well the ZRi is cheap as well as the kumho... so they SHOULD be comparable... as for the F1... was it a GSD2 or 3? The 2 was supposed to be a great summer tire, and the 3 is supposed to be a lot better.

 

it was teh 3

 

the 3 is a stellar tire... in a straight line (all stangs are good for, hahaha) you wouldnt notice much of a diff, and the GSD3's arent worth the money... they'd out corner kuhmo's and fuzions though (cause they are stickier, hence the quick wear), and in rain, the GSD3's would be noticibly better in all driving situations.