Bob Rouleau

From my pal in Ottawa I learned that caster is adjustable on the GT3. I have been told by race teams (Rennteam, Flying Lizard) that caster is critical on a GT3. Smart Racing has a neat camber adjuster for $1,500 a side). You need a minimum of 8 degrees of caster which can be difficult to get when you dial in enough negative camber for the track.

What my buddy discovered is that if you dismantle the front end, you will find two holes in the lower control arm (the big aluminum casting). A 996 has one dead center, the GT3 has two and if you use the outer hole your get more caster. More caster is good for high speed driving.

I'll be doing an Alignment on my GT2 soon and I'll check this out myself.

Another trick to get increased negative camber is to switch the front struts side to side - a trick my pal learned from another GT3 Cup race team.

I would really like to get my hands on a manual that tells us ALL these tricks. My dealer swears these things are NOT in the shop manuals for the GT2/3.

Best,

bob_dallas

Hi Bob - You are correct that caster is adjustable, however the standard hole provides 8 degrees of caster - even with -2.5 camber. I'm curious how much the outer hole provides although I'm not sure I need more than 8 degrees unless I go up to -3+ degrees camber which is unlikely for me. Please report back if you test it out.

FYI If you search back I think Viken posted a picture of the caster adjustment from a shop manual sometime late last year.

NJ-GT

Bob:

Thanks for that information on the caster adjustment.

AFAIK you can rotate the camber plates 180 degrees and get some seriuos negative camber in the GT3.

I like the idea of adding shims to the lower control arm, because it increases track width.

If you have a chance to take a picture on those two holes in the lower control arm and post it here, that'll be great.

Bob Rouleau

Bob - I must have missed Viken's post. I was probably reading the flame threads at the time <grin>.

My GT2 has only about 7.8 degrees of caster which is probably close enough. More would not hurt mind you. I'll report after my trip to the alignement shop/. Check out the other thread about the faulty gas hose. My buddy in Ottawa had his fail as well. I wonder if this is a trend.

macfly

I'm already running 9º caster and car feels like it is on rails.

bob_dallas

I think this picture that Viken posted shows the two bores for caster



There are two positions - one for "street" and one for "cup"

Thanks for posting the info about the fuel system - that's concerning. I'll check with my dealer to see if they know anything.

bob_dallas

Here's a link to the full discussion:

https://rennlist.com/forums/showthre...ight=alignment

Bob Rouleau

Bob D and Viken

The story about the two holes in the lower control arm (" big aluminum casting" came from the same guy who to quote Viken spewed "BS" about the fuel system on his GT3.

What is not clear to me is whether the second bore in the lower control arm would allow me to get more caster. I am not dressed to go look under my car to estimate the impact on the geometry right now.

Rgds,

Viken

FWIW, it was the dealer who was spewing B.S. Your friend is only guilty of moving the B.S. along. Not really his fault for believing what he heard.

Bob Rouleau

Viken - not to worry. My pal is a great racer and instructor but not very technical. The dealer is another story. Can you answer the question about use the alternate lower control arm bore as shown in the diagram you posted. Is it designed to provide additional caster for set ups with more negative camber? I would like more caster than I have now I think it would help straight line stability with minimal toe-in in front. I think this is what Andrew got when he had his car track aligned.

bob_dallas

You might want to talk to the guy that Marco references in this thread for more information about the caster holes or call someone who works a lot with the cup cars.

https://rennlist.com/forums/showthre...ghlight=caster

Viken

Not sure about Andrew's caster figure as that is way out of wack. It is almost impossible to steer that car with that much caster. I believe, the caster is not really adjustable on the GT3 in the true sense. The 2 holes are not for manipulating between 2 castor angles. They are there so that when you pack the arm with shims and you have -5 or -6 degrees camber as in supercup on glass smooth European circuits, you do not have so much castor that the thing can't turn without a vice on the wheel. It is a way of getting the castor back to the specified range (7.5-8.5) when many shims are used.

mds

The alternative bore will add caster. Think of it this way: this bore is offset toward the rear of the car relative to the center bore. Relocating the lower arm to that point will pull the lower end of the strut forward slightly, adding caster. I think there will be camber and toe changes also, both statically and dynamically.

mds

Viken, we posted at the same time. I will have to rethink what I said.

mds

Viken, one thing about packing with shims. On my car I got at most -3 camber by shimming. You can only add so many shims before you run out of threads on the bolts holding the arms together. I believe if you need Cup car camber (-4.5 to -5) your only choice is to rotate the strut tops. My car is at -2.6 camber and 8 caster and a bit of toe in now with rotated tops and 3mm of shims per side to add a touch of track.