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.
This book has to be the best $29.95 you will ever spend.
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