Correct Axle Housing Length to Fill Wheel Well of '74 Scamp with Widest Slicks Possible Without Cutting Structure

[Scramper]

Greetings All!

I am sure this question is not uncommon, but I cannot seem to work through the correct approach to solve it with confidence after looking at a lot of posts. I want to fill the wheel well without cutting structure as I will be using the car for drag racing in Sportsman/Pro class, and for street, and I will be moving the leaf springs inboard in order to accomplish it. I have the axle housing with a builder and we are trying to determine how much to shorten the housing to support the largest tires possible, while centering them in the wheel wells?

Many thanks in advance for your insights!

The tire in the photo below is a Cooper Cobra Radial G/T P235/60 R15, for reference.

 

[crackedback]

Figure out the wheel you want to run and measure with it centered in the wheelhouse.

 

[srduster340]

Even if you move the springs in you will not be able to run a big tire due to the inner wheelwell limitations. We fit a 275 tire on my brother's '70 Dart with Super Stock springs, in the original location on 15 X 7 police wheels with 4.25 back spacing. It did rub the outer wheelwell lip on turns. Trimming the sharp outer lip cured it. Sorry I don't have pics as he doesn't have the car anymore.

 

[Scramper]

Figure out the wheel you want to run and measure with it centered in the wheelhouse.

It seems to be the only sound approach as one custom shop that does a lot of A bodies told me the variation between cars based on wide tolerances in manufacturing is enough to need a car specific measurement.

 

[Scramper]

Even if you move the springs in you will not be able to run a big tire due to the inner wheelwell limitations. We fit a 275 tire on my brother's '70 Dart with Super Stock springs, in the original location on 15 X 7 police wheels with 4.25 back spacing. It did rub the outer wheelwell lip on turns. Trimming the sharp outer lip cured it. Sorry I don't have pics as he doesn't have the car anymore.

Thanks for this insight! From what I can tell a 275 tire would be the absolute max on this car as well, but I wasn't sure on the wheels. Dr. Diff sells a bolt-on kit for $175 that moves the leaf springs each inboard .5", so all things being equal (which they so rarely are!) with wheels like you mentioned with just a bit more offset toward the center, I could go a 275, and it may not need any cutting. Not that it would be a big deal as the car is far from show quality, and all my money is currently lined-up for go quality, so it isn't going to get pretty real soon! ;-)

 

[72bluNblu]

If you don’t cut the wheel wells, there’s no reason to do a 3” relocation. You can get all the clearance you can use with the stock tubs with DoctorDiff’s 1/2” offset. It still requires moving the spring perches.

Mopar A-Body 1/2" Spring Relocation Kit Offset Hangers & Shackles

With a Dart, that should get you to about a 275 without rubbing if you space it right.

As for the housing width, it depends entirely on what wheels you want to run. You should have about 12” from inner tub to the quarter lip, you can usually get a little more if you trim or roll the lip.

But without the wheels, there’s really no way to tell you what axle width will work best.

 

[Scramper]

If you don’t cut the wheel wells, there’s no reason to do a 3” relocation. You can get all the clearance you can use with the stock tubs with DoctorDiff’s 1/2” offset. It still requires moving the spring perches.

Mopar A-Body 1/2" Spring Relocation Kit Offset Hangers & Shackles

With a Dart, that should get you to about a 275 without rubbing if you space it right.

As for the housing width, it depends entirely on what wheels you want to run. You should have about 12” from inner tub to the quarter lip, you can usually get a little more if you trim or roll the lip.

But without the wheels, there’s really no way to tell you what axle width will work best.

I agree, and I am just not quite ready to do a mini tub on this car, though if budget were not an issue I might just go that way. I am thinking I will put a Caltrac suspension on it using the Dr. Diff 1/2" Offset bracket, and have the axle cut down by 1/2" on each side to bring the wheel just a bit closer to the inboard. That should be a good conservative approach that takes advantage of all the real estate available.

 

[Scramper]

I agree, and I am just not quite ready to do a mini tub on this car, though if budget were not an issue I might just go that way. I am thinking I will put a Caltrac suspension on it using the Dr. Diff 1/2" Offset bracket, and have the axle cut down by 1/2" on each side to bring the wheel just a bit closer to the inboard. That should be a good conservative approach that takes advantage of all the real estate available.

And, of course, moving the perches!

 

[Bodyperson]

I agree, and I am just not quite ready to do a mini tub on this car, though if budget were not an issue I might just go that way. I am thinking I will put a Caltrac suspension on it using the Dr. Diff 1/2" Offset bracket, and have the axle cut down by 1/2" on each side to bring the wheel just a bit closer to the inboard. That should be a good conservative approach that takes advantage of all the real estate available.

That seems like a lot of effort for 1/2 inch. It would be hardly noticeable in the wheel offset.

 

[33IMP]

Buying the correct backspace wheels, or even customs if you have to, is a LOT easier than narrowing a rear. And probably cheaper. (IMO, a hint. Buy wheels with as much backspace as you can get. If its too much, spacers can get the tire Exactly where you want it, and can account for differences side to side.)

 

[72bluNblu]

Yeah I really don’t think I’d have an A-body 8 3/4 narrowed to run a 1/2” spring offset in stock tubs.

On a stock Dart with an 8 3/4 and BBP axles the stock spring location is about 6” from the wheel mounting surface back to the spring. So figure with a 1/2” offset it will be about 6.5” with a stock width rear.

With a 275/60/15 you’re gonna want close to a half inch of spring clearance, and you’ll have a bit more than 1” of tire overhanging the lip of the rim. So you’re gonna want a 15x8 with a backspace of like 4.75” to 5”. That’s totally a backspace number you can get even with off the shelf 15x8’s.

Obviously you should measure your own car, since it’s gonna be tight and the body tolerances were pretty loose. But I really don’t see a need to narrow the rear axle. If you were cutting down a wider rear axle it would make more sense, or doing a mini-tub and running 15x10’s which come in a fairly limited range of backspace etc. In your case though a 15x8” with a 5” backspace should be pretty darn close, and it’s not like shortening the axle is gonna give you more real estate, it just changes the backspace needed.

 

[Scramper]

Yeah I really don’t think I’d have an A-body 8 3/4 narrowed to run a 1/2” spring offset in stock tubs.

On a stock Dart with an 8 3/4 and BBP axles the stock spring location is about 6” from the wheel mounting surface back to the spring. So figure with a 1/2” offset it will be about 6.5” with a stock width rear.

With a 275/60/15 you’re gonna want close to a half inch of spring clearance, and you’ll have a bit more than 1” of tire overhanging the lip of the rim. So you’re gonna want a 15x8 with a backspace of like 4.75” to 5”. That’s totally a backspace number you can get even with off the shelf 15x8’s.

Obviously you should measure your own car, since it’s gonna be tight and the body tolerances were pretty loose. But I really don’t see a need to narrow the rear axle. If you were cutting down a wider rear axle it would make more sense, or doing a mini-tub and running 15x10’s which come in a fairly limited range of backspace etc. In your case though a 15x8” with a 5” backspace should be pretty darn close, and it’s not like shortening the axle is gonna give you more real estate, it just changes the backspace needed.

That makes perfect sense, thank you for the detailed thoughts on this! I've never worked through this process before and it takes a bit to understand all of the variables involved!

 

[Scramper]

Buying the correct backspace wheels, or even customs if you have to, is a LOT easier than narrowing a rear. And probably cheaper. (IMO, a hint. Buy wheels with as much backspace as you can get. If its too much, spacers can get the tire Exactly where you want it, and can account for differences side to side.)

Thanks! I am now researching the wheel possibilities to make the fitment happen.