Autocross/race tire size

[mancini_mark]

Hi guys,

So, I ran my first autocross with my newly transplanted supercharged S52. I have a 3.23 LSD diff, and 17" style 42's with 235/45 (shitty Kumhos) rubber all around, with the Sachs Sporting kit and Hartge sways.

The car was fantastic, but a little tail happy with all that power. I'd hate to upset the handling balance with the equal size tires, but I'm thinking with that kind of power, oversteer is the issue. So, I'm thinking of going to staggered 18's, and running 245's up front with 275's in the rear. I know i might have to roll/pull the fenders to make that work, but I think I need more rubber out back i.e. 275 vs. the usual 265 section.

Opinions?

[shogun]

Opinions?

better give that engine to me for my 02/1998 E36 M3 as spare engine :)

and yes, I can confirm, that engine is nice, pull faster than the M70 engine in my E32 750.
Of course, much less weight with the E36 M3 chassis.
A real fun to drive.

[Mr._Graybeard]

Are you doing any left-foot braking? It'll help control oversteer in a RWD car. Basically, you touch the brakes to reduce traction at the front axle while you keep the throttle steady, which prevents the Gs from loading up front. With less adhesion up front, you reduce the tail-happiness by balancing out the level of traction between the front and rear wheels. It works.

[sneekens]

245/40/17 or 235/45/17 front

275/35/17 rear

[mancini_mark]

Hmmm. Might try that. I hope to be doing some of the BMW club's advanced schools this year to learn technique. To be completely honest, I was having so much fun drifting, I just stayed on the throttle in almost every corner. Not good for the lap times though.

[mancini_mark]

Exactly. Especially with a 9 psi Powerdyne blower on it. The last time I drove the car seriously was last year...when it had an M20 in it. So, pushing the car with double the horsepower was tricky, but way more fun.

[Mr._Graybeard]

The left-foot braking technique will let you stay on the throttle and keep the front end pointed in the right direction. It's best practiced on a loose surface -- a gravel parking lot would be ideal. Or, you might seek out some rallycross events in your area, like this one: http://www.w-a-g.org/events/rallycross/2010/info.htm

The rally guys really have left-foot braking down. They can be a little rough on their cars though!