If you tow a trailer using a tow bar there’s a risk that the trailer can swing from side-to-side if it’s not loaded correctly. What starts as a moderate trailer sway can quickly turn into a situation where it jack-knifes the car and trailer or flips over the trailer and (in the worst case) the car, too.
What causes trailer sway or trailer swing?
Trailer sway can happen with any type of heavy trailer where it’s connected to the car behind the rear wheels. Any of these can cause trailer sway:
- High-sided trailers like caravans can be influenced by strong, gusty side winds or buffeting from oncoming lorries – side winds can exert more than a ton of force on the side of a caravan
- Driving with a horse float can be challenging if the horse moves at the wrong time
- Changing direction rapidly (e.g. on twisting roads)
- Uneven tyre pressures in the trailer
How can you prevent trailer sway?
Correct trailer loading and balance
Having an unbalanced load where it’s heavy over the back of the trailer causes lift on the tow bar and that reduces the grip on your towing vehicle’s rear wheels. Keep the heavy items down low and near the centre of gravity.
Over-inflated tyres have less grip on the road and are more likely to cause the trailer to slide out on corners. Once the trailer grips again it will swing back and could create a pendulum motion. Low tyre pressure on one side will cause more drag on that side and will mean that the trailer will lean to that side as the tyre is flatter.
Scanning and anticipation
Looking ahead for risks and slowing down before you get to them is the most effective way of reducing risk. Slow down if you’re coming up to an exposed bridge where you could have strong gusts of wind, if you’re approaching big lorry coming the other way that will be pushing a pressure wave of air ahead of it, and if you’re coming up to a road with quick left-right turns.
Buying the right tow bar
Some towing hitches have more friction to make it more difficult for the trailer to sway. You could also use a fifth-wheel attachment as these sit either over or in front of the rear axle.
How can you stop a trailer once it’s swaying?
Trailer sway mitigation
Some cars have technology called trailer sway mitigation, trailer sway control or trailer stability control (depending on the manufacturer). This uses the same system and principles found in electronic stability control to automatically brake each wheel to bring stability back to the trailer much quicker than the driver can react. This system doesn’t use the trailer brakes, only the brakes on the towing vehicle.
Caravan electronic stability control
There are systems that detect the g-forces on your caravan and can apply the caravan brakes
If you don’t have trailer sway mitigation then you’ll need quick reactions:
- If you can apply the trailer brakes separately, do it immediately as it will drag the trailer and stop it swinging
- Don’t accelerate – you’ll make it much worse as you just increases the energy that the swinging caravan has
- Take your foot off the accelerator but don’t hit the brakes unless it’s an emergency (e.g. you’re about to hit another vehicle or go over a cliff)
- Steer gently against the motion of the trailer; as the car loses speed the trailer will come back under control automatically, but you need to keep it on the road and stop it from spinning you around.