Adjusting Camber on 996 GT3

Jeffers1 · 22 Jul 2014

I want to add a bit more camber to my car and was wondering what the best way to do it is. I currently have the following but it is the max I can get out of the eccentric bolts and slotted holes on strut tops.

Front -1.2°
Rear -1.5°

On the front I can either add shims to the lower arms or rotate the strut top to the 2nd set of holes. Which is best ? Adding shims adjusts it from the bottom of the strut increasing track slightly and rotating the strut top will obviously adjust it from the top. Does it really matter which route you choose, is there anything else that is adversely effect buy adjusting it at either the top or bottom ? Also what sort of angle does the various thickness of shims make as you can get 1mm, 2mm, 3mm & 7mm shims ? A final question on the front, the catalog shows 2 shims on the front, Nos 15 & 16 but 16 is not listed in the parts. What is actually fitted to the car as standard ?

On the rear I have the fixed lower arms due to my car not being an RS so I guess I have to buy the adjustable RS rear lower arms but the same question above applies regarding the additional angle provided by the shims. It also appears from the catalog that no shims are required as standard on the rear.

I have attached the relevant catalog pages for reference.

If anyone has gone through all this before and can answer the above then it would be greatly appreciated.

agtlaw · 22 Jul 2014

Turn the top mounts. From memory, that will give you up to 4 degrees to play with.

No expert but my understanding of the adjustable RS control arms (front and rear) is that they enable the ride height to be lowered significantly whilst still maintaining appropriate levels of camber using shims inserted between the two parts of the control arm. You probably don't need to do that unless you have a very low ride height?

Nick (NXI) knows more about this stuff. I think he has RSS control arms.

NXI20 · 23 Jul 2014

You rang?

The lower arms can allow a lot of camber if you turn the top mounts as well. The problem with the spacer method is that you will also affect the castor because the diagonal arms will pull the wheel carrier forward from its ideal position. This will lead to more skittish behaviour on bumpy roads and can also mean tyre to arch liner contact. To overcome that, you need the RSR adjustable diagonal arms.

If you are looking for less than 3 degrees, turning the top mount and slightly elongating the mounting holes will achieve that without the need to add spacers to the split arms.

You should be able to get over 2 degrees on the solid arms at the rear. More than that requires split arms and spacers. I use RSS split arms all round because they are rebuildable and also you can shim the ball joint pin to optimise the geo for bump steer when you lower the car. The standard split arms are a similar cost to the RSS arms but don't have those advantages so not a hard choice to make & they've endured everything I've thrown at them very well. I life the inner mono balls & the outer balls & pins so they get changed every 2 years. That's about 50 trackdays / 30K miles.

The arms AGTLAW is referring to are the Motorsport forged arms from the Cup car but last time I looked they were over £800 each. They are optimised to run at Cup ride heights but are overkill for a road car.

Every 3mm of shim will give you approximately .25 degrees of camber.

Jeffers1 · 23 Jul 2014

Thanks for the replies, I don't want to go too far with the camber as it is still a road car after all but was thinking of around 2° to 2.5° on both front and rear to see what difference it makes.

Am I correct when saying if I just rotate the top mounts on the front then I shouldn't need the adjustable control arms. With the top mounts rotated, in the outboard end of the top mount slotted holes and the eccentric bolt wound back to minimum what would be the minimum camber available and will I encounter any rubbing on the arch liner as the wheel will of moved inwards at the top ?

Also if I get the RSS rear arms and add 9mm of shims then that will give me circa 2,45° on the rear with the current 1.7°. Will this mean that I also need adjustable control arms on the rear ?

NXI20 · 23 Jul 2014

A good basic rule of thumb for those sorts of camber on road tyres is to have half a degree more on the front than the rear, so 2.5 F & 2.0 R.

You should get that on the front by turning the top mounts to race. The arch liner problem isn't at the top, it's at the front on lock but you won't get that problem.

On the rear, you don't need RSR diagonal arms unless you are running very low ride heights & arguably not even then. I run them because it eliminates the last bit of rubber bushing and so eliminates the final weak spot of the standard suspension.

Try to get as close to zero front toe as feels comfortable and around 15 minutes of toe in per side on the rear. The car will feel planted with those settings (the infamous 'Kussmaul' settings). Try to get around 20-25mm of rake front to rear to optimise & go enjoy

Jeffers1 · 24 Jul 2014

Excellent, thanks

I'll give that a try. I currently have 15mins toe in on the rears each side (30 total) with a coumple of mins toe out on the front each side. Makes it a bit lively on B roads but seems to work well on trak. I think adding that bit of extra camber should finish it off nicely too. Also noticed while poking around that my front roll bar is on the hardest setting so will try moving that forward a hole or 2. Rear is on the 2nd hardest setting.

Rake is currently at 9mm difference front to back so could increase that but I'll try and do 1 thing at a time. Is it best to drop the front or raise the back or do a bit of both ? wouldn't want to drop the front by much as I already struggle with speed bumps, ramps etc.

NXI20 · 24 Jul 2014

Toe out will be very twitchy on the road. Zero toe & going up a tyre size to 245 will give a much nicer front end which still has loads of grip & turn-in response.

If you're already as low as you think you want to be at the front, raise the rear. ARB settings should be used to fine-tune the balance & optimise front/rear grip. I have mine set quite conservatively, but then I've got stiffer springs & 2-way adjustable Motons which give me more options.

the rainge · 25 Jul 2014

Some great information on this thread from everyone.
One thing I'd add from my own experiences with setting my car up and changing things is that if you rotate the front strut tops but don't add shims in the lower control arms you loose castor.
I think when I did this my castor was about 7.30. Still within tolerance but I thought to low. I added 5 mm of shims and it brought it up to 8 degrees.

Adjusting Camber on 996 GT3

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