Our three-axle truck has a manufacturer's GVWR of 54,600 lbs. and 48,600 lbs. under the FWHA bridge formula. It is registered for 47,000 lbs. The curb weight (all equipment on board, fuel and water tanks full, no freight) is about 34,000 lbs., leaving a theoretical payload of 13,000 lbs.
The 54,600 lbs. number comes from 20,000 on each rear axle and 14,600 lbs. on the front axle. The 14,600 lbs. front axle was specified when the truck was built.
As you are finding out, straight truck weight and axle specs vary widely among trucks. When straight truck owners get into trouble with these specs, it is most often when too much weight falls on the front axle, such that legal front axle limits are exceeded. On poorly spec'ed trucks this can happen even when the truck is empty.
Pay attention to the placement of your rear axle(s) and lift axle if you get one. A single rear axle can carry 20,000 lbs. under the bridge formula. Tandem axles ("twin screws") can carry 34,000 (17,000 each). The closer the rear axle is to the front of the truck, the less weight the front axle will bear.
Lift axles come as pusher axles (positioned in front of the drive axle) and tax axles (positioned behind the drive axle). They are more effective when placed in front of the drive axle.
As jjoerger said, the bridge formula is important. It is explained
on this web site and very well explained in the front of the Rand McNally Motor Carriers' Road Atlas.
As you think through your straight truck options and trade-offs, you may find information about
our truck specs helpful. I posted this not to suggest that anyone should buy or build a truck like ours but to help people think the issues through.
