When I got my car brand new (MY06 WRX), still in the wrapper, it had 215/17/45 tyres on it. 225s on it now though. So offset is changed using spacers, yes? I thought the idea of that ws to make the wheel fit over bigger brakes. I'd have though machining wheels to bring them in closer to the hub s it where, would be a trifle dodgy! Making the wheel thinner might not be a great idea, especially when they are under load. Of course, I might be getting the wrongend of the stick - or wheel!