Tow Vehicle and Caravan Weighing Acronyms Explained - Or why is my Caravan Overweight ?
Updated: Mar 4
Tow Vehicle and Caravan Weighing Acronyms explained.
A cars towing capacity doesn’t always equate to how much it can tow.
So you’ve bought a new vehicle with a 3000kg towing capacity, which means you can tow a 3.0-tonne caravan, right?
Well, not necessarily.
There are other factors that determine how much you can tow, such as the towbar strength and total weight of the tow vehicle. As well as understanding the different factors, you also need to master towing terminology, some of which seems suited to people with white coats and slide rules.
So here goes …
Gross Combination Mass (GCM):
is the total weight of your rig ie: caravan and tow vehicle (everything loaded and coupled).
Gross Vehicle Mass (GVM):
is the maximum permissible weight of your towing vehicle when loaded.
This is specified by the vehicle’s manufacturer.
Tow Ball Weight:
is the maximum weight that your caravan can apply to your vehicles tow ball. This is specified by the vehicles manufacturer. You can use a measuring gauge (manual or digital) to measure the actual ball weight of your caravan at any given point in time, to make sure it’s within your vehicle’s limits. (as a guide it can be around 10% of your caravan trailer weight – but check your manufacturers recommendations.)
Aggregate Trailer Mass (ATM):
is the maximum permissible weight of your caravan when loaded, and without being
hitched to your towing vehicle: IE all up weight of caravan on its own. This is specified by the caravans manufacturer.
Gross Trailer Mass (GTM):
is the actual weight of your loaded caravan, at any given point in time, and hitched to your towing vehicle. IE: the weight supported by the caravans wheels.
GTM + Tow Ball Weight = ATM.
Sometimes called the unladen weight, is the weight of an empty caravan. Don’t be mislead about the tare weight. It’s the only weight you can’t be fined for.
If the caravan dealer has added solar panels, a battery and bike racks – then your tare will be more than indicated on the plate.
Adding these things on doesn’t change your ATM – but does decrease your load carrying capacity.