My Mazda RX8 has 18" x 8" stock rims with 225 Bridgestone Tires. Wanted to put on wider tires. What is the widest tire I can put on these stock rims? And what is the widest tire I should consider putting on this rim for this car? Was thinking about 255/45/18. Could this be just to wide for this car? Any comments would be appreciated.

depending on the tire you are using it will have a recommended rim width...as for the widest tire on that car, youd have to check your current clearances to see how much room you will have with a wider tire...

the current tires are 225/xx/18? what is the xx number?