Why two axles???? - Page 4 - Fiberglass RV


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Old 02-04-2013, 05:55 PM   #43
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Wheel bearings never used to be tapered, and still took the side loads. ............
I'm 60 years old and remember packing tapered wheel bearings as a kid. When was never to you?
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Old 02-04-2013, 06:01 PM   #44
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Wheel bearings never used to be tapered, and still took the side loads.

As for tire pressure, he meant with less load, you can run less tire pressure.

A dual wheel single axle won't track as well as a double axle will.
Never knew that, but I am just a Whipper Snapper according to Francesca.

Gotcha

Absolutely agree. Having towed hundreds of different trailers I can't think of one that had a single dual axle. Tandem duals I have used though.
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It's my understanding that tire pressure is based on the weight of the load.
My thinking is that it is based on the limit of the load, the max the trailer can handle. Even the chart you show is based on limits, not necessarily the amount carried. While one can lessen the pressure lower than maximum as the weight decreases, it is not necessary. Reace from Escape told me he recommends running at or near maximum pressure, as I have done with almost every trailer I have owned, including lots of construction and holiday ones.

One is not expected to change pressure for different loading for a give trailer with its specific tires. I would go crazy trying to pressure up and down trailer tires many times a day, if you used a tire pressure based on the weight of the load. Trailers get loaded and unloaded frequently. I know that this is to a much lesser degree with our travel trailers, but it still holds true.
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Old 02-04-2013, 06:46 PM   #45
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No one, least of all me, suggested changing tire pressure every time a trailer gets a couple of gallons of water etc. Most of us know within a couple of hundred pounds what our loaded trailers weigh, so it's easy to set an optimally high-end pressure and keep it there unless conditions dictate otherwise.

I actually learned this in this very forum, and had to "unlearn" always running the tires at the max...and I'm more than satisfied with the resulting improvement in the ride.

Francesca
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Old 02-04-2013, 07:00 PM   #46
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Wheel bearings never used to be tapered, and still took the side loads.
Yes, ball bearings handle axial loads as well. You could even use plain bushings, but there would be a thrust washer or other axial bearing surface (check out a kid's wagon or your lawn care equipment for an example). A wheel/hub bearing must handle both radial and axial loads to transmit a vehicle's sideways force, and it does handle both. Tapered roller bearings do very well for both, but are relatively expensive, so they are used where both directions of load are important.

Whatever the bearing type, side loads are carried through a chain of components, and like any chain each link carries the full load. The chain in this case includes tire tread, tire sidewalls, wheels, hubs, bearings, suspension components (such as leaf springs + bushings + brackets, or torsion axle arms + rubber + tube + brackets), and the frame. I offer no opinion here on which is likely to fail or how any of them are affected by the choice of single versus multiple axles.
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Old 02-04-2013, 07:26 PM   #47
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I wonder if this whole tire pressure thing could be just gauged by your eye and never to exceed the manufacturer’s weight limit? Say if you knew a tire could carry maximum weight at a certain maximum pressure while traveling at freeway speed because the manufacturer formulates these ratings at normal traveling speeds. Then you load your trailer to the maximum tire pressure rating, but you are 10 PSI under the recommended setting. You notice the tire will be deformed and squatting. Will the tire blow out or fail while parked? I don't think so. Its strength is not likely in question. It is at speed that the havoc happens. It is likely caused by all that deformation and puckering of the sidewall which has to straighten and re-pucker with each revolution of the tire. That causes friction within the composition of rubber and cords of the tire. Friction causes what? Heat. Heat can cause what? Meltdown. Blooey!
So why not just use our eyes to determine how much air is needed as we load our trailers? Eliminate excessive pucker without exceeding the tires recommended maximum? If it doesn't flex much it won't heat much. A lightly loaded trailer surely does not need maximum tire pressure.
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Old 02-04-2013, 07:41 PM   #48
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I keep a close eye on everything having to do with my tires, but for pressure readings I insist on using an old-fashioned mechanical gauge. I've had a slow leak a time or two, and mightn't have known it in time to prevent disaster otherwise.

It may be that I'm hypervigilant, but in my own defense I'll say there's nothing like a front end blowout at freeway speeds to teach one to be that way. (Non-towing incident, and the last time I let my husband tell me "there's plenty of life left" in tires that I was pretty sure were shot.)

Per the trailer weight charts:

Certainly, just as with a car, one should listen first to the trailer manufacturer per tire pressure. It's their design, and who knows what part pressure plays in the performance of the product itself.

And in the case cited by Jim, (fifty pounds for his Escape19), if his trailer has 3500 pound axles and load range "c" tires, fifty pounds of pressure is probably right about where he'd find himself in the chart anyway!

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Old 02-04-2013, 07:41 PM   #49
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I'm 60 years old and remember packing tapered wheel bearings as a kid. When was never to you?
I'm 30, and have done many vehicles with ball bearings. My '57 had them.
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Old 02-04-2013, 07:47 PM   #50
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I wonder if this whole tire pressure thing could be just gauged by your eye and never to exceed the manufacturer’s weight limit? Say if you knew a tire could carry maximum weight at a certain maximum pressure while traveling at freeway speed because the manufacturer formulates these ratings at normal traveling speeds. Then you load your trailer to the maximum tire pressure rating, but you are 10 PSI under the recommended setting. You notice the tire will be deformed and squatting. Will the tire blow out or fail while parked? I don't think so. Its strength is not likely in question. It is at speed that the havoc happens. It is likely caused by all that deformation and puckering of the sidewall which has to straighten and re-pucker with each revolution of the tire. That causes friction within the composition of rubber and cords of the tire. Friction causes what? Heat. Heat can cause what? Meltdown. Blooey!
So why not just use our eyes to determine how much air is needed as we load our trailers? Eliminate excessive pucker without exceeding the tires recommended maximum? If it doesn't flex much it won't heat much. A lightly loaded trailer surely does not need maximum tire pressure.
Russ
No, not even close. As an easy example, it's quite hard to tell the difference between 20 and 60 psi on my pickup tires.

To be honest, I always max out my trailer tires so I don't have to worry about it. I also tow faster than most here, so it gives the needed safety margin. When my camper is done and weighed, I might consider running them a bit under max, we'll see how it rides. Usually I just leave them at 80 psi.
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Old 02-04-2013, 07:48 PM   #51
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I'm 30, and have done many vehicles with ball bearings. My '57 had them.
Man, I am 55, and labeled a Whipper Snapper. Kinda curious as to what Francesca would label you.

BTW, '57 was a very good year.
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Old 02-04-2013, 08:15 PM   #52
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No, not even close. As an easy example, it's quite hard to tell the difference between 20 and 60 psi on my pickup tires.

To be honest, I always max out my trailer tires so I don't have to worry about it. I also tow faster than most here, so it gives the needed safety margin. When my camper is done and weighed, I might consider running them a bit under max, we'll see how it rides. Usually I just leave them at 80 psi.

Jared,
You are right about being hard to see the difference on an unloaded pickup. It is easier to see the difference when loaded. There are various ways to fine tune your pressures such as infrared thermometers and watching tire wear patterns etc. Eyeballing is just what it says. Mine says if it don't distort it won't distruct. Putting 80 psi in an unloaded vehicle will make the trip less than pleasant. You'll get good mileage though!
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Old 02-04-2013, 08:17 PM   #53
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Tandem axles are analogous to building a child’s wagon without a pivoting front axle for steering. If you built such a wagon you couldn’t turn unless you overcame the friction of the tires to the pavement, or failed a wheel or wheel bearing or the connection between the wheels and frame. The wheel bearings are likely not the weakest link, but probably the tire will most likely skid. Trailers are just like big kids wagons. The tires “scuff” when the trailer is required to change directions. Here again the tire to pavement connection is the weak link and the trailer turns. Are the tires going to wear faster than a single axle setup? Yep. Are the wheel bearings going to wear faster than a single axle setup? Maybe, as thrust loads are increased, but weight is shared with the other axle. Tandem axles do have advantages though. What if the resistance to turning is a good thing for stability? A dually axle with one wheel mounted inside the other (like trucks use) would carry the weight equally, but not scuff during a turn, so be no more stable than a single axle with only 2 wheels. It would turn easily and carry the weight but maybe not add the stability a tandem does. Also the inner outer wheel arrangement of a dually would take up valuable interior floor space in a travel trailer. The Wheel bearings would not have the mechanical advantage of a trucks rear axle either, as it is supported at the wheel and differential. These reasons may be why we don’t see this configuration used.
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Old 02-04-2013, 09:03 PM   #54
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Man, I am 55, and labeled a Whipper Snapper. Kinda curious as to what Francesca would label you.
....

I'm thinking...
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Old 02-04-2013, 10:04 PM   #55
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Jared,
You are right about being hard to see the difference on an unloaded pickup. It is easier to see the difference when loaded. There are various ways to fine tune your pressures such as infrared thermometers and watching tire wear patterns etc. Eyeballing is just what it says. Mine says if it don't distort it won't distruct. Putting 80 psi in an unloaded vehicle will make the trip less than pleasant. You'll get good mileage though!
Russ
One of my trailers has a 35 and 80psi tire, I can't tell a difference in how they squat with a 5000 lb pickup on it.
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Old 02-05-2013, 10:29 AM   #56
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One of my trailers has a 35 and 80psi tire, I can't tell a difference in how they squat with a 5000 lb pickup on it.
You will need to gauge those tires. The construction must be pretty rigid. My Scamp tires visually show me they are low by 5 PSI. More squat. I use a gauge to top them off.
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