Caravans and their tow vehicles rarely jack-knife and roll over – but when they do the results are catastrophic. The cause, and how to prevent it, is explained here in plain English.
The issue is not how your rig behaves in normal driving. It is what it will do in a strong emergency swerve, or hit by strong high side wind at speed. What happens is this. All motor vehicles are designed to automatically turn slightly away from disturbing forces. This also keeps them straight on cambered roads. This effect, called understeer, is totally vital for any vehicle towing a trailer via a tow hitch that is behind that tow vehicle’s rear axle.
When a tow vehicle yaws (sways) hitch overhang causes the trailer to yaw in the opposite direction. This causes (not just permits) the tow vehicle to yaw in the opposite direction. Minimising that overhang assists but the issue is inherent. If that rig yaws strongly at speed that vital margin of understeer is lost. The rig is then all-but certain to jack-knife and likely overturn.
Totally known and long understood causes of reduced understeer include overloading, incorrect tyre pressures, overly-corrected weight distributing hitches, too-heavy tow loads etc.
Also important is the ratio of laden tow vehicle weight to laden trailer weight, and how that trailer is designed and laden.
Tow ball mass too is vital – 10% of laden caravan weight is really needed and must stay reasonably constant. Overturning rarely has one single cause, but several minor ones that interact.
Why Caravans Roll Over – and how to prevent it explains all in truly plain English. It even includes a simple way of assessing the likely stability of your own – and what you can do to make it very much safer.
Colin Young
Founder and CEO
Caravan Council of Australia
Publisher Marketing:
In conjunction with caravan and other issues, your tow vehicle's margin of understeer ultimately determines your rig's stability and especially how it will act in an emergency swerve at high speed.
If understeer is reduced to zero (or minus) the tow vehicle will oversteer. If not corrected in time the rig may jackknife, especially at high speed.
Why Caravans Roll Over examines causes of caravan roll over in detail and in plain English. It provides ways to evaluate and improve the safety of your own rig. It identifies high risk situations and gives clear advice about how to avoid the dangers that are very much a part of towing a caravan.Originally trained as an RAF ground radar engineer, Collyn Rivers spent a brief time with de Havilland designing power systems for guided missiles, before becoming a test engineer at the Vauxhall/Bedford Motors Research Test Centre. He migrated to Australia in 1963, where he designed and built scientific measuring equipment. In 1971, Collyn Rivers founded what, by 1976, became the world's largest-circulation electronics publication, Electronics Today International. From 1982 to 1990 he was technology editor of The Bulletin and also Australian Business magazines and in 1999 started two companies: Caravan and Motorhome Books, and Successful Solar Books (now rvbooks.com.au and solarbooks.com.au). Anyone who has been an electronics enthusiast over the past 30 years or so will be well aware of Collyn Rivers. He was the founding editor of Electronics Today International (ETI) magazine which went on to have a number of very successful editions in the UK and elsewhere, as well as being very successful in Australia. Silicon Chip Magazine
