Eliminate rear inner wheels ?

[SKP101479]

Thank you!

Keeping the subject close as it pertains to Rving and not commercial activities,most of us particularly with tandem axles will never overload at the rear. As for my setup, many of you have seen it at the National Rally. The reasons for not singling were as follows, 256" WB, a garage with lots of storage (car too). When designing the build, I am great full to Henry Szmyt for his patience in helping me, not just rear axle loads were considered. Front axles on these trucks can be quite close to maximum load rating when loaded with accessory RV items ie drom boxes, Smart Car, motorcycles and such. This with fully loaded fuel and not towing to offload the front axle was a concern.

Those of us who use these trucks are among the safest most contentious RV'ers traveling the roads.

[peety3]

When I was tandem, I removed the inner tires on the center axle. Put the wheels back on with no tires to maintain stud spacing. The ONLY difference I noticed after I put some mileage on the set-up was that I was wearing the tread on the single center axle tires much faster than the dual rears. Hummm........ I found that interesting. I did hope that I might get a little extra on the MPG side, but in the end there was no difference. I also thought losing some un-sprung weight would improve ride - unfortunately I did not find this to be true either. I do understand that you are thinking about removing the inner tire on the rear axle, not the center. Are you planning on leaving the center dual? Or, are you thinking of removing all of the inner tires? An inquiring mind wants to know . BTW - to me the best place to carry a spare tire is on the axle. Those suckers are heavy and beyond my ability to hoist. They also take up a lot of room on the bed or behind the cab. I thought about just a tire with no wheel as a spare - but they fill up with water and host mosquitoes. Not sure how Vern does his spare. I think the is stronger than I am as well...... .

 

Unless you're ready to do a complete, total, unblessed/uncertified/you-take-the liability redesign/rebuild of your rear suspension, taking 2 tires out of an 8-tire tandem rig is NOT going to work. You might as well remove 4 or keep them all. Physics is not your friend here. Assuming you have air ride suspension, you're going to have a leveling valve tied to one axle or the other (doesn't matter which one). If the truck is sitting high, it'll release some air. If it's sitting low, it'll add some air. That air comes/goes from all four (or eight) air bags equally. Because the air bags remain the same size, in particular the same diameter (load-bearing) plate at the bottom, the load transferred to each axle MUST be the same (Newton lives) once the air settles down. As a result, when your tandems get to 17,000 pounds (50% of the typical 34,000 legal load for an 8' or shorter spacing tandem axle set), your 4-tire axle is sitting at 8,500, or 2125 per tire. Your 2-tire axle is sitting at 8,500, or 4250 per tire (aka probably near tire limits unless you've gone to super-singles).

 

The fix would be to swap out the air bags with a set that are about 71% the diameter of your originals (square root of 2, divided by 2). Since area of a circle is pi * r * r, reducing r by 29% results in a 50% decrease in surface area, so the weight distribution becomes 1:2 instead of 1:1.

 

Good luck if you've got a spring suspension. I suspect some black magic is possible with the equalizer bar sitting between the forward driver springs and the rear driver springs, but because those springs are supported at both ends, I'm not going to attempt the physics to see if you can fix it right at the equalizer bar.

[NoDirectionHome]

 

 

most contentious RV'ers traveling

ok, that's pretty funny

[peety3]

The fix would be to swap out the air bags with a set that are about 71% the diameter of your originals (square root of 2, divided by 2). Since area of a circle is pi * r * r, reducing r by 29% results in a 50% decrease in surface area, so the weight distribution becomes 1:2 instead of 1:1.

One other alternative that might work: IF you can find some sort of 2:1 proportioning air valve, you could proportion the air to the 2-tired axle's airbags to be half the pressure of the 4-tire axle's airbags. I just doubt you'd find anything in the Bendix catalog or similar that would do this for you. The risk I foresee is that most air suspensions have a minimum pressure of 10psi to prevent aggressive bottoming of the suspension, and you'd have to debate changing that (if it's even possible) to 20psi so the 2-tire axle never got below 10psi.

[oldride]

Ok lets say you have a blow out and you want to flex your muscles and change it your self.

1 do you break out the tire irons and start sweating or?

2 do you break out a 20 volt cordless and bust them off.

3 you can start putting them back on with the cordless but how do you torque them.

 

In my younger days in the army we just sweated until we were done.

 

I have been considering this single tire on each axle but have yet to make up my mind.

[Mark and Dale Bruss]

Tire changes are done by tire service companies who have the equipment and the muscle. Those companies are everywhere since semis are everywhere.

[alan0043]

Hi Everyone,

 

I am still reading and learning. Please keep the conversion going.

 

Al

[RickW]

Ok lets say you have a blow out and you want to flex your muscles and change it your self.

1 do you break out the tire irons and start sweating or?

2 do you break out a 20 volt cordless and bust them off.

3 you can start putting them back on with the cordless but how do you torque them.

 

In my younger days in the army we just sweated until we were done.

 

I have been considering this single tire on each axle but have yet to make up my mind.

 

 

If faced with a tire change I will flex the muscles in my dialing fingers. I doubt I would even change the tire here in my own shop if I do not have to. Not worth the aggravation. It is aggravating enough changing a trailer tire on the side of the road (not willing to wait for road service). But I will wait for road service if I have to for a truck tire. Even if you have the tire irons you also have to have the ability to reseat the tire before you can get air in it.

[NoDirectionHome]

That's the easy part. It's fairly common to loose a bead seat off-roading so I've had this for 20+ years. http://www.tooltopia.com/ken-tool-31433.aspx?utm_source=google&utm_medium=cpc&utm_campaign=paid_search_google_pla&scid=scplp6817139&sc_intid=KEN31433&gclid=Cj0KEQjw1v66BRCV-6rh6s-Biu8BEiQAelpui-hPnU4wht9QW0oxCpsPgqW4-SWgPqz9WwOV6DLIe6gaAv9g8P8HAQ

[Steve from SoCal]

That's the easy part. It's fairly common to loose a bead seat off-roading so I've had this for 20+ years. http://www.tooltopia.com/ken-tool-31433.aspx?utm_source=google&utm_medium=cpc&utm_campaign=paid_search_google_pla&scid=scplp6817139&sc_intid=KEN31433&gclid=Cj0KEQjw1v66BRCV-6rh6s-Biu8BEiQAelpui-hPnU4wht9QW0oxCpsPgqW4-SWgPqz9WwOV6DLIe6gaAv9g8P8HAQ

That ain't gona get it with a 22.5, you need a bead blaster. http://www.ebay.com/itm/Inflator-Blaster-5-Gallon-Air-Bead-Seater-Tire-Seating-ATV-Tractor-Truck-145PSI-/371453875057?hash=item567c605371:g:3pIAAOSwNgxWDXj3&item=371453875057&vxp=mtr

 

IF you have the tools it is not really hard to change a tire on a truck, it is grunt work however. Having said that, I prefer to have a spare tire, you are at the mercy of road truck with out. I had a tire blow on I 5 near Woodland, Wa. on a weekend, it was NOT cheap to buy a tire on the side of the road.

 

Steve

[rickeieio]

Ok lets say you have a blow out and you want to flex your muscles and change it your self.

1 do you break out the tire irons and start sweating or?

2 do you break out a 20 volt cordless and bust them off.

3 you can start putting them back on with the cordless but how do you torque them.

 

In my younger days in the army we just sweated until we were done.

 

I have been considering this single tire on each axle but have yet to make up my mind.

If you a single, or an outside tire, wrenches aren't necessary. A bit of the grand kids bubble solution and 2- 18" tire irons make quick work of these tires. Now, if you had 20" split rings which were 20+ years old, it's a whole 'nother ball game.

[Darryl&Rita]

Posting these for Vern;

 

 

 

 

 

 

 

 

 

 

 

[Wrknrvr]

The top photo shows the hub assembly. Notice how close the inside of the hub is to where the wheels bolt on.

 

The second photo shows a bare spindle. If you look close you can see where the bearings ride.

 

The third photo shows only the outer wheel on with the brake drum exposed.

 

I stopped at the local City Service Valcon yard but there were no single wheel axles there except the ones made for only one wheel.

 

In my travels the next couple days I will find some trucks like I am talking about.

 

 

Thanks Darryl. for helping

Safe Travels Vern

[Wrknrvr]

Yesterday I spotted two Sysco food service trucks pulling trailers with single outside tires only. They were the second short trailer behind the HDT.

If I can stop by by there distribution center and get a picture it will be posted.

There was another truck that was going the other way yesterday that had the same setup. It's hard to get a photo if they are on the highway especially going the other direction.

 

Safe Travels, Vern

[dan412]

My transfer dump trailer has three axles with only single wheels on all three came that way from the manufacture. don't know about doing it on drive axles.

[Wrknrvr]

Dan412

 

Just curious if you could post a picture of the brake drum and wheel.

 

I have seen several other trailers with single outer wheels. It's just hard to find them that I can get a picture of.

 

 

Safe Travels, Vern

[dan412]

Dan412

 

Just curious if you could post a picture of the brake drum and wheel.

 

I have seen several other trailers with single outer wheels. It's just hard to find them that I can get a picture of.

 

 

Safe Travels, Vern

I will try to get pics Monday My trailer has hub pilot wheels with centrifuge steel drums

[Scrap]

One other alternative that might work: IF you can find some sort of 2:1 proportioning air valve, you could proportion the air to the 2-tired axle's airbags to be half the pressure of the 4-tire axle's airbags. I just doubt you'd find anything in the Bendix catalog or similar that would do this for you. The risk I foresee is that most air suspensions have a minimum pressure of 10psi to prevent aggressive bottoming of the suspension, and you'd have to debate changing that (if it's even possible) to 20psi so the 2-tire axle never got below 10psi.

 

Nowadays you'd get a Hadley SmartValve to do that. Put their transducer in a suspension line and then send them your pressure/height table of what you want it to do. You get a program back, drop it in the valve, and good to go. Or if it is a trailer drop axle then you put in the advanced ABS unit and program it to what you want (max-min only, no resolution) and good to go.

[peety3]

 

Nowadays you'd get a Hadley SmartValve to do that. Put their transducer in a suspension line and then send them your pressure/height table of what you want it to do. You get a program back, drop it in the valve, and good to go. Or if it is a trailer drop axle then you put in the advanced ABS unit and program it to what you want (max-min only, no resolution) and good to go.

Color me confused, but are you saying you can program it to read line #1's pressure and deliver 50% of that to line #2? There'd be no pressure/height table and no need for a lever to sense height, as the height sensing would fight the existing valve on the other drive axle.

[peety3]

Hi Everyone,

 

I have a question or too. Is it possible to eliminate the rear inner wheels ? You would still keeping the truck tandem. It would be like putting on super singles but not as wide of tread. I keeping thinking that there could be some problems. But I can not put my finger on what the problem could be. Maybe bearings, axles, seals, etc.. Has this idea been discussed before. If this has been discussed please post a link to this subject. I am not planning on doing this, but was just curious. Anyone spend a night or too in a Holiday Express.

 

Thank you for any help,

Al

Discussions have been all over the map, but I think the end summary comes down to this (all references to carrying capacity are with the perspective of the rear axle(s) only; steer axle capacity remains unchanged, though you're responsible for weight distribution):

 

Option 1: remain classic tandem with 8 drive tires and retain all of your initial load capacity.

Option 2: Delete an axle ("single short/mid/long/custom") and cut your carrying capacity by ~50%

Option 3: Delete 4 of the 8 tires and cut your carrying capacity by 50%. Reusing the same wheels puts undue load on bearings. Switching to non-offset wheels returns bearing load to normal.

Option 4: Delete 2 of the 8 tires and cut your carrying capacity by ~45%. (Both axles share the loads 50/50, so the capacity loss by tire rating and regulatory restrictions on one axle gets mirrored to the unaltered axle.) Based on big5er's comment, you'd be illegal in Texas, and possibly illegal elsewhere (unless I misinterpreted "without tire" to mean a wheel without tire). You'd essentially have two "warm spares".

Option 5: Delete 2 of the 8 tires, make unique alterations to your suspension, and cut your carrying capacity by 25%. (Replace the air bags with new units 30% smaller in diameter, or procure a proportioning valve to change the air pressures in your existing air bags on the 2-tire axle to be 50% of the pressure in the bags on your 4-tire axle).

Option 6: Convert to super singles on both axles. Carrying capacity changes are now dependent on the new wheel/tire ratings (and state law, etc.).

Option 7: Convert one axle to super singles. Carrying capacity is essentially double the capacity of whichever axle/wheel/tire combo has the lower rating.

Option 8: What else belongs on this list?

 

Thoughts?

[Scrap]

Sorry, way behind, but I was thinking more along the lines of program it to be a leveling valve until 35psi (or whatever pressure at new axle rating is) and then hold. I suppose you could probably do the same but non electronically with a pressure reducing valve and relay into the supply of a regular leveling valve but it might burn a lot of air. I don't know how it works with y'alls exempt trucks but a regular truck has to be very careful with this because in many states if you aren't plumbed together or don't have very similar weights you are no longer considered a tandem. You have to now make bridge with two 20K's 52" apart and it doesn't work out.

[peety3]

Sorry, way behind, but I was thinking more along the lines of program it to be a leveling valve until 35psi (or whatever pressure at new axle rating is) and then hold. I suppose you could probably do the same but non electronically with a pressure reducing valve and relay into the supply of a regular leveling valve but it might burn a lot of air. I don't know how it works with y'alls exempt trucks but a regular truck has to be very careful with this because in many states if you aren't plumbed together or don't have very similar weights you are no longer considered a tandem. You have to now make bridge with two 20K's 52" apart and it doesn't work out.

If it's a leveling valve up to 35psi and then pressure-limited at 35psi, it becomes a 6k tag in effect (17k * .35, on the assumption that air bags are designed for max load at 100psi, and a <8' tandem set is limited to 17k per axle or 34k for the set). If your rear load is always >12k, this becomes a 6k "guaranteed" loading on the tag and everything else on the main. If your rear load is under 12k, the pressure valve could start a "race to the bottom" (the truck is too high, I'd better exhaust some air, all the way down to 0psi, leaving the 12k load on the main axle) or a "race to the top" (the truck is too low, I'd better add some air, all the way up to <70psi, taking weight off the main axle). Either of those could result in an "unweighted" drive axle, which could result in lots of tire slippage and differential wear.

 

I see where you're going with that, and it probably becomes a reasonable option within two range limits: rear axle load never dips below (2.1 * tag load) and never exceeds (tag load + 17k). It gives you more capacity than a single axle, and less than a full tandem set.

[rickeieio]

Good analysis. Now I'll throw another wrinkle into it. What if, the original suspension is sized so that at legal loads (34k/tandem) the bags are inflated to their "sweet spot" of 50% of rated pressure, or 50 psi?

 

I'll not attempt the calculation, as it's hot here and my brain needs to cool first.

[Dollytrolley]

Sorry, way behind, but I was thinking more along the lines of program it to be a leveling valve until 35psi (or whatever pressure at new axle rating is) and then hold. I suppose you could probably do the same but non electronically with a pressure reducing valve and relay into the supply of a regular leveling valve but it might burn a lot of air. I don't know how it works with y'alls exempt trucks but a regular truck has to be very careful with this because in many states if you aren't plumbed together or don't have very similar weights you are no longer considered a tandem. You have to now make bridge with two 20K's 52" apart and it doesn't work out.

 

Scrap.....

 

Your comments scared me so much I went out the old Shaker a counted my wheels .........twice...... and made sure that all of the tires were aired up to within 25 PSI of each other.........shucks I might even check some of the slack adjusters before I drive the darn thing again.......

 

With the 20 ft Morgan cargo box in the Shaker I have a fair bit of tail swing behind the drivers and so I can get some loads that tend to load the rear driver a bit more.........the deal is that actual weights sometimes are different than ..........CALCULATED weights............I just hate it when math and physics mess with what little mind I have left.......or right......whatever.......

 

Maybe I might break out the live data weight and balance spreadsheet and display some of my latest ........sins of weight distribution.....

 

Drive on...........(where did all that weight......go)

[peety3]

Good analysis. Now I'll throw another wrinkle into it. What if, the original suspension is sized so that at legal loads (34k/tandem) the bags are inflated to their "sweet spot" of 50% of rated pressure, or 50 psi?

 

I'll not attempt the calculation, as it's hot here and my brain needs to cool first.

Target pressure (in the bags on the 2-tire axle) = [pressure in bags at max legal weight] * [minimum weight on the tandem set in YOUR configuration] / 37,800

 

The more I think about this, the more I think this approach is risky to your inter-axle differential. It'll be about a 45/55 weight split between the two axles at minimum weight (probably can't stray too far from this, or the air bags for one axle or the other could approach their rated minimum (10psi?). This would create about a 70/30 weight split from the tire's perspective, making the 4-tire axle relatively light and inclined to spin out. Once loaded up to max, it becomes about a 25/75 weight split (assuming 12k min weight), which would be a 40/60 split from the tire's perspective, making the 2-tire axle relatively light and inclined to spin out. Based on a back-of-the-napkin guesstimate, it could also mean a 500-700 pound weight transfer change on the front axle (sample case was jeffw's rig, as discussed here: http://www.rvnetwork.com/index.php?showtopic=123511&p=846125 )