MINIMISING HITCH OVERHANG IS ESSENTIAL
Figure 2 shows why hitch overhang is such an
issue. When the tow vehicle yaws (sways), it
does not just permit but causes the trailer to yaw
in the opposite direction. The greater that hitch
overhang, the greater the resultant effect. Most
vehicles used for towing in Australia have an
average hitch overhang of 1.24 metres.
Equally important is the ratio of laden tow vehicle
weight to laden trailer weight (and where that
weight is in that trailer (it should never be at the
extreme rear). Here, I can only support the Caravan
Council of Australia’s advice of having that laden
tow vehicle heavier than the laden caravan. If
not, that mass-unbalanced rig may seem stable
in normal driving but will become unstable (given
sufficient disturbing force) at lower speed.
What really matters, however, is the ratio of that
hitch overhang to the tow vehicle’s wheelbase
(the distance from the front to rear axle). Here,
US imports typically score well. It is their longer
wheelbase (not just their often greater weight) that
makes vehicles like the Dodge RAM and big Fords
such a good choice for towing heavy caravans.
Towball mass, too, is vital: 10% of laden caravan
weight is really needed for any trailer longer than
4.5 to 5 metres. It must remain reasonably constant
despite the amount of water in the tanks.
That which truly matters is not how a rig handles
in everyday use, it is how that rig acts in
emergency swerves and high
side wind gusts.
FORCE
FORCE
TOW VEHICLE YAWS
ANTICLOCKWISE
Fig 2.
34 \
‘VAN YAWS CLOCKWISE
WIND GUST