A LOAD OF TOWING WEIGHTS
By Cha Ratnatunga
As members of the 4WD community, we look forward to going on a trip and loading up the 4WD is
the best trip stage. This is what it should always be, but we also cannot overlook how the vehicle is
loaded and whether it conforms to the limits set by the manufacturer.
So let’s look at some of the terminology to ensure that the vehicle and trailer are within the limits,
safe, legal and covered by insurance.
Kerb Weight
Payload
Gross Vehicle Mass (GVM)
Tare Mass
Aggregate Trailer Mass
(ATM)
Gross Trailer Mass (GTM)
Gross Combination Mass
(GCM)
Tow Ball Weight (TBW)
The weight of the vehicle with fluids including fuel.
The weight of the vehicle including all accessories, gear, passengers
and the tow ball weight (If a trailer is hitched).
The weight of the vehicle with payload only but excluding the trailer
(if hitched).
Generally refers to the weight of the caravan with accessories and
empty water and gas tanks.
The weight of the trailer with a full payload but unhitched from the
tow vehicle.
The weight of the trailer hitched to the tow vehicle
The combined weight of the vehicle and trailer fully loaded (GVM) +
(ATM)
The downward force of the trailer draw bar on the vehicle tow ball.
Generally this is 7-15% of the (ATM). High Tow Ball Weights cause
higher load on the rear axle causing the front of the vehicle to lift.
This can affect the vehicle steering dynamics. A low Tow Ball weight
can cause lift on the draw leading to trailer instability. The TBW
must not exceed the value specified by the vehicle manufacturer.
Brakes
When towing a trailer with a GTM less than 750 Kg, there is no legal requirement to have an electric
brake controller installed in the trailer. Trailers with a GTM of 750-2000 Kg require an electric brake
controller. There are a variety of brake controllers that operate mechanically and electronically.
Most controllers have a switch on the tow vehicle that enable the driver to control the amount of
braking on the trailer under different environmental and road conditions.
Rear Vision
Tow mirrors are essential if the trailer track width is wider than that of the vehicle. If the trailer is
obstructing the line of vision on the vehicles external rear view mirrors, then extended mirrors must
be used. Using cameras with monitor screens inside the vehicle is a supplementary aid for the
driver. Multiple cameras installed in different locations of the trailer can give a surround view from
different perspectives.