Cargo Securement and Weight Distribution
Cargo securement and weight - what is tested
Questions cover weight ratings, load placement, sliding the fifth wheel and trailer tandems, and the securement rules for tiedowns.
Weight limits
- Know four ratings: GVWR (vehicle), GCWR (combination), GAWR (axle), and tire load limits. The lowest one governs.
- Federal Interstate limits: 20,000 lb per single axle, 34,000 lb per tandem, 80,000 lb gross. Michigan uses its own axle and bridge formulas and permits heavier combinations on some routes, so scale the load and check the permit.
- Weigh each axle group: steer, drive, trailer, and gross.
Load placement and axle loading
- Put heavy freight on the floor, centered, over the drive axles - not at the trailer's rear, where it unloads the steer axle and makes the rig wander.
- Sliding the trailer tandems rearward moves weight off the drive axles and onto the trailer axles. It never changes gross weight.
- Sliding the fifth wheel rearward shifts weight onto the steer axle.
Securement
- The combined working load limit of the tiedowns must be at least 50% of the cargo weight.
- The system must resist 0.8 g forward, 0.5 g rearward, and 0.5 g sideways.
- Use at least one tiedown every 10 feet of cargo when side rails are used, and more for short, heavy items.
- Cargo must not block lights, plates, or the fifth wheel; doors must close and latch.
Worked example
Scale ticket: steer 11,000 lb; drives 34,600 lb; trailer 33,200 lb; gross 78,800 lb. Gross, steer, and trailer are legal, but the drives are 600 lb over 34,000. Sliding the trailer tandems rearward transfers weight from the drives to the trailer axles, which have about 800 lb of room. Move the tandems, re-scale, and confirm every axle is under its limit before moving.
Traps
- Confusing GVWR with GCWR.
- Thinking tandem or fifth-wheel adjustments change gross weight.
- Adding the working load limit of only some tiedowns instead of the whole system.
- Loading heavy freight at the trailer's rear and losing steer-axle weight.