rear tires

255/45r17 would be a good size tire all around. But, 275 is as wide as I have ever heard on a 17x8 wheel.

I know that '03-'04 Cobra owners have put 315s on stock 17x9 Cobra wheels.

'94-'99, '01-'02 Cobras have 17x8 wheels.

'00 Cobra R wheels are 18x9.5.
 
I'm running 275's all the way around, front and back. It has a tendancey to "jog" a little bit. I have a bump steer kit and and koni adjustables that help with that. Just makes it easier to rotate them if you know what I mean!!!

On 275's on a stock rim is as big as you would want to go. If you go any bigger, you are wasting your money because only the inside of your tire will make contact with the road. It would be like a bubble in the center, not good for traction. I am thinking about going to a 285 in the rear as I have 17x9's on all the way around to clear the brembos!!!