Vehicle, Caravan and Trailer Weight Terminology

Before you even think about hitting the road, there are certain terms you must become well acquainted with. They may be confusing at first, but the safety of you and your family relies on having an understanding of weight.

Tare Mass/Weight

This is the empty weight of your tow vehicle. Empty is defined as free of people, luggage and with only 10 litres of fuel in the tank.

Kerb Mass/Weight

Kerb Mass is simply Tare Mass with a full tank of fuel. Importantly, this does not include accessories such as roof racks or bull bars.

Gross Vehicle Mass/Weight (GVM/GVW)

Gross vehicle mass (GVM) is the manufacturer-specified weight of your vehicle, fully-loaded.

In other words, GVM is the Kerb Mass plus all accessories and Payload weight. GVM can usually be found on your vehicle’s weight placard inside the driver’s door.

Not sure what your Payload is? Keep reading to find out!


Payload is the maximum weight your vehicle can carry. To calculate Payload, deduct the Kerb Mass from the Gross Vehicle Mass.

If, for example, your vehicle has a payload of say 750kg, then pack accordingly. A family of five with luggage, food, water and alcoholic refreshments will quickly eat into this allowance (no pun intended).

Tare Trailer Mass (TARE)

Tare Trailer Mass applies to anything that can be towed.

For the purposes of this article, TARE is defined as the weight of the empty camper trailer.

It is important to understand that TARE is the dry weight. It does not include fluids such as potable and non-potable water or LPG.

Gross Trailer Mass/Weight (GTM/GTW)

Gross Trailer Mass is the maximum axle load your trailer can carry as specified by the manufacturer. GTM can be found on the trailer or in the owner’s manual and is the total weight of your trailer plus its Payload.

Tow Ball Mass (TBM)

Tow Ball Mass is the percentage of weight exerted on the tow ball by the camper trailer. If you’ve invested in a high-quality tow bar, you should be able to find TBM figures quite easily.

In most cases, TBM should be 10-15% of the GTM. TBM must also be included in Payload calculations since it will reduce the amount of weight the tow vehicle can safely carry.

Above all, ensure that your tow bar is appropriate for your vehicle and also for the camper trailer you intend to tow.

Aggregate Trailer Mass/Weight (ATM/ATW)

Aggregate Trailer Mass (ATM) is the combination (aggregate) of Gross Trailer Mass and Tow Ball Mass. 

Since the ATM is the maximum manufacturer-specified towing weight, it is essential you remember this number and never exceed it.

Gross Combination Mass/Weight (GCM/GCW)

Last but certainly not least is Gross Combination Mass. This is the maximum weight of your vehicle and caravan combined.

To determine this figure, calculate your vehicle’s GVM and the caravan’s ATM.

Both the GVM and ATM are proportional to one another and determines your vehicle’s maximum safe towing capacity.

A good rule of thumb to remember is that for every kilogram you add to the tow vehicle’s payload, you must subtract one kilogram from the maximum weight of the camper trailer you intend to tow.

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