bigger tire theoretically gives better lateral grip. it also creates more drag on straights, probably not a factor unless you're racing. bigger also means slicker in the wet. i've been using stock 225/50/16 for years... presently toyo RA1... which is a good track tire with reasonable wear and plenty stick unless you're into serious competition. you can probably find a 245 17" tire that will work if you feel you need more lateral grip.