Dean

Michelin recommends a minimum of 9" to a maximum of 11" for the 275/40-17. Your overall width should be around 10.8" on the 9" rim. By the way, since you are going to autocross the car, the tire weights about 27.3 lbs so a smaller (lighter) rim will help reduce unsprung weight a little. Good luck and let us know how you like the Sport.

Tommy