I was one of the 18/17 pioneers years ago. The 285x30x18 in front is superior to the 275x40x17 for two reasons: it's shorter (no rubbing issues) which provides very quick steering response, and it's about an inch wider (more grip). I debated about moving to 18's in the rear, especially given industry trends toward 18s and 19s, but John (CCW wheels owner) and I agreed that the short sidewalls on most 18" tires would be a disaster on a powerful Supra. The 315x35x17 offers more sidewall flex than a comparable 18" - allowing for better straight line "hook up." That said, in an ideal world (i.e. I had flared rear fenders), I'd love to run a 335x35x17, or maybe a 335x18. Note that I run mainly R (race) compound tires...