ATM – Aggregate Trailer Mass

atmThe total laden weight of a trailer, which includes the tow ball mass and whatever you add as payload (eg. water, gas, luggage). The ATM is specified by the trailer manufacturer and must not be exceeded.

GCM – Gross Combination Mass

GCM copy
GCM is the rating provided by the manufacturer of the tow vehicle. The maximum laden mass of a motor vehicle plus the maximum laden weight of an attached trailer is not permitted to exceed the GCM rating.

GTM – Gross Trailer Mass

gtmThe total permissible mass which includes whatever you add as payload (eg. water, gas and luggage) that can be supported by the wheels of a trailer. This does not include the mass supported by the tow ball.

GVM – Gross Vehicle Mass

gvm2The GVM is the maximum allowable total mass of a fully loaded motor vehicle, consisting of the tare mass (mass of the vehicle) plus the load (including passengers).


The payload is worked out by deducting the “Tare Mass” from the “ATM”. It must not be exceeded under any circumstances. Safety, insurance & warranty may be affected if the specified payload is exceeded.

Tare Mass

The unladen weight of the complete new trailer as delivered (including any options fitted).

Tow Ball Mass

The weight imposed on the tow vehicle’s tow ball by the coupling.