UberR32

Hey guys, first time posting in the Autocross section. Here's my dilema - I would like to autocross the vette in the SCCA Super Stock class, but I haven't found competitive tires (Kumho V710, Hoosier A6) in the stock sizes.

I find myself contemplating an Elise lately, because they're prefect track weapons and because the tire companies make tires to fit it!!! Please help me get into some tires so I can love the vette on the auto-x course too.

For reference, SCCA SS class requires the use of the same width and diameter wheels. For reference, the stock setup is as follows:
Front: 245/40-18 tire, 18"x8.5" wheel - 25.7" OD
Rear: 285/35-19 tire, 19"x10" wheel - 26.9" OD

I'd like the ability to keep competition mode on, so I think the tire diameter ratios should stay within 1-2%. That is, (Front,stock/Rear,stock) should be within 1-2% of (F,auto-x/R,auto-x).

So keeping the stock wheels, I came up with the following options:

Front:
1. 235/40-18 Pirelli PZero Corsa System (25.4" OD)
2. 245/40-18 Hoosier A6 (25.7" OD)
3. 275/35-18 Hoosier A6 (25.6" OD)
4. 265/35-18 Michelin Pilot Sport Cup (25.3" OD)

Rear:
1. 285/35-19 Pirelli PZero Corsa System (26.9" OD)
2. 305/30-19 Michelin Pilot Sport Cup (26.2" OD)
2. 325/30-19 Hoosier A6 (26.8" OD)

Using this, I came up with three realistic options:
1. 265/35-18 and 305/30-19 Michelin Pilot Sport Cup at $1602/set The right diameter ratios, probably good service life, but damn pricey.
2. 245/40-18 Hoosier, 285/35-19 Pirelli at $1374/set Will the mismatch make the car more neutral, or just make the rear feel greasy?
3. 235/40-18 Pirelli, 285/35-19 Pirelli at $1326/set Would I just be better on the runcraps?????????


Help me please. The Michelins are so damn pricey. I'm currently running my Miata, and a set of V710s is only $600. Maybe I'm just spoiled.

XPC5R

Most Hoosier/Kumho sizes run in the stock classes are slightly to radically oversized compared to the OEM sizes. Kumho does not have a wide range of 18" or 19" sizes available. I would suggest the following in Hoosier A6 sizes:

275/35/18 front
325/30/19 rear

This is not far off what competitive C5 sizes are (275 or 295/17 front, 315/18 rear) and will maintain a similar diameter differential front to rear.

They may appear squeezed on the rims (the rear mostly), but will still perform better than a similar Michelin or Pirelli at autocross speeds and temperatures.

Be sure to increase negative camber front and rear, as these tires really wake up with more camber. It will also help with wear/longevety as well.

02impactblue

Good Luck! I have been going over this since my c6 purchase back in January. I'm contemplating going back to a c5z06. I love the c6 but everytime I get my butt kicked at the track or autocross because I'm running street tires it makes me regret my decision to get the c6. The only choice is to pony up the $2700 for 18" ccw corsairs and get some toyo ra-1's or kumhos. It doesn't matter on the track but it will move you out of ss class for autox.

UberR32

Thanks for the suggestion. I was reluctant to try the 325 on a 10" wide tire, but given my alternatives, I think I'll give it a shot next season.

One more for you though - should I worry about the front or rear tires rubbing? I have not lowered the car from stock, but may lower it ever so slightly when I do the alignment.

NLowell

Why run 325/30/19 in the rear if 315/40ZR19 is available in the A6. I was thinking of running:

275/35/18 front
315/40/19 rear

Is the 325 a better fit? (I'm a newbie obviously)

69autoXr

Because the 315/40-19 is almost 29" tall, way too tall. Gearing would be thrown off and perhaps some of the electronics as well.

NLowell

but doesn't a 325/30/19 require a 12" rim (Hoosier actually recommends a 13" rim for this tire). Would that fit on the stock 10"?? Doesn't seem so but maybe I'm wrong.

TRACKMAN2

I Ran The 4 11x17 Rims From My C4 / 315's For Two Days And Didn't Have Any Problems.......kumo Vics

kermooni

I asked the same question earlier and no posts?

How about the Goodyear F1 GS-D3 for front and rear?

69autoXr

GS-D3's are street tires; we're talking DOT approved competition tires.

TRACKMAN2

sorry you did say c6 i thought it said c5

TTRotary

Another option is to run 4x 18x9.5 in C5 rear offset (the Y2K wheel), front and rear with 275s all around. Perfect fender alignment front and rear. You can run Toyos or Nitto R2 all around with that setup. These will fit just fine. If you have non-Z51 brakes, you can even run a 17x9.5 front to save a few bucks on tires and get better brake torque. You'll get more oversteer, but getting the car rotated faster for autox is a good thing, given this car's propensity to initial understeer.

tjZ06

He stated he wants to stay in SCCA Super Stock though. You can't even down-size and stay in SS.

BTW why would you want to retain Comp. Driving mode for AX? What your car will do on R-compound is way outside of what the logic of the system considers possible so it will step in waaaay too early. I don't know of a single fast AutoX driver running in Comp. mode. Wouldn't you rather know you're driving the car anyway?

If you decide you don't care about classes and don't have the Z51 front brakes 17x11" Grand Sport offset wheels work great on C6s.

-TJ

aggie88

I just started a new thread about the 275. I am contemplating this exact setup for SS.

I know the 325 in the back will work. So the 275 on the front 8.5 wheel should work too?

blkc6z51

That info was just what I was looking for.

kermooni

O.K. - These tires are only 0.5% circ off of original. But what size wheel would you use? 9" or 9.5" F and 12" rear? Can a C6 take these wheels?

aggie88

Here is a pic of the 325 Hoosier on a 19 X 10. Not optimum fit but it works - and far better tire than anything else for SS today.

Anyone have a shot of a 275 35 18 on the 18 X 8.5?

UberR32

To be honest, I've been driving a Miata in ES, so I don't know if I want Comp mode or not, but I'm reluctant to throw it away without trying it.

Also, our course has several lightpoles, and the two hard-headed guys who have hit them kept their feet in the gas in high HP cars (Cobra and M3). Both got speedy trips to the ER, and one passenger had a broken femur and messed up shoulder.

I do appreciate the comment that not many are using it, though. I'll probably just go easy on the gas.

TTRotary

Comp mode is perfectly capable of dealing with stickier tires. There is no difference in its effectiveness. This is because it works by comuting the differential between steering inputs and actual vehicle movement per the accelerometers and wheel speed sensors, and applies a brake as needed to redress the car. The traction of the braking wheel is equally enhanced by the stickier tires so it remains equally effective. Aside from the theory, I have run many track in events in my C5 corvettes with race brakes and tires and can attest not only to AH's capability, but also to it's usefullness as a learning tool.

If you are struggling through an autox course in Comp. mode, it is because your driving sucks. Concentrate on smooth inputs and Comp mode will intervene less and lap times will drop.

As to the Wheel / SS issue, my understanding was that any late model OEM wheel size is permissible, and so are even shock changes, but I have not run SS in years.

The Hoosiers do seem to fit OK, hadn't seen that yet.

UberR32

Aggie88,

That pic clears everything up for me - it doesn't look as bad as I expected it to look.

BTW, I think I saw you mention in another thread that you do more road course stuff. Any plans to come out to auto-x? I'm in a blue ES Miata (#161) right now.