Backspacing Deep Thoughts

[MIDEVIL214]

Current wheels are 17x9.5 with 3.50” backspace (aprox. -44 offset). Will a 9” wide wheel with 4.5” backspace (-12 mm offset) be inset .75” further? I’m removing a ¼” since the new wheel is .5” narrower overall.

I have duff disk knuckles which don’t flare out like 76-77 broncos and f150. The WH Clydesdale tire rod is where I may have some interference. I’m at work at the moment but seemed to recall having about 1” between the current 9.5” wheels and the rod end. Only losing .75" would technically still clear but be tight.

 

[DirtDonk]

Backspacing is a hard number, so whether a wheel is 9" or 9.5" wide won't change the relationship of the inner bead to the rod end. But the backspace does.
Now, offset is a whole different story! So for me, I like to stick with using backspacing for clarity and consistency.
Meaning that to my mind at least, going from 3.5" backspace to 4.5" backspace gets you a full inch further toward the rod ends with the new wheels.

The narrower wheel width can also effect tire sidewall location, but it's effect is extremely minimal, so that half inch change in width will probably not skew the tire clearance calculations if you need to do any.
But inner wheel bead location should be pretty constant depending on casting/stamping/forging profile differences.

I think...

Paul

 

[DirtDonk]

Oh, but being 17" wheels should minimize some of that effect for being further outward away from things too. Seems to me you should be good even with the Clydesdale.
Thanks for using our stuff too! It's a cool product who's size luckily does not always get in the way.

Your Duff knuckles supposedly mimic, or are at least similar to, the F150 SuperCab knuckles. Higher arm location, but without the outward curve of the Bronco disc knuckles.
The standard F150 knuckles are not a problem for most due to the arm location being lower and straighter than the '76/'77 Bronco knuckles.
It's the Bronco stuff that always caused the headaches.

Paul

 

[MIDEVIL214]

Makes sense to me. I was definitely over thinking the width vs backspace element. Look at me over here trying to sneak in an extra 1/4".

 

[DirtDonk]

Well, you can still dream. Right?

 

[DirtDonk]

It might be tight. Hopefully the 17 inch factor will come to your rescue.
Are you gonna mount the tire rod over or under?

 

[rjrobin2002]

I ran 4.5" back spacing with 17" wheels no problem.

 

[MIDEVIL214]

I have the tierod mounted over. Just measured. I’ve only got about .60” between the Clydesdale tie rod edge and the 17” wheel. 4.5” won’t work for me unfortunately. 3.5” backspace in the Bronco bolt pattern can be elusive. My current wheels are atx slab beadlocks . Looking for a lighter more street friendly setup.

 

[sprdv1]

Backspacing is a hard number, so whether a wheel is 9" or 9.5" wide won't change the relationship of the inner bead to the rod end. But the backspace does.
Now, offset is a whole different story! So for me, I like to stick with using backspacing for clarity and consistency.
Meaning that to my mind at least, going from 3.5" backspace to 4.5" backspace gets you a full inch further toward the rod ends with the new wheels.

The narrower wheel width can also effect tire sidewall location, but it's effect is extremely minimal, so that half inch change in width will probably not skew the tire clearance calculations if you need to do any.
But inner wheel bead location should be pretty constant depending on casting/stamping/forging profile differences.

I think...

good points

 

[sprdv1]

I ran 4.5" back spacing with 17" wheels no problem.

I've had that same experience too

 

[sprdv1]

Well, you can still dream. Right?

We call can LOL

 

[sprdv1]

It might be tight. Hopefully the 17 inch factor will come to your rescue.
Are you gonna mount the tire rod over or under?

I bet so

 

[ngsd]

You are not alone. That is a tough one that few can answer. I have a 68 with 77 front axle so stock disc. But it has the Duff steering (under) and t rex arms with Hellwig sway bar. So much going on I may just need to mount a tire to see but buying the wheels leaves you with having to return them if not.

 

[Yeller]

Due to the fitment issues and limited selection I’m on my last 5x5.5 truck. If I hadn’t just built the rear axle I’d swap it it 6x5.5 which has much better support