Call for safer tow vehicles

An outspoken caravan safety campaigner has put forward a strong argument as to why a tow vehicle should ideally weigh more than the caravan it's towing.

'Sharing the road' advocate and founder of the Truck Friendly program, Ken Wilson, recently likened the centrifugal forces experienced by an Olympic hammer thrower as similar to that of an 'under-weight' tow vehicle being pushed around by a heavy caravan.

"A person swinging the hammer in circles and eventually releasing it must be heavy and strong enough to resist those substantial energy forces so that they can remain upright in the throw circle and maintain control of the hammer prior to release," he explained on social media recently in a blog titled 'Why don't we see a lightweight hammer thrower at the Olympics?'.

"A lightweight tow vehicle (the athlete) can easily be thrown around by the centrifugal and other forces from a heavy caravan (the hammer)," Wilson said.

"It is therefore very important to caravan towing stability, and safe towing practice that the fully loaded tow vehicle is heavier than the fully loaded caravan under tow.

"The athlete with longer arms also has a slight advantage as longer arms means that the swinging circle diameter is slightly larger, meaning there can be more speed per rotation and more kinetic energy built up before the launch," he continued.

"Likewise, with a caravan, the more weight you have further away from the pivot point or axles of a caravan during caravan sway the greater the kinetic energy.

"Caravans with a lot of weight on the rear will have more kinetic energy built up during a caravan sway event and therefore will be harder to stop."

Also read: Thinking outside the caravan box - the case for a caravan wheel in each corner

Wilson said that unlike most big truck rigs which utilise a more stable 'overhung' hitch set-up commonly referred to as a 'dog trailer', the 'pig trailer' set-up used to connect most caravans in Australia is inherently unstable.

"The semi-trailer was specifically designed with the ‘fifth wheel’ or turntable over the rear axles for stability. With hitches directly over the rear axles, they do not have the yawing that pig trailers experience," he said.

"A typical caravan tow vehicle, however, has an overhung hitch where the hitch is 1 – 1.5m rear of the rear axle.

"This set-up means that when the tow vehicle front turns right the rear hitch moves left, with a flow on effect to the caravan of the caravan hitch moving left with the tow vehicle hitch and the rear of the caravan moving right.

"This action and reaction, due to the overhung hitch and pivot point (axles of the caravan being basically in the centre), cause yawing back and forth as the tow vehicle moves left and right.

"The longer the van the more pronounced the sway as there is more overhang to move left and right.

"The more weight that is on the end of this pendulum/caravan the more pronounced and unstoppable the sway will be."

As well as matching the tow vehicle's weight with the caravan's to help avoid a 'tail wagging the dog' scenario that contributes to caravan sway and a potential roll-over, Wilson also recommends loading any heavier items in the caravan over the axles, and to avoid putting heavy items like toolboxes on the rear bumper bar.

It's also important to check that both the tow vehicle and caravan fall within the legal and manufacturer stipulated maximum weights including the GCM (Gross Combined Mass).

Also read: How to stop caravan sway

Ken Wilson is the latest RV safety specialist to highlight a need for tougher tow vehicle laws, with Caravan Council of Australia founder Colin Young recently calling for some tow vehicles with insufficient weight and power to be prevented from hauling heavier caravans, even if they are legally allowed to tow up to 3500kg.

"There have been too many serious and tragic accidents, and many more frightening incidents, involving caravans on our roads," Young said.

"Obviously driver, road, and atmospheric issues frequently partially contribute to the cause of these events, along with mechanical failures of the tow vehicle or caravan.

"However, in numerous instances, the prime cause has been the fact that the tow vehicle was not suitable for towing the particular caravan."

Related: Strong case for caravan towing licence