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Estimating Axle Capacity Based on Axle Beam Diameter  


I am looking at a homemade flatbed trailer. The set up is gooseneck hitch, 25’ deck, main framing is 6”channel, 3” axles with 8 lug hubs, I can not find a tag or plate on the axles. It is currently registered as 10k GVWR and I would like to upgrade it if the trailer is built for more because I haul logs. Any help on further identifying what this trailer should be rated at would be great. Thank you.


Expert Reply:

An axle's diameter can provide at least an approximate idea of its actual weight capacity. 3-inch diameter axles are usually rated for 6K or 7.2K. This is reasonably consistent with the trailer's registered 10K GVWR.

We cannot tell you with certainty whether your trailer can be upgraded to a higher weight rating. The weakest link, the lowest-rated component on the trailer, will determine its maximum overall capacity. In truth this could be the tires, wheels, hubs, axles, suspension, frame or coupler. Only the engineers that designed the trailer know this for sure.

You might be able to find very similar trailer designs and see what their GVWRs are but there are no guarantees yours will have the same weight rating. Adding higher-capacity axles might increase GVWR but that would be the case only if the axles were the weakest link. You do not know how much safety margin was designed into the trailer and unless you have an engineering background I would be reluctant to load the trailer with any more weight than the 10K gross under which it is registered.

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