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balancing act
weight
& towing your camper
Towing a camper trailer is not just a
simple process of hooking up and taking off for your favourite
camping spot. As a duty of care to other road users there are a
number of rules and guideline limits you need to be aware of,
otherwise you could be breaking the law, voiding your vehicle
warranty or insurance in the event of an accident.
A vehicle and camper trailer must compliment each others maximum
capacities making for a safe combination in all situations. This
especially applies to lighter vehicles and soft roader 4wd’s
which have lighter tow capacities. If the ball weight is too
heavy, the tow vehicle's rear suspension will be forced down
affecting braking and also the vehicle’s steering when it is
most needed like during an emergency situation.
the law
In December 1998 an agreement was reached by all state ministers
of transport to implement a national towing regulation. One rule
put simply says the most you can tow is the amount specified by
the vehicle manufacturer or the capacity of the towbar - WHICH
EVER IS LEAST.
If you want to know how much your vehicle can tow, check the
owner’s manual or your vehicle’s sales brochure for the
manufacturer’s towing recommendations. Make sure the vehicle’s
towing capacity is more than the trailer’s weight, including its
load.
In the case where a motor vehicle manufacturer has not specified
a maximum tow weight, the limit is 1.5 times the unladen or kerb
weight of the motor vehicle if the trailer is fitted with brakes
or the unloaded weight of the motor vehicle if the trailer is
not fitted with brakes.
camper
trailer capacity
The maximum weight a camper trailer will carry is specified by
the manufacturer and is based on a number of factors including
the chassis RHS dimensions, maximum axle capacity, suspension,
bearing size and A frame design. Off road campers are built
heavier all round than an on road version mostly for weight
carrying and ruggedness in the hash outback conditions. A camper
trailer manufacturer would have had calculated all this in the
fabrication process.
the
drawbar
The National Code of Practice booklet ‘Building a Small Trailer’
which is available from motor registries, states drawbars must
withstand certain forces applied at the centreline of the
intended coupling without detachment or any distortion or
failure which will affect the safe drawing of the towed trailer:
Longitudinal tension and compression (N) 1.5 x 9.81 x ATM (kg)
Transverse thrust (N) 0.5 x 9.81 x ATM (kg)
Vertical tension and compression for rigid drawbar trailer (N)
0.5 x 9.81 x ATM (kg)
the towbar
A towbar must be stamped
by the bar’s manufacturer with both maximum ball weight and
maximum tow weight. If you are unsure as to how strong the
towbar is, have a chat to a reputable towing equipment
specialist.
brakes
A camper trailer must be fitted with brakes if the trailers
weight including its load exceeds 750 kg. There are different
types of brakes available such as mechanical overriders,
hydraulic overriders, electrically operated hydraulic and
electric. An electric brake controller must be placed within
easy reach of the drivers seat.
ball
weight
In a perfect world of smooth flat roads a 5% ball weight would
be ideal, however undulating roads and potholes producing
negative ball weights or strong crosswinds into the equation,
can have serious effects on the vehicle and camper causing the
combination becoming out of control.
The 10 to 15% rule of thumb ball weight of a fully loader
trailer gives a safety net and some room for error particularly
when it comes to a camper trailer with
weight shifting quantities that can vary greatly either forward or
to the rear of the axle as jerry’s of fuel and water are used,
the water tank emptied, firewood unloaded or food consumed.
Ball weight can be affected by a number of factors which can
quickly overload the front of your camper. The A frame can be
used to store an outboard motor, toolbox with tools and other
heavy gear, a spare tyre, gas bottles, fuel or water jerry’s and
a fridge packed with food. Attention to the 'balance' of the
camper needs to be maintained keeping the ball weight within the
limits and the calculated strength of the drawbar.
know
before you go
It is a good idea for a camper trailer owner to weigh his fully
loaded camper at least once on a weighbridge so he knows what
the camper and ball weight is. This will help with future
packing of the camper. Check the yellow pages under public
weighbridge. For the few dollars you will have piece of mind.
weight in
the vehicle
You should also be aware that your vehicle should do not exceed
the Gross Combined Mass (GCM). The GCM is the total weight of
the tow vehicle and the camper trailer, with everything loaded
in the vehicle and camper.
When your vehicle has a long range fuel tank, steel bullbar and
winch, cargo draws with recovery gear, full fridge, plus the
luggage and camping gear of five adults, it is possible that the
maximum allowable trailer weight has to be reduced so as not to
exceed the GCM.
terms
Vehicle Kerb Weight or Kerb Mass - this is the weight of
your tow vehicle as delivered by the manufacturer with no
occupants, payload or accessories.
Campers Kerb or Tare Weight is the weight as it left the
manufacturer and is usually the weight without water in the
tanks or gas bottles filled.
Gross Vehicular Mass (GVM) is the maximum weight the
vehicle is allowed to be operated at. GVM is the kerb weight
plus the payload. Operating a vehicle exceeding its GVM is
illegal, will void the manufacturer’s warranty and likely to
void your insurance.
Payload of a vehicle is the maximum capacity of the
vehicle itself for transport including the occupants and cargo
as well as any accessories such as bull bar, tow bars, winches,
and roof racks.
Ball Weight is the maximum allowable weight to be placed
on the vehicle’s tow ball.
Aggregate Trailer Mass (ATM) is the total weight of the
camper trailer when carrying the maximum load recommended by the
manufacturer.
Gross Trailer Mass (GTM) is the total permissible weight
recommended by the manufacturer of the camper trailer when fully
loaded.
Gross Combined Mass (GCM) is the total weight of the tow
vehicle and the camper trailer with everything loaded in the
vehicle and camper trailer.
calculating the ball weight
The loaded camper trailer unhitched with its jockey wheel and
wheels on the weighbridge will give you the Aggregate Trailer
Mass (ATM).
Now with the camper trailer hitched to the tow vehicle with only
the camper trailers wheels on the weighbridge will give you the
Gross Trailer Mass (GTM).
The difference between the ATM and GTM will give you the Ball
Weight.
by Rob
november
2011
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