Anyone who has towed a trailer knows the uneasy feeling of it pushing or pulling side-to-side, making the vehicle harder to control. That motion, called trailer sway, is a serious risk every trailer owner should be prepared to manage. What starts as a slight sway can quickly become a serious problem. The good news is that sway is predictable and preventable. By paying attention to weight distribution, tongue weight, speed, and equipment setup, you can keep your trailer stable and straight.
In this guide, we’ll tell you everything you need to know about trailer sway, including what causes it, how to prevent it, and what to do if it happens.
What is trailer sway?
Trailer sway is the side-to-side movement that occurs when a trailer shifts behind the tow vehicle instead of tracking straight. A small amount of sway is normal, especially once you’re driving faster than 45 mph. The problem starts when that movement becomes overly responsive to your steering and can build into an uncontrollable fishtail. Ongoing or heavy trailer sway indicates that your setup needs attention.
The more your trailer moves side to side, the greater the chance of equipment damage and unsafe driving conditions. If trailer sway escalates, it can result in:
- Fishtailing: the trailer swings wider and wider until it pulls the vehicle with it.
- Jackknifing: the trailer swings into a sharp angle with the tow vehicle, often during a skid or loss of control. This is most common with tractor-trailers.
- Vehicle and trailer damage: severe sway puts stress on suspension and hitches, and in extreme cases can flip your trailer.
What causes trailer sway?
Trailer sway happens when the balance between the trailer and tow vehicle is disrupted by factors like uneven loading, crosswinds, or differences in speed. When outside forces push against the trailer or weight isn’t properly distributed, the trailer can begin shifting side to side instead of tracking straight. Each swing throws the balance off a little more, and without correction, the motion can build until it becomes difficult to control.
Several factors cause trailer sway to be more severe or more likely to happen, including:
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- An overweight or unbalanced load: Uneven or rear-heavy weight distribution of your trailer’s load shifts the center of mass, making trailer sway harder to control
- A long trailer: longer trailers catch more wind, which increases side-to-side movement
- Improper tongue weight: too much or too little weight on the tongue of your trailer increases instability.
- Excessive speeds: your trailer will be less stable if your speed exceeds what your setup can safely handle
- Large or fast-moving vehicles passing nearby: the rush and pull of wind from other vehicles can cause your trailer to sway unexpectedly
- Strong crosswinds: wind can catch the sides of your trailer, quickly leading to sway
While some of these factors are inevitable, it’s possible to limit trailer sway by removing risk factors, stabilizing your trailer, and following all towing laws in your area.
How to prevent trailer sway
Careful load distribution, proper tongue weight, the right tires, and trailer sway control devices all make a measurable difference in how smoothly your trailer tracks behind you. Even when conditions like crosswinds or passing traffic are out of your control, a stable setup and smart driving habits help keep sway from escalating into a real hazard. Here are the most important ways to prevent sway:
1. Balance your load with proper tongue weight
The most critical factor in trailer stability is tongue weight, which is the amount of downward pressure the trailer is putting on your tow vehicle’s hitch. Your tongue weight should be 10–15% of the trailer’s total weight.
- Too little tongue weight will cause an increase in trailer sway that is more reactive and difficult to control.
- Too much tongue weight will overload your towing vehicle with unnecessary weight and possibly max out or surpass your vehicle’s payload capacity.
Tongue weight can be adjusted by shifting the weight inside your trailer. Moving coolers, bags, or other heavy gear toward the tongue will increase tongue weight, improving stability. Similarly, moving weight to the back of the trailer will decrease tongue weight, relieving pressure on your vehicle’s towing capacity.
2. Follow the 60/40 rule
A good rule of thumb for safely loading your trailer is to pack 60% of the cargo weight in front of the axle and 40% behind (called the 60/40 rule). This method lessens trailer sway by distributing the weight toward the tow vehicle instead of farther behind, where it can throw the trailer off balance. Some trailers are designed with an axle that is closer to the rear of the trailer, making it easier to balance the weight toward the front.
3. Use the right tires and tire pressure
If your trailer is balanced but you still experience excessive trailer sway, it’s possible that your tires are the culprit. For a stiffer, more stable ride, you can increase your tire pressure (within the safety rating). If your tow vehicle has passenger-rated (P-rated) tires, you’ll want to upgrade to LT (Light Truck) tires or higher, depending on your vehicle. P-rated tires aren’t designed for towing stability, and LT and higher-rated tires can handle higher pressure and greater sidewall stress.
Learn more: 5 Best Horse Trailer Tires & How to Choose
4. Slow down in wind or bad weather (or in general)
Excessive speed makes sway worse, especially when wind or large passing vehicles push against your trailer. Reduce your speed below highway limits if conditions call for it. Some brands or trailer types even have a recommended maximum speed.
5. Match trailer length to your tow vehicle’s wheelbase
The wheelbase length of your vehicle limits the length of the trailer you can safely tow. A helpful rule of thumb is to divide your vehicle’s wheelbase (in inches) by 5 to find the maximum trailer length (in feet).
Wheelbase in inches ÷ 5 = maximum trailer length in feet.
For example, an F-150 with a standard cab has a wheelbase of about 123 inches. Using the formula (123 ÷ 5 = 24.6), we know that the maximum trailer length should be 24.6 ft. .
6. Use trailer sway control devices or features
Sway bars, sway hitches, and sway control features provide mechanical resistance at the hitch that stabilizes a trailer’s side-to-side movement and lowers the risk of fishtailing.
Sway bars
Sway bars are kits you can install on one or both sides of your hitch that stabilize the connection between your trailer and towing vehicle. Sway bars are compatible with most hitch setups and, while not required to tow a trailer, are one of the simplest ways to improve safety on the road.
As a general rule:
- For trailers under 10,000 lbs: Install one sway bar on the left or right of your hitch.
- For trailers over 10,000 lbs: Install two sway bars on either side of your hitch.
Note: Sway bars should be tightened for long highway drives and loosened for lower-speed turns around town.
Sway hitch
A sway hitch is a standard hitch with built-in sway control bars that use friction or cam-style systems to dampen side-to-side motion as you drive. Many sway hitches are designed to handle a wide range of trailer weights, giving you stability without the need for an extra adjustable attachment.
Sway control
Some vehicles have a trailer sway control feature, which automatically detects sway and counteracts it by braking or adjusting engine power. Similar to a traction control system (TCS) or lane keeping assist (LKA), this is a built-in feature designed to keep you safe on the road.
What to do if your trailer starts swaying
If trailer sway begins while you’re driving, the first step is to stay calm and avoid sudden steering or braking. Panic leads to overcorrection, which can make the problem worse. Instead, gradually slow the trailer with its brakes to bring the trailer back under control and stabilize your setup.
If you experience trailer sway, here’s how to bring your trailer back under control:
Stop accelerating and slow down the trailer
Slowly remove your foot from the accelerator. Keep your wheel straight, and gently apply your trailer’s electric brakes to gradually slow the trailer’s speed. Once the trailer straightens out behind your towing vehicle, you can release the trailer brakes and continue driving.
What not to do:
- It is critical that you do NOT use your vehicle’s brakes to slow down. If you slow the tow vehicle instead of the trailer, the trailer will push harder against the hitch, making the sway worse.
- Never try to correct the trailer sway by steering the tow vehicle from side to side. This usually amplifies the problem.
Find a trailer you can trust at Ken Feagin Truck & Trailer
We make trailer safety a top priority, which is why we only choose well-built, reliable, and durable trailers. If you’re in the market for a new trailer or have more questions about trailer safety, please come by or give us a call—we’re happy to answer your questions and help you find exactly what you need. Whether you’re from Asheville, Hendersonville, Spartanburg, or Greenville, SC, we’re located right down the road in Campobello, SC, off of exit 5 on I-26.
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