Looking forward to buy a new cargo trailer so I could convert it to a camper. I was wondering, when I check the axles should I see them perfectly straight with the naked eye?

Is there a way I could make sure the axles/frame won't cause problems in the long run?


No, axles should not be bent. To double-check you would need a known straight-edge, like a level or a "square" (which is actually shaped like an L), and hold that up against the axle(s) If you see light between the two then the axles are not 100% straight. The measuring tool should be pretty long, approximately the same length as the axles.

If this measurement technique is not possible, you may be able to measure from the ground to the axle tube at several intervals. This might reveal any discrepancies but they would have to be significant enough to measure.


No, bent axles are definitely a bad sign.

If you're looking for a cheap and cheerful way to check for straightness, get a laser pointer. If you set it next to axle on one end, you can run a reflector right down the axle and see that the dot isn't moving relative to the hopefully straight axle.


Apparently, yes in some cases.

According to eTrailer, an online merchant of trailer related items:

Trailer axles typically have the bow ... in them to help compensate for the vertical load they bear and still have proper wheel camber. This way when the load is put on them the axle will flatten out and the wheels will be aligned properly.

Square axles are a bit of a wild card though as they aren't as standard as the round tube axles. I have seen totally straight ones and I have seen curved ones.

The purpose and effect of this curvature is further elaborated in an Eastern Marine article:

Most trailer axles are designed with a “bend” in the tube that will deflect when the load (weight of the trailer) is applied. This will theoretically bring the trailer wheel camber toward a 0 value that is the best setting for most trailer applications. This will allow the tires to wear evenly and allow the longest tread life. ...

Both Sprung axles and Torsion axles typically are built with a slight positive camber but custom axles can be specified with or without camber. A trailer that runs long distances without a load may be better without axle camber. An example of this might be a long distance boat transport trailer.

As to whether the bend would be visible: at minimum if you held a straightedge up to the axle (long level for instance) it should be visible. It may be hard to detect otherwise, particularly because you often can't get a good unobstructed view of the axle.

Just because some axles have deliberate curvature doesn't mean all bends are good! The axles the articles are describing would I think always have either a consistent, gentle curve or at least be symmetrical. This is distinguished from bends from damage which would almost certainly not be symmetrical (left-right) and could show other signs of proximate damage from whatever caused it.

(In my own experience, on the bent axle on my now wrecked utility trailer the bend occurred at a relative weak point - where the wheel / hub spindle met the thicker part of the axle.)

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