Why Caravan Rollovers Happen
Our article listing caravan rollover reports in the media is an unfortunate reminder of how common this type of accident is in Australia.
RV Books is working with Australian insurance companies to find out how many rollovers there are each year in Australia and whether rollover numbers are increasing or decreasing. Further work is needed to determine the exact cause of these accidents, but there are some fundamental principles of physics involved that can be causative factors in caravan rollovers.
Please read this article to make sure you don't become another rollover statistic.
In the videos below, a caravan has become unstable with catastrophic consequences. These accidents were due to a range of factors both within and outside the driver's control.
Factors within the driver's control include speed, weight of both the caravan and tow vehicle and the distribution of that weight, particularly in the caravan.
Factors outside the driver's control include road conditions, wind resistance and side winds.
What is interesting about all three videos is that the accidents happened whilst towing on a flat road in a straight line. No bends, hills or obvious cambers. This is quite common.
A caravan rollover does not happen as the result of one factor - there are many forces at play:
High Absolute Speed
A caravan rollover rarely happens at low speed. The tow vehicle and trailer combination is usually travelling at high speed when a rollover happens, often in association with overtaking another vehicle.
Exceeding Critical Speed
Critical speed is the speed at and above which an unstable tow vehicle and trailer becomes impossible to correct if subjected to a strong enough disturbing force.
Above critical speed, anything can happen and if it does, happens within a few seconds and with little or no warning. That is why drivers often say 'it felt so stable before the rollover'.
Every tow vehicle and trailer has a unique critical speed. Some rigs that have a much heavier trailer than the tow vehicle (or inadequate tow ball mass) may have critical speeds well below the towing speed limit.
Overweight Trailer and/or Tow Vehicle
If a trailer or tow vehicle is loaded beyond any of the maximum weight limits of trailer, tow vehicle or towing equipment manufacturers, it risks becoming unstable. It is also illegal.
Incorrect Trailer Weight Distribution
Heavy loads at the front, rear or top of a trailer causes instability. Caravans that have rolled over are sometimes found to have heavy loads in these locations.
Tow Ball Mass
Having inadequate tow ball mass is a significant contributing factor to rollovers. Without adequate tow ball mass, the trailer will seek to deviate from the path set by the tow vehicle and may cause the trailer to sway. Sway is often the pre-cursor to a rollover.
Tow Vehicle/Trailer Weight Ratio
If the weight of the trailer is too high in relation to the tow vehicle (irrespective of the maximum weight capacities of each) and the combination is subject to an external force, the trailer will dictate what happens next.
With a trailer attached, an overhung hitch acts as a lever on the rear of the tow vehicle. The distance from tow vehicle rear axle to tow vehicle tow ball needs to be as short as possible to minimise this leverage effect. Long distances between axle and tow ball (sometimes as a result of user modification to the tow bar or tow ball) is asking for trouble.
These are factors over which a driver has no control. When not towing, these factors can be relatively innocuous for passenger cars, but with a trailer behind they can assume a significant role. They include:
- a wind gust, which can be natural or caused by a vehicle coming in the opposite direction
- increased or decreased air pressure as a result of overtaking or being overtaken
- road camber, which can gently push a trailer off to the side of the road. (Over-) compensating for road camber can send a tow vehicle and trailer sharply towards the middle of the road
- adverse weather and road conditions
Avoiding Caravan Rollovers
The best thing you can do to avoid becoming involved in a rollover is self-education (exactly what you are doing now). And when you are on the road:
- do not exceed the speed limit (especially when overtaking)
- do not overload or incorrectly load either your tow vehicle or (especially) your trailer
- make sure your tow ball mass is correct
- do not tow using a tow vehicle that is lighter than the trailer
Find out more about each the factors described above in our general and technical articles and in our books.
Then put this knowledge into action by buying the right tow vehicle and trailer combination and loading and driving it sensibly in accordance with our guidelines.
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