What is payload capacity? Axle weight and load distribution calculation

What is payload capacity

Payload capacity is the maximum load weight a vehicle can carry. It is stated on the vehicle registration, and exceeding it is subject to a fine.

The calculation is simple:

maximum laden weight − vehicle's tare = payload capacity

Example: a tractor-trailer combination with a maximum laden weight of 40 tonnes and a tare of 15 tonnes has a payload capacity of 25 tonnes.

Tare varies by trailer type and equipment. A refrigerated trailer is heavier than a curtain-sided one because of its cooling unit, and carries less load at the same maximum laden weight.

Axle weight is a separate limit

This is the point most often overlooked. There are two separate limits, and each is checked separately:

1. Total weight — the vehicle as a whole
2. Axle weight — the load falling on each individual axle

The total weight can stay under the limit while an axle overload still occurs. The cause is load distribution: if a heavy, compact load is concentrated in one section of the trailer, the axles in that area exceed the limit.

A weighbridge measures both the total and the per-axle figures. This is why, for heavy loads, a stowage plan is prepared in advance: the load is distributed evenly along the trailer and the centre of gravity is kept in the middle.

The same logic in a container

Container transport involves two separate capacities, and they get confused.

The container’s own limit: the maximum gross weight is shown on the CSC plate. Deducting the container’s tare from this gives the load that can be carried.

The limit on the road leg: the vehicle travelling from the port to the warehouse is subject to its own payload capacity and axle limits. Even if the container’s capacity has not been filled, the road limit can become binding earlier.

There is also a common assumption error: a 40-foot container does not carry twice the load of a 20-footer. The two containers’ maximum gross weights are close to one another; a 40-footer offers double the volume, not double the weight.

The consequence is this: for dense loads (steel, ceramics, liquids, marble), using two 20-foot containers instead of a single 40-footer is often necessary. A 20-foot container that looks empty by volume can be full by weight.

A numerical example

Suppose a container has a maximum gross weight of 30,480 kg and a tare of 2,200 kg.

30,480 − 2,200 = 28,280 kg  → theoretical load capacity

However, if the destination country’s road weight limit requires the vehicle carrying this container to stay within a total of 40 tonnes, and the tractor plus chassis tare is 15 tonnes:

40,000 − 15,000 − 2,200 = 22,800 kg  → practical load capacity

If the 5,480 kg difference is not accounted for in planning, the load is held at the port or part of it has to be unloaded.

Common mistakes

Trusting the registration figure without calculating axle distribution. Staying under the total limit is not enough.

Confusing container capacity with the road limit. The two are calculated separately, and the smaller one governs.

Assuming a tare value. Trailer and container tare varies; the actual value is read from the registration and from the marking on the container door.

Treating VGM as independent of this calculation. The declared gross weight must be consistent with the actual loading plan.