bob_dallas

Question for the cupcar owners or knowledgeable people. What's a "typical" alignment setup on a GT3 cup car - specifically camber and toe if possible. I'm playing with alignment specs and I'm trying to explore some possibilities. It will probably be more aggressive than I want on my road car but should give some good datapoints. Also, I realize it could vary by track depending on how much you dial it in for a specific track but I'm looking for ranges here.

mds

Bob, although this doesn't address your cup car question, it might be helpful. Here is what I ran at Infineon last week on my street GT3:

Front height 115mm, caster 8.5°, toe per wheel +4', camber -2.5°, swaybar 1 off full stiff, pressure 33psi hot
Rear height 128mm, toe per wheel +13', camber -2.5°, swaybar 1 off full stiff, pressure 36psi hot
Corners balanced within 25lbs
Rear wing in standard position.
Michelin Pilot Sport PS2 (N2) tires

With this setup, the car has a slight bias toward mid-corner understeer in long sweepers, at least at times. Good turn-in, good transitioning between understeer and oversteer. Tire wear is slightly biased toward the outer edges, both front and rear.

I am going to run Laguna Seca in a couple of week. I may try a bit more negative camber and a swaybar change for slightly reduced understeer.

Bob Rouleau

Bob

My setup is similar to MDS. I also run negative 2.5 all around. I use zero toe in front (it is a little darty mind you but turn in is very crisp) rear toe is 3/32 total. Caster is not adjustable unless you buy the extra bits from Motorsports. Bars are the same as MDS and I have played with the wing shims. Max downforce is wonderful in fast sweepers but reduces straight line speed. I screwed up my courage and put it back to the stock position. Ride height is as per the way I got it, plenty low enough! I run on Pilot Sport Cups or Pirelli P0 Corsa tires. I have run it on the OEM Pilot Sport2 N2 and I was pleased.

Note that with 2.5 neg camber you will wear out the inside edges while street driving pretty fast. For occasional track use I'd go for a milder neg 1.5. My cars see most of their miles on the track where they are the most fun. Set up this way the car is much better than the factory alignment. A fellow instructor who has an identical car tried mine and did better lap times with my street tires than he did with his car (stock setup) on R compounds. The same guys took 2nd overall in this years North American Ferrari Challenge by the way.

On tires, the Michelin Cups have the best grip in the dry but are lousy in the wet. The Corsa is way better than the street tire and is usable in the wet. I put them on and leave them on unless I expect very cold temps and or heavy rain.

As MDS observed the setup can change from one track to another. Perhaps it is the stickier tires but I do not have much understeer in fast sweepers (100 MPH) on my home circuit. I had he reverse, had to take a later apex so I could accelerate sooner. More wing angle cured that but shaved 10 MPH off my top straight line speed. Compromises - compromises :-) The season ended (snow dammit) before I could try softening up the rear bar to tame the "assy" nature of the car. I am probably a wuss but I don't like opposite lock at over 100 MPH.

bob_dallas

Thanks guys - I'm going to try to stick close to 2 all the way around as a compromise to reduce street wear on the inside but still allow the tires to work more on the track. I was asking about cup car alignment because I'm wondering if they run more front camber than rear. I think the car can handle it and looking at the race RS/RSRs they clearly are running more front camber but they're pretty extreme examples.

My thought is that I can dial it out to a little more neutral with more front camber and it won't wear as bad as heavy camber in the rear because of the weight bias. My gut is to go with -2.1 to 2.2 front and -1.9 to -2.0 in the rear.

I ran -2.1 front with 6' of toe and -2.5 degrees rear with 15' of toe. Fronts wore fine with combined street and track but the rears wore the insides with a lot of street driving.

Bob Rouleau

Bob_D

Sounds about right to me. Note rear toe also causes a lot of wear. You can trade stability for wear as you know. Cup cars can have a very different setup because the suspension is not the same as our cars. I took a close look at Johannes Von Osterbeeks car this fall and his suspension is way different from ours. His car also handled way better! His set up is done by the guy who founded Smart Racing Products, he is the chassis guriu for Rennteam. That's where I saw the nifty caster adjusters. There is also the matter of racing slicks which generally like a lot more negative camber than DOT approved R compounds.

Regards,

bob_dallas

Thanks Bob - Yeah, compromises all around but I think I can make it good enough to satisfy myself. I know someone who's running slicks right now with less camber than I'm talking about running and it hooks up pretty well. I can't imagine what it would do with about -3 or so like those really need.

BTW - should have said that those alignment specs at the bottom of my last post were what I used to run on my old 996 with coil-overs. I had a lot of combined miles on that car so I got a pretty good feel for what worked and how it wore.

You're right about toe causing wear - might try to reduce it a little although I don't want it too twitchy since it does see alot of road miles too. I see you have 0 up front and 3/32s (about 4') in the back - I probably won't go that aggressive.

I may have to get a trackside alignment kit and play with the shims - see if I can tweak it out for a heavy track day and then remove the shims without screwing up toe. Better yet - maybe I'll play with it while it's on the aligment rack and see if it works there, then buy a kit.

Johninrsf

MDS Please check your PMs. Look forward to hearing from you.
John

Todd Serota [TracQuest]

Some Cup Cars are running as much as 4 or 5 degrees negative in front, but as has been noted, their set up is quite different and not particularly relevant to our street GT3's and GT2's.

On my 996 Cab and now my GT2 I run 2 degrees negative all around, with 0 toe in front and 3/32" total toe in the rear. Although this set up is still a compromise for the track with many tires, it works quite well. However, even 2 degrees negative chews up the insides of the tires if any significant amount of street driving is done. My cars are always my daily drivers so I put many more street miles on than track miles and have had to deal with this problem over the years. In fact, given that my next TracQuest isn't until Laguna Seca on March 1-2, I'm seriously contemplating dialing the camber back to a moderately aggressive street setting: 1.25 degrees negative all around.

Btw, speaking of alignment, I have a question for all of you. When I had my GT2 set to 2 degrees negative all around, the right front got to 2 degrees with nothing but the stock 1 mm shim, while the left side needed 4 mm of additional shims. I find it very unusual that the two sides would be so different. Has anyone had a similar experience? Aside from that, what do you all think of this?

bob_dallas

Hi Todd - were you present during the alignment? I've had mixed success with alignments on coil-over suspensions and found it's best to be there and verify things personally. Do you know what the max camber they could get without the shims was?

Another question, tied to Todd's comments - has anyone played with the shims on an alignment rack to see the impact overall? What I'm hoping is that I could change the shims myself to make a slight adjustment - say 30' -45' for street vs. track, although the rear would still have to be changed at the towers. Or, has anyone seen or heard of camber plates for the GT3/GT2 that would allow self-adjustment. Basically trying to find a way to allow me to adjust without paying for an alignment everytime.

I might buy some trackside camber/toe tools and play with that too.

Bob Rouleau

Todd, the camber is normally set by moving the upper shock mounts in holes which are oval. They are never quite the same side to side but normally the discrepancy is 0.x not 3 freaking degrees. Sounds very weird. You can get about neg 1.5 without shims usually. You can also grind out the holes a bit to get neg 2 without the shims. Apparently this is ok but if you want race specs like neg 3, neg 4 the shims are the right way to go.

I got neg 2.5 with only one shim but I am damned if I remember what they were. The Rennteam guys told me these cars are very fussy about ride height and caster. Their car stuck like superglue.

Todd Serota [TracQuest]

Hi Bob:

I think you misread what I said re the alignment discrepancy. On one side, my shop was able to obtain 2 degrees negative with the stock 1 mm shim. On the other side, two 2 mm shims (for a total of 4 mm) had to be used to get 2 degrees negative. The difference of "3" (actually 4 - 1 mm vs. 5 mm total) wasn't in degrees, it was in mm - the thickness of the shims needed. I don't know what was obtainable on the other side with no additional shims - a bit more than 1 degree, I think. That would make the difference a bit less than 1 degree side to side.

I wasn't there when the alignment was done because the shop that did it is one of the best race shops around. I have asked the question you've posed, namely how much negative camber could they obtain on the lesser side without using extra shims, but haven't yet gotten a response.

As for making your own camber changes, I'm pretty sure that changing camber would change other alignment settings as well, so I'd think it's pretty involved.

racergt3cup

bob_dallas,
we run 4.5 sometimes 5 deg neg' camber on our gt3 cup car, but on michelin cup slicks , fact is your tire wear woes are simply a fact of generating mechanic grip, i've never seen high grip and low tyre wear, by the way do not try high levels of camber on road compound tyres as they just don't have the side wall rigidity and will fail!!!!!!

bob_dallas

thanks for the comments - I'm aware of the different camber requirements of different tires, I was just trying to get some additional datapoints. I run R compound tires on the track right now and might try out slicks at some point. My challenge is finding a "compromise" alignment that I'm happy with unless I can find some camber plates or some easy way to switch between track and street alignment. I guess I'll play with it a bit.

When you say 4.5 - 5 deg neg camber is that all the way around? The crux of my question is how much people have experimented with more negative camber in front vs. rear and the balance of the car.

Thanks /bob

Todd Serota [TracQuest]

Racergt3cup will obviously know from personal experience, but the Cup cars I've seen have all had dramatically more negative camber in the front - like 4 to 5 degrees vs. about 2 to 2.5 degrees in the rear.

bob_dallas

Thanks Todd, I appreciate that info. That's what I was thinking from pictures and looking at cars but was looking for a 3rd party verification. I had a friend tell me I was crazy for thinking I needed more camber in the front than rear of any 911 but it makes sense given the handling characteristics, etc.