I don't carry a spare but I think the offsets are the same for the Z and the U. Here is the front and the rear wheel offsets. I think If I were going to get an extra wheel, and if it was going to be an CFM, it would be a front with the front width tire. If another aftermarket, I think I would go with a 4+2 or a 5+2 - 4/110 and still put a front wheel width on it.

