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.
* 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
* 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
- 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
* 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
* 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
* 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.
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
Sway is caused by many factors, and the first one most people
think of is tongue weight. While too little tongue weight can quickly lead to
sway, there are other causes. They also include tire pressure (both vehicle and
trailer), wheelbase of the tow vehicle, weight/mass of the tow vehicle, length
of the trailer, weight of the trailer, loading of the trailer (side to side as
well as front to rear) and vehicle speed. Outside factors also play a
part, road type, road condition, weather (wind/rain) and other vehicles around
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
All photos are
thumbnails, click to see an enlarged version
The photo to the left shows the friction sway bar
installed between the tow vehicle and the trailer.
The mounting point on the trailer for the sway
bar. In our case this is a plate bolted onto the trailer A frame,
but in many cases it is welded on.
Note the smaller "second" ball to the right of
the 2" towing ball. This is the attachment point on the tow
For more information, read the U.S. Department of
Being Equipped for Safety
Revised: May 08, 2007