What tire size do I need for 17x8.5? I've looked in all these threads and I can't find a tire size for this rim size. They are OEM C6 Rims. I found the back tire size which is a 18x9.5(285/35/18) I drive a 2001 Z28.

 

pretty sure the OEM C6 wheels didn't come in 17x8.5/18x9.5.
The C5 wheels did (Y2K, not sure about the wagon wheels), and stock tire sizes are 245/45/17 and 275/40/18. The 285/35/18 you found will fit too.

 

Stock wheels on a C6 are 18x8.5 and 19x10.0.

The Wheel and Tire FAQ - General Topics indicates the wheel widths required for various size tires. This is the only one that works with a 17x8.5" wheel:

 

What about a 245/40/17?

 

245/40-17 is only 24.7" diameter. That's 1" too small. You want a tire diameter of 25.7 - 26.1" to match the stock tire sizes.