” THERE DOESN'T SEEM TO BE ANY
LOGIC TO HOW SOME MANUFACTURERS
CALCULATE THEIR VEHICLES' GCM.”
THE DEFINITION
If, at this point, you're confused, don't be
despondent. You're not alone. The Australian
Design Rules, the 'bible' to which all vehicles
on Australian roads must conform, defines
GCM as, “Gross Combination Mass – value
specified for the vehicle by the ‘Manufacturer’
as being the maximum of the sum of the
‘Gross Vehicle Mass’ of the drawing vehicle
plus the sum of the ‘Axle Loads’ of any vehicle
capable of being drawn as a trailer.”
The first time I read that definition, I got a mild
headache. But it makes complete sense. For
any tow vehicle and trailer combination, the
actual weight of the rig compared to every
other weight rating of the tow vehicle or the
trailer can be altered depending on weight
distribution, load positioning, and even by the
angle of the road the rig is resting on. But the
total weight of the whole rig cannot be altered
without physically removing or adding weight
to the rig itself. It makes it easy for owners
to ensure their rigs are legal and it makes it
just as easy for law enforcement agencies to
determine if they’re not.
UPGRADES?
Hopefully, you’ve read GoRV’s recent articles
explaining the various weights and measures
regarding caravans and tow vehicles.
If you recall, we looked at three popular
tow vehicles, the Nissan Y62 Patrol, the
Toyota Land Cruiser 200 Series, and the
Ford Ranger Wildtrak.
They are considered among the best vehicles
for towing loads approaching 3.5 tonnes
but, as we discovered, you can’t put much
more than an additional 260kg worth of
passengers, cargo and accessories in them,
due to limitations in their GVM or GCM ratings,
when towing a 3.5-tonne caravan.
Potential upgrades offered by second
stage manufacturers can be as simple as a
suspension upgrade or as complicated as a
six-wheel-drive conversion. We could debate
the merits of increasing the towing and
weight-carrying limits of a vehicle beyond
what the original manufacturer ever envisaged
but, the fact remains, these upgrades are
available with engineering sign-off.
Use a weighbridge to determine if the
combined weight of van and vehicle are
within the vehicle's GCM limitation.
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