My '72 Dart has a stock-width B-body rear under it, and minitubs.

Do I have any off-the-shelf choices for rear wheels that will allow me to run 325-50x15 tires? Or will I have to get a pair with custom backspacing...

thanks
Charles

That is pretty common installation. The B body rear end is about 2 inches longer and you gain about 3 inches per side with the mini tubs. It is easy to mock up and decide tire and rim size.Put the car on jackstands and try any available rim/tire and measure the amount of clearance to the inside. Most manufacturers sell rims with a backset that will let you locate the tire where you want it.

68gts383: I am going thru this also. I have a recent purchase a 65 Dart roller w the springs/perches relocated way to the inside of the frame rails. Do I need to throw a wheel/tire on there & see how much sidewall clearance I have to the half moon circular wheel wells on each side? This is my 1st time w this & it seems like I would run out of available space on the wheel wells(on the inside part at least) way before I would come close to hitting these (relocated) springs.

You measure from the ball of the tire(side wall) That tells you how much clearance or distance that you can move in.Then measure the backspace of the rim that you use in the mock up.The backspace of a rim is measured using a straight edge. measure from the outer lip of the rim to the mounting surface that contacts the axle flange.When doing your math keep in mind that you need about 3/4 inch clearance between the sidewall of the tire and the wheel tub. Hope this helps 68GTS383

OK I measure from the ball (the bulge) of the sidewall to the wheel well lip on each side & need 3/4" clearance on each side then I need that(the outside measurement) amount more rim width for the outside and on the inside I need that(inside measured amt) more rim width which would be an increase in backspacing of that (measured) amount?. EDIT So If I have 2&3/4" measured on the inside and 3&3/4 on the outside & my test rim is 4&1/2 wide w 3" backspacing I need a 9&1/2" rim w a 5" backspacing?.

The inside dimesion will tell you how much more backset that you can use.Without the wheel in place you can measure from your outer wheel lip to the wheel tub minus 1 1/2 inch and it will tell you how wide of a tire that will fit.Tire manufacturers provide these tire widths and recommended rim widths.