The wheel manufaturers are really pushing the whole "offset" thing on rims these days. They're going for keeping correct scrub radius by keeping the wheel centerline in the same spot. But when dealing with wider wheels, sometimes you have to sacrifice that for correct backspaceing to prevent rubbing. The issue nowadays, is that most newer cars center the wheel directly over the spindle centerling, whereas older cars weren't on center. New cars and trucks are sensitive to changes in offset.
When you look at wheels, insist that they give you the backspace dimension. If they can't/won't provide it, look elswhere.
