Sway

Some of these points are my own thinking, but most of them I have learned from others, including people on the pop-up-times message board, on the alt.rv.pop-up-trailers newsgroup, from the #pop-up-trailers chat room, from RV service techs, and from professional truckers. This is a bit long, but the information it contains is learned from the painful experience of a lot of people.

Austin_Boston

Before towing:

* Know the actual weight and the ratings of all of your equipment. Overloaded suspensions can significantly contribute to sway. Get your rig weighed. Most who do so find out that they weigh a lot more than they think.

* Know your tongue weight. Most trailers require 10% to 15% of their total weight to be on the tongue to "trail" correctly. generally, more is better, but much more than 15% may actually increase the likelihood of sway, especially if the tongue weight approaches or exceeds the tongue weight rating of the tow vehicle. Note that this applies to pop-ups, travel trailers, and utility trailers. Fifth wheels often run at 25-30% tongue weight (because the tow vehicle can take it), and tractor-trailers average near 50% tongue weight. That should tell you something.

* Load the trailer evenly from side-to-side. Don't put all the heavy stuff on one side of the trailer. Putting heavy items in the center makes it easier to make sure the trailer is loaded evenly.

* If your tow vehicle requires it, use a weight distributing hitch. Among other things, a WDH makes sure the rear axle is not overloaded, which can contribute to sway, and makes sure the front axle is not under-loaded. If there is not enough weight on the front axle, it won't be steering you, the trailer will. Note that a WDH can not be used with some trailers or with some tow vehicles, so find out what's allowed with your equipment before you buy or install a WDH.

* Keep the tires (on both the tow vehicle and the trailer) properly inflated. Soft tires will allow the tow vehicle (and the trailer) more side to side movement. Over inflation can also be a problem, causing the trailer to bounce excessively. Also, light truck tires are stiffer than passenger car tires, and therefore may reduce the likelihood of sway.

* Use a sway control device. This is recommended by nearly every tow vehicle manufacturer, and is required by most 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...for a price $$$). There are a few WDH's that have friction control built in. Some trailers (some of those with surge brakes) don't allow sway bars. In that case, you will need a tow vehicle that is stable enough to tow without one. Whichever sway control device you have, make sure you are using it properly. It's important not to rely on a sway bar to band-aid a bad situation. Fix the problem, then use a sway bar for added insurance. Sway bars do fail, and if you are relying on it when it does, you can be in big trouble.

* Avoid dynamic loads. Dynamic loads are anything that can move while you are towing. A half gallon of milk isn't going to make you sway, but a half filled water tank or gray water tank might contribute to a problem. So would a slide out that breaks loose, or a large object that could roll or slide around inside the trailer.

* Get trailer brakes. This is one area where electric brakes have an advantage. Practice reaching for the brake control. I reach for and test the brakes every time we hook up.

* All else being equal:

- A tow vehicle with a longer wheelbase is less likely to allow sway.

- A heavier tow vehicle is less likely to allow sway.

- A stiffer tow vehicle suspension is less likely to allow sway.

- A shorter distance from tow vehicle rear axle to tow ball is less likely to sway.

- A longer distance from trailer axle to tow ball is less likely to sway.

- A tandem axle trailer is less likely to sway.

- A lighter trailer is less likely to sway.

* Defects in the alignment of the trailer wheels or axles will contribute to sway. If your trailer has hit some major potholes, have the alignment checked. Unfortunately, there is usually not much that can be done about alignment that doesn't include replacing the axle. Also, a tongue or coupler that has been damaged so that it is off-center essentially mis-aligns the trailer and can increase the risk of sway.

* Use all the same type and rating of tires on the trailer. A significant difference in the rolling resistance or handling between the two sides of the trailer can contribute to sway.

* Tow the trailer level. Get a draw bar that is the correct height so that the trailer is neither tongue high nor tongue low. If you can't get the exact height you need, towing an inch or two high is better than towing an inch or two low.

While towing:

* Avoid high speeds. Although sway can occur at any speed, it's likelihood goes up with speed. A trailer that is rock solid at 65 mph may, without outside input, break into sway at 75 mph.

* Avoid sudden moves. Yes, I know...there's not much you can do when that jerk cuts you off...but try to avoid sudden lane changes and speed changes.

* Know that sway is more likely when going downhill. Usually, when severe sway occurs, the trailer is trying to go faster than the tow vehicle. Obviously, this is more likely when going down hill. Engine braking will hold back the tow vehicle, and the trailer gets in a passing mood.

* Be aware of what is around you. This is good driving practice anyway. Don't let a passing truck catch you by surprise.

* Be aware of cross winds. This summer, we found ourselves driving hundreds of miles across the Navaho reservation in Arizona on a road that could probably be safely traveled at 80 mph. But because of the cross winds, we couldn't go over 60.

* We have learned to let the slipstream of passing vehicles push us around a bit. If we avoid "fighting" the slipstream, the whole rig is much more stable. It is my instinct to stay in the exact center of the lane unless changing lanes. I had to learn to let the draft from the front of that passing truck push me over 6 inches or so. When the back of the truck went by, it would draw me back by 6 inches and we ended up back in the center of the lane.  The subtle movements from fighting that slipstream, combined with the differing and changing wind forces on the trailer and van were enough to start some minor sway. When I started letting the draft "take me for a little ride" the sway completely disappeared.

* Passing buses may be worse than passing trucks. They seem to be for us.

When sway happens:

* Don't panic. Rapid response is important, but it must be controlled and not sudden.

* Don't try to steer out of it. I am convinced this is the single worst thing you can do. By the time you feel the tow vehicle move in one direction, the trailer is already going the other way. Just hold it steady and try to stay in the lane. Notice I didn't say stay in the center of the lane. Just stay in the lane.

* Don't slam on the brakes. This can be almost as bad as trying to steer out of sway. The trailer wants to pass you, and braking, especially hard braking, makes it want to pass even more.

* Gently apply the trailer brakes. The trailer is trying to pass you. Make it slow down just enough so it can't. Over-applying the trailer brakes can cause the trailer's wheels to lock up. When that happens, you're into a serious life and death situation.

* Slow down, but do it gradually. Don't take your foot off the gas, just back off a little. Generally, speed makes sway worse. But if you find the sway getting worse as you do this, go on to the next tip.

* If you know that your trailer is stable at higher speeds, give it just a little gas. Remember that the trailer is trying to pass you. If you are accelerating, it can't do that. There are situations where this definitely won't help. If your trailer frequently or easily sways at 72 mph, then it will sway worse at 75, so accelerating will not help.

* Move away from the source of the sway. If the sway was caused by a passing truck, and there is room to change lanes, try slowly moving into the next lane away from the truck. If you do this suddenly, it will make things worse, so do it gradually. Don't do this if the road surface is significantly different in the next lane. If the rolling friction or smoothness of the adjacent lane is very different (different type of pavement, different amount of wear, rumble strips, etc.), it can set up an uneven drag on the trailer that can worsen sway.

Final comments

There is no way to know in advance whether a particular setup will sway. In my own situation, I know of people with the same 2000 Astro and the same 2000 Bayside that tow without a sway bar and without sway (The Astro's manual requires a sway control device for this trailer). But I have had our rig sway (under poor conditions) without any sway control at speeds as low as 50 mph. Although there are trailers with bad reputations for sway (sometimes deservedly), any trailer can sway.

I now use a Reese Mini-350 WDH, which reduces the load on the rear axle, levels the tow vehicle and trailer, and absorbs moderate sway. I have replaced the stock rear shocks with load sensing shocks to stiffen the suspension a little. I have also taught everyone to be selective when they choose what to pack, and have removed a number of items from the trailer in order to reduce the total weight. I never tow with water in the tanks.

I have tried to be as complete as possible with this post (including repeating some of what others have already said), but I am sure there are other good suggestions that people will make, even suggestions that seem to contradict what I have said here. Sway is a complicated issue, and there are many factors that come into play. What is important is finding the factor or factors that work in your situation, and address them effectively.

If you've never experienced sway, please, please don't let this frighten you. The vast majority of trailer sway situations are resolved very quickly and easily without damage or injury. But don't ignore frequent sway. If it keeps happening, the trailer is trying to tell you something. Listen to it!

My thanks to "Austin_Boston" on the Pop-Up-Times message boards for the content above as well as proofreading for this page.

Our Friction Sway Bar

Always load you trailer evenly, side to side as well as front to back.  Do not carry a load that can easily shift from side to side (like a half full water tank).  Check you tires before every trip for uneven wear, and maintain the air pressure at or near the rating if you are loading the trailer to the max weight.  While you are checking the tires, get in the habit of checking the lug nuts.  Maintain 10 - 15% of you trailer weight on the tongue, but keep an eye on the tongue weight rating of your trailer.

No matter what size tow vehicle you have, I am a firm believer in trailer brakes and sway control.  When you think about an emergency stop with 2000 pounds hooked to the back of your vehicle and/or a line of semi trucks passing you at 80 mph I think you will agree. We have a Reese "friction" type sway bar installed between the tow vehicle and the trailer.  For less than $200 it is cheap insurance.  Another type of sway control is a weight distribution hitch.

For more information, read the U.S. Department of Transportation brochure:

 TOWING A TRAILER
Being Equipped for Safety

   Revised: May 08, 2007