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Educate me on backspacing and offset

NYC Bronco

Full Member
Joined
Feb 21, 2017
Messages
169
School me on this. what happens if you buy the wrong offset and or backspacing? 1) you are stuck with a look you don't like and maybe some rubbing 2) just the headache of doing a product return?

I'm running 31x10.5 tires, 15" wheels, on a '76 with stock suspension. the tires are still very new but I want to get some Indy Mag slots. Is there a "stock" sizing? It seems the bes thing to do is to remove a wheels and look for the stamping/marking? and or measure?
 

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
Ignoring interference with other components, for your tire size, you should choose a wheel with 0.2" offset (basically 0" offset) to achieve similar geometry to stock. I personally think incorrect scrub radius leads to a lot of handling issues with these trucks.

backspace.jpg
 

light.jade

Newbie
Joined
Nov 26, 2020
Messages
5
What if you bump to a 16”. Does it change backspace or off set?


Sent from my iPhone using Tapatalk
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
School me on this. what happens if you buy the wrong offset and or backspacing? 1) you are stuck with a look you don't like and maybe some rubbing 2) just the headache of doing a product return?

I'm running 31x10.5 tires, 15" wheels, on a '76 with stock suspension. the tires are still very new but I want to get some Indy Mag slots. Is there a "stock" sizing? It seems the bes thing to do is to remove a wheels and look for the stamping/marking? and or measure?

Wheel ,manufacturers only offer a limited number of backspace/offset choices. I wanted 15" Indy slotted mags. The tie rods interfered. I put on a set of 1.5" spacers. Spacers are a pain because you have to remove them before removing the drums. But on the positive side, I love the stance now.;)
 

Yooper74

Full Member
Joined
Aug 13, 2020
Messages
322
I'm finding backspacing to be a huge PIA. From what I can gather the early bronco's should be 3.5" or less of BS to not run into issues. Nearly every wheel I have found (that I was interested in) is 4" to 4.5" of BS.

I'm probably going to order a set today that is 4.5". Mount them up and figure out from there how big of a spacer I need.
 
OP
OP
N

NYC Bronco

Full Member
Joined
Feb 21, 2017
Messages
169
So I went with the Indy Mag 15x8 with the backspacers from WH. Wrapped my existing BFG 31x10.5

193563804_10159555124587146_5427723327113091513_n.jpg


189734024_10159555124612146_6607270105878107165_n.jpg


189725041_10159555120122146_1879096122168469236_n.jpg
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
Looks nice and hate to rain on the show, but backspacers add some serious issues if not maintained. Just check them often, which is the pain.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,346
I'm finding backspacing to be a huge PIA. From what I can gather the early bronco's should be 3.5" or less of BS to not run into issues.

I don't think you're reading that here. There are tons of members running quite a bit more backspacing than that and not having any issues. Many with up to 4.75" backspacing. Just not on '76's and '77's with 15 or 16 inch wheels.
Everyone else is not so limited. It's ONLY the '76 and '77 Bronco steering knuckles that cause the trouble with 15" and 16" diameter wheels. At 17" which is becoming a popular size, this wheel interference issue is no longer an issue.

All the rest of the Broncos from '66 to '75, or those with disc brakes from a Ford F150 or full-size Bronco do not have such limitations. For those you simply have to choose your backspace along with your wheel width and tire size in order to clear the body and other items.
Just like you would have to do with literally every other vehicle on the road. You can change the tire and wheel size only just so much before you need to narrow down what and where the tire is going to rub. Because it's going to rub something if you do not choose carefully.

Paul
 

Spaggyroe

Full Member
Joined
Dec 9, 2019
Messages
284
School me on this. what happens if you buy the wrong offset and or backspacing? 1) you are stuck with a look you don't like and maybe some rubbing 2) just the headache of doing a product return?

I'm running 31x10.5 tires, 15" wheels, on a '76 with stock suspension. the tires are still very new but I want to get some Indy Mag slots. Is there a "stock" sizing? It seems the bes thing to do is to remove a wheels and look for the stamping/marking? and or measure?





A - looks certainly are a factor, but there's more to it. Too much positive offset, and you can run into interference problems with steering and suspension parts. Too much negative offset, and as previously mentioned, your scrub radius gets a little out of whack and your rig can have some poor steering / driving characteristics. You might experience more rubbing on the fenders too.

B - Some tire shops may not let you return the wheels after they've been mounted, so be careful there. Ask ahead of time. Some of the Bronco vendors carry the indy mag slots, and would certainly be able to advise you on what works best.

Here's a graphic that I lifted from discount tire's website that might help.
 

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