Weight Terminology Guide
Our helpful guide to understanding the many acronyms and weight terms used in the wonderful world of caravaning & towing
ATM (Aggregate Trailer Mass)
This is the tare mass of your caravan plus its maximum payload. It’s the maximum your caravan is allowed to weigh in transit.
This is a rating set by the manufacture but in some cases be upgraded.
ATM = TARE Mass (Caravan) + Maximum Payload
GCM (Gross Combined Mass)
The gross combined mass is a combination of the maximum allowed mass of the trailer and the maximum allowed mass of the vehicle.
GCM cannot be upgraded.
GCM = GTM + GVM
GTM (Gross Trailer Mass)
This 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 in some cases upgraded.
GTM = ATM – TBM
GVM (Gross Vehicle Mass)
The limit on weight that the car’s wheels can support – including the weight of the TBM and passengers. This is a rating set by the car manufacturer. In some cases the GVM can be upgraded.
GVM = Vehicle TARE Mass + Maximum Payload
Maximum Payload (Caravan)
The maximum weight that can be loaded into the caravan for towing. This does not include the weight of people inhabiting the caravan while stationery, but does need to take into account water, gas and accessories you’ve added to the caravan since purchasing it.
This rating is set by the manufacturer. In some cases can be upgraded.
Maximum Payload = ATM – TARE Mass (Caravan) – TBM
Maximim Payload (Tow Vehicle)
Payload is any mass you add to the vehicle’s tare mass.
For tow vehicle’s, this includes passengers, luggage, aftermarket bull bars and the tow ball mass. Payload does not include standard specifications set by the manufacturer such as fuel and coolant.
TARE Mass (Caravan)
This is the mass of your trailer – for our purposes, your caravan – as specified by the manufacturer, with no payload.
TARE Mass (vehicle)
This is the actual mass of the tow vehicle – how much your car weighs at manufacturer specification (different manufacturers have different interpretations on fluids) and with no payload.
TBM (Tow Ball Mass)
This is the mass exerted on the tow ball by your caravan.
When your caravan is hitched, this mass has to be included in your tow vehicle’s GVM.
Where can I find these?
You can generally find the TARE, ATM, TBM and GTM stamped on the vehicle identification number (VIN) plate.
With exception to TARE… as long as you do not exceed any of these figures, then you shouldn’t have any problems towing your caravan.
Still not making any sense?
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