Why two axles???? - Page 5 - Fiberglass RV


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Old 02-05-2013, 12:38 PM   #57
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Quote:
Originally Posted by Jared J View Post
One of my trailers has a 35 and 80psi tire .


A passenger car tire and-what-an LT?

You've got nerves of steel, Jared!


Francesca
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Old 02-05-2013, 01:20 PM   #58
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Quote:
Originally Posted by Francesca Knowles View Post


A passenger car tire and-what-an LT?

You've got nerves of steel, Jared!

Francesca
The lt is 35 psi, st's are 80 psi.
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Old 02-05-2013, 05:05 PM   #59
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Quote:
Originally Posted by MC1
In a tight turn there is a lot of side load pressure on dual axle trailer bearings but the wheel bearings seem to handle it well. Torsion axles are designed to "give" a little in a tight turn. This is normal.
This is exactly what I was talking about. Thanks for posting that picture.

I was climbing a hill on a state road in North Carolina heading towards Mt Mitchell when I noticed smoke coming from a bearing. I pulled over to check on it and found myself on soft shoulder and could not pull forward. I was very afraid to back up even though there was no traffic. Backing up was my only option because I did not have four wheel drive on my tow vehicle. I was able to back up and get going again but it was a frightening experience as I was worried someone would fly down the mountain and cause a wreck. Backing up put additional stress on the wheel bearing. I could not safely service it there so I proceeded on.

Wheel bearings are adjusted to be fairly tight. There is no flex in wheel bearings. And yes thry do carry high loads--the entire weight of the trailer. A tandem axle set up, if heavily loaded with tires under high pressure means there has to be give somewhere because both axles can't turn at the same rate like a single axle can.

I watched one tire roll past me down the freeway after I cleared the pass over the mountain. I was able to continue on only because I had tandem axles, even though that was the cause of the failure. The tight turns I made backing up were the main reason this bearing failed so early. Since then I have avoided sharp turns with tandem axle trailers and watched my tires in my rear view mirror.

Dually wheels on a single axle would have scrubbed in this situation but held up IMHO. Narrow tires on a single axle trailer do the best.

While "dry" sailing in San Francisco, at the Brickyard, we stored our 30' boats on trailers. There were two types of trailers in use, single and tandem axle trailers. We would push these to the hoist to launch our boats. People helped each other so it was quite obvious which trailers were easy to turn and which were not. Tires and springs would flex, but not enough to eliminate loads on the bearings and spindles.

There is a trade off between single and double axle trailers. It is a complex trade off and a function of axle location--farther from the tow ball the better, axle width, and axle spacing.
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Old 02-05-2013, 05:18 PM   #60
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Originally Posted by Night Sailor View Post
......... The tight turns I made backing up were the main reason this bearing failed so early...........
No offense, but I don't think that this is correct.
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Old 02-05-2013, 05:23 PM   #61
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Generally speaking tire pressure is a function of weight. It is also a function of contact area. A bicycle will need more pressure than a fat automobile tire. But for typical purposes--cars and trailers, weight is the factor to consider along with manufacturers (both auto and tire) recommendations.

Tires can fail just sitting there. I've heard gunshot like sounds and watched my new tire decompress right in front of me. Far better to happen that way than freeway speeds. I am gradually putting tire pressure monitors on my vehicles for safety. I am waiting for a package for a dually with six tires. My Volvo has an after market kit I put in and I use it to match pressures on all tires.

Probably the most significant factor is heat which is a function of tire pressure. A tire that flexes too much gets too hot and fails. A gauge is mandatory IMHO even if you have sensors, and if the tire seems obviously bulging, you are way low and need to add air quickly.
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Old 02-05-2013, 05:33 PM   #62
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I do. I was carrying a heavy load. It never would have happened with a heavier duty single axle.
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Old 02-05-2013, 05:37 PM   #63
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No offense, but I don't think that this is correct.
I am no axle scientist, but I can't see it either Tom. We would be having failures all the time then.

I do believe that there would be lots of pressure placed on the bearing, but ones properly installed and maintained are designed to handle it.
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Old 02-05-2013, 05:40 PM   #64
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I know of many of these and there is no abnormal bearing failures.
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Old 02-05-2013, 05:47 PM   #65
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Originally Posted by Night Sailor View Post

This is exactly what I was talking about. Thanks for posting that picture.

I was climbing a hill on a state road in North Carolina heading towards Mt Mitchell when I noticed smoke coming from a bearing. I pulled over to check on it and found myself on soft shoulder and could not pull forward. I was very afraid to back up even though there was no traffic. Backing up was my only option because I did not have four wheel drive on my tow vehicle. I was able to back up and get going again but it was a frightening experience as I was worried someone would fly down the mountain and cause a wreck. Backing up put additional stress on the wheel bearing. I could not safely service it there so I proceeded on.

Wheel bearings are adjusted to be fairly tight. There is no flex in wheel bearings. And yes thry do carry high loads--the entire weight of the trailer. A tandem axle set up, if heavily loaded with tires under high pressure means there has to be give somewhere because both axles can't turn at the same rate like a single axle can.

I watched one tire roll past me down the freeway after I cleared the pass over the mountain. I was able to continue on only because I had tandem axles, even though that was the cause of the failure. The tight turns I made backing up were the main reason this bearing failed so early. Since then I have avoided sharp turns with tandem axle trailers and watched my tires in my rear view mirror.

Dually wheels on a single axle would have scrubbed in this situation but held up IMHO. Narrow tires on a single axle trailer do the best.

While "dry" sailing in San Francisco, at the Brickyard, we stored our 30' boats on trailers. There were two types of trailers in use, single and tandem axle trailers. We would push these to the hoist to launch our boats. People helped each other so it was quite obvious which trailers were easy to turn and which were not. Tires and springs would flex, but not enough to eliminate loads on the bearings and spindles.

There is a trade off between single and double axle trailers. It is a complex trade off and a function of axle location--farther from the tow ball the better, axle width, and axle spacing.
My car trailer probably has 50k miles on the original bearings. It was loaded heavy, and used in the farm in fields. It was cranked into tight spots. Something was wrong with your bearings, not the turns. Poor grease, moisture, spalling, loose, too tight, etc.
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Old 02-05-2013, 05:49 PM   #66
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As you all know I'm no expert on this subject-else why would I have started this thread?

But I do like to investigate all plausible theories, and according to some other sources the "sharp turns can destroy a tandem's wheel bearings" scenario put forth by Conrad is well accepted in some experienced quarters.

Here's a quote from one such discussion:
Quote:
Typically you cannot or would not try to move the trailer in a very tight turn with your truck. However, it seems like boat yards and boat dealers think nothing of moving your boat in very tight turns. What usually happens if you have a tandem axle trailer is that one wheel is not as heavily loaded as another, and that tire will be forced sideways. This puts too much load on the wheel bearings. If the dealer's yard is paved, and if the pavement was clean and dry, and if the tires have good traction, pushing the tire sideways takes a lot of force. The wheel bearing could have been damaged by too much sideways pressure.
Source: Strange trailer wheel bearing failure

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Old 02-05-2013, 06:40 PM   #67
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Perhaps dual axle bearings are different on boat haulers and I believe there may also be springs in lieu of torsion on some boat trailers and their spacing also appear different. All of these may explain Night Sailor's poor experience.
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Old 02-05-2013, 07:17 PM   #68
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Interesting point-

I wonder if we're talking about two different kinds of axles- though if I understand correctly that torsion-types don't "equalize" loads as do spring-types, it seems like the stresses would be greater on a torsion axle's wheels.

In any case...hey, Conrad!

Which kind of axle was on the blown-bearing trailer?

Francesca
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Old 02-05-2013, 07:41 PM   #69
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More than likely the high forces on the bearing while scrubbing through a turn failed a bearing that was near the end of its usefulness. I doubt a new properly adjusted bearing would fail.
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Old 02-06-2013, 04:53 PM   #70
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Quote:
Originally Posted by Francesca Knowles
Interesting point-

I wonder if we're talking about two different kinds of axles- though if I understand correctly that torsion-types don't "equalize" loads as do spring-types, it seems like the stresses would be greater on a torsion axle's wheels.

In any case...hey, Conrad!

Which kind of axle was on the blown-bearing trailer?

Francesca
Conventional springs. I don't remember if they were mounted individually or linked. I traded the trailer to a welder for welding work as I felt the design to be flawed.

The amount of stress on the axles was alarming to me, and that in conjunction with the failure led me to believe it was poorly designed. This was a relatively short trailer--maybe 25' long with the tandem axles more centered. A longer tongue would have helped.

This was a car hauler and heavily loaded. The axles seemed to be sting enough. I had the tires aired up to the max to haul a heavy K5 Blazer.

It was probably a combination of factors however I suspect the most critical factor was side loads in tight turns. In the future, I would avoid backing and making tight turns with tandem axles in the future, or else consider airing down tires to provide more flexibility. Now if the axles are set back far, as is typical of larger trailers, I would not be as concerned. Even a triple axle Avion, where the axles are 22' back from the tongue.

One final point. Getting stuck hauling a trailer means backing up and sharp turns. For this reason I am firmly convinced 4 wheel drive tow vehicles are preferred. It is much better to pull forward than back awkwardly. I would not use anything but a 4x4 for heavier trailers.
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