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Old 06-22-2014, 10:52 AM   #61
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Originally Posted by cadman99 View Post
Getting way to technical now. However in the midst of the discussion I have realized that with 7000lbs of axle and 7000lbs of load the suspension is used up at the start with somewhere around 1/2" of travel left. Kinda of wonder if this may lead to premature failure.
Yes. At rated load (3500 pounds in your case) the torsion axle arm is SUPPOSED to be horizontal. The rotation above horizontal is the "overload shock absorption" rotation.

I said it before, I believe you have the wrong axles on your trailer.
You should be contacting the MFR. "premature failure" may be an understatement in your case.
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Old 06-22-2014, 10:57 AM   #62
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Originally Posted by Herk7769 View Post
Yes. At rated load (3500 pounds in your case) the torsion axle arm is SUPPOSED to be horizontal. The rotation above horizontal is the "overload shock absorption" rotation.

I said it before, I believe you have the wrong axles on your trailer.
You should be contacting the MFR. "premature failure" may be an understatement in your case.
The "premature failure" Herk is speaking about is to the axle, not the frame as the load is spread out over 192 sq. in. of the frame. (48" x 2" x 2 = 192 sq. in.)
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Old 06-22-2014, 11:07 AM   #63
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I love all the bickering about stress, load and strain...
Run a finite element analysis on something like this and they'll be similar, with the moments/strain in between the leaf springs reversing a little, while the moments/strain along the tube that the torsion axle being fairly constant until the ends of the tube-then the moments/strain will spike just like with the leaf springs.
6 to one, half a dozen to the other...
Look at a big rig leaf spring and you can see how a frame should be designed in a perfect world-thicker at the main stress points and tapering down at the ends.
As long as the frame doesn't bend, I'm good with either design-but prefer leaf with shocks because it allows for more suspension travel.
Anybody make the popcorn yet? I like extra butter.

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Old 06-22-2014, 11:14 AM   #64
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...Run a finite element analysis on something like this and they'll be similar, with the moments/strain in between the leaf springs reversing a little, while the moments/strain along the tube that the torsion axle being fairly constant until the ends of the tube-then the moments/strain will spike just like with the leaf springs...
Won't get into a debate, but if you run a finite element analysis on the frames as used in both applications, I think you will find more stress on the spring suspension anchor points. Have fun. I still like the torsion axles with shocks over any spring suspension trailer I've ever had.
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Old 06-22-2014, 11:37 AM   #65
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Torsion axles are smoother or ???
Inquiring minds want to know.
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Old 06-22-2014, 11:42 AM   #66
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Torsion axles are smoother or ???
Inquiring minds want to know.
Sure has been my experience comparing my present 5er with torsion axles & shocks to the other 7 spring axle trailers I've had since 1975.
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Old 06-22-2014, 12:42 PM   #67
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Torsion axles are smoother or ???
Inquiring minds want to know.
I think after having torsion axles on my past flagstaff I would say they are probably smoother and when a bump was hit the jolt on the camper seemed less defined or not as harsh.
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Old 06-22-2014, 01:33 PM   #68
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Originally Posted by cadman99 View Post
Too many assumption here ----

The problem is many of us can easily surpass the GAWR (Gross Axle Weight) because the weight of the trailer plus contents is greater than the axle(s) rating. If you upgrade the axles to carry more weight we assume the weight of the new axles will be greater but we don't know how much. Could be just larger bearings which would have a minimal effect on overall weight (GVWR). (How much difference can there be betweeen 3500lb and 4000lb axles?)

The second problem is where the weight is located. If located near the center the effect in minimal. We also assume that the trailer frame and it's structure are calculated as part of the GVRW rating.

I think if you look at any particular trailer model and the varying interior arrangements it is next to impossible to alter the structure for each different configuration. So the assumption is the trailer structure bears some of the structural integrity; but how much?

Given these assumptions (trailer is usually overloaded anyway) it would seem wiser to upgrade the axles along with the tires and possibly wheels.

When building your trailers the manufacturer must meet minimum standards in order to pass stringent DOT/NHTSA regulations and safety standards. Here is one that pertains to your axle fitments.

"On RV trailers, the sum of the GAWRs of all axles on the vehicle plus
the vehicle manufacturer’s recommended tongue weight must not be
less than the GVWR. If tongue weight is specified as a range, the minimum
value must be used."

Once we - the owners - take control of our trailers it becomes our responsibility to insure we do not exceed any of the safety values (GAWR - GVWR) provided to us by the trailer builder.

Footnote: Overloaded Recreational Vehicle (RV).

The FMVSS have requirements for the manufacturer to use proper tires and rims for the gross axle weight rating (GAWR) and the gross vehicle weight rating (GVWR). The manufacturer may determine the GVWR by adding cargo capacity (if any) to the curb weight of the vehicle as manufactured. The wise consumer, before purchase, will determine if the vehicle has sufficient cargo capacity to carry the weight of water, additional equipment (such as televisions, and microwave ovens), and luggage. The manufacturer’s certification label must show the GVWR. The GVWR must not be exceeded by overloading the vehicle. There is little the government can do to assist a consumer who has purchased a vehicle that has insufficient cargo capacity for its intended use.

That's from a NHTSA FAQ page.

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Old 06-22-2014, 01:56 PM   #69
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If, in fact, a RV trailer is fitted with undersized axles NHTSA would be forced to initiate a recall if the manufacturer did not do it themselves. All costs to make the trailer conform to it's specifications would be paid by the trailer's manufacturer.

So do some homework. With undersized axles you can force the trailer's manufacturer to replace them free of all costs.

But, remember that your dealing with the builder. All that is really required is a new cargo sticker that lowers the cargo capacity enough to allow the installed axles to fit the trailer's minimum specs. That is a solution the trailer builder can use with enough cargo flexibility to do it.

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