8 3/4

General-Duster said
Nice reply 72 Blu.

So you are saying any axle up to 60'' width, can be used in an early A-bod if you use the correct back-spacing?
All you have to do is re-jig the perches.
I only said this about the Demon/Duster because I have worked on those with factory steel wheels.
If you fit a 57 inch axle in, there is still plenty of room so a 66/67 axle will also work.
I heard folks going to wider 60 inch B-bod axles in with custom made wheels, just not in the UK?
Folks here like to use a correct 57inch A-bod axle in an early car as they can get some wheel choice 'off the shelf'.

It just depends on what you want to do. If you want to use factory wheels with factory offsets then you should stay with factory axle widths, with the possible exception of the Duster/Demon/Dart Sport and Barracuda. Their extra quarter room allows a wider axle, but even then it depends on what tire width and backspace you want to run. For example, even with my 68-70 B body 8 3/4 (60-1/8" wide) I was able to run 15x7 cop wheels (4.25" backspace) with 225/60/15's. I couldn't have fit wider tires though. With a 65-67 B-body 8 3/4 I could have managed 235's or maybe 245's.

For 17" and larger diameter wheels, the "off the shelf" backspacing available actually works better with a wider axle most of the time because those wheels are generally intended for modern cars that use a lot more backspace. And if you're trying for a more "pro-touring" look with wider wheels up front, the wider rear axle actually evens up the front and rear track width. A-body's have a wider track in the front then they do the rear, especially with BBP front disks. Again, for example on my car I run 18x9's up front, with a +35 offset. With my B-body rear axle my rear wheels are 18x10 with a +38 offset. If I used an A-body rear axle, that offset would need to be more like +15. My wheels are staggered anyway, but with a factory width rear axle the front and rear offsets for going to wider tires are totally different. Run a wider rear axle and you can run 4 of the same wheels if you do it right.

If you look at the 8.8 Ford explorer rear axle swaps some like to use two "short side" axle tubes, while others have made it work just fine with the original rear axle width. Just depend on what you want to do for wheels. Always better to figure that out first. For me, I always start with wheels and tires. If you're going to modify the rear axle, or are looking for one, it's better to pick wheels and tires first and then figure out the axle width to make them fit. If you already have the axle, then you can spec custom wheels. Just a matter of how you're setting up your car and what your situation is. With as much as A-body axle housings cost these days, it's almost easier to have a longer one shortened than find an original. And yeah, if you're doing that then just pick your favorite wheels and make the axle width fit them.