by Collyn Rivers
Tow Vehicle & Caravan Weight Definitions
Australia’s key caravan weight definitions fully illustrated.
To tow safely and legally in Australia, knowing tow vehicle &caravan weight definitions is vital. Those shown here were valid as of June 2020. These definitions may change. New RV legislation may be announced in late 2020. It is not, however, likely to be enforced until 2022 or 2023.
The wording of each definition is that of RV Books. It is simpler than the technical originals. This enables you to focus on safety.
Weight limits are set by vehicle, trailer and tow equipment makers. These include limiting tyre and axle loads. Australia-wide legislation precludes your exceeding these limits.
You need to know your tow vehicle and trailers weight limits. These are normally on a compliance plate. If not, check the instruction manual. Or consult the manufacturer.
Do not confuse maximum permitted weights with actual weights. Maximum weights are set by manufacturers. (‘Mass’ can be seen as ‘weight throughout this article),
You can check actual weights on a certified weighbridge. Find your nearest weighbridge here
Tow Vehicle Weight Definitions
Gross Vehicle Mass (‘GVM’)
The vehicle’s maker sets Gross Vehicle Mass. It is the most it can legally weigh on public roads. The weight includes driver’s, passengers’, accessories, luggage and fuel. It includes the trailer nose weight. Exceeding Gross Vehicle Mass is illegal.
How to check your vehicle’s Gross Vehicle Mass
Drive the fully-laden tow vehicle and coupled trailer onto a weighbridge. Weigh the tow vehicle only.
Gross combination mass (‘GCM’)
Gross Combination Mass a tow vehicle and its laden trailer’s maximum allowable combined laden weight. It is set by the tow vehicle maker. The GCM includes the weight of all passengers, accessories, luggage. Furthermore, the weight of everything in the caravan. This includes gas and water. Exceeding Gross Combination Mass is illegal.
How to Check
Drive the fully laden tow vehicle and coupled caravan onto a weighbridge. Weigh both at once.
Maximum towing capacity
Maximum Towing Capacity is the maximum weight a tow vehicle may legally tow.
This applies to a tow vehicle (only). It is set by the tow vehicle manufacturer. The rating applies to any tow vehicle. It includes the weight of everything within that towed.
Many caravanners and vendors misunderstand this rating. Most trailers are used by tradespeople and military. These trailers rarely exceed 4 metres. Few exceed two tonnes laden. Caravans are a small segment of this market. As of 2020 they are covered by general trailer legislation. This, however, may change. Exceeding maximum towing capacity is illegal.
How to Check
Tow the fully laden caravan onto a weighbridge and (whilst coupled) weigh the caravan only.
Maximum towbar mass (weight)
Maximum towbar mass likewise limits towbar pulling weight. The maximum towbar weight may also be stipulated.
This term applies to the tow vehicle (only). It is a maximum weight rating set by the towbar manufacturer. You can check your laden caravan‘s maximum towbar weight on a weighbridge. Exceeding maximum towbar mass is illegal.
To check maximum towball mass, tow the fully laden caravan onto a weighbridge. Whilst coupled weigh the caravan only.
Maximum TowBall Weight (mass)
Towball mass is the down-force exerted on a tow vehicle’s towball. Or other forms of coupling. It is a weight rating. It must not be exceeded.
Vehicle and tow hitch makers set maximum towball weight. You must use whichever is least.
The caravan maker usually recommends towball weight. It is illegal to exceed it. Never reduce it.
How to Check
Weigh using towball scales directly under the coupling of the fully-laden caravan.
Aggregate Trailer Mass
Aggregate trailer mass is the maximum permitted laden weight of a trailer when not coupled to a tow vehicle. It is set by the trailer manufacturer. The ATM includes the weight of everything loaded. This includes water, gas and jockey wheel down-force. Exceeding the ATM is illegal.
How to Check
Tow the fully laden caravan onto a weighbridge. Lower the jockey wheel. Disconnect the caravan from the tow vehicle. Weigh the caravan only (including the weight on the jockey wheel).
Gross Trailer Mass (GTM)
Gross Trailer Mass is the maximum permitted laden weight of a caravan when coupled to a tow vehicle.
The caravan maker sets this weight. It includes that of all caravan accessories, luggage, water and gas. It excludes jockey wheel down-force. Exceeding GTM is illegal.
How to Check
Tow the fully laden caravan onto a weighbridge and, whilst still coupled to the tow vehicle, weigh the trailer only.
Maximum Coupling Load
The maximum coupling load is the maximum weight a trailer’s hitch can tow. Furthermore, a maximum down-force may also be stipulated.
This weight rating is set by the tow-hitch maker. It includes the weight of all towed accessories including luggage, water and gas. Moreover, be aware exceeding maximum coupling load is illegal.
How to Check
Tow the fully laden caravan onto a weighbridge and, while it’s still coupled to the tow vehicle, weigh the caravan.
Tare Weight (Mass)
Tare weight is the claimed weight of a caravan ex-manufacturer and ‘ready for service’. This weight may be incorrect. Optional extra’s are dealer-supplied and fitted. They are, however, rarely included as tare weight. If not reduces the legal payload.
How to Check
Weigh the uncoupled trailer, with jockey wheel down and no payload, on a weighbridge.
Maximum Payload
The maximum allowable payload means ‘allowable weight of a caravan‘s contents.’ It applies to the caravan only. It is calculated by subtracting the caravan‘s Tare Mass from its Aggregate Trailer Mass. The maximum payload includes the weight of all luggage and personal items in or on a caravan. Furthermore, water, gas and all added accessories are included.
How to Check
To calculate your Maximum Payload allowance, subtract the actual Tare Mass (as weighed above) from the ATM.
There are many reasons to stay well within maximum weight limits. Find out more by reading our articles on towing dynamics. Furthermore, for a full explanation, buy our book Why Caravans Roll Over – and how to prevent it.
