“ The CCA is frequently asked by vanners to provide clarification of the different caravan and tow vehicle ratings and masses , usually because they have been stopped on the road by authorities and have had their vehicles weighed , or because they have experienced a very nasty swaying or jack-knifing incident on the road ,” Mr Young said .
CARAVAN RATINGS AND MASSES
Gross Trailer Mass ( GTM ): a fixed rating allocated by the manufacturer of the van . The GTM rating must not exceed the lowest of the axle-group ratings . The axle group comprises the wheels and tyres , the suspension structure and springs , and axles and wheel bearings .
Aggregate Trailer Mass ( ATM ): a fixed rating allocated by the manufacturer of the van .
Tare Mass : An actual mass that must be measured . Tare Mass is the actual measured mass of the vehicle as it leaves the manufacturer , fitted with everything that was stated on the purchase contract . For the purposes of Tare , the van is empty , as are the gas cylinder ( s ) and the water tank ( s ).
Ball Loading : An actual mass that must be measured .
Fig 5 : Note that the van is hitched in the first diagram , and unhitched and resting on the jockey wheel in the second diagram . The difference between these two readings is the ball-loading . Be aware that ball-loading is dynamic – it will change according to how the van is loaded .