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. We are happy to discuss if your caravan can 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 upgrades can be confusing so it is a good idea to contact us.


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.


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 and rear axle 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 increased with an ATM upgrade. You can contact us to find out if your caravan can be upgraded.

Maximum Payload = ATM – TARE Mass (Caravan) – TBM

Maximum Payload (Tow Vehicle)

Payload is any mass you add to the vehicle’s tare mass.
For tow vehicle’s, this includes fuel, passengers, luggage, aftermarket bull bars, all accessories, and the carvans tow ball mass. 

TARE Mass (Caravan)

This is the mass of your trailer – for our purposes, your caravan – as specified by the manufacturer, with no payload. We have found that this figure is not always correct which can have an adverse effect on the caravans 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.

Your vehicle axles will react to the weight going on the ball. The additional weight on the vehicle will cause weight to move from the front axle to the rear. Here is the calculation for a 300kg ball weight.

300kg x 1.4 = 420kg, so that ball mass becomes an additional 420kg on the vehicles rear axle.

Where can I find these?

You can generally find the TARE, ATM, TBM and GTM stamped on the vehicle identification number (VIN) plate, usually in the front or side storage compartment or on the drawbar.

With exception to TARE and GTM, as long as you do not exceed any of these figures, then you shouldn’t have any problems if stopped by the authorities.

Still not making any sense?
Give us a call for no charge, friendly and accurate advice.


Having weighed over 1,100 caravans our results have shown that over 70% the caravans assessed were overweight in at least one of the regulated categories.
Don’t be a risk taker, if you don’t know your weights, you should.

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