Blue84TA

Im in the process of backhalving my Transam and need to know how wide to make my 9" rear end. Im going to run 15"x15" Weld Prostars (4.5" backspace) with 31"x18" wide tires. I already have the rims and could order the tires and mock it up for some measurements but the car wont be done until next summer and i really dont want to have $600 worth of tires sitting around and dry rotting for a year before i drive on them, so if anyone has run the same size rims and tires i would appreciate the help.

Jon

AlkyIROC

I made my diff before I back halved the car. I eyeballed the width and made the diff 40" wide and it's 45" from axle flange to axle flange.

I did my framerails on 26" centers. I use 15 x 15 rims with 5.5" backspace. I was running 32 x 14 tires for a few years and this year picked up some 32 x 16. They still fit with no problems. The 16" is the tread width. According to MT, my 32 x 16 tires are 18.5" across the sidewall.

With your 4.5" backspace and 18" tires, you'll probably want to narrow the diff slightly more to keep it under the fenders.

For mock up, see if any local racers have a worn out set that they can give you for nothing. Once they're worn out, they can't usually sell them. There's always worn out 32 x 14 tires around. 31 x 18 could be hard to find. It's not a common size. I had some old Hoosiers for mock up until I finally bought some new MT tires. The old tires held air and that's all I needed them for.