What type rim is it on your car? what year do you have?
the stock 99-01 Cobras are 17X8 that's why I'm asking..
17X8 the MAX is 275/40/17
17X9 the safest max is 295, but I've seen 305-315 (I think those should only be used on the 10 inch wide rim though)
If it is a 9 inch rim the 295 will fill it out nice!