Yeah, so to give you a little more info. Offset is calculated by the distance of the mounting pad of the wheel from the center line of the width of the wheel. Positive offsets mean the mounting surface is more outboard from the center line of the wheel, negatives are more inboard.So would I be better off going with the +35 offset or even +35 and 5mm spacer? Or are you saying I need to go higher than +45. You'll have to excuse me I'm not well versed on wheel terminology (first set of aftermarket wheels I'll be buying).
As you increase the offset of a given wheel, it brings the wheel in closer to the car as long as you're talking about the same width wheel.
Stock G8 wheels are 8" +48et.
Stock CTS-V Gen 2 wheels are 19x9" +51et front and 19x9.5" +56et rear for sedan/wagon wheels. CTS-V Coupe wheels are 19x9" +51et front 19x9.5" +40et rear. Sedan/wagon wheels are perfect fit rear, and fronts need a small spacer to make sure they clear everything on the suspension of the G8.
In general, BMW fitment wheels won't work on a G8; many are around +20et for their offset, so they're too outboard to be good fitment. This is the trap many fall into. We have the same bolt pattern of many European cars, but our offsets are all much higher.