The trailer builder sets a target figure to build to. That figure is the trailer’s ultimate GVWR. Once established, other safety values are mandatory for the builder to achieve in order to provide NHTSA figures certified by the builder, as correct, and displayed on a permanently attached federal certification label (found on the LH forward external section of the trailer).
NHTSA writes safety instructions (regulations) containing minimum safety values for the trailer builder to follow. They are in a series of numbered regulations grouped together in the Federal Motor Vehicle Safety Standards (FMVSS) documents. Those that are required to be on the certification label are, GVWR, all GAWRs, recommended tire and rim sizes appropriate for that fitment and the recommended (correct) tire inflation pressures.
Within the FMVSS other instructions are found, in this case 571.110 applies. One of the instructions is the establishment of a hitch weight that must be published. Its part of the trailer's certification process and is used one time only. Its weight is added to the total GAWR weight. The sum must equal or exceed GVWR.
When a prospective buyer does a PDI on a trailer they should always compare the items on the trailer with the items on the certification label. If all items are satisfactory and the trailer is sold to that buyer the trailer’s safety is in the hands of the consumer.
As an owner, weight, balance and proper tire maintenance are of up most importance. Loading a trailer beyond its GVWR is probably going to overload the tires and axles and sometimes even the rims.
When we look at how close our axles are normally spaced its quite common to assume they are carrying equal weight. Well that’s just not so and that axle or single tire that is carrying the most weight is probably destine for trouble. Remedy; Pack your trailer for a trip and then go to some scales and see what and where the weights are.
USN - RET - PDRL
DOD - RET - Journeyman Aircraft Mechanic
SSA - RET