Australian axle group limits
| Axle group | General Mass Limit |
|---|---|
| Single steer axle, single tyres | 6.0 t |
| Single axle, dual tyres | 9.0 t |
| Tandem axle group, dual tyres | 16.5 t |
| Tri-axle group, dual tyres | 20.0 t |
| 6-axle semi-trailer combination | 42.5 t gross |
| 9-axle B-double | 62.5 t gross |
These are the national General Mass Limits under the Heavy Vehicle National Law. Western Australia and the Northern Territory have their own heavy vehicle laws with similar limits. Higher Mass Limits apply only to accredited operators on approved routes.
How to estimate the load on each axle group
Treat the deck as a beam resting on its supports. For a semi-trailer, the supports are the kingpin (which passes load to the prime mover) and the trailer axle group. Each item's weight is shared between the two supports in proportion to how close it is to each one: an item right over the axle group puts almost all its weight there, and an item halfway between puts half on each.
Add up every item's share for each support, add the tare, and compare each total with its limit. The kingpin share is then split between the steer and drive axles by the same method along the prime mover.
- Measure the position of each support (kingpin and axle group centres) from the front of the deck.
- For each item, find its centre of gravity along the deck.
- Split its weight between the two nearest supports by distance.
- Total each support, add the vehicle's tare share, and compare with the limit.
How to fix an overloaded axle
- Drive or steer axle over: move heavy items rearward, toward the trailer axle group
- Trailer group over: move heavy items forward, but check the drive group after
- Swap heavy and light items of the same footprint so the layout still fits
- Spread heavy items along the deck instead of grouping them
- On a B-double, move weight between the A and B trailers
- If no arrangement works, the load is too heavy for the vehicle: split it
Why it matters
Overloaded axles damage roads and tyres, lengthen braking distances and can make steering light. Under Chain of Responsibility laws, the consignor, loader and scheduler can all be responsible for a mass breach, not just the driver. Checking axle loads when the load is planned is far cheaper than finding out at a weighbridge.
Axle checks in TRUXE
TRUXE estimates the load on each axle group from where every item sits in the plan, including multi-trailer combinations, and flags any group over its limit. A rebalance option swaps same-size items to bring the worst group down while keeping the layout valid, and shows the before and after.
Frequently asked questions
What is the axle weight limit for a tri-axle trailer in Australia?
20.0 t for a tri-axle group with dual tyres at General Mass Limits. Higher Mass Limits allow more for accredited operators on approved routes.
Can a truck be overloaded if it is under its gross mass?
Yes. Each axle group has its own limit, so poor placement can overload one group while the total is legal.
How do I work out the weight on the drive axles of a semi?
Work out the load at the kingpin by sharing each item's weight between the kingpin and the trailer axle group by distance, then share the kingpin load between the steer and drive axles the same way along the prime mover, and add tare.
Does TRUXE replace a weighbridge?
No. TRUXE estimates axle loads when the load is planned so you can fix problems before loading. Actual axle weights depend on the real vehicle tare, fuel and load, so weigh the vehicle where the law or your site requires it.