Kevin_k

So I posted in a different part of the forum and got a bunch of conflicting response so I thought I would try here instead.

https://www.corvetteforum.com/forums...post1588946050


This will be my third season doing HPDE events. First year I used street tires. Second year I got a deal on a set of Hoosier R6. They were awesome but did not last long. I ended up cording the right front after four track days and had to get a new set for the front. After another five or so track days again right front corded. This time I had even swapped the tires around after 2 or three events but still ended up cording the right front again.

This year I picked up a set of R888 275/40 17 front and 295/30 18 rear. Wheels 17 x 9 TSW Nururing and 18 X 10.5 TSW Nurburing. The guy I got them from said he had a Vette just like mine and they were what he used. I put the tires on the car when I got home and they did not look right to me.

I checked the formula for calculating overall tire diameter and found that the fronts are almost ¾” larger than the rear

(Cross Section with X 0. Aspect ratio) X2 /25.4 + Wheel Diameter = Overall tire diameter in inches
Front 275/40 17
275 X .4 = 110 X 2 = 220 / 25.4 = 8.661 + 17 = 25.661
Rear 295 /30 18
295 X .3 = 88.5 x 2 = 177/ 25.4 = 6.968 + 18 = 24.968

From what I understand I should have some rake in the car so that the rear is 1/2 an inch higher than the front when measured at the jacking points to keep the aerodynamics right at high speed. If not the rear end of the car will lift. Well with these tires that is completely opposite of what I have. The other issue is the effect on the TC/AH system, but I usually turn it off unless it’s raining. I don’t want to do something dumb that will be unsafe and end up with me ending a track day broken or worse. My goal is to be safe and have fun. At some point I would like to move to a square setup so I can move the tires around to all four corners.

So am I going to be able to run these tires or do I need to get two new tires?

ErnieN85

They are not that far off stock for a C5Z06 they should work fine.
If your worried try them on the street first if no codes come up you will know for sure

Gordy M

With C5Z wheels you should would be better with 315/30x18 tires in the rear. This would help keep a better aspect ratio and keep the AH nannies in bay. The rear tire has to be at least equal to or larger than the rear and a 0.7" difference is even better.

RDnomorecobra

You can use them. Abs will not notice. Some people have AH issues , some like me never have. I run 315/30-18 square. Drive them and if AH acts up turn it off and work up to speed gradually if doing so makes you nervous. You will likely find like all before you that the car handles better with no nannies.

froggy47

Close enough but not ideal, should be fine.

edwardo99

I have run those exact sizes autocross racing and track. On my 2000 (non-Z06) it would send the TC crazy. No issues once TC turned off.

Bill Dearborn

You will need to turn off Traction Control to get the car out of the garage but that will be the only function impacted by the tire size. With the larger diameter tires in front the EBCM will apply the rear brakes to control the rear tire slippage it thinks it is seeing. It will even do it coasting down hill in neutral.

I have run this several times on both C5s and C6s and you don't need to worry about turning off TC since you get a big reminder as soon as you try to move the car forward.

Bill