I bought some '05 SC430 18" rims and covered them with Continental ContiSportContact 2 (235/40ZR18). I got a great deal on the rims which were brand new at the time for $500 on ebay. The difference in handling is clearly night and day and the wet traction, which was my main issue with the stock setup, is no longer an issue. I'd recommend at least 17" rims and a lower profile tire. If you're looking to stay with ride comfort, then 16" rims will do fine.