Galun

I just went through this and I figure someone may find this to be helpful in the future. I installed the GT3 front control arms in my car to get additional negative camber, and I was trying to figure out how much shims I needed to buy. In the end I couldn't find that information, but during my alignment I found out that each 2mm in shims translate to about 0.25 degrees of negative camber. In the end I added a total of 17mm in shims to get it to -3.3. There was more room to go but I ran out of shims.

Paul 996

Galun,

Interesting post. I am curious is anyone knows the correlation of inward movement of the top of the spring/shock to negative camber. the factory holes are slotted about 1 inch and some do extend those slots and also add the adjustable camber plates up top to allow more movement.

Galun

I am not sure how much camber adjustment the top will allow. What my guy did was to first max out the negative camber on the top, put in the shims, and then adjust the top to my desired camber setting. I was able to get to -3.3 with the top maxed out, then adjusted down to -3.0 which was my target. I figure there was another room to at least slip in another 2mm shim easily.

I imagine different ride heights will impact the amount of maximum negative camber you can get, but I figure an approximate conversion of 2mm shim = 0.25 degree neg camber will be a good start for others. Oh, when in doubt, just buy more shims to begin with. A 7mm piece of shim at around $50 sure feels like a rip off, but it's better to buy enough of them to have spares then to try to cheap out and ended up buying 2 times and doing 2 alignments like myself.

Bob Rouleau

Galun, when I used shims alone to get Neg 2.5 on my 996GT3 I ended up with so much caster (9.8 degrees) that the tire rubbed on the fender liner. The preferred method seems to be to rotate the shock into the spare hole provided (with a knock out). This gives about neg 2 with the top adjustment near full positive. It does not change caster however so there are no rubbing issues. The slot up top allows about 3/5 degree adjustment only.

Regards,

Paul 996

Bob,

My understanding is that the 996's shock/spring top isn't able to be rotated like the GT3s. Pls correct me if there is a way ! seriously.

-paul

AudiOn19s

Correct...have to buy the factory monoball mount for the GT3. However it was my understanding that turning the factory GT3 mount did change caster as well...just not as badly as the shims. I believe it was NJ-GT that spent time on an allignment rack confirming this.

Andy

Galun

Humm, why would it change the caster? It looks like the shims just push the lower control arm out and won't necessarily tilt it.

Is there an easy way to look at the caster angle without going on an alignment rack? What will it do to handling? I never really thought about caster angle....

ArneeA

Interesting thread. Great thread.

Galun

I just spoke with my alignment guy. He told me that my caster was around 3 - 4 degrees, so -3 camaber, 0.1 toe, and around +3 caster. The top part with the elongated holes can give about 1 degree of camber adjustment.

Bob Rouleau

Galun - the usual caster spec is about 8 degrees. On the GT3 the geometry is such that shims cause increased caster. Perhaps the 996 is different. On my Boxster S (2001) I simply elongated the slots at the top of the shock mounts to increase the maximum camber.

On a GT3 it took over 20 mm of shims to get neg 2.5 - but this may not be the same on a regular 996.

Best,

Paul 996

small hijack here. sorry Galun but still slightly on topic.

Some of you commented on elongating the slots at the top of the shock mounts to increase the available negative camber. Any advice on the best tool(s) to do so and have it end up looking semi clean? Also how long have you elongated?

Thanks in advance!! -Paul

10 GT3

First, 7-8 degrees caster is correct for a GT3, not a Carrera. The optimal range is 6-7 degrees. Keep in mind the hub carriers are different as well as the alignment of the strut assembly that results in 1 more degree of caster on GT3s versus Carreras. I get -1.6 with a ROW M030 and GT3 control arms and a 7mm shim pack. I am not out of slotting. We suspect I will be -1.8 with them all the way in. Even with the 7mm shim pack, I have to run my control arms RSR style (left on right and right on left) and run the track arms in the offset holes to control rubbing and keeping the track arms from binding up. In fact, they are pretty hard to line up even moved out this far (you have to keep the controls arms loose to bolt them on). I get very close to 7 degrees caster like this, just inside the normal range. If the control arms were swapped back to normal from side to side or the track arms are in the center holes, I go up to over 8 degrees caster and even the stock wheels/tires rub (we've tried this on my car).

It should not take 20mm to get -2.5 on a GT3. Whoever did the aligned screwed up big time! First, it sounds like the never pushed the upper mounts in which can get up to -1.5 on a GT3. The GT3 has an adjustable upper spring perch. You are supposed to rotate it 180 degrees and move the stubs for more camber. I've seen race GT3's with -3.5 in front with a significantly smaller shim pack that that. How bad does it rub? How bad track arms binding up in movement? Have you started tearing the track arm bushings? You can get -2.5 out of the front of a GT3 with the perches rotated, pushed in and only a 3mm shim pack (advantage of the lower adjustable suspenion of a GT3 over a Carrera that can only get -1.0).

I am going in for another alignment. I am still wearing more on the outside edge of my MPSCs and my inner temps are about 10 degrees cooler than the outer. I am going to move up to -2 to even it out. My rears are dead even at the current -1.9, so we are leaving them alone. If you start talking to alignment guys at TRG and Ruf, they don't recommend to go over 10mm unless you want problems. If I didn't change anything on my car other than switching to PSS9's with adjustable upper perches at the same ride height, I would be at -2.6 in front with the same 7mm shim pack.

With a 17mm shimpack, I wouldn't be able to turn my wheels more than 2/3's. I don't think I could even get the stock track arms to bolt up without tearing the bushings. The are other problems also that wil have to be taken into account to run a huge shimpack like that. If you check the GT3 forum, there is a thread about how you will need longer tie rod ends because there isn't enough adjustment. There are custom race parts that can fix these issues for race cars, not to correct mistakes people making on street cars.

Galun

Which ones are the track arms? Are they the tie rods?

My GT3 control arms were installed L/R swapped.

I was able to get 17mm of shims without any rubbing or wheel turn issues.