Why Caravan Rollovers Happen - updated Dec. 2018

Pic: NT Police

Pic: NT Police

Introduction

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 are causative factors in caravan rollovers.

Please read this article to make sure you don't become another rollover statistic.

Rollover Videos

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.

If you have any difficulty watching these videos on our site, you can see them here, here and here.

Rollover Factors

A caravan rollover rarely happens as the result of one factor - there usually several forces involved.

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. The forces involved increase with the square of the speed, e.g. the forces involve with a rollover at 100 km/h are four times higher than those at 50 km/h.

Exceeding Critical Speed

Critical speed is the speed at and above which an unstable tow vehicle and trailer becomes literally impossible for the driver to correct if subjected to a strong enough disturbing force. Yaw (sway) builds up within a few seconds, the rig typically jack-knifes and is likely to roll over. There usually little or no warning. That is why drivers often say 'it always 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 laden trailer is heavier than the laden tow vehicle (irrespective of the maximum weight capacities of each) and the combination has swaying that escalates, the trailer is likely to dictate what happens next.

Overhung Hitch

With a trailer attached, an overhung hitch acts as a lever on the rear of the tow vehicle. That overhang 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 virtually a recipe for swaying.   

External Factors

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 (side) 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

This topic is too complex to fully explain in article form. RV Books, however, is currently completing a low-priced mini-book. It is by Collyn Rivers - who has spent much of his life studying and working in this area. The book explains all (in plain English). It contains a section that enables owners to obtain a reasonable estimate of their rig's stability and suggestions of what can be done to improve this.

The book (in downloadable digital form from this website) is currently planned to be on sale by March/April 2019 - and obtainable directly from this website.   

RV Books' forthcoming publication

This topic is too complex to fully explain in article form. RV Books, however, is currently completing a low-priced mini-book. It is by Collyn Rivers - who has spent much of his life studying and working in this area. The book explains all (in plain English). It contains a section that enables owners to obtain a reasonable estimate of their rig's stability and suggestions of what can be done to improve this.


The book (in downloadable digital form from this website) is currently planned to be on sale by March/April 2019.   

Avoiding Caravan Rollovers

Our forthcoming book will explain more: meanwhile - 

  • 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.

why not buy a book?

This article is based on content from our featured RV books. These books contain extensive information on a range of topics of interest to RV users and potential buyers. By purchasing a book, you are not only educating yourself but also supporting the work of independent RV writers. If you have found this article useful, please also visit the RV bookshop.

 

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