Tub and spring relo

reguardless of your rearend width aren't you still limited by the width of your tubs? I know with my Cuda, when I moved my springs and tubbed it, with 16" wide tubs, I could go with either 10 or 12 inch rims but no tire tread wider than 15" (but remember sectional width is wider than the tread).I was going to narrow my rear but decided it was cheaper to buy wheels with a deep backspace. With my stock rear, and measuring from the outer face of the drum to the inner tub wall, I have 10" and approx. 6" to the outside tub wall. So I am going with 12" wide rims with a 7.5" backspace (cuz the price of wheels double over that). With all the tires I looked at their sectional dimentions were always 3+" wider than the tread width so it shouldn't rub and still fill the tubs up with a little room to spare.