what the widdest tire you can put on that size rim????

 

Rim width recommendations vary from manufacturer to manufacturer, but 285/35-18 appears to be the widest recommended on a 9.5" wide wheel.

 

I've seen 315/35-18 wrapped around C5 wheels on a 4th gen F-Body before

 

That tire would probably work ok on the 18x10.5 ZO6 wheels, that sounds like too much for the standard 18x9.5 C5 rear wheels. The biggest I would go on my 18x9.5's C5's is a 295/35/18, I've heard they fit pretty good on them. Thats the tire size that came on the Z06.

 

I've seen people go over Niagra Falls in a barrel, but I don't think its a good idea

 

I have 295/35s on my C5 wheels. They seem to work just fine.