Offset I believe is a measurement of how removed the hub mounting surface is from the center of the wheel, i.e. a 0 offset 15x10 would have 5” of wheel width on either side of the plane of the inside mounting surface. Most modern wheels have positive offset (toward the wheel face) while most vintage mags for RWD car seem to have negative offset (or “deep dish”. This resulted in little interference with brakes/suspension/frame, but usually meant death to fender well lips. Backspacing is a measurement of the mounting surface to the inside edge of the rim. On the front of a Vette, you’ll want to mimic the backspacing of the original 15x8’s, but depending on the tires you want to run, you’re just going to have to do a lot of measuring and you’ll probably be challenged by the offset options given to you buy vintage wheels with big tires.
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