Does anyone know what the widest size tire you can fit on a S197 GT500 rim? Looking at buying some for my 2005 gt but need to know if i can fit a 295 or 305 on the rear

 

I've read 315 is the widest on the 2007-2009 GT500 wheels, but the tire wear isn't optimal.

I plan on putting 305's on mine shortly.

 

Difference between what can FIT, and what's recommended, by the manufacturer, your local installer, common sense, etc.

Just look up some representative 295 or 305s (or 315s) on TireRack and see what it says.

The 295/35-18s I see recommend 10" or wider, the 315s 10.5".