Axle load is one of those technical concepts that comes up frequently but is rarely fully understood. Yet getting it wrong — or ignoring it — can lead to an overloaded axle, a tyre pushed beyond its limits, unstable handling and, in serious cases, mechanical failure. Whether on a light trailer or a commercial vehicle, understanding how to calculate the load per axle and how to keep it within safe limits is essential before loading and setting off.
Axle load: definition and role in road safety
Axle load is the total mass acting on a given axle of the vehicle or trailer. It results from the weight of the chassis itself, the weight of the load being carried and how that load is distributed along the length of the vehicle.
This figure directly determines the mechanical integrity of the axle, tyre wear and the stability of the combination. An overloaded axle deforms, overheats and ages prematurely. It can also cause asymmetric tyre wear, heavier steering and a significant increase in braking distances. This is why every axle has a maximum permitted load, set by the manufacturer and regulated by law.
For road trailers, the load per axle is a critical value, directly linked to the trailer’s MAM. The closer a trailer is loaded to its MAM, the more precise axle load management needs to be. An axle undersized relative to the actual load it carries wears out far sooner than its rated lifespan.
Calculating axle load: the basic formula
Calculating the load per axle starts from a simple principle: the total laden mass of the vehicle is distributed across the axles. On a single-axle trailer, the entire weight rests on that one axle. On a twin-axle trailer, the load is shared between the two, more or less equally depending on where the load is positioned.
The basic formula is:
This formula applies when the load is evenly distributed along the trailer’s length. In practice, that is almost never the case: the position of the load shifts the centre of gravity and changes the actual distribution between axles. This is why each axle’s load must be checked individually, not just the overall total.
A practical example: a twin-axle trailer with an unladen weight of 300 kg carrying 900 kg of cargo. Total laden mass is 1,200 kg. With an even distribution, each axle bears 600 kg. But if the load is concentrated towards the rear, the rear axle may end up bearing 800 kg while the front carries only 400 kg — a potentially dangerous imbalance.
| Configuration | Total laden mass | Load per axle (even distribution) |
|---|---|---|
| Single-axle trailer, 750 kg MAM | 750 kg | 750 kg |
| Twin-axle trailer, 1,500 kg MAM | 1,500 kg | 750 kg per axle |
| Twin-axle trailer, 2,000 kg MAM | 2,000 kg | 1,000 kg per axle |
| Twin-axle trailer, 3,500 kg MAM | 3,500 kg | 1,750 kg per axle |
Where to find the maximum permitted axle load
The maximum permitted axle load is not a value to calculate: it is set by the manufacturer and recorded on the vehicle’s official documents.
For a motor vehicle, it appears on the V5C registration document. For a trailer, the value is shown on the tare plate fixed to the chassis, which states the MAM and the maximum load per axle. It may also appear in the manufacturer’s technical documentation.
Since September 2021, UK law was updated to allow drivers who passed their category B test on or after 1 January 1997 to tow trailers with a MAM of up to 3,500 kg — provided the combined weight of vehicle and trailer does not exceed 3,500 kg — without needing a separate B+E test. For trailers above that threshold, a full B+E licence remains required.
It is important never to exceed the maximum axle load stated by the manufacturer, even if the trailer’s overall MAM has not been reached. An individual axle can be overloaded while the trailer’s total weight stays within limits — simply because the load is poorly distributed. If you are unsure how many axles your trailer has or where to locate this information on the registration document, our guide on the number of axles on a trailer’s V5C shows exactly which fields to look up.
Load distribution and its effect on axle load
Load distribution is the most underestimated factor in axle load calculations. On a single-axle trailer, the entire load rests on the central axle: load position does not affect the per-axle load figure itself, but it directly determines the noseweight and therefore the stability of the combination. On a twin-axle trailer, the position of the load’s centre of gravity directly changes the distribution between the two axles.
The basic rule is to place heavier items above or slightly ahead of the axles, and to distribute weight symmetrically from side to side. A lateral imbalance creates unequal loading across the two sides of the same axle, leading to asymmetric tyre wear and unpredictable behaviour in bends and under braking.
- Place the heaviest items at the centre of the platform, above or slightly forward of the axles
- Check that the load is symmetrical on both sides of the axle centreline
- Avoid concentrating weight at the rear of the trailer, which lifts the front and destabilises the combination
Axle load and noseweight: the connection that matters
Noseweight — the downward force exerted by the trailer drawbar on the tow ball — is directly linked to how weight is distributed on the trailer. It is a separate figure from axle load, but it follows from it.
A noseweight that is too low (below 25 kg) indicates that the load is too far back: the trailer tends to lift the coupling, reducing rear-axle grip on the towing vehicle and creating a snaking risk. Excessive noseweight overloads the rear of the towing vehicle and compromises its handling. According to the UK Highway Code, the ideal noseweight is typically 5 to 7% of the trailer’s laden weight, within the limit stated on the tow ball or in the vehicle handbook — usually 75 to 100 kg maximum.
These figures apply regardless of the trailer’s MAM. For trailers operating close to the 750 kg threshold, the regulations on 750 kg GTW trailers and load limits set out how noseweight interacts with the broader legal framework. Checking noseweight and axle load together before any loaded journey is always the right approach.
In summary
Calculating axle load means dividing the total laden mass by the number of axles, then checking that no individual axle exceeds its maximum rated capacity as shown on the tare plate or registration document. This check must account for the actual position of the load, not just the total weight being carried. An axle loaded within the manufacturer’s specified limits, with a balanced load distribution, is an axle that lasts — and a combination that handles safely and predictably.