If the rotors measure 12" or more you are going to need 16" wheels, 13" rotors need 17" wheels, 14" rotors need 18" wheels. You might get away with 12" rotors and skinny front runners, but thats a toss up depending on the wheel. Rears are a definate on size though. But I have heard that a couple of guys got by using 15" wheels with 12" rotors, but they had to grind material off the caliper to get minimal clearance. Thats a risk I would not take.