11 Causes of Trailer Sway and How to Stop It – Myths and Facts

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Trailer sway is the stuff of nightmares. It’s a classic case of the tail wagging the dog. It’s the number one cause of RV accidents in this country.

If you’re the sort of person who can’t help but rubberneck when driving past a car crash, there’s no shortage of nail-biting trailer sway footage on YouTube. Here’s one I curated for your horrified enjoyment:

Now that I’ve made your palms a little sweaty, let’s make sure you stay on the correct side of a dashcam recording.

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Table of Contents

What Is RV Trailer Sway?

Trailer sway is also known as fishtailing or whipping. It’s a persistent side-to-side swaying motion, usually at higher speeds.

It’s caused by the side-to-side motion of the trailer. This can be due to crosswinds, uneven roads, insufficient tongue weight, or evasive driving maneuvers. I’ll talk more about common causes of trailer sway below.

Trailer sway is insidious because it’s so difficult to predict. Under some circumstances, a swaying trailer will quickly re-align with the tow vehicle. In others, a swaying trailer will continue to sway in increasing oscillations until it completely overwhelms the tow vehicle and BOOM! – crash! This can happen in a matter of seconds.

Do All RVs Have Trailer Sway?

No, not all RVs are subject to trailer sway. It only affects towable RVs (although motorhomes can have their own sway problems!). And because 5th wheels pivot directly atop, not behind, the rear axle, the trailer sway problem mostly affects travel trailers – which just so happen to be the most popular kind of RV!

Trailer sway has literally caused RV owners to quit the lifestyle because they’re so terrified of losing control. It’s a serious problem if you’ve never towed an RV before.

(This is one reason why practically no other country allows drivers without a special permit to tow something so large and so heavy.)

As American RV owners, we enjoy unparalleled, unfettered access to public highways and larger-than-life RVs. That’s a privilege not to be taken lightly. Your safety – and the safety of those around you – depends on it.

If you intend on towing an 7,000-lb mini-house, you need to learn how to mitigate and eliminate trailer sway.

11 Common Causes of Trailer Sway

1. Insufficient Tongue Weight

One of the most common causes of trailer sway, particularly for travel trailers, is insufficient tongue weight. Tongue weight must be at least 10-15% of the gross trailer weight for travel trailers, and 15-25% for fifth wheels.

You should always weigh your camper trailer before every trip to determine proper gross trailer weight and tongue weight. If you haven’t weighed your camper, assume tongue weight should be 10-15% of the GVWR. That is the more conservative option.

Without sufficient tongue weight, this can happen:

2. Poor Weight Distribution Adjustment

This is really just a subcategory of “insufficient tongue weight.” But if your WDH isn’t set up correctly, it can be returning too much weight to the tow vehicle’s front axle and the trailer’s rear axle. This effectively reduces tongue weight. Too much, and you’re out of the frying pan and into the fire!

3. Stiff Crosswinds

If you’ve ever driven across Wyoming, you’re familiar with wind’s incredible power. The broad, flat side of your towable RV is nothing but a sail. Crosswinds will attempt to push your RV right off the road – but it’s coupled to your tow vehicle with a coupler or 5th wheel hitch, a rotating pivot point.

And if we go back to high school science, we realize that this is a classic lever-and-fulcrum situation. Your RV has become a multi-thousand-pound lever trying to pry and spin your tow vehicle out of alignment. The trailer applies a steering torque to your tow vehicle.

Do not drive in stiff crosswinds. Listen to the DOT. There’s no amount of careful driving that can save you from a hellbent crosswind.

4. Semi Truck Gusts

I used to ride a Honda Rebel 250cc motorcycle (not much bigger than a dirtbike) down the Interstate. I rode at wide-open throttle every mile – out of safety! I couldn’t let a semi truck pass me trundling along at 50 mph; the crosswinds alone could rip me out of the saddle!

Give semi trucks a wide berth as they pass you. They create a powerful bow wave and vacuum vortex that will blow you out and then suck you back in a few seconds later. It’s very disorienting.

5. Too Small a Tow Vehicle

There. I said it. I said what your RV salesman won’t!

Ok, so here’s what I mean. Does a smaller or shorter tow vehicle cause trailer sway? No, not technically …

But once a trailer starts swaying, it’s up to your tow vehicle to resist it. And a lightweight, short-wheelbase SUV just can’t handle the fishtailing of a massive RV.

There are three design geometries you want to watch out for:

  • What’s the tow vehicle wheelbase? In other words, how far apart are the front and rear axles? The longer, the better! It’s like the difference between a sea kayak and a whitewater kayak.
  • What’s the tow vehicle rear overhang? The farther away the tow vehicle hitch from the rear axle, the more susceptible the vehicle will be to the effects of trailer sway.
  • (Bonus) What’s the width of the axle? Generally, a wider tow vehicle, such as a dually truck, will tow with much more stability than a narrower vehicle, like a crossover SUV.

6. Underinflated Tires

Underinflated tires are squishy tires, where the sidewalls can bow and compress. Inflate your tires to the correct pressure!

7. Evasive Driving Maneuvers

The last time I hit a chipmunk while driving, I almost cried. I hate needlessly killing animals. But if I’m towing a trailer, chipmunks and turtles had better get out of my way, because I’m not swerving!

When towing an RV camper trailer, avoid quick changes of direction.

  • Merge slowly
  • Turn early and turn wide
  • Crawl around hairpin turns
  • Drive like Grandma
  • Follow the 3-Second distance rule

8. Potholes and Rough Roads

Anything that pushes your RV sideways can cause trailer sway. Potholes, rumble strips, asphalt cracks, and other road imperfections can all cause sideways forces.

Your solution to rough roads is simple: Reduce your speed. This is particularly important in construction zones, where clearance is minimal, and any trailer sway could become catastrophic.

9. Rain, Ice, and Snow

If your trailer tires lose traction, the trailer may begin to slide or slip due to its own weight. Here’s a guide to driving in RV in winter weather conditions.

10. High Speeds

A full explanation of why increased speed amplifies trailer sway is beyond the scope of this guide. People much smarter than me have composed full dissertations in differential equations on the physics of this matter.

According to ProPride, speeds above 45 mph tend to create trailer sway in any trailer!

Here’s a Changing Gears guide to how fast you should really be driving your RV.

11. Driving Downhill

Towing downhill can cause your trailer to roll faster than your tow vehicle – especially if your trailer brakes are old and worn out. When your trailer wants to move faster than your tow vehicle, it will begin to yaw (sway) to one side.

Bonus: NOT Weight

Did you notice what’s not on this list?

Weight!

That’s right – the total weight of your RV doesn’t really factor into trailer sway conditions.

With that said … the full answer is a little more complicated.

  • Because while a lighter RV may not be less susceptible to trailer sway, a lighter camper is less likely to overwhelm your tow vehicle.
  • And a lighter camper of the same length and height as a heavier camper will respond more quickly to sideways forces.

So while weight doesn’t cause trailer sway, it does affect the aftermath.

How to Stop Trailer Sway

Step 1: Let Off the Gas Pedal to Reduce Speed

Resist the instinct to stomp on the brake pedal. Without getting too technical, what usually happens is your tow vehicle stops “faster” than your trailer, which means your trailer wants to accelerate into your tow vehicle – and if it’s off balance, that’s exactly what it’ll do.

If you’re going downhill, apply light pressure to the brake pedal to gradually and safely slow down.

Now, some people suggest slightly increasing your speed to reduce trailer sway. This is because accelerating the tow vehicle naturally tries to bring the trailer into alignment. If, for instance, your trailer gets knocked off course by a pothole, a slight acceleration can bring the trailer to heel.

But don’t do this!!

Because your panicky human brain isn’t a supercomputer than can calculate the exact cause of trailer sway. Because if you’re wrong, and the trailer sway is due to improper loading or sideways forces, then you’re just adding fuel to the fire. You’ll only amplify the oscillations and increase the risk of an all-out high-speed rollover crash.

Step 2: Keep the Steering Wheel Straight

Don’t oversteer. Keep the wheel straight, even if the tow vehicle begins spinning left or right. Cranking the wheel back and forth will only amplify the problem.

Step 3: Manually Activate the Trailer Brakes

If possible, manually activate the trailer brakes from the trailer brake controller. Most of the time, your trailer brakes are activated when you push on the brake pedal (and in the case of a proportional brake controller, are linked to the intensity of the push as well). Since you don’t want to stomp on your brake pedal, you’ll need to activate the trailer brakes manually.

Step 4: Pull Over at a Safe Place

Congrats – you didn’t become a statistic!

But you need to sleuth out what went wrong. Is the camper loaded improperly? Were you driving too fast? Are the crosswinds too strong? Do you need to adjust the friction on your anti-sway bars?

Take your time. Your life is literally on the line!

You Are Towing With a Weight-Distribution Hitch, Right?

Look, I get it. As an RVer, you’re drowning in gadgets. Do you really need on more? One that costs several hundred dollars?

Yes, you do. I’m not a “retail therapy” kind of guy, but if you’re towing a travel trailer, a weight-distributing anti-sway hitch is mandatory. Forget all the myths and misconceptions about WDHs; you need one!

Essentially, an anti-sway hitch either dampens the sway or locks the pivot point. Now your tow vehicle and trailer move as one.

This is not a what’s-the-best-weight-distribution-hitch review article. But I do want to quickly break down your options into three categories:

The Good: Friction Control

Your typical entry- to mid-level weight-distribution hitch, like a basic Reese, Curt, or Husky, uses an adjustable friction pad to dampen sway. Details vary by manufacturer, but they all work more or less the same way. You can adjust the amount of friction depending on your setup and road conditions.

There’s nothing inherently wrong with an anti-sway friction control bar. But they don’t really eliminate the problem; they just mitigate it. If you put a lot of miles on your RV, or you’re towing with a marginal TT/TV combination (aka, short-wheelbase SUV), then you can do better.

The Better: Variable Resistance

Now we’re looking at something like the Blue Ox SwayPro, the Andersen No-Sway WDH, or the Equal-I-Zer. All great hitches, and they all employ some clever mechanism that can modulate the resistance to lateral swaying. Many experienced RVers soon upgrade to one of these hitches.

The Best: Lock It Out!

The two big names in premium travel trailer hitches are Hensley and ProPride 3P hitch. Of these two, the ProPride 3P hitch has a reputation for being easier to use.

I haven’t used either one. But they’ve achieved near cult-level status. Airstream owners, in particular, seem to go absolutely ga-ga over the ProPride 3P hitch.

Yes, they’re expensive: $2,000+. But buy once; cry once!

***

There’s no perfect hitch – not even a ProPride 3P. If you’re limited to 500 lbs hitch weight, for instance, you might not be able to afford the weight of a ProPride. You might be better off with a lightweight Andersen WDH, which is one of my favorites.

Just don’t wait for an accident to make your decision.

Ross

RV engineer by day, intrepid blogger by night (and occasionally weekends). This website is all about how RVs work, and sometimes why they don't. Bookmark pages that you find helpful, and join my email list for exclusive monthly awesomeness.