Originally Posted by Merv

From my calculations,... stay 245 up front ... very,very slight stretch ... stock 9" rim with a +47 takes roughly 20mm to sit flush ... puts you at +27 at 9" so the offset differance is 27-12 for your new rim offset which = 15 mm past the fender. Than you need to add 6mm for the extra 1/2 in width of your new rim (quarter inch to each side of the centreline of the rim. ...