RV FEATURE
a weight distributing hitch (WDH), it in effect
levered up the rear of the tow vehicle and
levered down the front. A smaller amount was
also transferred to the caravan’s tyres. This
was later adopted for locally made caravans
(typically) over 2000 kg.
SIDE FORCES
While a WDH wholly or partly counteracts
excess tow ball weight, it does not reduce the
side forces imposed on the rear of the tow
vehicle when a conventional caravan snakes.
Further, as it reduces the effect of tow ball
weight from the tow vehicle’s rear tyres, it
reduces their ‘cornering power’. This is rarely
an issue in normal driving, but it may become
an issue unexpectedly in an emergency swerve
and/or by side wind forces, for example from
closely passing trucks.
In effect, a WDH assists to solve one issue
but imposes another. Heavy caravans towed by
a vehicle that is lighter need a WDH. That tow
vehicle cannot otherwise cope. But with a WDH
in use, experts in this field state it cannot corner
as effectively as before. It has, in fact, become
a major part of the US J2807 Recommendations
for Towed Vehicles, accepted by all US and most
of Japan’s vehicle makers.
Since 2015 or so, a prominent WDH maker
has advised users to adjust WDHs to restore
only 50% of that ‘lost’ weight from the front of
the vehicle: this lessens undesirable effects.
Caravanners can reduce the risks in various
ways: Never speed, particularly on motorways
or downhill. Never have anything heavy at a
caravan’s extreme rear. Choose a tow hitch
with the shortest possible overhang. Never
increase tow vehicle front tyre pressures for
towing. Ideally reduce by about 3-5 psi (20-
35kPa). Its rear tyre pressure needs to be
about 5-7 psi (35-50 kPa) higher when towing.
It can be proportionally lower for tow ball mass
below 200 kg: some adjustment is advisable
but exactness is not critical.
SPEED
When towing, do not even think of exceeding
100 km/h (and this does not imply even that
speed is safe for all caravans). Also, be ultra
careful of any caravan that has less than 5%-
7% tow ball weight.
Be aware that a fundamentally unbalanced
rig may appear fine in normal and mildly
‘abnormal’ driving. It is rare to encounter the
forces high enough to trigger a jack-knife —
but some do.
By far the major risk (for most rigs) is speed:
the heavier the caravan and lighter the tow
vehicle, the lower the speed at which a jack-
knife is likely.
If your caravan is heavier than your tow
vehicle, in my opinion it would not be wise to
rely on a WDH for towing stability, but fine for
borderline situations.
The only ethical advice is to either buy
a heavier tow vehicle or lighter caravan,
as adding a WDH fixes one problem but
introduces others. The rig may well feel more
stable but its ultimate cornering power is
inherently reduced. That loss can be reduced
(but not eliminated) by adjusting the WDH.
If stability remains a concern, consider
purchasing a fifth wheeler. Because their point
of attachment is directly (or almost directly)
above the rear axle(s) of the tow vehicle, they
are inherently more stable than a caravan
because if either the tow vehicle or fifth
wheeler sways slightly, one does not in any way
affect the other.
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