Whats teh biggest tire i can fit on my 95 camaro with out modifying anthing? I have 18 inch Z06 wheels on it right now im lookin at getting a set of nittos for the back just how wide can i go???

 

Depends on the width and the offset of the wheels. "18 inch Z06" wheels doesn't provide enough info.

With the correct offset, many people have put 315's in the back - likely to require some hammering, even with the correct offset on the wheel. A couple have used 345's - can't imagine how they fit them in there.