Caravan tow weights explained

Your compliance plate will have a number of acronyms that are important to understand

For your tow vehicle

GVM - Gross vehicle mass- 

This is the maximum your car is allowed to weigh ( This will be on your car compliance plate)

GCM- Gross combined mass -

This is the total your car and its caravan is allowed to weigh

How much can you carry in your car?

To calculate this you need to check your compliance plate and get the following information

  • Tare Mass or tare weight ( this is the weight empty , no fuel no luggage, no extras like bull bar tow bar roof rack winch and no people.) 
  • Gross Vehicle Mass  GVM or GVW (This is the maximum your vehicle can weigh when fully loaded including the down force from the caravan )
  • Payload ( How much can it carry) just deduct Tare mass from GVM and you will arrive at payload noting that this will reduce with every accessory passengers and luggage added.
  • Allowable down force on the tow bar  ( specified by the tow bar manufacturer and your car manufacturer, whichever is the lowest)
  • Towing capacity will be listed in your cars manual if not check on line or with a dealer, noting that this a maximum towing ability provided that all the other factors are taken into consideration, just because the manufacturer says your tug can tow 3500kg doesn't mean that it can legally, your Gross Combined Vehicle Mass GCM must not exceed specifications as well.

For your caravan or camper trailer

Ball weight-

This is the weight that the van places on the car at the tow ball ( usually around 7% to 10% of the van weight)

Your Caravan / Camper trailer will specify ball weight of an unloaded van,

Your tow bar manufacturer will specify the maximum ball weight that the bar can carry.

Your Vehicle manufacturer will specify the maximum ball weight that the car can carry.

ATM- Aggreate Trailer Mass ,

This the total weight of the caravan including everything that is in it, including water food, clothing   & waste when not coupled to the car

GTM Gross Trailer Mass

This the weight  of the fully loaded trailer imposed on the trailer’s axle when it is coupled to the tow vehicle.

GTM will always be less than ATM as some of the trailer weight is transferred to the tow vehicle when the trailer is coupled to it.


Confused over the terminology? ATM? GTM? Learn More about the Acronyms used when weighing your caravan or rig.



Tow bars, from 1992 all bars will have a plate attached that lists the maximum towing weight, the maximum ball load, and the make and model of vehicle the bar was designed for.

if this weight is higher than the cars specified then the car tow-able weight is used, if the bar weight is lower than the car tow able weight then the bar weight is used, so it is important to have a tow bar that is properly designed to match or exceed your cars towing capacity.


Car GVM, Gross Vehicle Mass

GVM is the weight of a laden vehicle as measured under the wheels

Measured by having the vehicle weighed , best done with the normal full load including passengers fuel camping gear etc in the car.


Van TBM  Tow Ball Mass

TBM is the weight imposed on the tow vehicle by the coupling of a laden caravan or camper,

Measured by placing a scale under the tow ball 

Van GTM Gross Trailer Mass

The mass transmitted to the ground by the axle or axles of the caravan when coupled to the vehicle

Measured by weighing the caravan while coupled to the car

Van ATM Aggregate Trailer Mass

The mass of the laden caravan including the tow ball mass

Measured by weighing the caravan including the tow ball mass when not coupled to the car, this can be calculated by adding the ball weight to the GTM

GCM Gross Combined Mass

The combined weight of both the tow vehicle and the caravan

Measured by weighing the car and caravan together or separately and added together

AGL Axle Group Loading

The Load applied to each axle group

Car Front Axle, Car Rear Axle ,Caravan Axles 

Caravans usually have the AGL ( Axle Group Loading) in their compliance plate 

For the car it is usually shown in the owners manual in the towing section.