Originally Posted by Floating Cloud
What you first need now is the GVWR, then the max loaded weight allowed for the trailer and then the GCWR, all given by the manufacturers. You add the first two to make sure you will not exceed the third (GCWR).
Close, but not quite. Neither the tug nor the trailer needs to be loaded to its Gross Vehicle Weight Rating
(GVWR), so you only need to add the tug's curb weight
(not GVWR) to the trailer's equipped but empty weight
, and compare that total to the tug's GCWR: whatever is left over is your allowance for driver, passengers, cargo (in tug and trailer) and water etc. in the trailer tanks.
If you use the gross weight ratings (GVWR), you will be considering the worst possible case; you may choose to do this, but it is not necessary.
The tug's curb weight and the trailer's empty weight can be from manufacturer's specs or, preferably, by actually weighing.
In addition to GCWR, the limits imposed by the tug's GVWR, Gross Axle Weight Ratings (GAWR, front and especially rear), and hitch weight limit all need to be considered; however, I agree that GCWR is a good place to start.