I'm looking at buying some new wheels and R-compound tires for my GSR. I've decided on Toyo RA-1s and Kosei K1 Racing rims. Now the question is what sizes? I'd prefer to stay with 15" rims, but would consider 16" if experienced trackers recomend it. In either case, what's the widest possible width I can get without causing rub. 215? 225?

This is for the track, not autoX. And the car still has the stock suspension (for now).

Thanks!