by Collyn Rivers
Towing Without a WDH
Towing without a WDH (weight distributing hitch) is often feasible. A WDH is not needed if a tow vehicle’s laden weight is equal to or exceeds that of the laden caravan. Nor is a WDH needed for any trailer under 4 metres. A WDH may even cause instability.
Many caravanners ask about towing without a WDH
A WDH attempts to compensate for issues better avoided. One is towing a laden caravan that exceeds the laden weight of whatever tows it. It is, for example, common to see 2500 kg (laden) dual-cab utes towing 3500 kg (7715 lb) caravans. Another is towing a caravan longer than six or so metres.
For on-road stability, a conventional caravan needs to be nose-heavy by 8-10% of its laden weight. When hitched to its tow vehicle that (typically 200-350 kg [440-770 lb]) pushes down the rear of that vehicle. In doing so, that levers up the front of the tow vehicle. This reduces the weight on the tow vehicle’s front tyres.
Where, however, that tow ball weight is comfortably within the laden tow vehicle’s payload, that front tyre weight reduction is too small to be an issue. It is, however, necessary to increase tow vehicle rear tyre pressure by 50-70 kPa (7-10 psi).
Some caravan owners fit a WDH because a sales-person advised it. Or by following misleading advise on Australian caravanners forums. Fitting a WDH when not needed, can introduce unwanted issues. Towing without a WDH is preferred unless really needed.
Weight distribuing hitch. Pic. Jayco.
How a Weight Distributing Hitch works – and its unwanted effects
A Weight Distributing Hitch is, in effect, a springy light beam. By levering up the rear of the tow vehicle, it restores weight (down-force) from the tow vehicle’s rear tyres to its front tyres. While a good and useful concept, a WDH only counteracts tow ball downforce. By reducing tow vehicle rear tyre loading, those tyres become less able to counteract the yawing caravan‘s side forces on the rear of the tow vehicle.
The overall effect of a WDH is thus to reduce the rig’s ‘cornering power’. It does so by an appreciable amount. The USA’s J2807 Standard notes that ‘cornering power’ is reduced by 25%. Furthermore, those strong side-forces on the tow vehicle’s rear tyres may even cause those tyres to steer the tow vehicle. If that happens a jack-knife is virtually inevitable.
The above does not imply that the rig inevitably misbehaves at speed – but it is more likely to if ‘hit’ by a strong enough side force – such as wind gust. Or by cornering too fast. There is, however, a correlation between tow ball mass and safe speed. The lower that mass, the lower the safe speed. There is a very strong argument for that traditional 10%-12%. In the USA it is often 14%.
Towing Without a WDH – Summary
Fitting a WDH to a rig that does not need one is not only pointless. It introduces issues that do not exist without one. Towing without a WDH is feasible if the laden caravan weighs the same or less than the laden tow vehicle. Towing without a WDH is also feasible for correctly laden caravans less than six or so metres (about 20 feet).
If the weight issue is only minor, towing without a WDH is feasible by carrying the caravan’s spare wheel in the tow vehicle.
A full explanation of Towing Without a Weight Distributing Hitch (WDH) is feasible is in our book Why Caravans Roll Over – and how to prevent it.