Trailer Sway: What Causes It and How to Stop It

If you've towed for any length of time, you may have felt it: the trailer starts to wiggle behind you, and the wiggle grows. That's trailer sway, and it can turn a calm drive into a scary one in a few seconds. The good news is that most sway can be prevented, and knowing what to do when it happens makes a big difference.

What sway looks and feels like

Sway is when the trailer swings side to side behind the tow vehicle, like a pendulum. It might start as a gentle shimmy you feel through the steering wheel. If it keeps going, the trailer can start pushing the back of your vehicle around.

It often shows up:

• When a semi truck passes you
• In strong crosswinds, especially on bridges and open highway
• Going downhill, when the trailer is pushing
• After a sudden steering move

The most common causes

1. Not enough tongue weight. This is the big one. When too much of the load is behind the trailer axles, the trailer acts like a pendulum. The fix is to load about 60 percent of the cargo weight ahead of the axles. Our tongue weight guide explains how.

2. Too much speed. Sway gets worse as speed goes up. A trailer that tows fine at 55 mph might start to sway at 70.

3. Low or mismatched tire pressure. Soft trailer tires or tow vehicle tires flex more and make the whole rig less stable. Check pressure cold before every trip.

4. A load that shifts. If cargo slides during the drive, the balance changes. Strap it down properly. See our tie-downs guide.

5. A tow vehicle that's too light for the trailer. A heavy trailer behind a light vehicle has more leverage to push it around.

6. Rear sag. Too much tongue weight can lift the front of your vehicle, which takes weight off the steering tires. A weight distributing hitch can help level things out.

How to prevent sway

• Load it right: about 60 percent of the weight in front of the axles, heavy items low and centered
• Check tire pressure on both the trailer and tow vehicle
• Strap everything down so the load can't shift
• Keep your speed moderate, especially in wind or on downhill grades
• Stay within your ratings for towing capacity and payload
• Consider a weight distributing hitch, many of which include sway control. Both of our rental trailers can have one added. Ask when you book.
• Set up your brake controller correctly if the trailer has electric brakes

What to do if the trailer starts to sway

This is the part to remember. Your instincts may tell you to do the wrong thing, so it helps to think it through ahead of time.

1. Ease off the gas. Don't hit the brakes hard. Let the rig slow down gradually.
2. Hold the steering wheel steady and straight. Don't try to steer against the sway. Quick corrections can make it worse.
3. If you have a brake controller, gently apply the trailer brakes by hand with the manual lever. This pulls the trailer back in line behind you. Only the trailer brakes, and only lightly.
4. Don't speed up to "pull out" of it. That's a myth, and it can make things much worse.
5. Once the sway stops and you're under control, signal and pull off somewhere safe.

After a sway event

Don't just get back on the road. Something caused it, so find out what:

• Did the load shift? Restrap it.
• Is the tongue weight too light? Move heavy items forward.
• Are the tires properly inflated?
• Is the hitch and ball mount tight?

Then drive a little slower for the rest of the trip.

Know your brake controller

Using the manual lever on your brake controller is one of the best tools for stopping sway, but only if you know where it is without looking. Practice reaching for it in a parking lot before your trip. Our guide to trailer brakes and brake controllers explains how they work.

The takeaway

Most sway comes down to loading, speed, and tires. Get those right, and you'll rarely feel it. If it does happen: off the gas, steer straight, gentle trailer brake, and stay calm.

You can find these tips and more on our Towing Safety page. Follow us on Facebook for a new towing tip every week.