RV FEATURE
TRAILER TERMS
In the second article, we took a close look at the
various initialisms and terms that apply to towed
vehicles such as caravans and camper trailers…
Tare: This is the total mass of the trailer when not
carrying any load, but when ready for service and
with all fluid reservoirs (if fitted) filled to nominal
capacity except for fuel, which shall be 10L only,
and with all standard equipment and any options
fitted. This includes any mass imposed onto the
drawing vehicle (when the combination vehicle is
resting on a horizontal supporting plane (towball
weight).
Of special note, fluid reservoirs do not include
water tanks and waste water tanks, such as those
fitted to caravans.
Gross Trailer Mass: GTM is the mass transmitted
to the ground by the tyres of the trailer when
coupled to a towing vehicle and carrying the
maximum load recommended by the manufacturer
or importer, approximately uniformly distributed
over the load bearing area. It does not include the
weight imposed on the towball.
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Aggregate Trailer Mass: ATM is the total
mass of the trailer when carrying the maximum
load recommended by the manufacturer. This
includes mass imposed onto the towing vehicle
when the combination vehicle is resting on a
horizontal supporting plane. If you were to put
your caravan on a weighbridge on its own and
resting on the jockey wheel, this is the weight you
would measure against ATM. Basically, it is the
maximum allowable total weight the trailer.
Maximum towball mass: This rating is not
defined in the ADR’s Technical Requirements;
however, it is the maximum weight imposed
by the trailer onto the towing vehicle when
the combination vehicle is resting or when it is
connected to the towing vehicle. The maximum
towball mass should be noted on the compliance
plate of the trailer, though in our experience this
is not always the case. Often, only the unladen
towball weight of the trailer is noted. If in any
doubt, consult the van’s manufacturer.
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