[ponjohn]

If you were setting up a rear leaf spring suspension from scratch, mini-tub, buy wheel package then rear end....What is the ideal rim backspace?

Approximately 1/2 the rim width? or?

Thanks.

[BruceWilkie]

Good question... I have always liked the idea of keeping wheel offset within close range of factory offsets for bearing load/life considerations. Flashback to "old days" of highly jacked up cars with tires sticking outside wheelwells just to get that deep dish look...and saw several that lost axle retention or had bearing failures.

[charlie66]

I would think in the middle of the rim..

[johnta1]

You need the rims and tires that you will be using to do it correctly.

The tires usually stick past the rim, some being different distances.

Use the combo you like then set the up and measure the distance between the innermost dimensions.

Measure the outer most dimension to see what the fender lip to tire would be.
Figure what you want for innerbody to tire clearance then use that for rails.

The distance between the rim bolt surface would be the rearend width.
(you could use any backspacing you want that way, like popular sizes)

[ponjohn]

Originally Posted by johnta1

You need the rims and tires that you will be using to do it correctly.

The tires usually stick past the rim, some being different distances.

Use the combo you like then set the up and measure the distance between the innermost dimensions.

Measure the outer most dimension to see what the fender lip to tire would be.
Figure what you want for innerbody to tire clearance then use that for rails.

The distance between the rim bolt surface would be the rearend width.
(you could use any backspacing you want that way, like popular sizes)

Correct.

I noticed some companies offer rims on the inch and some are the 1/2 inch. So it'll be best to determine most popular. However, I don't see me changing rims often.

I just want to get the rim/ tire properly positioned in the wheel well then order the the rear.

[Rob B]

Do you know anyone who is running the same rim/tire combo your thinking about? When I mini tubbed mine, I borrowed rims/tires from a friend and set it up in the wheelhouse then bolted some junk axles to them with a piece of pipe in the middle. Adjusted the placement then tacked the axles to the tube. took it all out from under the car and then measured the width of axle face to axle face to give me an exact measurement. I was having a reared built from Moser so I wanted to have a specific backspacing for my rims which would have required a narrowed width from a stock width dimension. I ended up having the housing built 1" shorter on both sides. If your staying with a stock width housing and just moving the perches, then your going to have to have a backspace that might not be as centered on the rim as you would like depending on how wide and tall you go with your tires. Tons of info out there on this for both X and F bodies. Just depends on how you want the offsets for the front and rear of the rim to look. Personal preference.

[Rob B]

If I'm not mistaken, I believe my rims are 4.5/5.5.

[ponjohn]

Originally Posted by Rob B

Do you know anyone who is running the same rim/tire combo your thinking about? When I mini tubbed mine, I borrowed rims/tires from a friend and set it up in the wheelhouse then bolted some junk axles to them with a piece of pipe in the middle. Adjusted the placement then tacked the axles to the tube. took it all out from under the car and then measured the width of axle face to axle face to give me an exact measurement. I was having a reared built from Moser so I wanted to have a specific backspacing for my rims which would have required a narrowed width from a stock width dimension. I ended up having the housing built 1" shorter on both sides. If your staying with a stock width housing and just moving the perches, then your going to have to have a backspace that might not be as centered on the rim as you would like depending on how wide and tall you go with your tires. Tons of info out there on this for both X and F bodies. Just depends on how you want the offsets for the front and rear of the rim to look. Personal preference.

That was my thought process but never thought of the axle idea.

My old 71 Ventura was narrowed 1.5" each side. I am going to buy the rim / tire package.

15 x10 4.5 BS 295/ 65/15 DR.

Do you remember the BS on your front rims?

[69FIREBIRD76MM]

I was using 15x10's, 5.5" b.s. on my car, I bought a new 9" , 1" shorter, now I am buying 15x 10's with 5" bs. My suspension is all stock, if I decide to relocate the shocks inwards I can go 6"b.s. on the rims with no tubs.

[Rob B]

Originally Posted by ponjohn

Do you remember the BS on your front rims?

They are the normal 15x4's skinny's up front. Think those are just centered.

[alloy indian]

For maximum performance you would get the smallest back space possible. Make the rear as narrow as possible. Five or six inches of axle is a lot of unsprung weight removed for free! Shorter axles equal lighter axles. Lighter equals quicker ET's!