This seemed a little weird when I first read it in another forum, I'd like the benefit of your opinions/experiences.
Supposedly someone is running around with smaller tires on the inner rims, not just narrower but obviously shorter. I don't have the details, but the belief is that when the truck is not loaded he has most of the ride of a 3/4 ton, but when it IS loaded the inner tires get to meet the pavement and share the load. He also believes that the inners get little/no wear during the 90% or so of his driving when unloaded.
I suppose I believe that this COULD be done properly if you know enough about the ...errr, well "everything" about the tires, loads, any axle flex, etc. Part of me says it is totally NUTS, part of me says "why not ?"

So, is this something any of you have come across or done ?

Yeah, opinions welcome :)

This is when I'm glad I have SRW.

That would be an unwise thing to do in most circumstances as different height tires would have different load capabilities - you would be de rating the axle that you were using. Also logic suggests that partial loads would cause problems with the inner tires coming in contact with the road irregularly - thus causing stresses to the system.. I have never seen this done, and it certainly is not commercially available, so caution suggests that it should not be done.

If it was done, strong mud flaps, covering the entire rear should be fitted, to stop the large stones such a set up could fling at anything behind - somewhat like a tennis ball launcher.

Mylash

As long as we're talking opinions..... ):h

There are multiple concerns I would have with this setup. :o: First/foremost, when placing a load on the rear axles all the weight is going to be on the outer tires, the inner tires will only start bearing load when the outside tires squat down far enough for them to start supporting the load. For this to happen the outer tire will likely contact the inner and you will generate excessive heat, big time, possibly resulting in failure of the sidewall of the tires. Someone with more techie knowledge of tire stuff can jump in on this stuff. :confused:

This setup begs the question "Why have a dually if you are not going to use all 4 wheels?" I'm guessing the logic is sort of like the "tag axle" approach in that you only use the extra tires when needed. There likely is a reason tag axles are separate from the drive axles, maybe consistent rolling ratio? Won't a smaller diameter tire turn at different revolutions than a larger tire on the same rim and same axle? Wouldn't this cause stress on the axle? He likely won't notice this until he puts a significant load on the axle. ;)

Food for thought. I'm anxious to see what the heavy haulers think of this setup. Fingers, RF3, ...? Later. JJ :)

I'm with JJ. Different size tires side by side on dual wheels would have to be a bad thing. When the load was heavy enough for all the tires to be touching the different size tires would be trying to travel a different distance on each revolution. One tire or the other would have to be sliding all the time. My bet is the smaller tire would slide and chew the tread off in very short order.

I just cant think how the guy thought that would work! :eek:

My weigh in is: As a commercial hauler, falling under DOT, its against the law. On a DOT inspection, you are required to have "tires of same make, size and rating" across each axle (single) or both axles (tandem). This does not mean that you have to have the same tire size and rating on front and rear, just across or left to right (49 CFR). The reason why? MJB described it perfectly. It has to do with revolutions per mile. Larger tires have fewer Rev/Mi. than smaller ones. In wet or icy conditions, the forced slipping of all tires would cause lack of control (since the tires are in a constant skid), and be extremely UNSAFE.

The "tag axle" explanation also does not apply. Heavy trucks that are so equiped have air bags that lift and lower the "tag(s)" manually as required to spread the load in accordance with "bridge laws" (see a trucker's road atlas for specifics on BL).

The required sidewall flex necessary to get the inner duals to be effective (begin to bear weight) would require severe under-inflation of the outer duals in such a sittuation, which would cause eventual damage to the radial plies, and premature failure of the tires. Second, no manufacturer will honor warranties on tires that are used in this fashion, for all of the reasons given here and above by others.

We must be reading from the same sources, because I've answered this question elsewhere. This guy (doing this) is also using "dry air" (Nitrogen) to inflate his tires, claiming that he is gettin up to 2 MPG better mileage. But, at $20.00 to get all his tires filled with Nite, even if his MPG improvement claims are true, there is no way he is recouping his cost. The military does use Nite in aircraft tire, but only because of its non-freezing properties (you don't want any icing in your tires when landing), and non-flamability (when your a-- hole is sucking flames in a crash, tires don't need to provide more O2 to feed the fire).

That fella is an amateur engineer with tooooooooo much time on his hands and no knowledge of natural physics. Leonardo DV he ain't. Some folks suffer from permanent anal insertion of their craniums.

RF

That fella is an amateur engineer with tooooooooo much time on his hands and no knowledge of natural physics. Leonardo DV he ain't. Some folks suffer from permanent anal insertion of their craniums.

Don't sugarcoat your words RF3, tell us how you really feel! :lol: JJ :)

JJ, did that sound combative? Oh my:eek: !

I don't always mind many of the hairbraned ideas that I see out on the road, as long as they do not endanger others. Its a natural state of survival of the fittest. While nature knows how to weed out the heard, mankind assists by placing hard obstacles along the roadways. ):h

However, those that try to promote others to follow their leads, places more of these avoidable safety hazards on the road. This, in turn increases the chances that un-natural culling will take place. NOW THAT does get "up my nose" :mad:. So I do my best to warn others, and keep an eye out for mother nature's wrath, no matter what form it takes.:rant:

That's why I don't believe in having too much truck. Its not the trailer that worries me, it is what the trailer will do when one of these half-baked concoctions decides to tangle with our rig :( . I want to ALWAYS come out on top, which is not possible with a SRW-LT/heavy trailer combination (sorry ROCKIN, but I've been there, done that, and framed my soiled jockey's to show to the unbelievers -:t ;) ).

RF

Whoever is doing that is an idiot.. bearing wear and overheating of a tire that is too big and holding most of the load when it is loaded is the first things that come to mind.. If I thought any harder, I would prob be calling the guy more names instead.

Maybe it would be better to buy an extra set of (single) tires and wheels for the rear and bolt them on when he is not running a loaded truck?

VR :muahaha:

vetterdstr, you may be onto something? Isn't it possible to put a wide set of tires on the rear of a dually, sort of like they use on dragsters but with tread? I thought I had seen something like that on a truck, really looked cool!:cool:

Arrbee, kind of getting the impression that this isn't such a good idea? ):h Insanity rules baby! :ro) JJ :)

I've requested DETAILS !
As I said, the info is secondhand. Supposedly "his father before him" did it with some success.
I'm a sceptic, usually in both the 'for' and 'against' directions at the same time (-:

For each cm of width you get 8.5mm of axle height (17 on the diameter, but we're interested in radius here). I havn't done any arithmetic on it and I don't know by how much tires "squat" as a function of size, load and pressure.
I s'pose you could monkey around with say 50 psi to keep the arithmetic simple and say that 1,000 lbs would require 20 sq inches of surface to support it - the tire will squat until it's contact patch reaches 20 sq ins (neglecting wall stiffness for the first approximation). You could add the next 100 lbs, 22 sq inches and so on, at some point the inner tire comes into play and you can run the math for both of them. I could believe that there is a size difference and load range that would work. I'm not YET ready to declare the guy an idjit
I take the point of legality seriously, though I doubt that many 1 ton recreational trucks would actually get stopped and inspected to that level of detail. I suppose that if a cop was driving behind you and NOTICED that the inner tires weren't touching the ground you'd get stopped. "Gee Officer, that IS interesting. I'll have to get my mechanic to check that out, thank you VERY MUCH." {act dumb}. OTOH if the inners are clear of the pavement then the outers are probably not overloaded, so THAT shouldn't get you a ticket.

Another point could be if you used the stock size for the inners and the next size(or two or three sizes up) up for the outers. You'd need specifics to know if either tire actually gets overloaded, given that the bigger tire can carry more load than the stock tire.

Don't worry, I'm NOT planning to do this. Just chasing it through to see if there's anything to it.

Yep, its possible to put a large single tire on.. :exactly:

Some people just dont want to do things the right way like putting 2 different size dual tires on... ):h

VR :)

Don't worry, I'm NOT planning to do this. Just chasing it through to see if there's anything to it.
I didnt think you were going to do it... :Nonono:

I own and operate a business which uses a couple of large trucks and trailers from 10 wheelers up to 22 wheelers and 63'.5" long. something like this would not fly with anyone of my setups.. so when I hear of someone doing it on a pickup truck.. (not you of course) I am VERY quick to call him an idiot! ):h

VR :)

Just my 2 cents... I just put 235's on my Dually all the way around. ended up having to use a 1/8th spacer between the duals. I have the same seperation no as when the 215's were on her. looks good too.

03 radio flyer. the tires do not have to be of same make,but all else applies

??? Make? Thought I had taken that out..I meant the same tread type, range and size, which often can mean make in some sizes (i.e. 19.5) RF

Just my 2 cents... I just put 235's on my Dually all the way around. ended up having to use a 1/8th spacer between the duals. I have the same seperation no as when the 215's were on her. looks good too. Something odd there... ???
235mm - 215mm = 20mm, which is a little over 3/4 inch (25.4mm /inch)
The way I figger it, them sidewalls should be closer by a little over 3/4 inch, so how do 1/8 inch spacers put them to the same separation as before ?
Methinks they're still 5/8 (or more) closer.

Just keep the old rims and tires in case you have a warranty claim, you might have to put them back on.