Weight Distribution and Trailer Handling
Ratings that matter
A combination must be legal by gross combination weight rating (GCWR), each axle's rating, tire rating, and the bridge formula. The kingpin load is carried by the tractor's drive axles and fifth wheel; the steering axle needs enough weight to steer but not more than its rating. Typical limits are 12,000 lb on a steering axle and 34,000 lb on a tandem, but always use the vehicle's placard.
Moving weight
- Slide the fifth wheel rearward to move weight off the steering axle and onto the drives.
- Slide the fifth wheel forward to add weight to the steering axle.
- Slide the trailer tandems forward to add weight to the drive axles and remove it from the trailer axles; slide them rearward for the opposite effect.
- Keep side-to-side weight balanced; a heavy side increases rollover risk and tire failure.
Worked example
Scale: steer 12,500 lb (limit 12,000), drives 31,000 (limit 34,000), trailer 32,000. The steer axle is 500 lb over. Move the fifth wheel rearward in small increments, then reweigh. The trailer's kingpin load shifts onto the drive axles, reducing the steer axle while staying under the drive rating.
Traps
Believing that legal gross weight means legal axles; sliding tandems with a loaded trailer without checking clearance; forgetting that fuel and driver weight count; overloading the steer axle to fix a trailer axle problem.