Gary K

I'm ready to pull the trigger and order up some A7's for my C5Z. SSR class, so running stock wheels. I was going to go with the 295/315 sizing but I ran across some discussion regarding the A6's and it sounds like stuffing 315/335 tires on is actually faster. If I'm spending the money on A7's, might as well go all in and spend a bit more on bigger tires.

Should I expect the bigger sizing in the A7 flavor to be faster like the bigger A6's were?

Does anybody know if the A7 sizing will allow the bigger tires to fit like the A6's did?

Anything I need to do when stuffing the bigger tires on? I have an alternate set of Fikse wheel in stock sizes with 1/4" less offset (still legal)...would those be better to use with the bigger tires? Or keep the tires tucked in with the stock wheels?

Thanks for any help!

69autoXr

Not sure if it's actually faster or not, but the fastest C5Z at Nats last year was on the bigger combo, and after talking with a multi-time National Champ who is familiar with these cars and local to me, I decided to go for the big combo when I bought new A7's this year. They are mounted on stock wheels and are ready to go. According to Hoosier, the A7's >245 sizes are the same physical dimensions as the A6 (the smaller sizes had new molds and are a bit bigger A7 vs. A6). The C6 GS/Z06's are all running 315's on their 9.5 fronts, and in my mind you need as much front tire as you can get in autocross so I viewed this as an advantage for them. It would be nice if us C5Z guys could +1 our front wheel diameter to be able to get rid of the goofy looking big sidewall of the 315-17, but that's just an aesthetics thing in my mind.

To prepare, I test fitted the big combo A6's on my car and have ran a few events with them last fall and this spring. In the rear you'll probably need to use a small spacer to keep the tire from rubbing the inner fender, I tested with 1/8" and it was adequate, and I also have 5mm spacers in case I need a little bit more. I don't use any spacers in front. If there is any rubbing front or rear at this point I haven't noticed it.

All that said, there have been plenty of fast guys running the 295/315 combo. I don't expect that the bigger tires are going to transform me from back-marker to front-runner, but I did want to maximize my opportunity when I bought new tires.

brenb

To my eye the 295/315 A6 vs A7 are the same width.

Keep in mind that going with the larger sizes will negate some of the C5 advantage of being more narrow than the C6 as they stick out a bit past the body (on OE wheels.)

fatbillybob

Wow! those are some pretty big sizes on narrow stock wheels. I have run 7 sets of A7's for road racing. In T1 we ran 315 and in T2 295. IMO the tire needs to be supported by the wheel. So if you got a 315 puckered up on 10.5" wheel you got the same rubber on the ground as the 295. In fact you might even compromise the sidewall support and could have negative effects. I would be very surprised you could even get a 335 on a 9.5" C6 wheel. I mount my own tires. But if you guys are doing it with success I obviously have no clue of what I am talking about.

brenb

Welcome to national level autox.

69autoXr

To clarify, it's 315 on the front 17x9.5, and 335 on the rear 18x10.5. I also mount my own tires.

froggy47

I don't think you can do 1/4 " rim offset PLUS a spacer. In SSR. Just sayin.



On my SSP I run 335 on 12" and they stick out a lot. Stiff springs keep them off my stock fender, but with oem springs I would plan on some tire to fender contact FWIW.

Solofast

A few years ago the hot setup in A stock was Solstice on what looked to be relatively tall 285 HoHo's.. That car had (IIRC and I could be wrong) something like a 8 inch wide rim.. It was pretty silly looking and by all rights it should have been a disaster, but it really worked and those cars that were running that setup were flat hooked up. They were blowing by cars that had more "normal" setups.

After that I'm not surprised that some strange things actually work. It depends on the tire, the sidewall height and stiffness, the suspension, the surface, the driver, the phase of the moon that the tires were made under... Somebody tried it and it worked and when they kicked butt doing it, everybody else jumped on the bandwagon...

Go figure...

69autoXr

Correct, you're allowed 1/4" total offset variation, between spacers and wheel dimensions. My comments and experience are all regarding stock wheels. The OP's wheels with the 1/4" allowance built in are out of my realm.

dhowdy

285s on 8s, yup.

talon95

Actually it's 7mm now I think. They changed it since almost everything uses mm now.

talon95

And I think the real benefit (if any) of running the 315/335 combo is resistance to overheating. It's easy to overheat the A6 (and probably A7) on a longer autox course, so the bigger tire helps by just being a bigger heat sink. Possibly helps durability/wear also. They've got to be less responsive in transitions though.

froggy47

I will put my 2 cents in here, I an sure talon95 won't mind, but yeah you also might have trouble (me) getting the tires warm.

Haven't used water yet this year.

Gary K

Thanks for the input everyone. I was also thinking the larger sizes might just resist overheating better while also being a little harder to get heat in them in cooler weather. I'm kind of leaning towards the smaller 295/315 combo now.

69autoXr

No, it's still 1/4" in the rulebook for SSR. Not sure why the update didn't carry over.

Had a great weekend in Toledo running on my 315/335 A6's. Got to run with Sam Strano all weekend. Though I'm a good ways behind him my car felt the best it ever has, very confidence inspiring on a fast, big speed carrying course. Sam and I talked about the bigger tire setup and he described it as being less "edgy" which I can definitely agree with, it certainly felt more forgiving and driveable. I don't even notice any real numbness in transitions, the car basically did whatever I asked it to do.

strano@stranoparts.com

And it works.

strano@stranoparts.com

The wheel offset thing. the SEB kind of picks and chooses what rules they apply to SSR vs Street. Wheel offset of 7mm? No, but we have to abide by the stupid tire production date rules. More ignorance.

Anyway, regarding the 295/315 vs. 315/335. Basically it's been said but I'll make sure I say it too. Both are fast, I ran the same times on a C5Z with both tires on the same day, same course, 15 minutes apart. The bigger ones are less crisp and have a more tolerant slip angle window in which to work. Mind you slip angle also wears tires quicker, as does squeezing them more which crowns them and A6's like to wear the centers already. And you do make the car wider, particularly in the front, which may or may not matter. Pick your poison.

Really depends on what you like best. Would recommend folks try both if possible. If you base a lot of cones already, wider isn't better.

And Chris had also changed front bars too, which was some of the help, but the bigger tires do certainly offer a touch more wiggle room for mistakes.