I just got a set of 18x9 FR500's with 255-45-18's on them! max psi on the tire states 51 psi! I haven't put Gage on them yet but their as hard as rocks !! I need feed back on what psi other's are running on similar tires!......Thanks!

 

That spec on the tire sidewall is the maximum pressure for that tire - its not neccessarily the pressure you should be running on your car. In a perfect world, I'd tell you to set them at 32 PSI, go run some laps on a racetrack and then use a tire pyrometer to check the tire temps across the tread, changing the pressure and repeating the lapping/temp checking until you get consistent temps across the tread (too high PSI = higher temps in middle of tread). However, I know that's probably outside the realm of possibility. Since the stock 235-18s are spec'ed to be set at 32 PSI, I would set yours at 34-35 PSI and see how that works for you - tweak as appropriate.

The other thing to remember is that lower profile tires = better handling/response=harsher ride quality. You may just find (when you get around to checking the pressure) that the installer set them at about 35 PSi - its just that the lower sidewall makes the ride harsher (but gives better handling).

 

What does the GT500 recommend for TP?
It has the larger tires. . . .