sh410 wrote:
My question is how was the GVWTR of 18000# established?
Should it be something less?
Or is it simply the sum of the axle rating plus something for the hitch weight.
It certainly can't be the tire capacity.
Here are the definitions. As an engineer, I believe that like tires and their load capacity, axles as well as frames and hitches all have their own maximums and formulas which engineers use to generate the specific numbers on the vehicle data sheet.
GAWRGVWRRegulations require that the sum of the load capacity of all the tires on any axle exceed the GAWR. This requirement can be meet with as little as 1# but usually on trailers the safety margin selected by the RV trailer mfg seems to be closer to 100# while on motorhomes the safety factor seems to be much larger.
GVWR is usually less than the sum of Front GAWR + Rear GAWR for motorized units and less than the sum of the axles + pin loading max for trailers. This is one reason so many of the "tire weight and inflation police" that lurk on these threads, seem to harp on the idea of getting the actual loading for each tire. The other reason is that for 95% or more of the units on the road the side to side distribution is not 50/50 and the axle to axle load distribution is not 50/50.
