Illegal to run singles on dually?

[OnlyCummins]

I may buy a '92-'93 W250 or W350 CC (Club Cab AKA Extra Cab) with manual & was wondering if I could get away with running singles on the outside if I bought the W350? Really have no need for a dually but '92-'93 W250's CC with manuals are rare so adding the W350 to my search will improve my chances of finding what I want.



I've seen trucks in my area running with less than 4 tires in the rear. Examples include a '90ish Ford truck running singles on the inside but that didn't look 'right' & a pre-'88 GM with service body with only 3 tires which really looked ugly! I know both trucks have been running like that for some time so I thought perhaps there's no law against it.

 

[TowPro]

Maybe you can find the right rims, and run 1 tire as wide as the 2 that came off? Then do some Bombing so you still can get smoke out of them I bet you could find this setup in Texas. I never seen tires on pickup trucks as wide as they run in Texas.

 

[OnlyCummins]

I wouldn't run tires any wider than the front bc I'm too cheap & don't want reduce fuel mileage in any way (part of being too cheap). My idea is to run singles on the outside for the added stability & only run duals when I truly need the extra capacity.

 

[klenger]

I wonder if running only the outside tires would put excessive loads on the wheel bearings. I assume that with dullies, the tires are centered around the bearings, and if you only had one set on, it would put a lot of leverage on them.

 

[fkovalski]

klenger- Interesting question, but I do not believe that a single tire would cause extra stess as you hypothisize because the upward force of one tire (either location) or two is transmitted via the mounting flange located between the (two) wheels then laterally along the axle shaft. A force diagram should compute (ideally) same stesses regardless of tire configuration. Simply put- the dual wheel offset puts the load at the same location.

 

[RustyJC]

The two dually tires in combination act like a wide single wheel and tire with it's centerline at the mating surface of the two dually wheel flanges - IOW, halfway between the two tires.



On the other hand, a single dually wheel (the outer, let's say) would create a moment at the wheel-to-hub flange due to the lever arm (offset) between the mounting flange and single tire centerline. When both dually wheels are mounted, the moments cancel each other.



On the front wheel, this is compensated for with the offset spacer bolted to the front hub which the dually wheel bolts to. This spacer places the centerline of the single tire directly under the hub mounting flange - it counteracts the offset of the dually wheel used in the front.



Rusty

 

[OnlyCummins]

I don't know how dually rims are mounted to the 'flange' (if one even exists) but the moment arms would only cancel if both rims are EXACTLY the same in offset/backspacing AND were mounted in EXACTLY the same way on either side of the 'flange'. Don't know if that's the case but accepting it is, I feel that whatever moment arm would exist with just the singles would be negligible & could safely be ignored (fingers crossed).

 

[Philip]

offset spacer bolted to the front hub which the dually wheel bolts to

First gen trucks do not use this item.



You can run it on a single dually rim. It would look like @#$%$ unless you hang a flat bed on it.

 

[RustyJC]

Originally posted by OnlyCummins

I don't know how dually rims are mounted to the 'flange' (if one even exists)... ...

The dually wheels are mounted to the hub flange with lug nuts.

... ... but the moment arms would only cancel if both rims are EXACTLY the same in offset/backspacing AND were mounted in EXACTLY the same way on either side of the 'flange'.

The inner and outer dually wheels are identical and interchangeable; thus, they have the same backspacing. The centerline of the pair of wheels is effectively offset from the hub flange by the thickness of the inner dually's mounting face.

I feel that whatever moment arm would exist with just the singles would be negligible & could safely be ignored (fingers crossed).

If the wheels had a 6" backspace and the truck were loaded such that each rear wheel carried 2000 lbs, the moment would be 1000 ft-lb (2000 lbs x 0. 5 ft) of loading at each rear axle hub - a load the rear axle hub bearings were not designed to take since the engineers assumed that both wheels would be used.



Rusty

 

[OnlyCummins]

RustyJC,



Darn, darn & triple-darn!



I've never really paid much attention to how dually rims were mounted but now that I've dug up a line drawing I see what you're saying. I admit tho, at 1st I was in denial , staring at the drawing hoping for a flash of insight or a "eureka" moment showing it ain't so but, of course, neither materialized.



Ok ... I'll try a different tack.



How critical, really, is that additional loading? Because I'm wondering how is it that folks are able to run 10 or 12 inch wide rims on 1/2 ton drivetrains, never mind 3/4 or 1 ton drivetrains?



Here's an example: Suppose backspacing on a OEM rim 6. 5" wide is ~3. 25" & the rim is replaced with one that's 10" wide with ~4" of backspacing (to somewhat compensate for the added width). If I'm figuring this right, wouldn't the 10" wide rim also yield an ~6 moment arm & the resultant equivalent loading assuming an equivalent load? If that's the case, how are they able to get away with it? If they can't, do you have any idea how much bearing life has been reduced, worst case, in terms of mileage. 30K miles vs 10K miles or ... ?



I'm just trying to get a handle on whether it'd be worth toasting the bearings in order to run singles. 10K-15K mile bearing change intervals might be ok for me so long as the time period was a year or better. If I was really racking up the miles quickly tho then doing a bearing changeout every 3 months or so would get old pretty quickly.



It looks like my original question should have been "Whether it was safe ... ".



Thnx for edumacating me on the subject. I really appreciate the time you've taken to reduce my ignorance. Now if I could just get my brain cells to cooperate ...

 

[TPCDrafting]

There is a Veterinarian running around here that has an early second gen. that has always run a single wheel on his 3500. He ran the inner tire for the longest time and now recently I've seen him running the outer. I'm not sure if he's experienced any problems with this but I do know it looks pretty bad. (not a good bad either. )



I've never had a dually and maybe someone could answer this, but wouldn't running 4 tires on the rear extend the life of the tire? The rears on my 2500 wear quicker than the fronts mostly due to heavy trailers and my right foot, but I would think if doubling the tire surface area in the back would create better tire wear, thus making it more economical to run 4 tires rather than 2. Personally if I were looking for a truck and didn't need a dually, I would keep looking for the right truck. Have you checked our classifieds?

 

[B.G. Smith]

3/4

From th e Dexter axle website.



http://www.dexteraxle.com/



"Axles fitted with Dual wheels should never be operated with only one wheel in place or with one of the two tires flat. Doing so can seriously overstress the wheel bearings and result in bearing failure. " Why wouldn't it be possible to run 3/4 ton wheels? bg















Copyright © 2001 Dexter Axle Company. All Rights Reserved.

 

[Snow man]

Locally there is a white 3500 2wd quad cab,probably an 01 or 02,running around withthe outside wheels only. The thing that gets me is he has a huge Lance camper,looks to be an 11ft+,on it full time. I cannot see why he would do this with all the weight on it. He must have air bags becasue the truck sits level,and he is running the stock hub caps/wheels. The stress on that axle must be incredible. It looks real dumb from behind,like its going to bend in the middle.

 

[paccool]

A lot of the big rigs in this area are running a single wide tire rather than the duals so it must not be a problem. I see a lot of the gravel and rock haulers doing this and they are loaded heavy. The wheels are backspaced to put the tire about in the middle of where the duals were located. The single is not as wide as the duals.



Other than this, I don't know much more about the setups.



Stan

 

[RustyJC]

Originally posted by paccool

A lot of the big rigs in this area are running a single wide tire rather than the duals so it must not be a problem.

If the single wide tire is mounted on a wheel that is backspaced such that its centerline is on the same plane as the centerline of the pair of dually wheels (i. e. , the face where the two dually wheels contact each other), then there's no geometric problem. I believe I said this in the first paragraph of my first post.



However, that's not what's being discussed here. The question at hand posits removing one wheel from each pair of dually wheels and running on only the other remaining dually wheel. That's a completely different scenario than the replacement larger single wheel/tire situation you describe.



Rusty

 

[paccool]

OK

 

[Extreme1]

Originally posted by OnlyCummins

Here's an example: Suppose backspacing on a OEM rim 6. 5" wide is ~3. 25" & the rim is replaced with one that's 10" wide with ~4" of backspacing (to somewhat compensate for the added width). If I'm figuring this right, wouldn't the 10" wide rim also yield an ~6 moment arm & the resultant equivalent loading assuming an equivalent load?

Nope, it would be 1" from the flange surface (plane) to the centerline of the rim. So you would have the load (lbs) multiplied by the 1" then divided by 12 to get foot pounds. That would probably be tolerable.



I recommend running the dual tires. As stated above, duals wear about half as much as non-duals. I run about 40 psi (as recommended by Dodge) to have some ride quality out back.



The object is to have the axle/hub flange centered on the tires surface so that the load applied to the axle is verticle, not a bending moment.

 

[Paul Herioux]

"How critical, really, is that additional loading? Because I'm wondering how is it that folks are able to run 10 or 12 inch wide rims on 1/2 ton drivetrains, never mind 3/4 or 1 ton drivetrains? "





I have a couple of young customers that followed the recommendations put out in most of the 4x4 rags of adding all extra tire width to the outside of the wheel. All but one of these customers are running Chebbies with IFS. They average about one wheel bearing every 10 month for each truck. Excessive side load will kill any bearing. It kills the unitized bearings faster because they are spaced closer together increasing the side load effect. I would suggest running all 4 in the rear.

JMHO,

Paul

 

[OnlyCummins]

Well ... it looks like I won't be buying a dually.



Thnx everyone for your replies.

 

[Extreme1]

Don't bail out to soon! I wasn't looking for one when I bought mine but it was "high milage" and the only second generation cummins/auto truck I could find. I had to drive to the far side of Iowa to get it.



The dually is much more stabile when towing a large (5th wheel) trailer. It is also much more stabile when towing any trailer in snow. I really didn't want a dually when I bought it and I almost traded parts (boxes, rear dif, wheels, etc. ) with a friend that had a 2500 but now I'm really glad I didn't.