[Gaz64]

Originally Posted by strictlypersonl

I wasn't talking about the rim, I was talking about the tire's tread corner, which is approximately the same no matter what the rim width. The centerline of the tread stays with the centerline of the wheel, so the place most likely to rub (the corner of the tread) moves out about 3/4". The widest point of the tire (at the bulge) moves out about half that amount.

Originally Posted by xb-60

You're spot-on Bob. The outer edge of the rim for both setups is in exactly the same place; the inner rim on the 8.5" wheel is 1.53" further out; that makes the centre of the 8.5" wheel (and hence the centre of the tyre) 0.78" further out, so the outer edge of the (same size) tyre moves out that much as well.
Cheers,
Glen

Yes boys, you are both near enough correct, sorry for confusion.