by Rob Caldwell - Updated May 2017 Truck wind forces on This paper explains how overtaking a fast moving truck, or being passed by one can exert dangerous truck wind forces on . The original of this paper ‘ and Trucks Sharing Roads...
For decades both caravan owners and vendors have emphasised the need for a laden tow vehicle to at least weigh as much as the laden caravan. Length and caravan stability, and where weight is distributed over that length, is now being seen as more significant.
Making caravans more stable is readily possible by design, loading, and tow vehicle use and choice. This article by Collyn Rivers explains how. It also provides practical guidelines for buying a caravan and tow vehicle, their loading and on-road usage. For a full technical explanation of why rigs can be unstable please see my Caravan and Tow Vehicle Dynamics/. See also Why Caravans Roll Over/
Wheels falling off trailers, wheel studs breaking and wheel nuts loosening still happens. Here is why it happens, and how to prevent it. Wrecked wheel bearings and fractured stub axles are also common. That fastenings such as wheel nuts may be caused, not just permitted, to loosen is rarely covered in engineering training. The causes and prevention are however well known. This referenced article by Collyn Rivers explains how and why in rigour and detail.
Should I grease my tow ball is asked by caravan owners worldwide. A recent poll in Australia’s Caravanners Forum.com showed that slightly over half do so, but primarily to reduce wear. That seemingly overlooked by almost all respondents is that tow ball friction plays a vital role in reducing caravan sway. Those who grease them unwittingly prejudice safety for the possible need to renew the towball every ten or so years.
In the early 1900s, trailers with central axles, towed by trucks with overhung hitches, were unstable. This escalated as towing speeds increased. Fruehauf (USA) realised hitch overhang imposed lateral forces on tow vehicles. As trailers yawed clockwise, that overhang caused tow vehicles to yaw anti-clockwise. And vice versa. The longer that hitch overhangs, the greater the effect.
The current (February 2018) Australian RV rules and regulations are outlined here by Collyn Rivers of RV Books. Those for trailers under 4500 kg (9920 lb) will change in late 2018 but details are not yet available
Australia has two main and seemingly interdependent caravan industries. One makes caravans of varying stability. The other makes devices (of varying effectiveness) intended to increase that stability. Both are curious. Not all makers appear to understand the more basic laws of physics involved. Or perhaps assume immunity from them. So presumably do owners of ultra-long caravans. With a few rare exceptions, there is a caravan design need for change. And for caravan owners to realise a caravan’s inherent stability issues.
A weight distributing hitch is not needed if the laden weight of the tow vehicle is equal to or exceeds that of the laden caravan. Nor is a weight distributing hitch needed for any trailer under about 4 metres.
Caravan suspension has requirements that are very different from tow vehicles. This is only too often misunderstood. Here’s why and what it should be.
That caravans roll-over yet most vehicles don’t show trailer dynamics is not understood or is ignored. Trailer dynamics simply explained tells why. The main cause is that hitch extending from the tow vehicle’s rear. It not only allows but causes both tow vehicle and caravan to sway (yaw). Worse – if one yaw’s clockwise it causes the other to sway anti-clockwise. The further the tow ball behind the tow vehicle’s rear axle, the greater that effect.
Do caravans need independent suspension is a marketing rather than an engineering issue. This article explains why caravan beam axles are generally better.
A conventional caravan must always be a compromise. This is because it is towed via hitch at some distance behind the tow vehicle’s rear wheels. If that vehicle sways clockwise, that hitch overhang causes (not just permits) the caravan to sway anti-clockwise. If the caravan sways clockwise, it causes the tow vehicle to sway anticlockwise. is essentially an unstable concept but safe within limits.
The maximum caravan weight safe to tow depends on what tows it. This article by Collyn Rivers explains why – and how to know what it is.
Long end-heavy caravans have a need for a Weight Distributing Hitch (WDH). For all, though, it inherently reduces tow vehicle stability. Here’s how and why.
Reducing caravan sway (yaw) necessitates minimising its causes – and only then adding devices promoted as reducing it. This article shows why and how.
Fifth wheel caravans are safer than conventional caravans. They are fundamentally more stable on road and far less likely to overturn. Further, because up to two metres more is usable space, they provide that much more living area. They increasingly challenge caravan and motor home sales.
Driving across Africa is now politically impossible. Our 1960 such two-way expedition across all Africa was the very last known. We started in mid 1959 – and exited the Sahara on 28 April 1960. The track was closed that night. It has never re-opened. Further, Africa’s centre, right down to Zambia, has ever since, been far too dangerous to even consider.
On the surface, the Australian RV industry is healthy. But underneath all is far from well. A great deal needs changing. There are lots to do. RV Books explains the RV industry changes needed.