OP wrote:
What I don't understand is, why isn't vehicle GVWR the sum of adding the 2 axle ratings?
Some state size and weight regulations may read the sum of the FAWR/RAWR is it a trucks GVW(R).
The vehicle manufacturer sets GCWR/GVWR/FAWR/RAWR. No one knows how its determined and it can change from year to year.
GCWR number can be changed by a simple gear change/tranny change/ETC and isn't id'd on the truck anywhere nor is it required to be.
GVWR is required to be on the trucks certification placard but isn't used legally to determine how much load the trucks axle/tires may carry.
The GAWRs are also required to be on the truck certification placard and is used to determine how much load a trucks axle/tires may carry. The GAWRs also determine the size of the brake system the mfg has installed on the vehicle.
Good point on 2500 vs 3500 SRW differences being tires/wheels and heavier rated rear springs.
