I did a bunch of calculating before I bought rims and tires. I wanted to keep the stock outer diameter so my speedo would be accurate. If you want to do any calculations for tire size, PM me and I'll send them to you. Bottom line, I found that 225/45/17 worked great. The tires are Nitto Neo-Gens. They're great on the street, but I have no track experience to speak of, so I can't help you there. I talked with a mustang guy I work with before buying tires and he said, based on experience, Nittos (particularly the 555) held up much better to track driving than the Kumho.