Cal Club Autocross Forums

I figured this would be one of the best places to ask this, hoping you guys can help shed some light and help me go the right way. Im Time Attacking a Chevy cobalt. Car weighs 2900lbs with driver, fully fueled. Currently I am running a 225/45/15 RS3 or a set of Kosai K1's (miata parts, ftw) However, as we dial the car in, its just not enough tire for the car. The only rules in my class is "Treadware must be above 140" Im considering a 245 or 255 tire. Thoughts? What tires/ wheels would be a good choice here? I'd like to run a 16" wheel to get a little more clearance over my brakes, but wouldnt be opposed to a 17" (aside from cost, heh)

Thanks

[quote="Chris Hofmann" However, as we dial the car in, its just not enough tire for the car.[/quote]

More details. In what way is it not enough?
Are you spinning the tires everywhere, and need more width to put your excess power down?
Are you locking the tires up even w/ ABS...
or are you just over cooking the corners, and need to slow down?

Larger tires equal more mass to rotate, which can effect gearing, and acceleration/deceleration rates, an addition to providing cornering grip. When I was driving the Integra... I needed more rubber to keep up with the Mini's. I could almost keep up with them in the corners, but they trounced me on launches, be it regular Solo events, or ProSolo's.
Problem was I didn't have enough power to even spin the tires off the line at a ProSolo launch w/ 5k clutch drop. More meat was not going to help me accelerate any faster.

Generally speaking 225's sound reasonable for the car.

We are using all of it, sidewall to sidewall when on the track. The back end is light ( its a gutted car) and it still skates and slides around a bit when cornering. The car does push too, because it carries speed well but can't seem to hold it in the corners. It was suggested to me that a wider tire would help the car and its excess weight at the track.

Don't know how any of them will stand up on the track... but the hot tires in ST right now (200TW)

Bridgestone RE71
Toyo R1R
BFG G Force Rival
Hankook RS3

and I know a lot of Chump cars also run
Falcons RT615K
Federals 595RS (or 595RSR some sizes are 140, others are unrated)

Chris Hofmann wrote: and it still skates and slides around a bit when cornering.

And you're sure that is due to the tires?

Well, I've learned that the GM Time Attack Program ran a 245/40/17 tire. And its been suggested that at 2900lbs with driver, a 225 might not be adequate to carry the most speed thru corners.