Axles

My question: why doesn't the manufacturer calculate this when they specify the cargo capacity? Perhaps because of the variables regarding exactly how much will the tongue weight affect the cargo capacity. But not doing so surely shortchanges the actual net cargo capacity of the trailer.

They already have. Two 4400 pound axles will not support a gross weight of 9000 pounds unless the tongue weight is calculated into the equation and deducted from the remaining coach weight. If the tongue weight is about 13 percent of gross or 1170 pounds and 20 percent of that is redistributed back to the trailer axles or about 230 pounds the math says 9000 gross minus 1170 for the tongue leaves about 7830 pounds for the coach on the axles plus the redistributed weight of 230 or so for a coach net no tongue weight of about 8060 pounds on two 4400 pound axles that have a combined rating of 8800 pounds. This works out to almost exactly the same number as the manufactuer provided and leaves no cushion.