I agree. I don't think you'll have any issues the way you're using your pod, unless you get really unlucky and drop into a giant pothole or something. In my case, I ran around (carefully!) all last summer on unsurfaced roads with a WDH on a heavy trailer and didn't bend my Lippert axle, but I don't figure my luck would have held out too much longer doing that.  

Its going to depend a lot on how you load your trailer and where you travel with it. IIRC mcarter, you don't boondock much so you probably roll out relatively light on your axle and probably don't hit a lot of unsurfaced roads? WDH tension adds load as well.  Do you know what your loaded axle weight is? Mine really is right around 3500 with my WDH tensioned, no doubt over 1750 on the slide side and under on the curb side. 

As has been pointed out a few times, most folks never have a problem with their axles getting bent. 

That being said, I would switch to a Dexter if I replaced my axle both because they do seem to have a better reputation in some circles but also just because I didn't get a straight answer from Lippert. That kind of thing turns me off just on principle. 

But for about $100 I figured I'd start with the cheapo reinforcement option and see if that takes care of the problem. I'd have well over $1000 into a new 5200 lb axle, brakes, and wheels. And if it ain't broke don't fix it, its not like its going to leave me stranded somewhere. The failure is that it just picks up some negative camber. 

Good question.

Lippert has 3500 lb and 5200 lb torsion axle ranges. When I called them to see if I could buy a higher rated axle and read him the model number (which includes the frame attachment spacing) the first sales tech I talked to said they could sell me a 4400 lb rated axle but it was "identical in all respects" to the 3500 lb one I already had, other than the label. He said he checked the configuration with his engineering staff to be sure. 

But when I called back later to confirm I got a different sales tech who said they were told not to tell people that and said I would need to buy a 5200 lb axle if I wanted a higher rating. 

 If the 4400 lb axle was truly "identical" it would have the same inboard mounting points. So I'm left wondering what the first guy I talked to and his engineering group were thinking. The only thing I can think of is that they have a customer who buys that same axle and has them put a 4400 lb label on it. We know that Lippert provides the same 3500 lb axle to FR which they derate to 3000 lbs for the smaller rPods, so maybe they do the opposite as well on some other trailer? 

Here's how I look at it.  if my axle fails in spite of the axle tube reinforcement it will presumably be some other component besides the axle tube that fails, like the torsion arm, rubber cords, or the spindle, all of which are most likely the same on any axle in the 3500 lb product range.  So if any of those fail it wouldn't make sense for me to get another 3500 lb axle anyway. 

If I ever do have to get another axle I think I'll try a Dexter one, they seem to be perceived in the industry as having a better quality product. 

But, if the axle failures are indeed in the tube itself and not the rubber cords, spindle, or torque arm, the reinforcement will take care of the problem and give me about a 50% increase in capacity (which is also about 5200 lbs). 

Assume no warranty if you modify the axle in any way. Lippert's warranty specifically excludes that.  OTOH, none of the reinforcement fixes we've worked on here actually modify the axle itself, and they are all easily removable. If mine fails even after reinforcement I'll upgrade to a 5200 lb one which wouldn't be covered anyway. 

If the other trailer was an rPod then Lippert made both the axle and the trailer frame, so if the failure was a bent axle tube it would be difficult for Lippert to say they weren't accountable for effects of the inboard frame rails on their axle. 

In reality the axle section between the supports does nothing to help with axle bending, so supporting it in the center doesn't help. There really isn't a need for the axle tube between the supports at all, other than to reduce the risk of twisting the trailer frame. That's how these work:

https://timbren.com/blog/products-page/asr35hds11/ 

But even with outboard frame rails you can't get the wheel loads right under the frame members so with the Timbren axles you need a crossbar to carry the moment (torque) so you don't twist the trailer frame. You potentially have the same issue with your axle end supports but I think you're OK as is. A crossmember couldn't hurt though. 

The rubber in the axle tube ends won't do anything to support the steel tube, its way too flexible. The tube is very stiff, so the deflection at which it fails is pretty small, only about 0.2 inches IIRC. That's why a flat tube with no crown is a clear indicator of a failed axle. 

If someone really wanted to make up a welded part that would solve the axle bending problem without replacing the axle itself, I think the best approach would probably be to fabricate a tube the same length as the axle tube that attaches to the frame and axle at the existing locations and also extends outboard to provide a vertical downward support for the axle ends. It wouldn't need to be clamped to the axle tube at the ends (or the center) to work.  

The part would also act as a replacement for the riser kit. Call it an axle reinforcement/riser kit combo. If you made it up from the same tube section as the axle it should roughly double the load capacity of the existing tube and provide about the same additional height as the existing riser kit. 

So I vote that marwayne and Toyanvil get together and make a kit using offgrid's design and I'll be one of the first to buy one.  [note to marwayne:  My dad moved from northern Minn. to avoid the kind of cold you have right now and ended up being nice and warm in Bakersfield.  You could head down there for a couple months in the winter as we go to Colombia, to escape the cold. ]

Marwayne, I understand you're not an engineer. I am, and all I'm trying to do is help.  

Your point about Toyanvil's design is valid, it does create a moment (torque) on the riser. That's why I suggested he bring the diagonal load up as high as possible to keep the moment load on the riser down to minimum. He did that and I think he'll be OK, but I didn't run the numbers. In my design, all the forces are vertical so its not a problem.

What GlueGuy and I are pointing out is that your design doesn't adress the underlying problem which is a cantilever which is too long. The bending stress on the axle tube starts at zero out at the wheels and reaches a maximum at the axle supports. The longer the distance between the wheel and the support point (the cantilever length) the higher the bending stress is. 

If the bump loads on both wheels are the same (say you go over a speed bump too fast) then the stress on the axle tube is the same between the supports as it is at the supports. Changing the distance between the supports  (which is what your design does by adding an additional support point in the center) doesn't change the bending stress on the tube. So, you will still reach the yield stress point of the steel at the same bump load as if you didn't add your support. Once you hit yield the steel tube will not return to its original curvature and you'll have negative camber. 

I hope that all makes sense. 

Re testing to see if any one of these solutions solves the problem is not really practical or necessary. You'd have to set up a controlled experiment where you overloaded your trailer axle with the reinforcement by an known amount, and show that everything is OK. Then remove the reinforcement and load it to the same point and show that the axle fails. Oops, now you have a bent axle  .  

No one is going to actually do that and its not necessary. The engineering of cantilever beams is very well understood. Buildings are designed using these same formulae (no testing needed)  and occupied by thousands of people safely. 

If the middle tube section has no 'give', the deflection will be transferred outward, or so it seems to me. 

i think there is a misunderstanding here of the forces involved. As GlueGuy says, the issue is that the cantilever created by the inboard axle mounting points to the frame is too long. Toyanvil's and my approaches adress this by supporting the axle tube outboard of those mounting points, reducing that cantilever load on the axle tube. 

Unfortunately, Marwayne's approach does not provide this support. 

Here is the load diagram and the stress equations (just think of it as flipped upside down).

Originally posted by marwayne I did the same as Toyanvil. Toyanvil stated that nothing is attached to the frame but to the risers, that's what I did.Toyanvil attached on the outside, I attached it on the inside.

It looks like yours is the middle ground between the other two designs.

It will be interesting to read updates on how each of the three designs work in real life.