Trailer sway - what is it and how to deal with it
Wednesday, 26 June 2019
Trailer sway is frightening.
It can be deadly.
Imagine heading up the highway with a caravan in tow on a bright day, overtaking a slow truck in a passing zone when, without warning, a wilful van wants to swap ends.
Oncoming truckers pull to the side of the road.
Travellers behind pull back and hold collective breaths.
There’s a studied silence in the cabin as a bucking van tries to throw the outfit off the road and into the bushes.
What happens next could - in a matter of seconds - be catastrophic.
Trailer sway - or yaw or fishtailing or snaking - is probably more common on today’s roads than Australian accident statistics may reveal; some vanners may only mention incidents over an evening ale.
And remedies for trailer sway are not always intuitive, says Stefan Drew at Melbourne Trailer and Caravan Supplies.
“The severity of trailer sway ranges from a sudden frightening, but short-lived incident, all the way to causing a complete loss of vehicle control,” adds Stefan.
He’s a proponent of electronic stability controls on caravans to best control situations before they become an accident.
WHY DOES THE TRAILER SWAY?
A swaying van or trailer can be caused by a number of issues:
- Underinflated tyre pressures.
- Uneven or over-loading.
- Poor, uneven hitching.
- Inappropriate speed.
- Oncoming vehicles.
- Low pressure area when passing another vehicle.
It can happen on good bitumen and in good weather.
And once a van begins to sway that swinging, snaking motion may increase through the fulcrum at the hitch point.
(This is where fifth-wheelers have an advantage with the tow point over the vehicle’s back axle.)
WHAT DO I DO WHEN IT DOES SWAY?
So what to do? Most experts agree:
- Stay calm and hold a steady course.
- DO NOT try and steer out of the sway.
- Get off the accelerator.
- Don’t brake the tow vehicle.
- Apply – gently - the van’s electric brakes with dashboard controller.
Pull over and check load, tyres and hitch level.
Most sway problems appear to begin with an uneven load upsetting the dynamics of the rig.
Vanners have responsibilities here to check the distribution, and weight, of their loads plus tow ball limits; also check the vehicle’s handbook for any towing limitations.
Some new vehicles sold in Australia, such as Ford’s Ranger, now have trailer sway systems inbuilt where “for moderate sway, the front brakes will engage in a left-right alternating pattern to generate a yaw movement in the vehicle that counteracts the trailer sway.
For more severe sway, engine torque is reduced to zero and brake pressures are applied to all four wheels in order to reduce the vehicle’s speed below the trailer’s critical speed.”
Today there are also electronic stability controls for vans which monitor trailer sway, or yaw, and correct inconsiderate moves by braking the wheel(s) on one side of the van.
These can be retrofitted to trailers with electric brakes; best check through AutoGuru with one of the many car and towing experts around the country.
Bruce McMahon is a Queensland-based journalist who’s spent a fair slice of his career dealing with automotive matters.
His first car was a 1949 Riley Roadster, followed by a mix of machinery from Porsches to Jeeps, Alfa Romeos and Range Rovers through to the current four-wheel drive Mazda ute.
He’s driven the Nurburgring and the Tanami Tracks.