Heavy Vehicle and Load-Specific Knowledge (Code 3)
What this domain tests
This domain tests the numbers and the physics: what the vehicle may legally weigh, how the load must be spread and secured, and how a heavy combination behaves differently from a car.
Mass vocabulary
- Tare: the empty vehicle's mass.
- GVM: gross vehicle mass, the maximum the vehicle itself may weigh.
- GCM: gross combination mass, the maximum for vehicle plus trailer.
- Payload = GVM − tare. Every axle also has its own rating, so you can be under the GVM and still overload an axle.
Loading and securing
Keep the centre of gravity low and centred, with the heaviest items over or just ahead of the drive axle. Distribute so no axle exceeds its rating. Secure with rated straps, chains and tarpaulins, then re-check the lashings shortly after moving off. Mark projections and check total height, because a high load changes clearance and raises rollover risk.
Air brakes and descents
Let pressure build before moving. The low-pressure warning typically sounds around 4,5 bar, after which the spring brakes apply. On a long descent, select a low gear before the crest, use the retarder or exhaust brake, and brake in short firm applications rather than riding the pedal, which fades the brakes.
Worked example
A truck with a GVM of 15 000 kg and a tare of 6 000 kg is loaded with 10 000 kg. Reasoning: maximum payload is 15 000 − 6 000 = 9 000 kg, so the load is 1 000 kg over the GVM and illegal before axle ratings are even considered. Action: offload 1 000 kg and re-check each axle.
Traps
Confusing GVM with GCM; ignoring axle limits; skipping the coupling check on an articulated rig; descending on the brakes alone.