trailer sway

Just the word sends shivers down the spine of every traveller.  Nothing will ruin that wonderful feeling of heading off with your family camping than your first experience of sway.  So what causes it, and how can you avoid it? 

As you head off down the road with your most precious cargo in your tow vehicle, the salesman you spoke to about your trailer and what you need to know are a distant memory.  Something about hitch height, tongue weight, load placement?  Surely you know what you're doing.  Just pack your gear and head off.  You've done it a million times before.  This is just the same only now with this nice new trailer you can pack more gear in, right?  Wrong !  All of these things now become even more important than they were before.


But before we look at hitches, tongue weight and load placement, lets look at things we have little or no control over that can affect sway.

Wind can create havoc when towing a trailer.  Thirty mile an hour crosswinds suddenly hitting the side of your trailer can blow you right off the road.  Your trailer suddenly pitches to the left from a big gust.  Instinct kicks in and you pull the wheel to the right to bring it back in line.  Just what the trailer didn't need and now it pitches to the right.  You pull the wheel again to the left and on and on it goes until disaster occurs and you find yourself in an extremely life threatening situation.

The best way to avoid this situation before is occurs, is slow down.  If you really need to travel on a extremely windy day, take it slowly.  If at all possible, do not travel at all in these conditions.  Park until it is safe to continue.  Wind can also take it's toll on your fuel mileage, particularly when pulling a heavy weight.

Another cause of sway that you can have little control over is the passing of busses or large trucks.  Trucks push a large volume of air in front of them and a low pressure area behind them which affects vehicles alongside of them  as they travel down the highway.  The severity of this can change depending on the size and shape of the truck and the wind conditions at the time.  As the truck comes alongside to pass you, you will first feel your trailer and then your tow vehicle being pulled into the truck's "bow wave"  As the truck passes, the low pressure zone will then push you away.  This causes you to first steer in one direction to hold your rig away from the truck, and then in the opposite direction to bring it back in line.  This in itself is not particularly dangerous, but if your trailer is not correctly hitched, levelled or weighted, this could quickly turn to disaster.

Motorhomes and fifth wheel trailers tend to have less problems with sway.  The stability of a fifth-wheel trailer lies in its design.  The hitch is located over the truck's rear axles which limits lateral movement.  The conventional trailer however has a ball attachment, and the fact that this is located approximately 5 feet behind the rear axle of the tow vehicle makes it more susceptible to lateral instability.  This creates two pivot points - the ball and the center of the axle. 

Lastly, poor trailer design can contribute significantly to sway.  If there is significant weight behind the axles (which causes the tongue weight to be light) and if this tongue weight is than 10% of the total trailer weight, there will be a natural tendency to sway.

Instability and sway can be considerably reduced by using a weight distribution hitch (which in effect moves the weight back on to the front axles of the tow vehicle) and a sway control bar.  See articles on WDH and Sway Control Bar.

Using a sway control device can give you peace of mind. It is recommended by nearly every tow vehicle manufacturer, and is required by law for over a certain weight. The cheapest and most common is a friction sway bar, but there are others (a dual cam sway control system is very good at preventing sway from ever getting started).  Whichever device you decide on, make sure it is the correct one for your particular situation.

Lastly, avoid high speeds, sudden movements and don't forget what is actually keeping you on the road – tires.  Although sway can occur at any speed, it's likelihood will increase with speed. A trailer travelling 65 mph may seem steady, but at 74 mph could easily brake into a sway.  Any sharp pulls on the steering wheel in any direction will be felt two fold in your trailer.  Always be alert and allow ample time to react smoothly and safely.

A sway is more likely to occur when going downhill. This is brought about by the trailer trying to go faster than the tow vehicle (pushing it along).  Normal engine braking will hold back the vehicle, but with the additional weight of a trailer, it becomes very difficult as the trailer continually tries to overtake.

Take it slowly, stay alert and arrive safely and in one piece at your destination.

other articles that may interest you
towing terms
tow hitch
weight ratings
sway prevention
trailer tires
tow vehicle
weight distribution
scale weights
trailer wiring
trailer towing
tongue weight
backing up
loading the trailer
general maintenance



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