RV FEATURE
GoRV has provided extensive explanations for
the various weight ratings that apply to
caravans and tow vehicles, so we won’t do so
again here. Click the relevant buttons on page
37 for instant access to these explanations.
But we will note here that often a prospective
tow vehicle’s Gross Combined Mass (GCM)
rating will be less than the sum of the vehicle’s
Gross Vehicle Mass (GVM) rating and towing
capacity rating, in which case the GCM rating
will be the limiting factor.
The rear-axle rating of the tow vehicle must
also be considered to ensure that it is not
exceeded. Due to the hitch overhang, the ball
loading applies a leverage ‘moment’ (force X
distance) such that the additional loading on
the rear axle is actually more than the ball
loading itself.
Additionally, the actual ball/coupling load
exerted onto the tow vehicle’s towbar at any
time must not exceed the downward ratings
of both the tow vehicle and the towbar, which
are required to be provided by their
manufacturers. It is expected that the caravan
manufacturer will provide the maximum
permissible ball/coupling load that the vehicle
was designed for when loaded in a
reasonable and typical manner.
STABILITY
Having a caravan sway – or jack-knife – is an
extremely frightening and dangerous
situation. There are three major factors that
determine stability/handling on the road:
1. The length, weight and design of the
caravan.
2. The manner in which it is loaded.
3. The speed and road/atmospheric
conditions.
It is absolutely essential that the ‘tail never
wags the dog’; that is, it is important that the
tow vehicle has the ability – primarily mass –
to control the caravan, rather than the other
way round.
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