tire size needed

[yellow98svtconv]

I have a 98 svt cobra mustang and bought 18x9 inch rims for the front and back

what is the biggest and tallest tire I could fit on the front and the bibbest for the rear without modification??

[Mystic_Cobra]

The stock size on the 2000 Cobra R was 265/40ZR-18. That was the only Mustang with 18" rims (2005 will also). That size should fit for sure. Go to tirerack.com and look up the hight and rim width requirements for 275/40-18, 275/35-18, and 285/35-18. You can probably go one size bigger on the front and one or two sizes bigger out back. I know people run the 285 on 9.5" rims, but I don't know if they'd be too much for a 9" rim.
I have 275/40-17s and they don't rub. You can compare the dimensions of them from tirerack data also.