Scott, comparing autoX (we ran this event a few days ago) vs. track driving (Willow Springs, the fastest racetrack in the West).

http://vimeo.com/10223189

Bob Rouleau

Rad, my RS runs stock tire sizes and is set up with the rotated shocks and shims to get 2.5 neg. No way do the tires stick out. Elsewhere I have seen that you are running much wider front tires, maybe then it is an issue but with 235's in front, there are no clearance problem with shims. Note in my experience, less caster gave me more understeer not more.

Serge944

From what I understand, strut hat rotate alone -> too little caster. Shims only -> too much caster (wheel rubbing front fender liners).

I plan on rotating the hats, fine tuning with shims, and getting offset thrust arm bushings to gain back some of the caster loss:

NJ-GT

Good to know about the 235 not sticking out with the camber shims. I prefer camber shims, more caster, less understeer, wider track.

In my old RS I had the strut top rotated to clear the 265x19 Hoosier and MPSC tires, but we also added shims to get the caster back.

cgomez

I forgot you love driving Flinstone mobiles! (there's never a tire wide enough for you!)

I agree with Bob. Ive run -3.5 (in my 997S with GT3 arms) and -2.5 in my GT2 using shims and the tires fit well within the fender and bodywork, including 245 hoosiers.

The caster effect is BIG plus at the track. Don't underestimate it. helps a lot with turn-in grip (more progressive load) and controllability in high speed corners (that's why I run wheel-well-plastic-eating levels of caster in my Cayman racecar)

Bob Rouleau

Yup that's what happened to me too. Rotated the struts and nudged the shock in the adjustment slot. When we did the alignment the caster was way too low. So, backed off the slot adjustment to minimum and added shims in the lower arm to get the right combination of caster and camber. I wonder if putting the bolt in the other position in the lower A arm would have served the same purpose? Preferred to do it with shims since it allowed for fine adjustment since there is no caster adjustment on the stock suspension.

That set up is pretty standard up here and none of the half dozen 07 RS had issues with tires sticking out using 235's. You have the magic touch getting 265's under there!

Best,

TTurbine

But since my current stock alignment on the Left fron tire is -.2.45 negative camber without any previous adjustment my car has 5000 miles only,, isnt there a problem that there is something that might be bent to provide this sort of camber without any previous adjustments? or are the strut towers rotated to the max from the factory?

TTurbine

Okay finaly did the front suspension to -2.4 negative camber without shims...

the caster is a little bit lower on one side thought about 6.5 compared to 8.05 on the left

should i back the camber a little? and use shims to fine tune it?

Or should i just install adjustible thurst arm bushings to fine tune the caster?

Bob Rouleau

You have too little caster. You want 8 degrees. Back off the camber adjust and use shims to get about 8 degrees of castert and -2.5 degrees of camber. The difference of 6.5 versus 8 on the other side is huge. Your car will turn in better to the left than to the right. Straight line stability will be negatively impacted. That job was botched. Shims are cheap. Do it right.

best,

TTurbine

Where can i order the shims?

So basically i have to back off the camber a little on the left buy rotating the struts say maybe 90 degrees and then add shims to get 2.5 negative camber and more caster correct? maybe 5mm shims?

Would there be any negative effect if i used shims on one side to achieve 8 caster ( longer control arm ) and left the other side with 8 caster as it is?


Thanks for the info Bob