Fast Eddie I

Looking for track tire combinations [front and rear] that have worked for others on their C6Z. Recently, there has been numerous retailers offering amazing prices on scrubs and new discontinued track tires. Matching available tire sizes, manufacturer and tread compounds to your needs however can be very challenging.

I'm comfortable with the max widths that can be utilized using similar OEM offsets. In front, I've run up to a 285 width with no obtrusion or rubbing. Others on the forum have indicated that a 295 will be OK. Another in my track club tried a 305 with disastrous results. For rears, up to and including a 345 width has worked satisfactorily. That said, and relative to track tires, it is the sidewall height/aspect ratio/overall diameter that needs to be addressed to ascertain whether the front-to-rear rolling relationship will trigger a traction control default.

My theory is that a computer default [trouble code] is recognized when the front and rear rolling diameters vary significantly from OEM specs. C6Z OEM 275/35-18 and 325/30-19 tires have a diameter relationship [rear versus front] of 1.043:1. I and others in my group have used combos ranging from 1:038:1 to 1.071:1 with no adverse impact. Assuming my theory to be correct, I am interested in sizes you have used that fit the car while not triggering any trouble codes? I am particularly interested if you are running 18" wheels on both ends.

Thanks in advance.

shane p

I several people with 295s on the front and they all rub. I think the 295 tires are a bit taller and thats what is causing the rub.

Dirty Howie

I don't think a 295x30x18 will rub.


DH

shane p

You might be right, a couple of my friend have them and they rub but now that you mention it, I think they have 19s on the fronts. I will ask.

c5racr1

I used 305/645/18 on ccw 18 x 11 fronts, no rub, rear 325/660/18 and 315/680/18 on 18x12 rear ccws no rub. I’m currently running 325/705/18 on the rear with 18x13 rears and they do rub

shane p

They are 295x35x19. Disregard everything I have said.

Sox-Fan

315/30/18 front and 345/30/19 rear. Fit fine. If I turn all the way to one side and back up they do rub the factory brake duct.

(note: the car is accelerating picture. ride height is actually lower.)

GT Racing Tires

You could run Pirelli P Zero DH compound slicks in 285/645/18 and 325/680/18. YES A NEW SIZE, 325/680/18. I have customers running 285/645/18, 305/645/18 or 305/660/18 on the front and 325/660/18 or 325/705/18 on the rear. The 325/660/18 isn't ideal for the rear.

Dirty Howie

What is the "660" is that a "30" profile??


DH

BrunoTheMellow

Slick tires use tire diameter in mm as the second dimension rather than ratio of width

shane p

We are in the process of getting 335/30/18 to fit up front.

bullitt4110

I have a set of Toyo R888R 295/30/18 and 335/30/18 that I’ll hopefully be mounting in the next week or so, I think as long as your offsets on your wheels are good you shouldn’t have any issues

PRE-Z06

Buddy runs 335 Rivals square on 18x12 and 13” wheels, so fronts are actually slightly taller being on narrower rims. No issues running in Comp mode, but fronts rub though not as bad since he’s gone to coil overs. Personally I’d go 18x11/12 with 315/335s, hope that helps.

Dirty Howie

Have you run these before? These are the tire/size am contemplating. Just need to get the wheels. Are you mounting on a 10inch front wheel?


DH

bullitt4110

I have not but hoping for the best haha. They’re going on a set of Signature wheels 18x11 front and 18x12.5 rear.

Fast Eddie I

Thanks for all the informative posts. May I assume that all the combinations and sizes that were run resulted in no engine management, ABS or traction control codes?

As stated in my original post, I had been informed that a significant mis-match as compared to the OEM rolling diameter ratio [front to rear] would result in a performance adjusting code. I'm sensing that advice may have been misguided???

I appreciate everyone's input.

Boosted_Z

I also use R888R on 18x11 - 18x12 Forgestar wheels on a c6z with no issues. Offset I believe is 36F 50R. I switch from 275/35r18 / 325/30r19 often. Overall keeps same rake but lowers about .4” when i switch. No traction/handling sensor issues. I set all alignment / ride height/ rake/ exc with my 295/335 combo . When I put the “stock” sizes on, it just raises vehicle about .4” and give more ground clearance for off season use .

295/30/18 & 335/30/18 have very similar height contrast as 275/35/18 & 325/30/19

Dirty Howie

Ratio of R888R tires is 1.0376, almost exactly what OEM 1.04 ratio is. So no computer issues.

I'm curious about your wheel/tire selection. Seems like your front wheels will stick out an inch more that stock. Your total front/rear width is much more square than stock stagger. How does it handle??


DH

Bill Dearborn

The hot set up on a C6Z is 18x11 front wheels with 315/30/18 Hoosiers and 18x13 rear wheels with 345/35/18 Hoosiers. That is what most people ran from 2005 on. The 18x13 wheel will touch the upper control arm at full droop so you can't torque the lug nuts until the suspension is depressed a little by lowering the jack. A 7 mm spacer will push the wheel out just enough to clear the uca and extended thread lug nuts will keep your thread engagement proper so you don't have to use longer studs. The tire diameters are almost identical to the stock tire diameters so you don't have any issues with TC or engine Drag Control. 345s put a lot of rubber on the ground. Front 315s are 25.6 inches in diameter and rear 345s are 26.8 inches in diameter. Stock tires are 25.6 inches in front and 26.7 inches in the rear. Can't get much better than that. Tire wear can vary the diameter by that much.

Ran them on my C6Z and continue to run them with my C7Z. If I use the Pirelli's I drop to an 18x12 rear wheel because the 325 tire is too small for a 12 inch wide wheel.

By the way Phoenix sells used Hoosiers if you don't want to pop for new ones.

Bill

Boosted_Z

Correction for me - Offset IS 18x11-36F 18x12-50R

Very hard to give handling opinions - If you want best setup, 315/345 is hands down, a killer setup. I have used this once before with great success (borrowed friends spare set).

I setup my car for 295/335 due to overall tire options/no rubbing/I only do events for fun. Still has a light understeer feel upon entry till I get in throttle, but noticeably better than 275/325.