Loads, weights, dimensions and securing
What this domain tests
This domain tests whether you can load a tractor-trailer legally and safely: maximum dimensions, registered weights, axle loads, payload and load securing. The exam often uses a simple weight calculation and a load that could obscure lights or fall off.
Dimensions and weights
- General maximum dimensions are about 2.55 m width, 4.0 m height and 18.75 m for a vehicle combination, unless a special permit applies. Know your own combination's figures.
- The registered gross train weight is the maximum for tractor plus trailer plus load. The trailer's gross weight and the tractor's gross weight are separate limits; neither may be exceeded.
- Axle loads also have limits. A heavy load placed too far back can overload the trailer axle and reduce the tractor's steering axle load.
- Payload is not the same as the trailer's gross weight. Payload is gross train weight minus the unladen tractor and unladen trailer, and it may be further limited by axle loads.
Securing the load
Use straps, chains, nets or solid sides rated for the load. Secure against forward, backward and sideways movement. Do not rely on the load's own weight. The load must not obscure lights, reflectors, the number plate or the driver's view. Mark projecting loads clearly. Check the load again after a short distance.
Worked example
A combination has a permitted gross train weight of 7,000 kg. The tractor weighs 3,200 kg and the empty trailer 1,300 kg. The simple payload is 7,000 minus 3,200 minus 1,300, or 2,500 kg. You load 2,400 kg of grain, which is under the train-weight figure. But the trailer axle limit is 3,000 kg and the trailer's empty axle load is 1,000 kg, so the load on that axle must not exceed 2,000 kg. If the grain is placed too far back, the axle limit is exceeded even though the total is legal. Redistribute or reduce the load.
Traps that cost marks
- Confusing trailer gross weight with payload.
- Checking only total weight and ignoring axle loads.
- Leaving lights or the number plate covered.
- Using too few straps or straps with insufficient rating.
- Forgetting that a high load can exceed the 4.0 m height limit.