Re: C6 Z06 Hyper-sliver dark wheels have arrived....
The fronts are 8.5" with a 56mm offset & the rears are 9.5" with a 40mm offset.
^Previously stated by 4CE FED...
I have the 18 x 9.5s for my fronts and 18 x 10.5s for rears in the same style wheels... Fronts need no spacing whatsoever, just some notching of the front side of the upper a-arm for clearance. Rears needed a 1/2" spacer and longer wheel studs. I got a set of ARP 2.5" wheel studs for the rear and ground 5mm off them to make the new lugnuts fit, since they aren't an open design. I recommend grinding the studs BEFORE installing them. At their full length they're a royal PITA to install, but it's do-able with the right tools and a TON of patience.
I'll post some pics of my setup with exact specs in the near future. I'm just waiting on some decent looking brakes to put behind the wheels, but they're not going to be available until Feburary (I'm going to be the guinea pig for them).