I Know this is in reference to the 28-29 fenderwells which I haven't had a lot of experience with as I have the 30-31 style. On the 30-31, remove the cotter key from the main arm back of the cross member. loosen the castle nut so you can move the main arm, also loosen the plate nut on the arm. After this is done, drop the tire in the well, adjust both the arm and the plate to fit, tighten the nuts. I have had Goodyears, Firestones and now 16" Goodyears on my cars and they all fit. The only difference is with the 16" I have to defate it by a few pounds because of the width. This way the arm and the position of the tire and wheel will look right where where it should be