Understanding Weights

Knowing your weights and caravan towing capacity is essential for safe towing


Tare mass is the base weight of the van at manufacture without payload or after-market accessories, without water in the tanks or the gas bottles filled.


ATM (Aggregate Trailer Mass) is the maximum manufacturer specified weight of your loaded caravan or trailer and is measured unhitched and sitting on it’s jockey wheel and axle(s).This is a rating set by the manufacturer and cannot be exceeded.


GVM (Gross Vehicle Mass) 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).


GTM (Gross Trailer Mass) is the maximum weight your trailer can be at its axle(s) and is sometimes referred to as the axle capacity. Typically this is measured while the caravan or trailer wheels are sitting on a weighbridge but the hitched tow vehicle isn’t.


TBM (Tow Ball Mass) is the effective mass on the tow ball from the trailer hitch. The maximum TBM is not typically specified by the manufacturer but as a guide should be up to 10% of the ATM.


GCM (Gross Combined Mass) is the rating provided by the manufacturer. When you weigh your tow vehicle and your caravan or trailer when they are all loaded up.


Ball Weight The Force ( in Kg’s) exerted downwards on a vehicle’s tow ball by your fully packed caravan. When your caravan is hitched, this mass is included in your tow vehicle’s payload.


Axle Load How much weight the front and rear axles can handle safely. The combined sum of both axle ratings usually adds up to more than the GVM, giving a bit of leeway  as to where the weight is distributed throughout the vehicle.


Payload is all the bits you add on or load up to take away (usually about 300kg allowance).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