I am looking for an answer to this question too, so I'm tagging on to this thread. From what research I have done so far, you can fit 18" wheels on the IS-F and still clear the brakes, but I have not independently verified this with my own set of track wheels / tires. 18" slicks will probably still be a lot of $$, but less than 19" (if you can even find them...i can't).