“ WHEN A TRAILER'S DRAWBAR RESTS
ON THE TOWBALL, THAT WEIGHT IS
CARRIED BY THE TOW VEHICLE ”
Vehicle payload capacity: The amount of weight
that the tow vehicle can carry. Subtract the Kerb
Mass from the GVM to arrive at this figure.
Maximum towing capacity: This is the total
weight of a trailer that can be towed by the vehicle,
including the trailer’s towball weight.
Maximum towball download: This is the
maximum amount of weight that a trailer can
transfer onto the tow vehicle. What is not well
understood is this towball weight must be added
into your calculations when assessing the total
weight of your vehicle against its GVM. When
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the drawbar of a trailer rests on the towball, that
weight is carried by the tow vehicle.
Gross Combined Mass: GCM is the value
specified for the vehicle by the manufacturer as
being the maximum of the sum of the GVM of
the tow vehicle plus the sum of the axle loads of
any vehicle capable of being drawn by the tow
vehicle as a trailer. If a complete rig is put on a
weighbridge, the total weight of the rig cannot
exceed the GCM.
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