Towing Weight Definitions Guide

Understanding these key terms and abbreviations is essential for safe and legal towing.

Vehicle Weights

Kerb Weight The weight of your tow vehicle with all fluids (oils, coolant, fuel) but no payload, people or accessories.

Tare Weight The empty weight of your caravan or trailer with no gas in bottles, no water in tanks, and no gear, food or belongings stored. When referring to a tow vehicle’s tare weight, this means showroom condition with only 10 litres of fuel, no passengers, luggage or accessories.

Maximum Weight Limits

Gross Vehicle Mass (GVM) The maximum allowed weight your vehicle can carry, including fuel, people, gear, accessories and includes the tow ball mass of anything being towed.

Gross Trailer Mass (GTM) The maximum weight the trailer or caravan can weigh when hitched, considers only the weight across the trailer or caravan axles.

Gross Combined Mass (GCM) The maximum combined weight of the tow vehicle and what is being towed.

GCM = GTM + GVM

Tow Ball Mass (TBM) The weight applied to the tow vehicle’s coupling or tow ball (also known as tow ball weight).

Aggregate Trailer Mass (ATM) The maximum allowed weight that the caravan or trailer can be when unhitched. This is the weight across the axles and the towball mass.

ATM = GTM + TBM

Payload This is the difference between the ATM and Tare. Payload includes gas in the gas bottles, water in the tanks, food in fridge, clothes and gear in cupboards and lockers, storage boxes and tunnel boot.

Payload = ATM - Tare

Key Takeaways

These weights are legal limits that must not be exceeded. If you are found to be overweight your setup is classified as un-roadworthy. An un-roadworthy vehicle is not covered by insurance. Weigh your loaded vehicle and trailer or caravan to ensure compliance before travelling.