Why two axles???? - Page 3 - Fiberglass RV


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Old 01-28-2013, 01:04 PM   #29
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It seems to me that brakes on both axles would be a REAL redundancy feature...am I to understand that some dual axle fiberglass trailers don't have it?

If a trailer's heavy enough to require two axles to carry "X" load, surely they should both be braked in order to stop the same load!

Francesca
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Old 02-04-2013, 03:41 AM   #30
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Making a sharp turn forward or more commonly backing can put tremendous side loads on the spindles. If you are carrying a heav load qt higher pressures this could be a real problem. I had a bearing failed because of this. Single axles turn and bank better. My preference would be dual wheels on each side with a single axle. I am surprised more trailers are not build like that.
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Old 02-04-2013, 04:07 AM   #31
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Making a sharp turn forward or more commonly backing can put tremendous side loads on the spindles. If you are carrying a heav load qt higher pressures this could be a real problem. I had a bearing failed because of this. Single axles turn and bank better. My preference would be dual wheels on each side with a single axle. I am surprised more trailers are not build like that.
I'm not, they don't tow well. Bearing failures are rather rare, and almost never due to scrubbing.
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Old 02-04-2013, 05:45 AM   #32
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Bearing failures are rather rare, and almost never due to scrubbing.
For certain. This sideways action should be easily handled by bearings. The vast majority of trailers have 2 or more axles.
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Old 02-04-2013, 01:39 PM   #33
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A big mystery to me is why single-axle trailers are so much more the norm in Europe!

And we're not talking itty-bitty trailers like some of ours, either:







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Old 02-04-2013, 01:48 PM   #34
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Weight, I'm guessing. They're already pushing the limits with their tow vehicles. They can also only tow around 50-55mlh in most areas there.
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Old 02-04-2013, 03:00 PM   #35
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Agree, pretty much the weight!

Also consider no WDH's are used over there.







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Old 02-04-2013, 03:18 PM   #36
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The "side loads" are absolutely not handled by the bearings. They are handled by sidewall and suspension flex. Tire pressure is purely a function of the weight carried. If you are loaded heavy with higher tire pressures this is a real concern.

Anyone who pushes an unhitched trailer can tell you the rolling resistance is greater with tandem wheels, particularly when turning it is difficult.

Tandem trailers may track better, handle wide bumps better, and resist sway better than single wheel axles, however dual wheels on a single axle would be just as resistant to sway and turn much easier. The trade off would seem to be ease in turning versus ride over wide bumps.

The last factor discussed, tracking, is a function of the location of the axles. Axles farther back on the trailer provide better tracking. The Element trailer is a single axle trailer that performs well in that regard. Here is a radical idea. If you have a heavy duty tow vehicle and want superior tracking, carry 50% of the trailer weight on the hitch and put a tandem axle at the extreme rear of the trailer. The reason this isn't done is because of the difficulty backing and it would be impossible to wrestle around by hand without a wheel on the front.
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Old 02-04-2013, 03:24 PM   #37
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Agree, pretty much the weight!

Weight, huh? Makes sense- Jim said earlier that a second axle adds about 400 pounds of weight. Leaving that puppy off would sure bring the weight down on some of the units owned by folks in this forum!


This explanation does make more sense to me than the "tire redundancy" argument, unless tire standards among European trailer manufacturers are higher than among North American companies.

As for "greater stability" of two axles, the length of some of those European units sorta puts that one to rest. Of course, the speed limit for trailers is almost universally 55 mph in Europe- that probably has a much greater effect on tow stability than the number of axles on the trailers!

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Old 02-04-2013, 05:08 PM   #38
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The "side loads" are absolutely not handled by the bearings. They are handled by sidewall and suspension flex. Tire pressure is purely a function of the weight carried. If you are loaded heavy with higher tire pressures this is a real concern.
I've gotta respectfully disagree on this. Wheel bearings are tapered to handle side forces, otherwise there would be nothing that could handle these forces while allowing the wheels to turn with little to no friction. Sidewalls do take up some of the shock effect of side forces, but are not designed to stop the forces of the load. Suspension flex is designed pretty much for vertical forces, and to provide a better ride for the load.

Kinda confused on the last part of this too, maybe you can clarify. Tire pressure is totally independent from the weight carried. Whether I have a trailer with the tires at 80 lbs with the 4,000 lb load, or with a 14,000 lb load, the tire pressure is pretty much the same. If you carry heavy loads, you want to have your tires near maximum pressure.
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Old 02-04-2013, 05:32 PM   #39
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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.
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Old 02-04-2013, 05:35 PM   #40
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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.
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Old 02-04-2013, 05:36 PM   #41
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Tire pressure is totally independent from the weight carried. Whether I have a trailer with the tires at 80 lbs with the 4,000 lb load, or with a 14,000 lb load, the tire pressure is pretty much the same. If you carry heavy loads, you want to have your tires near maximum pressure.
It's my understanding that tire pressure is based on the weight of the load. That's why the number on a car door, for example, is usually below the tire's actual maximum capacity.Any particular tire has a range within which it can be used on many different vehicles, each at a particular (under the max) pressure determined by the vehicle manufacturer.

And here's a chart for trailer tires that more or less illustrates the same thing:




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Old 02-04-2013, 05:40 PM   #42
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It's my understanding that tire pressure is based on the weight of the load.

Francesca
Agree.
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