by Collyn Rivers
Weight Ratio
Safe caravan towing depends on the tow vehicle always being under the driver’s control. That ability is compromised if the caravan is heavier than the tow vehicle. It also reduces the safe towing speed. In this article, the tow vehicle/caravan weight ratio is explained.
A caravan heavier than its tow vehicle is like a dog with an overweight tail, it may sway so much its tow vehicle cannot control it. Swerving strongly at speed to avoid a head-on collision induce this. So too may a strong side wind gust. That wind may be natural or from a close passing truck.
NOT a good tow vehicle to caravan weight ratio (Pic: source unknown)
The Ideal Caravan Weight Ratio
A century of caravan towing shows that a laden tow vehicle must weigh at least that caravan being towed. This has long been accepted in the UK and Europe. There, laden caravans must not exceed about 80% of the weight of the laden tow vehicle. And that’s despite most having towing speed limited to 80 km/h. Many such countries limit the maximum weight of caravans and towing combinations.
Australia currently (2020) has no current legislation on tow vehicle/caravan weight ratios. Many local of our caravans outweigh their tow vehicle. Despite this, they may travel at 100 to 110 km/h. The accident rates steeply increased in 2015. That year many new over two-tonne (twin-axle) caravans were sold.
Limit towing to 80%
RV Books recommend newcomers limit towing to 80% or so of the weight of the tow vehicle. Furthermore, to confine speed to 80 km/h for a few hundred kilometres as they gain experience. Whilst doing so, the caravan should be significantly lighter than the tow vehicle. Experienced caravanners could tow up to about 100%. It is, however, preferable to keep a 10% margin. It may be critical in an emergency swerve.
Towing risk is speed-related. The greater the weight of the caravan to tow vehicle the lower speed should be. Ideally, never exceed 100 km/h – particularly while overtaking.
For safe towing, your actual laden weight of the tow vehicle should be as high as legally possible, and the laden weight of the trailer adjusted accordingly. Never vice versa.
tow ball mass and safe towing speed are related. The lower that mass the lower is safe towing speed.
To learn more about towing dynamics, read our technical articles on Moments along a Beam, the Double Pendulum Principle and Overhung Hitches.
RV Books Why Caravans Roll Over – and how to prevent it explains, in plain English, exactly what happens. And why. It shows how to assess your own rig’s probable stability. It also tells how to increase that vital stability. The book includes a technical explanation and extensive references.
