16th January, 2019

Educate yourself and avoid unwanted infringements!

TARE? GVM? GCM? ATM? …….WTF? What do all these crazy acronyms mean? If you are towing a Trailer of decent size, its vital to understand the industry lingo, but also what you can and can’t do within the weight restrictions applicable to your situation. Complying by maximum vehicle limits is not just for safety – its the law. The legislation is controlled at state-level, so there is subtle differences depending on which one you are driving in. If you are planning a multi-state journey, do your homework and look up what the requirements are for each state.


Terminology Decoder

Thank you to our friends at Caravan Clubs Queensland, who have provided us with the following information.

Tare Mass

The mass of a vehicle, measured unoccupied, with fluids at normal capacity aside from fuel, which is assumed at 10L.



The maximum load capacity of the tow vehicle + trailer as specified by the respective Manufacturers.


Gross Vehicle Mass (GVM)

The maximum laden mass (including payload) of a motor vehicle/tow vehicle as specified by the Manufacturer.


Aggregate Trailer Mass (ATM)

Total mass (including payload) of a Trailer when carrying the maximum load as specified by the Manufacturer.


Gross Trailer Mass (GTM)

The mass transmitted to the ground by the ‘Axle(s)’ if the tracker when coupled to a tow vehicle and carrying its maximum load.


Tow Ball Mass (TBM)

The weight imposed on a tow vehicles tow bar by the coupling of a trailer. (Tow Ball Mass = Aggregate Trailer Mass – Gross Trailer Mass, or ATM – GTM)


Gross Combination Mass

= Gross Vehicle Mass + Gross Trailer Mass, or GVM + GTM


But Weight, There’s More…


Other aspects to consider include:

  • Tow Bars – Ensure they are rated high enough to suit your Aggregate Trailer Mass (ATM). The Tow Bar Manufacturers must label the maximum rating on the tow bar by law.


Make sure you have the right tow bar for the job!

  • Safety Chains – These are compulsory no matter what size trailer you have. Trailers under 2500kg ATM must be fitted with at least one safety chain. Trailers 2500kg ATM+ must have two safety chains. Chains must have a rating at least equal to the trailer ATM. The link or d-shackle between the chain and the vehicle must have the same rating as the chain.