RV FEATURE
MAXIMUM TOWBALL DOWNLOAD
Maximum Towball Download is the maximum
amount of weight that a trailer can transfer onto
the tow vehicle. Again, it should be stated either
in the vehicle user manual or on the tow hitch
itself. 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 the drawbar of a trailer
rests on the towball, that weight is carried by the
tow vehicle.
GROSS COMBINED MASS
The Gross Combined Mass of a tow vehicle is the
value specified for the vehicle by the manufacturer
as being the maximum of the sum of the Gross
Vehicle Mass 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 weigh bridge, the total weight of the
rig cannot exceed the GCM.
Finding out the GCM of your particular tow vehicle
can be difficult. Some manufacturers state the
GCM on the compliance plate but many do not.
A GVM upgrade should come with
a second stage compliance plate.
Some manufacturers, meanwhile, state the GCM
as simply the sum of the maximum towing capacity
and the GVM. Some state a GCM for their vehicle
on their website or in the vehicle's user manual.
It can also change depending on the year the
vehicle was manufactured.
If the vehicle has had a GVM upgrade, the GCM
may or may not have been increased as well. The
second stage manufacturer' compliance plate may
not state a GCM, either, adding more confusion.
If you have the slightest doubt about your vehicle's
GCM, you must consult the manufacturer of the
vehicle and/or the manufacturer of the GVM
upgrade, if one has been fitted.
It is vitally important to ascertain these ratings on
your tow vehicle if you are to ensure you remain
legal. If, after consulting the manufacturer, you
still have doubt, visit your state road authority.
It will have up-to-date information about your
vehicle and can help make sense of what is stated
on the compliance plate.
Next month, we'll look at how to ascertain a
trailer’s weight limit and the pitfalls you're likely
to face.
Upgraded load ratings on a Land Cruiser.
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