Originally Posted by Ford Apostate
I thought all the different standards were with how they figured tow ratings. I would have thought payload rating was pretty straight forward or are you referring to how they figure GVWR? I can't find a good explanation of how that is done.
The GVWR is the maximum for the vehicle regardless of any upgrades made to the suspension/tires etc.
One of the major factors for GVWR is the braking system The DOT determine braking distances that must be adhered to. That being said they also set the standards for trailers.
So for an interesting example.
Say you had any one of our trucks with a single axle trailer loaded with yard mulch.
Truck had one driver and a full tank of gas = 6200 lbs
Trailer gross weight was 3,500 lbs tounge weight = 350 lbs.
Adjusted weight of the truckis now 6550. ( Tounge weight+vehicle)
Gross combined weight is 10,050 lbs.GCWR
These # are all within spec and reasonable and the braking system needs to be able to stop this safely.
Same truck 6200lbs
Dual axle travel trailer with electric brakes 6000 lbs tounge weight 350 lbs
Adjusted truck weight 6550 (same as before)
Gross combined weight is now 12,550 lbs.
By law that 6000 lb TT would have supplmental braking as such it would be easier on the truck than the first case from a stopping standpoint. Fuel economy would be worse. More weight more work.
So why can't I carry the additonal weight in the truck if the brakes can handle it in the first palce. More than likely it the individual axle weight rating from those suppliers. I'm an old Ford guy and for those that are familar with them there were two 250's. The heavy duty with solid front axle and the wishbone front end. The bearing set difference between the two was one tell tail on the difference in load handling ability amoung others.
The point that I was trying to make is there are several factors dertermining the spec's for a vehicle. If you always assume you have a supplemental breaking system then you would be unsafe in the first example.
Hope I didn't add more mud to the water.