Those are OEM offsets though, (the OP wasn't listing factory offsets) you do realize that when people buy custom wheels for their car, they typically don't use OEM offsets, they usually go for more "poke", so that the custom wheels sit a bit further out and fill out the fenders better. Those Vossen offsets the OP quoted are from the Vossen website for wheels that fit the C8. The fronts range from +20 to +42mm and the rears range from+30 to +50mm. These would be similar to adding aftermarket wheel spacers to your OEM wheels, which look fantastic and make the car look aggressive. You can certainly order your Vossen with OEM offset numbers, but why would you? Unless you like the wheels to have the factory "tucked in" look, but, where is the fun in that?