You have to stay with the stock width/height and the offset has to be withing 1/4 inch. I'm pretty much an "R" compound virgin, but I'd suggest Kuhmo Victoracers. They'll last a lot longer than Hoosiers, can be driven in the rain until the tread gets too shallow, cost less, and you can get away with changing them at home and driving to really close events. on a 17 X 7 you can probably only get a 225 on there, but I'd hunt through www.sccaforums.com and look through the stock class posts (or make your own plea there for help).