What is GTM on a caravan?
The most the van's own axles may carry once it is loaded and hitched to the car.
GTM is the most the caravan's own axles may carry when it is loaded and hitched. At full load it is about the ATM (Aggregate Trailer Mass) minus the ball weight, because the car carries part of the load. Trailer brake rules use GTM.
Also called Gross Trailer Mass.
- Rated as - the most the hitched van's axles may carry
- Marked on - the van's compliance plate, beside the ATM
- Protects - the van's axles, suspension and tyres
What GTM measures
When you hitch up, part of the van's weight moves onto the car's tow ball.
GTM caps the rest: the load on the van's own axles and wheels.
The axles, suspension and tyres each carry a rating.
The plated GTM is the most they may carry together.
GTM across the caravans we list
Among the caravan ranges we list, using each range's published figure, the middle GTM is about 2,750kg.
Half are above that figure and half below it.
How GTM, ATM and ball weight fit together
ATM is the whole loaded van, unhitched.
Ball weight is the share of it that sits on the tow ball once hitched.
At full load, GTM is about ATM minus the ball weight.
A van can sit inside its ATM and still go over its GTM.
That happens when heavy gear packed behind the axles lifts weight off the ball and onto the wheels.
Where to find the GTM
The GTM is stamped on the van's compliance plate next to the ATM.
To check against it, weigh the van still hitched, with only its wheels on the weighbridge.
Release a weight-distribution hitch before you weigh.
Why GTM decides the brakes
Trailer brake rules use GTM.
Over 750kg GTM a van needs brakes.
Over 2,000kg GTM it needs brakes on every wheel and breakaway brakes.
How a rear load shifts weight onto the axles
These figures are made up and rounded to keep the sums simple.
Take a van with a 2,500kg ATM and 250kg on the ball.
Its axles carry about 2,250kg.
Move heavy gear from the front boot to the rear and the ball weight might fall to 180kg.
The axles then carry about 2,320kg, so check that figure against the plated GTM.
Common mistakes with GTM
- Skipping it - a rear-heavy load can push the axles over GTM inside the ATM
- Mixing it up with ATM - ATM caps the whole van, GTM caps the axle load hitched
- Weighing it wrong - keep the van hitched, a weight-distribution hitch released, and only its wheels on the scale