I'm looking into buy a narrowed 12 bolt that has been shortened 3" on each side. It has fit into a 4th gen lt1 car and has all the provisions for LCA's, TA Brakes ect. Right now I have a 15/8 welds with a 5.5 backspacing. If the rear end is narrowed 3" on each side, and I want to run a 10" rim, will a 15/10 with a 3.5 backspace be okay? I want this to go in with no cutting of anykind. Let know what you think. Thanks in advance.

 

15 x 10 Welds require a 7.5" backspace with a stock 4th Gen rear axle assembly width. If you narrow the rear by 3" on each side, you will need a 4.5" backspace, to put the tires right where these are:



Running a 3.5" backspace will move the tires about 1" outside the fenders..... maybe slightly less if you are running a tire narrower than what's in the picture (ET Drag 28 x 10.5 - 15W).

 

Injuneer.

Thank you so much for the info. I want exactly what you have. If I end up doing this, I'll need to get the 15/10 with a 4.5 BS and do a ET Drag 28 x 10.5 - 15W. The tire looks real good on the car. Everything else I would hope will match right up like my LCA's, TA, driveshaft and ebrake.

 

I had to cut the bumper cover to fit that tire in there. The axle assembly had already been moved back 1/4" when I was running Hoosier QTP 28x11.5-15's. They grew enough when trap speed went over 125MPH that the tire tread was rubbing on the metal leading edge of the fender opening.

 

injuneer,
when you moved the rear back 1/4 inch did you ever worry about the driveshaft yolk pulling out of the trans? or when you had your shaft made did you have a longer slip travel just for that reason?
so since you can fit that wide of a tire under under the fender lip is there any real reason to narrow the rear?