Cause and effect of backspacing

[Bronco Boomer]

Dear Bronco Yoda(s),

Let me begin by saying I am doing a body off build and it is my first Bronco. There, the stage is set for the appropriate ridicule!

I have been reading lots of threads with regard to wheel offset and backspacing, but would like to revisit the topic to achieve better definition of the cause and effects of adding more backspace.

Scenario: ’75 Bronco with ’76 disc brake setup. 3.5” suspension lift and 2” body lift and a Heim Joint steering setup. This Bronco will be a daily driver with the occasional off-road weekend. There will not be any extreme off-roading or rock climbing.

I have found a few types of rims that I would like to install, but they all come with a 4.5 to 5.5” backspace. They are all 17” rims with either 8 or 9” width. I plan on going with a 33” x 10-10.5” wide tire, but if all fits well I may go with a larger tire later.

If I understand the threads correctly, I will have no issues with the brakes or steering linkages and that the interference issue will be with the radius arm. I also understand that I can adjust the steering to prevent that interference, but will lose some steering.

So Yoda, the questions of the day are: How much adjustment is required for this scenario? AND what will the effects be on the steering?

Thanks in advance for mentoring a green Bronco Jedi!

 

[mortimersnerd]

You shouldn't have too much interference with 33's and a 4.5" backspace. Not a big deal. I'd go with 17x9 wheels if you think you'll go to bigger tires in the future. The extra width can be beneficial when running a 12.5" wide tire. If you're unlikely to go bigger than 35's, consider a 15" wheel. Tires are significantly cheaper and still plentiful at 35x12.5x15".

 

[toddz69]

Dear Bronco Yoda(s),

Let me begin by saying I am doing a body off build and it is my first Bronco. There, the stage is set for the appropriate ridicule!

I have been reading lots of threads with regard to wheel offset and backspacing, but would like to revisit the topic to achieve better definition of the cause and effects of adding more backspace.

Scenario: ’75 Bronco with ’76 disc brake setup. 3.5” suspension lift and 2” body lift and a Heim Joint steering setup. This Bronco will be a daily driver with the occasional off-road weekend. There will not be any extreme off-roading or rock climbing.

I have found a few types of rims that I would like to install, but they all come with a 4.5 to 5.5” backspace. They are all 17” rims with either 8 or 9” width. I plan on going with a 33” x 10-10.5” wide tire, but if all fits well I may go with a larger tire later.

If I understand the threads correctly, I will have no issues with the brakes or steering linkages and that the interference issue will be with the radius arm. I also understand that I can adjust the steering to prevent that interference, but will lose some steering.

So Yoda, the questions of the day are: How much adjustment is required for this scenario? AND what will the effects be on the steering?

Thanks in advance for mentoring a green Bronco Jedi!

To adjust the steering stops, turn your wheels to the point where the tires are close, but not touching, the radius arms, and then adjust the steering stops (bolts) accordingly. If the stops have never been touched on your truck, they may be tack welded to the knuckle and will need to cut loose (grinder, etc.) so they can be adjusted.

I would also double-check the fit of 4.5" rims, even though they're 17s with your '76 knuckles. I imagine there's enough clearance with the extra 1" radius but it doesn't hurt to check (4.5" BS definitely won't fit with 15" wheels).

Todd Z.

 

[Bronco Boomer]

#mortimersnerd and Toddz69,

Thanks for the input. It would be logical that this size tire has been on many a Bronco. I am failry confident that I will have to do exactly what you stated Todd and am not overly concerned about actually adjusting the steering. I just do NOT want to end up with a significant reduction in steering.

 

[welndmn]

Will your rear fenders be cut?

 

[broncnaz]

You really dont have to adjust the steering stops you will feel when the tires hit the radius arms.
Cant really answer for sure if the tire will hit but I ran 33x10.50s with 3 5/8 BS and they didnt rub. Installed 33x12.50 on the same rims and they rub So you may or may not rub with 4.5in BS.
While there are some people running the larger Rim size theres not a lot of people running them yet Mostly due to poor rim selection and BS options and cost of rims and tires. But there are more people running them all the time just have to deal with drawbacks when and if they arise.

 

[Bronco Boomer]

@ welndmn

Yes the fenders have been cut and flared.

@ broncnaz

Based on your input, it sounds as if 4.5" BS with 10-10.5" wide tires MAY rub a little. In your scenario, 7/8" less BS, but 2" wider tire (should result in 1" further towards radius arm).

Thanks for the assist. More info is good.

 

[welndmn]

With a 4.5 BS rim, I'd plan on some 1.5" wheel spacers.
Most people running stock EB axles with a "normal" 3.5 - 3.75 BS wheel run a 1.5" wheel spacer to help with rubbing and give the bronco a wider stance that it needed from the factory.
Search around here for pics with and without wheel spacers so you can see the difference.