I have 17x8 rims with 245/45/r17 whats the biggest tie I can go with on my 2001 cobra

 

245 is the correct width for an 8" rim, if you want to run a wider tire then you should buy wider wheels. People run 10 or 10.5" rims with 315 tires on 94-04 Mustangs without much problem.

 

I have a 2004 GT with the polished 8" wheels that the 01 Cobra's had. I have 275/40s (fuzion ZRi) on all four corners, and they look good. All tire manufactures will say that the tire is too big for the wheel, and I wouldn't say they are wrong. 275s are supposed to be mounted on a 9-11" rim. But they will fit, if your local shop will mount them, somewon't for liability reasons.

The ZRis are a bit smaller then some of the other 275s, and they have a "rim guard" that keeps the tire from looking funny when mounted on a smaller rim.

good luck.

 

275s definitely fit and don't look bad (i'm running them on the rear) but they don't wear perfectly as the inside wears faster.