Have you talked to CCW about this ? They are quite knowledgeable about fitment. I agree about going with the same size front and rear and slight width difference doesn't make any difference in traction for street driving. If you are concerned about squeezing every little bit traction available, get stickier tires which allow you to run a narrower size and avoid clearance problems. Start with hard-compound DOT-R tires such as Pirelli PZero Corsa, Michelin Pilot Sport Cup, Toyo R888, and Hankook RS-3.