A load can be legal on gross weight and still overweight on the drives, because of where the pallets sit. This trailer load planner shows the floor layout, finds the load's center of gravity and estimates the weight on each axle group, so you can see a problem before the scale does.
How it is calculated
- Layout: pallets go nose to tail in the pattern that fits the most on the floor, the same way as in the pallet and linear feet calculator.
- Heavy pallets go either over the middle of the loaded floor or at the nose.
- Center of gravity (CG) = sum of each pallet's weight × its distance from the nose ÷ total freight weight.
- Trailer split: freight weight on the trailer tandem = freight × (CG − kingpin position) ÷ (tandem position − kingpin position). The rest sits on the kingpin.
- Tractor split: the kingpin load divides between steer and drives by how far the fifth wheel sits ahead of the drive axles, divided by the wheelbase.
- Empty weights of the tractor and trailer are added to each group.
The checks use 12,000 lb on the steer (a common practical limit), 34,000 lb per tandem and 80,000 lb gross, the federal Interstate limits for tandems and gross.
A worked example
26 pallets in a 53 ft van: 20 at 1,400 lb and 6 heavy at 2,000 lb, 40,000 lb of freight. With the heavy pallets over the middle and the tandem 40 feet behind the kingpin, the CG sits about 21.7 feet from the nose and the example rig estimates about 33,000 lb on the drives. Move the same 6 heavy pallets to the nose and the CG moves forward to about 20.2 feet; the drives climb to about 34,400 lb, over the tandem limit, with the same freight and the same gross. Try it in the planner and watch the drive line.
How to load a semi truck well
- Heavy in the middle, light at the ends. It keeps both tandems close to even.
- Fill side to side. Gaps let freight shift and change the split on the road.
- Leave the last row light so the doors don't take the weight on an incline.
- Scale, then slide. Moving trailer tandems shifts weight between drives and trailer axles; see the tandem slide calculator.
At a busy dry van trailer loading dock you rarely load it yourself. What you can do is ask for pallet weights on the bill of lading and check the plan before you sign. Common patterns are shown in 53 ft trailer loading patterns, and what changes when trailers are stacked on a carrier in stacked trailers. Hauling preloaded trailers is covered in power only dispatch.
The rig's empty weights in the planner are an example. Results are estimates; the scale ticket is what counts.
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