About To Tow A Vehicle?

2 vehicles towing on a snow tracks.

Understand the Acronyms & Terms For Weights on Your Vehicle I.D Plates

With the holiday season fast approaching many of us are going to take a vacation and with that the prospect of towing, yet do you know how to identify the correct terms to ensure a safe journey?

Thanks to the Motor Trade Association of WA (MTA), we have a guide to breaking it all down.

TARE Mass (Vehicle or Caravan)

TARE Mass is the amount your vehicle or caravan weighed as it left the production line as specified by the manufacturer – including fluids like fuel and coolant in the tow vehicle, and with no payload or dealer added accessories. This does not include water in the tanks or gas cylinders in the caravan.

Aggregate Trailer Mass (ATM)

Aggregate Trailer Mass is the TARE mass of your caravan plus its maximum payload. It is the maximum your caravan is allowed to weigh in transit. This is a rating set by the manufacturer and cannot be exceeded. Imagine your caravan sitting on a weighbridge not attached to a vehicle.*

ATM = TARE Mass (Caravan) = Maximum Payload

Gross Vehicle Mass (GVM)

Gross Vehicle Mass is the maximum weight the vehicle can weigh fully loaded, including the weight of the car, passengers and luggage. This is a rating set by the car manufacturer. GVM also includes tow ball mass when the car is hitched to a caravan or trailer.*

GVM = Vehicle TARE Mass = Maximum Payload


Payload is any mass you add to the vehicle’s TARE mass. For tow vehicles, this includes passengers, luggage, aftermarket accessories and the tow ball mass (TBM). Payload does not include standard specification set by the manufacturer such as fuel and coolant.*

Maximum Payload (Caravan)

Maximum payload is the maximum weight that can be loaded into the caravan for towing. This does not include the weight of people inhabiting the caravan while stationary but does not need to take into account water, gas and any accessories that you or the dealer have added to the caravan since acquiring it. This rating is set by the manufacturer and cannot be exceeded.*

Payload = TARE = ATM

Gross Combined Mass (GCM)

The gross combined mass is a combination of the maximum allowed mass of the trailer and the maximum allowed mass of the vehicle.

GCM = Gross Trailer Mass = Gross Vehicle Mass

Tow Ball Mass (TBM)

This is not always accurate as loading the caravan can drastically change the TBM. TBM is the mass exerted on the tow ball by your caravan. TBM should be checked after the caravan has been loaded to ensure it does not exceed the caravan or tow vehicles specifications. When your caravan is hitched, this mass is included in your tow vehicle’s payload or GVM*. Changing the location longitudinally or heavier items will increase or reduce TBM.

Gross Trailer Mass (GTM)

GTM is the maximum weight of the loaded caravan that can be supported by its wheels, not counting the portion supported by the car when hitched. This rating is set by the manufacturer and cannot be exceeded.*

Back view of a caravan for vehicle towing.

GTM = ATM – Tow Ball Mass (in most cases)

Generally, you’ll find the TARE, TBM, GTM and ATM stamped on the vehicle identification plate. With exception to TARE, as long as you do not exceed any of these figures, you should not have any problems towing your caravan. Keep in mind the ‘weakest link’ – meaning you cannot exceed the maximum specification of any component, caravan, tow vehicle, towing apparatus, wheels, tyres, axles and chassis.

*Modification can be made to the suspension to increase the manufacturer’s specifications if applicable and approved by an engineer and relevant Department of Transport. Modifying vehicles GTM, ATM, GVM is not always possible due to some components maximum capacity being exceeded or approval not being granted.

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