Axle Overload After Pallet Repositioning
A 4x2 tractor with a tri-axle semi-trailer is presented at a weighbridge before a 420 km run. The steer axle is 7,420 kg against a 7,500 kg limit; the drive axle is 11,600 kg against an 11,500 kg limit; the trailer axles are 12,850 kg against 13,000 kg. Gross combination weight is 31,870 kg against 32,000 kg. The load is 26 pallets of bagged resin, 18,000 kg total, evenly stacked but with a 450 mm gap behind the headboard. The tractor wheelbase is 3.6 m and the kingpin-to-trailer-axle distance is 9.0 m. The driver says the load was 'pushed back' to close the rear doors. The vehicle is due to leave in 30 minutes. A colleague suggests moving two 500 kg pallets from the rear row to the headboard gap.
1. Evaluate the weighbridge figures and the colleague's suggestion. Include an approximate load transfer calculation and state whether the vehicle can leave as loaded.
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The vehicle cannot leave as loaded: the drive axle is 100 kg over its limit. The steer axle has only 80 kg margin and the trailer axles 150 kg, so any correction must be small and controlled.
The colleague's suggestion is unsafe. Moving 1,000 kg from the rear row to the headboard could move it roughly 10 m forward. Using the tractor wheelbase, the approximate steer-axle transfer is 1,000 × 10 / 3.6 ≈ 2,780 kg. That would put the steer axle far over 7,500 kg and unload the drive axle excessively. It would also leave the rear of the trailer light and unstable.
A better correction is a modest rearward move within the trailer to transfer load from the kingpin to the trailer axles. Moving 400 kg about 3.0 m rearward changes the kingpin load by approximately 400 × 3.0 / 9.0 ≈ 133 kg. Drive axle becomes about 11,467 kg, trailer axles about 12,983 kg, and steer remains unchanged. Re-weigh before release.
2. Outline the load-restraint checks and documentation required before the vehicle is released.
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The 450 mm headboard gap is a restraint problem, not just a load-distribution problem. Under braking the pallets can slide forward, change axle loads, and damage the headboard. The gap should be closed with rigid dunnage or the load restrained so forward movement is prevented. Check that pallets are intact and stacked square, that lashings or straps are rated for the load, and that their angles and attachment points are suitable. Use edge protection where straps contact sharp corners. Confirm the load cannot move sideways or rearward.
After repositioning, re-weigh each axle and the gross combination. Record the revised load plan, the weights, the restraint method, and the driver's instructions. The driver should understand that the load was repositioned because the drive axle was overloaded and that the headboard gap must not reopen. If the correct distribution cannot be achieved with the available pallets, reduce the load or use a different vehicle.