What Back Space?

[elwaupo]

Ok, I have a question that I’ve been meaning to ask. I have a 69 Camaro with a 10 bolt rear end which measures 60” width. I also have a 12 bolt rear end out of an earlier Nova that measures 57.57 width that I was planning on using. My question is: what back space would be appropriate for the widest wheel for the rear?

[JayBird]

Decide on what size tire you want to run, buy the tires and mock them with rear diff in car. Measure with a tool like wheelrite, etc. This is the only proper way to get exact fit as all these cars can be off 1/4 to 1/2" which can make the difference between clearing and rubbing.

[dhutton]

Stock Camaro would be 9.5” with a 5.5” backspacing.

Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

60-57.75=2.25
2.25/2=1.125
5.5-1.125=4.375 backspacing

Don’t forget to adjust for any offset introduced by non stock brakes.

If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

Don

[Rod]

Stock Camaro would be 9.5” with a 5.5” backspacing.

Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

60-57.75=2.25
2.25/2=1.125
5.5-1.125=4.375 backspacing

Don’t forget to adjust for any offset introduced by non stock brakes.

If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

Don

^^^^ yep

[elwaupo]

Stock Camaro would be 9.5” with a 5.5” backspacing.

Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

60-57.75=2.25
2.25/2=1.125
5.5-1.125=4.375 backspacing

Don’t forget to adjust for any offset introduced by non stock brakes.

If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

Don

I agree, that is great information! Thank you

[elwaupo]

I think they would have to be special ordered, most wheels are either 4” or 4.5” backspace

[joeko23]

Try searching for a euro bolt pattern like 5x120. That’s same as 5x4.5” bolt pattern. Much more options out there. You can use an offset calculator to see what the conversion is from mm to inches. For example if you plug in 12” width rim and want to have 5.5” offset that equals 25mm on the calculator. Plenty of 5x120 wheels that are 12” wide with 25mm offset.

https://tiresize.com/wheel-offset-calculator/

[68Formula]

Try searching for a euro bolt pattern like 5x120. That’s same as 5x4.5” bolt pattern.

You meant 4.75" bolt spacing, not 4.5" which is the Camaro pattern.

[joeko23]

You meant 4.75" bolt spacing, not 4.5" which is the Camaro pattern.

Yup! Sorry

[dhutton]

I think they would have to be special ordered, most wheels are either 4” or 4.5” backspace

Go with 4.5” backspacing and add a small 1/8” or so spacer if needed.

Don

[badbu68]

Since nobody else mentioned it, if you're planning on putting disc brakes you need to factor in rotor thickness and wheel spoke to caliper clearance.

[dhutton]

Since nobody else mentioned it, if you're planning on putting disc brakes you need to factor in rotor thickness and wheel spoke to caliper clearance.
Post #3:

Don’t forget to adjust for any offset introduced by non stock brakes.

Don

[Alwhite00]

4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.

[BonzoHansen]

+1 they are not the same
4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.

[68Formula]

4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.

To add, it creates a lot of stress on the studs which could result in failure.

OP,

The wheels would need to fit hub centric to the car they are going, and then PCD variation bolts (aka wobble nuts) could be used to properly mate the lugs to the wheels. Here's a good explanation: https://www.team-bhp.com/forum/tyre-alloy-wheel-section/168043-pcd-variation-bolts-aka-wobble-bolts-myth-versus-reality.html

I'm sure there are people that have gotten away with bolting them straight on (after all, there is some tolerance variation to everything), but that doesn't make it a good idea.

[joeko23]

Check out this thread. I personally put 5x120 on my Camaro. The wheels I purchased come setup for conical lug nuts. I also bought a hubcentric adapter and everything bolts up and is free of vibrations. People have done this and are currently doing it. Maybe I’m just making myself feel better about the situation. Time will tell.

https://www.thirdgen.org/forums/wheels-tires/738077-5x4-75-vs-5x120.html

[BonzoHansen]

A while back one of the engineers from AME put up some diagrams showing the stress on studs for both proper 120.65 fitment and 120. The 120s had so much more stress on the studs. Iirc his comments were along the lines of lots of folks do it, but I wouldn't. I decided he's smarter than I am, I'll listen to him. To each their own. I like headrests, 3 points, US made suspension parts and no one in the back seat with rollbars too lol.

[dhutton]

I remember that thread with the FEA analysis. The trouble was that he did not post a scale with his simulation results which made it pretty much impossible to draw any real conclusions from. He subsequently deleted it.

Don

[elwaupo]

�� That’s a lot of information

- - - Updated - - -


Go with 4.5” backspacing and add a small 1/8” or so spacer if needed.

Don

Thats looking like the best bet, keep it simple

[elwaupo]

Post #3:

Don’t forget to adjust for any offset introduced by non stock brakes.

Don

I’m running the stock disc brakes at least for now. Hopefully that won’t be a problem.

[elwaupo]

I’m looking at an 18”X9.5”, 5X4.75, wheel bolt pattern 5x 120.65, backspace 5.49” and +6mm, would that wheel size work with my set up, would I need a spacer?

[dhutton]

I’m looking at an 18”X9.5”, 5X4.75, wheel bolt pattern 5x 120.65, backspace 5.49” and +6mm, would that wheel size work with my set up, would I need a spacer?
Is this for the rear? It should work with a stock width rear end but it’s tight.

If it’s for the front I think that’s too wide….

Don

[elwaupo]

My current 12 bolt measures 57.75” wide

[dhutton]

My current 12 bolt measures 57.75” wide
So you would need a spacer roughly 1” thick if I did the math right.

Don

[elwaupo]

And I just happen to have one 😁

[elwaupo]

Ok, final question on this fitment, daughter wants to stay with the stock Rally look, will a 15”x10”, 4.5” or 5.5” back space fit?
Remember my rear end width is 57.75 wide