Preferred rim width for a 285?

[MountainBikeRoamer]

CONCLUSION:

Went with 17x8 American Racing AR172's - the "Baja" rim - in matte black.
(paired up with 285/70R17 BFG KO2's.)

(Incidentally - the identical setup to what the white lifted E350 in the photo I posted a couple days ago parked outside Action Van's shop has.)



What decided it:
1) For whatever reason --- Larry at Action Van has been consistently of the opinion that a narrower rim was somehow a preferred choice, in that he felt a narrower (8") rim applied force differently to the suspension than did a 9" rim, and stated his experienced opinion that the Ford van's I-beam suspension was better arranged, geometry-wise, to work with an 8" wide rim. (I honestly don't see how the rim width makes any difference in this equation, all other things being equal (285 width tire and 0 offset), but that was his take.)

2) All that opining on Larry's part aside, he said that 9" was still not a problem....and so I was still ultimately planning to go 9".....but it turned out that the AR172 was in pretty short supply nationally at the moment in that size.

In any event --- Boywonder posted earlier that he is running the same size/offset/width and that it works fine for him.....so game on.

There's nothing left now....but to BRING ON THE LIFT KIT!!!

[Jsweezy]

I think you made the right decision because with the 17s you don't have to worry about brakes in the future and with an 8" rim you can still fit 35s if you wanted to later as well.

I like the wheel choice too!

[Flux]

Let's do this:

take your thumb and your pointer finger and spread them an inch apart. So yeah, there's really not much there.

John at Agile had the same opinion on things, 17 was better for brake clearance. He had been doing a bunch of the 8.5 wide rims, but said 8-9 works fine. He was able to score me a set of Pro-Comp 7069's 17x9 0 offsets at a good price and take care of that for me. So I too am on the 17" kick with classic looking rims.

Cheers!!

[SheepShagger]

Originally Posted by MountainBikeRoamer

1) For whatever reason --- Larry at Action Van has been consistently of the opinion that a narrower rim was somehow a preferred choice, in that he felt a narrower (8") rim applied force differently to the suspension than did a 9" rim, and stated his experienced opinion that the Ford van's I-beam suspension was better arranged, geometry-wise, to work with an 8" wide rim. (I honestly don't see how the rim width makes any difference in this equation, all other things being equal (285 width tire and 0 offset), but that was his take.)

You don't want a 0 offset on a 9" rim, you want a backspacing of 4.5. That's a 0 offset on a 8" rim, but a -12 offset on a 9" rim.
BTW, he is right, 8" with 4.5"BS will put less stress on the axle/hub than 9" with 4.5"BS

[MountainBikeRoamer]

Originally Posted by SheepShagger

You don't want a 0 offset on a 9" rim, you want a backspacing of 4.5. That's a 0 offset on a 8" rim, but a -12 offset on a 9" rim.
BTW, he is right, 8" with 4.5"BS will put less stress on the axle/hub than 9" with 4.5"BS

Ok this description of different suspension loading forces makes sense to me -- but only if (as you're describing) the two rim widths had an identical back spacing of 4.5" (which would result in different offset numbers.)

But both rims I was evaluating had identical offsets of zero, not identical back spacing. So they would load the suspension identically (applying their load perfectly centered at the mounting-face of the wheel against the hub.)

As a totally naive question here -- why would you want a 4.5" back spacing on a 9" rim? That yields a negative offset as you mentioned (not what I was pursuing) and thus the uneven suspension loading that has been mentioned. Is this 4.5" back spacing you indicate as desirable on a 9" rim something that would be required to make sure the inboard edges of the rim clear part of the brake or suspension structure? Regardless of rim width, if a 285 tire is mounted on a rim with zero offset, then tire clearance in/out is always exactly the same -- so tire clearance shouldn't be the reason for chasing a 4.5" back spacing on a 9" rim.

American Racing produces their AR172 rim in both 17x8 and 17x9 sizes with zero offset. (With corresponding 4.5" and 5" back spacing respectively.) EDIT: MY BAD! They don't produce the 17x9 in a zero offset, it is indeed a 4.5" back spacing on this model as well (-12 offset.) I think the Cragar Soft 8 steel wheels I was looking at came in this spec however.) My main question remains, however:

**** STILL trying to understand why a 17x9 with zero offset (5" back spacing) would be an issue. Again, it is a true zero-offset (tire perfectly centered in/out relative to mounting face).

It seems (with what information I am aware of) that a zero offset would be ideal on a 17x9 for many reasons (preserving suspension-load geometry and steering characteristics --- and also perhaps avoiding any additional tire scrub on fenders/bumper that a deeper-dish (negative offset) rim might induce.)

Thanks!!!

[JoeH]

Good questions. I find backspacing and offsets confusing. My understanding is that the main issue is how far the wheel sticks out and potential rub issues.

Most of us are running 2" spacers on each side in order to match the WMS-WMS front and rear anyway. Unless you have a D70 rear axle. Hence all the issues with semi-float axles breaking.

[SheepShagger]

Originally Posted by MountainBikeRoamer

Ok this description of different suspension loading forces makes sense to me -- but only if (as you're describing) the two rim widths had an identical back spacing of 4.5" (which would result in different offset numbers.)

But both rims I was evaluating had identical offsets of zero, not identical back spacing. So they would load the suspension identically (applying their load perfectly centered at the mounting-face of the wheel against the hub.)

The "problem" load is the load furthest away from the unsupported hub or mounting surface. The further that is the more load it creates on the hub & axle. So by maths only, 9" on 0 offset is 1/2 further out than 8" on 0 offset, so that's 1/2" creating more leverage on the load. In reality once the same size tire is mounted that will probably be reduced to 1/4" and make absolutely no difference. That's why I said by math only, this is all theoretical and will probably make no difference to the life of the hub. BUT, that wasn't the question, I was simply answering / confirming what someone had said to you. A 9" rim will put more load on the hub that an 8" rim both with 0 bs.

Originally Posted by MountainBikeRoamer

As a totally naive question here -- why would you want a 4.5" back spacing on a 9" rim? That yields a negative offset as you mentioned (not what I was pursuing) and thus the uneven suspension loading that has been mentioned.

Even back spacing or an offset of 0 is not optimal for load, BUT ignoring that. You want 4.5 on a van because back spacing is governed by what suspension components the wheel will hit as you turn the steering. 4.5" is as close as you can get on most 4x4 and 2wd without hitting some part of the suspension on full lock. On the van you have the added problem, that if the wheels sticks out much beyond 3.5 from the hub you run the risk of hitting the back of the fender on full lock. (Unless you lift or move the axle forward). So 8" with 4.5bs or 0 offset is optimal on the Van. Not for loading purposes but for fitting and not rubbing purposes.

Originally Posted by MountainBikeRoamer

**** STILL trying to understand why a 17x9 with zero offset (5" back spacing) would be an issue. Again, it is a true zero-offset (tire perfectly centered in/out relative to mounting face).

That wheel would be an issue on my van it would absolutely hit the control arm in the rear and swar bar in the front on full lock. But mine is a 4x4 Quigly, so things will be different to you.

This is a good visual, plug in the numbers and see the wheel & tire move.
Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

[MountainBikeRoamer]

Hey, first off SheepShagger --- thanks for taking the time to go through this and clarify a bunch of stuff!!!
Very helpful and enlightening.

But I'm gonna still keep questioning some of this

Originally Posted by SheepShagger

The "problem" load is the load furthest away from the unsupported hub or mounting surface. The further that is the more load it creates on the hub & axle. So by maths only, 9" on 0 offset is 1/2 further out than 8" on 0 offset, so that's 1/2" creating more leverage on the load. In reality once the same size tire is mounted that will probably be reduced to 1/4" and make absolutely no difference. That's why I said by math only, this is all theoretical and will probably make no difference to the life of the hub.

Okay, we might be splitting hairs on this detail.

You've stated that with the same tire width mounted on two rims of the same offset (zero) but of two different widths (8" or 9"), the suspension-loading results are near-negligible....and I think I have concluded it to be completely negligible (as in, zero difference....as it's the *tire width* (and sidewall height, triangulated) which truly determines how much leverage is imparted to the suspension, not the rim width (if we are talking zero offset for both cases.)

In short, the outboard-most point of the tire tread, where it touches the ground, is the outermost point of the "imaginary lever arm" acting on the suspenson (and bearings, for that matter). And that defines the maximum leverage imparted to the suspension.

And two rims of zero offset (tire perfectly centered over mounting face), with the same tread width, will set that outermost tread surface at the same outboard dimension. (One half of 285mm = 142.5mm outboard of the wheel mounting plane.) Irrespective of rim width.

No biggie though, all good.

Originally Posted by SheepShagger

BUT, that wasn't the question, I was simply answering / confirming what someone had said to you. A 9" rim will put more load on the hub that an 8" rim both with 0 bs.

I think you meant to say 0 offset here, but I get ya. Despite that -- I've always been talking about chasing a zero offset setup for all rim examples, 17x8 or 17x9. (Actually *locating* a 17x9 with zero offset is pretty difficult however. I think the only one I've found is the Cragar "Soft 8" steel wheel in 17x9.)

Originally Posted by SheepShagger

Even back spacing or an offset of 0 is not optimal for load,

Ok, again curious --- what offset would be ideal for load then? A zero offset perfectly centers the rim over its mounting face. Admittedly the bearings are set farther inboard than that, however (at least for the front hubs.) It seems that "ideal loading" would be based on an engineering-driven offset that would position the rim perfectly over the bearings, so they aren't side-loaded or torqued whatsoever.

Again, here, I'm just seriously wondering.
What is the "ideal for load" offset for a wheel on an Econoline?

It seems like it would vary quite a bit based on axle configuration, as the location of the bearings (in/out) is different for each different configuration. As such, I'm starting to think there's no such thing as an "ideal load offset" that truly applies as a "one size fits all" to every configuration of E-series.

Originally Posted by SheepShagger

BUT ignoring that. You want 4.5 on a van because back spacing is governed by what suspension components the wheel will hit as you turn the steering. 4.5" is as close as you can get on most 4x4 and 2wd without hitting some part of the suspension on full lock. On the van you have the added problem, that if the wheels sticks out much beyond 3.5 from the hub you run the risk of hitting the back of the fender on full lock. (Unless you lift or move the axle forward). So 8" with 4.5bs or 0 offset is optimal on the Van. Not for loading purposes but for fitting and not rubbing purposes.

Okay cool, that's what I was looking to understand.

(And what I was finally guessing --- that a 9" rim with 0 offset would crash into some inboard suspension or steering components.

Again man, thanks!!! This has been great to get conversation around. I think I'm ultimately pretty happy that I ended up with an 8" rim width, based upon a lot of the possible issues it sounds like the 9" rim can open up, relative to contacting suspension/steering components on the inside edges. (With a zero offset, anyway.)

[Flux]

So here's a question that kind of falls in here:

Tire I am looking at for a 17x9 -6 offset, 4.75 backspace rim is

LT285/70/R17 ~3200@80psi

Next tire up from that is

LT305/60/R17 ~3200@65psi

The 305 is about an inch wider at the tread and measured on a 9" wheel and having a 0.7" wider section width. Both are right around 32.7 dia

Is there an advantage to moving up to a slightly wider tread and 65psi tire that handles the same load over the 80psi tire?? Better yet, what would be the differences there outside of the extra 60 bucks a tire?

[Jsweezy]

Flux - my first thought was gas mileage will drop with that extra inch but when your already under 15mpg anyway who really cares ha ha.

Other than that I'll leave it to the pros on here.