dp201

I'm transitioning from a C6Z to a C7 GS A8 for HPDE events in the spring. I generally run in the advanced group with MPSS tires. I'm currently trying to decide what wheels/tires to run and would like to get a more aggressive setup than I currently have. Since I don't trailer my car, 18" wheels with slicks all around is out of the question. I was thinking of something like NT01 or R888Rs but not sure about what wheel sizes to go with. For those that track their C7 GSs, I would like to know what wheels/tires seem to be working well. Also, I would like to know if my current C6Z wheels (18/19) would work on the new car or even if someone has tried 19" wheels all around. Any suggestions for track setup would be appreciated.

c5racr1

Been tracking a 17 GS a8/ cup tires or 18x11 18x12 ccws with Hoosiers, and Pirelli slicks. That is the only 2 tire set ups i tried.

TCorzett

I recently ordered a set of 18x11 and 18x12.5 for track use in the spring. Will be starting with Rival S (315/30-18 and 335/30-18), eventually moving to NT01 or R888R in the same sizes. In the future if I want to run slicks... Hoosiers (315/30-18 and 345/35-18) and Pirelli (305/660-18 and 315/680-18) should also work with the wheels. If I really wanted to run the Pirelli slicks in the future I'd probably have gone with a 18x12 in the rear, but I'm leaning more towards the Hoosiers (if I ever get to that point).

dp201

I would seriously consider the 18s with the NT01 or R888R. Do you think that there would be any issues with fitment or the nannies? What brand of wheel will you be running with this setup? Thanks for the suggestions.

TCorzett

I hope there are no issues with either... I will know more when the wheels arrive. Outside diameter of the various make/model of tires are slightly different, but the ratio of front/back is fairly similar to the stock MPSS (none of the tires I mentioned above have the same ratio as stock). I ordered Forgeline GS1R Open Lug (w/caps) from CW4L (a forum sponsor); Gerry knows his stuff and was very helpful throughout the ordering process.

Bill Dearborn

You could go with a set of 18x11 front and 18x12 rear wheels from either CCW or Forgeline. Then go with 315/30/18 fronts and 335/30/18 rears Rival S tires. That will get you a set of tires that have a ratio of rear/front of 1.015 compared to the stock tire ratio of 1.031 for the stock ratio. That is a little less than 2% off the stock ratio which should make all the nannies happy. Overall diameters will be a little lower but the ratio is what counts. The lower diameters will make your speedo read higher, count more miles on the odo and increase fuel mileage slightly. The NT01s come in that size but they are DOT R tires that won't hold up as well on the road getting to and from the event. The autocrossers seem to like the Rival S.

With wheels that size you can continue to use them with Hoosiers and Pirelli Slicks if you ever decide to trailer the car.

Bill

Z06_BluByU

you might like the pirelli pzero corsas.. but they arent cheap

dp201

Thanks Bill. I'll take a close look at this wheel/tire combo. I currently run XP10/XP8 pads on the C6, but I may move up to the XP12/XP10s due to the increased weight and stickier tires.

Lasco001

Currently the fastest tire for the road and the racetrack is the Michelin Cup 2
The tire works perfectly on the GS, so the vehicle is very fast.
I have some customers, which we drive with XP8 front and back.
Important is a very good cooling for the brake

If you drive XP12 the cooling needs to be much bigger, otherwise you will have a long pedal very fast, because the heat in the brake calliper becomes too big.

Cölestin

Lasco001

C7 GS on the Nürburgring

dp201

I have the Quantum cooling ducts on my C6Z along with the XP10/8. Was wondering if the cooling on the new GS is adequate, or having to go with aftermarket cooling. Sounds like you're saying that XP12 might be a little too aggressive. I like my current setup, so maybe I'll stay in the XP10 or 8 range. Thanks for the feedback on this.

dp201

Awesome photo. Looks like a very nice setup on the GS - badass!! Very lucky to run the Ring.

c5racr1

Gm makes a front brake cooling duct for GS/z06. I use them and found they help keep the brake temperature reasonable.

dp201

Thanks. I always like to go with a GM performance part whenever I can. Especially with a car still under warranty.

village idiot

I run 18s and run R888Rs, 315/30 front and 335/30 rear. I wish there was a 315/25 front, but such is life. Nice and cheap, relatively speaking, at $1300 a set to my door. That size was perfect imo, running stage 3 front aero and stage 2 rear. When I pushed too hard, I got a nice 4 wheel slide. Running them on the signature SV108 wheels.
Running 1.2 camber, +0.5mm front toe, -0.5mm rear toe and max caster within spec.

With that said, if i want to drive to a track, cup tires are pretty awesome. You'll understeer a lot more because the front is 30mm narrower per side, but it's a great way to drive there and back without issue on runflats. I keep the R888R in my garage at the track and Cup tires in my garage at home for when I go to a different track.


One that doesn't come stock?
I had no problems at COTA running RBF 600 with good pads (Hawk DTC 70/50). My brake pedal got a tid bit spongy so I'd probably run 660 next time, but I ran 5 sessions no problem.

dp201

Thanks. I can't seem to find an OD on the 315/30 - 18 to calculate the ratio front to back. Checked Toyo and Tire Rack. I'm sure that you would have mentioned any issues with the nannies though, if there were any.

village idiot

Just do the math.
315/30/18:
25.4mm = 1 inch
315mm = 12.40"
12.40 * 0.30 = 3.72
So 18" (wheel) + 3.72 *2 (two sidewalls for overall height) = 25.44


So new sizes:
315/30/18: 25.4"
335/30/18= 25.9"
Ratio (R:F): 1.02

OEM sizes:
285/30/19 is 25.7"
335/25/20= 26.6"
OEM ratio (R:F): 1.035

Not much difference. I didn't have any problems with the nannies. That's probably the most aggressive tire and widest tire you can run and drive to the track. You can't drive to the track with a race slick- too easy to puncture.

TCorzett

Received my new wheels today and everything fit perfectly. Had zero issues on the shake-out drive, but I was keeping it gentile. I had TPMS sensors installed (and the tires mounted) before they were shipped and everything synced-up with the car without me having to do anything.

dp201

Glad to hear everything fit well and nannies are ok with it. Great looking wheels, not inexpensive, but add a lot to the appearance and should hold up well on the track.

ERND IT

I'm looking for a similar setup for autox/track days for my 17GS M7 - so I may use that configuration,too - Forgeline GS1R 18x11 and 18x12.0 with the Rival S 315/30-18 and 335/30-18.

Thanks for posting that this was a successful combination - so much has been said about the car's nanny's complaining about different wheel sizes, etc. good to know this works well.
I have a set of CCW 18x11 18x12 that I ran on my C5Z for track, but haven't tried to put them on the
GS yet. I really like the Forgelines, so may get rid of the CCW's and go with those...