Trailer sway is the side-to-side oscillation of a trailer that occurs while towing. When trailer sway begins, the trailer starts rocking from side to side, and the motion can transfer to the tow vehicle if not corrected immediately.
What Causes Trailer Sway?
Trailer sway is caused by forces acting on an improperly balanced or undercontrolled trailer. The most common causes include:
- Too much tongue weight at the rear: When more than 60% of the trailer’s cargo is loaded behind the axle, it makes the rear of the trailer heavier than the front, which promotes sway.
- Insufficient tongue weight: Tongue weight that is too low (less than 10% of the trailer’s Gross Trailer Weight) reduces the coupling’s ability to stabilize the trailer.
- Speed: Sway is more likely at highway speeds above 55 mph. The higher the speed, the more severe the sway can become.
- Wind and crosswinds: Strong gusts from passing semis or crosswinds push the trailer sideways, initiating oscillation.
- Overloaded trailer: A trailer loaded beyond its rated capacity handles unpredictably and is more prone to sway.
- Soft tires: Underinflated trailer tires allow excessive sidewall flex, which can amplify trailer movement.
How to Stop Trailer Sway
If trailer sway begins while driving, do not brake hard or try to steer out of the sway. Hard braking and counter-steering can make sway worse and cause a jackknife or rollover.
The correct technique to stop active trailer sway:
- Ease off the accelerator — reduce engine power gently and let the vehicle slow naturally.
- Hold the steering wheel firmly — resist the urge to steer against the sway; keep the wheel steady and pointed straight ahead.
- Apply the trailer brakes manually — if your brake controller has a manual override, apply it to slow the trailer independently of the tow vehicle.
- Pull over safely — once the sway stops, pull off the road to inspect the load, check tongue weight distribution, and adjust cargo position before continuing.
How to Prevent Trailer Sway
Preventing trailer sway starts before you leave the driveway. Follow these best practices:
- Load 60/40: Place 60% of the trailer’s cargo weight in front of the axle and 40% behind it.
- Set correct tongue weight: Tongue weight should be 10–15% of the trailer’s loaded weight. Check it with a tongue weight scale before every trip.
- Use a weight distribution hitch: For trailers that exceed 50% of the tow vehicle’s weight, a weight distribution hitch levels the truck and trailer for better stability.
- Add a sway control device: A trailer sway control bar or integrated sway control system provides friction resistance to dampen side-to-side motion.
- Drive at appropriate speeds: Stay below 60 mph with a heavy trailer, especially in wind or on unfamiliar roads.
- Check tire pressure: Inflate trailer tires to the pressure listed on the sidewall, not the tow vehicle’s door placard.
Trailer Sway vs. Fishtailing
Trailer sway and fishtailing are related but different. Trailer sway refers to the oscillating side-to-side motion of the trailer. Fishtailing occurs when the rear of the tow vehicle itself swings from side to side because the trailer’s momentum is pushing it. Severe trailer sway can lead to fishtailing and ultimately a loss of control.
Electronic Trailer Sway Control
Many modern tow vehicles have Electronic Stability Control (ESC) systems that include integrated trailer sway control. When the system detects abnormal trailer movement, it automatically applies individual wheel brakes and reduces engine throttle to bring the trailer back into alignment. These systems work best as a safety net — proper loading and hitch setup should always come first.
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- What Is Tongue Weight? The Complete Guide
- What Is GVWR? Everything You Need to Know
- Trailer Sway Control: How It Works and When You Need It
- How to Load a Trailer Safely for Towing
- Towing Glossary: A–Z Definitions for Every Tower
- New to Towing? Start Here
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