Tire Size, Wheel Width, aaargh!

[Steve Towers]

Today I bought a set of C5 Corvette OEM mag wheels. Problem: Is it reasonable to run 315/30's on the rear on a 18 x 9.5 wheel? (Think Hoosier A6). If not, I'm on 305 Kumho's. Please weigh in about "pinching" a rear tire. The fronts (17 x 8.5) should be fine with either tire.

[Jason Rhoades]

I ran 335/30-18 on a 10. You'll be fine, but of course the tire would be happier on a much wider wheel.

[Michael Wood]

We run 295/30-18 A6's on 8.5" rims in FS, so, yeah, the 315 on a 9.5" isn't too much of a stretch (no pun intended). I'd also go so far as to say the 315 A6 will work better on the rim than the 305 V710, because of the sidewall/bead profile differences. Like Jason said, it would be happier on a wider rim, but we do all types of wierd stuff with tire size/sidewall profile/contact patch in Solo, it seems.

[Rad_ Delgado_]

Steve,

Savini's car is on 275 and 285. A 315 fits on the 9.5" wheels, I tried this on A6.

The problem I see is that you're only increasing contact patch width by 13mm (0.5"), but you're running a 0.7" taller tire on a car that already has a tall 2nd gear, and 2nd gear will be even taller. So, I think you are going make the car slower.

[Steve Towers]

Rad,

Thanks for the input. So, are you recommending 295's (Hoosier) or 305's (Kumho)? That, in a nutshell, is what I'm trying to sort out. Also, .7 taller than what? I'm currently on 305 Kumho. The diameter of the 295 and 315 Hoosiers and the 305 Kumho is only a few tenths different.

[Jason Isley BS RX8]

Steve,

Savini's car is on 275 and 285. A 315 fits on the 9.5" wheels, I tried this on A6.

The problem I see is that you're only increasing contact patch width by 13mm (0.5"), but you're running a 0.7" taller tire on a car that already has a tall 2nd gear, and 2nd gear will be even taller. So, I think you are going make the car slower.

Tony posted his tire setup over on the Corvette forum:

Actually, I won the Toledo Pro on 295's... My car is the one everyone is talking about with the Stranoparts setup on it. By the way, welcome to A stock! We can sure use some more folks here! I am running exactly what Sam told you, including the Z06 front bar. The car is very neutral, and is an absolute blast to drive! He should have everything you need available at stranoparts.com
As far as wheels go, I picked up a few sets of factory Magnesium wheels that needed paint work right here on the forums at a great price. They are super light (within a pound of CCW's at less than 1/4 the price) or you could get a set of thin spokes (+ about another pound per wheel as I understand it).
If you have any other questions, feel free to pm me. I'll try to keep an eye on the thread to see how you make out!

I also did test on 285's at a local Hershey event. Mounted on the exact same wheels, the width is almost identical while the 285 is clearly shorter. I'm thinking the best answer might be to have both mounted up and run whatever you need depending on the course. Bearing in mind that the car will be a little less forgiving on the 285's (less sidewall, shorter gear). At least that was my experience. At another recent local Warminster event, where a local SS competitor in a C5 who regularly trophys at national events was just getting to the rev limiter in his car, I never touched it and put over a second on SS. Gearing? I'm sure it didn't hurt. This was a fast course, but I'm thinking with all that room in Lincoln, those will be fast courses as well.
What kind of 60' times were you getting on the 285's? I cut some low 2.0's in Toledo on 295's. Just curious. Lincoln should be similar grip.

Tony Savini

I also initially liked the idea of a short tire for gear multiplication, however, the gearing change is not as great as you might think. The speed difference for a non-Z06 C5 in 2nd gear at redline is 73mph-285 VS 75mpg-315. In a low speed turn, say 35mph in 2nd gear, the car on 285s is at 2900rpm, while the car on 315s is at 2800rpm. I would take the width, the car has good Tq and the extra sidewall will make it easier to get off of corners.