What’s Wrong With This Picture?

Learning good trailer construction by examining bad is a great way to focus on details.  This photo shows 4 points of “less that careful thought” in the way the trailer is built.  Can you pick them out?

A Do-It-Yourself Trailer Build

This trailer caught my attention because it’s a creative example of a Do-It-Yourself trailer build.  In general, the idea is great, and the trailer construction is pretty good.  However, looking a little closer, there are some details that can use some better attention.

I’m pretty sure this trailer started life as a mobile home foundation.  You can tell that by the size and configuration of the I-Beams as well as the cross members.  At some point it was drastically shortened and reconfigured into a 16′ flatbed utility trailer — and it looks really beefy.  They did a nice job on most of the trailer construction, but missed a few key pieces in the design.  Unfortunately, these key points also affect the way the trailer performs.  Let’s have a closer look.

Trailer Construction Example

Trailer Construction Example

Can you pick out the 4 issues with trailer construction in the photo above?

1.  Contact
Trailer Axle Equalizer Contact
Close Up View Of Trailer Construction With Equalizer And Spring Contact On The Trailer Frame

The most obvious issue, is contact of the spring eye with the trailer frame.  That’s not a happy situation as it defeats the purpose of load sharing with the equalizing rocker.  (There are some good illustrations in the Equalizer Action article.)

There is more wrong in the trailer construction than I was able to quickly diagnose.  While just looking at it, because the trailer is sitting almost level, it gives the impression by the positioning of the equalizer that the tongue is really high.  It’s not.

I suspect one of the axles is not centered on the leaf spring, or there is a stack spacing issue.  It could be as simple as poor bracket spacing, but I could be wrong.  Anyway, just looking at the equalizer rocker, one issue for contact is the height of the bracket which the rocker pivots on.  It’s the same bracket for the stationary ends (front and back) for the springs.  Even if everything else was sitting properly, that short bracket does not allow the rocker to pivot enough.  This customer story, and solution, is so similar.

2.  Protection

The second issue should also be fairly obvious.  Notice the rust on each of the welds where the spring mounts connect to the frame.  When the welder finished, he either did not paint the welds adequately, or he did not clean the welds prior to painting.  Of course, this is only a problem if you want the trailer to last.

3.  Loads

The third issue may not be so obvious.  Look at the material used for the I-Beam.  These are very stout axles that were originally on a mobile home.  The suspension is also very stout (meaning high load capable).  Why then, are the thick brackets which carry big loads welded directly to the thin web of these I-Beams?

Trailer Construction and Frame I-Beam End ViewYou can get a better feel for this by looking at the trailer construction at the rear of the trailer, and by reading this article about stress.

The solution?  We recommend some added material at the point of connection.  A simple strip of steel (3/8″ or 1/2″ thick) between the I-Beam and the suspension brackets (extending 6″ beyond the brackets front and rear) will distribute load stress from the spring connections to the I-Beam much better.  It’s not that the beams are weak, it’s the high local loading.  Such a strip will also minimize welding in the high stress areas of the main beam.  Remember that welding changes the local molecular structure which weakens the beam.

4.  Purpose

I may get some argument about the 4th issue.  I have seen success, and I’ve seen bad hiccups using mobile home axles, wheels and tires.  You can spot these easily.  The wheel connection to the axle at the inner perimeter of the wheel is a characteristic of mobile home axles.  The issue is they are hard to balance, and they often have other weird problems.  Most tire shops won’t touch them, so if you need service, that can be a real problem.  If you have the choice, it’s usually better to use purpose built “trailer” axles.  Especially if you plan to use it a lot.

As an interesting side note, the owner says this trailer has an obnoxious vibration starting around 38 mph, then gets worse going faster.  To me, that sounds like a classic tire balance or rim alignment issue.  The owner has taken the trailer to several places trying to get it fixed, but most won’t touch it.  It may also involve the spring and equalizer issues, yet I think it’s all related in the trailer construction.


I applaud the builder of this trailer, though they need a little more research — like perhaps Axles 101.  They took a mobile home frame that was likely trash, then repurpose it as a heavy duty, deck over utility trailer.  I think it’s awesome.  With some revisions, this has great potential.  I don’t know how old it is, or anything about it’s life, but thank you for letting us use the example.

For a lot more information about trailer construction and design examples, please read the full set of articles on “What Makes A Good Trailer?”  We wish you the best of success.


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