Controlling Sway
Causes of poor tow-vehicle/travel-trailer handling
may seem elusive, but remedies can be fairly simple

by Bill Estes

Were it not for the tendency of many travel trailers to sway at least occasionally, the fifth-wheel trailer may not have grown so popular. Certainly, fifth-wheels have strong attributes. Travel trailers do, too, but the fifth-wheel does not, indeed, cannot sway.

The travel trailer's Achilles' heel is the way it's hitched to the tow vehicle - at a point often four or five feet behind the axle. Thus, the trailer has the necessary leverage to move the tow vehicle's rear to one side or the other, which has the effect of steering the tow vehicle. This steering effect can go into oscillations, which are fondly known as fishtailing - another name for sway.

By contrast, the fifth-wheel hitch pin is centered over the axle, unable to move laterally, which makes the fifth wheel trailer virtually immune to this motion.

While many tow vehicle/travel trailer combinations handle quite well, and their owners greatly enjoy their travels, sway may occur in a substantial number of others, creating uneasiness, white-knuckle experiences or even accidents. The trauma is unnecessary because sway can be tightly controlled in most cases. Many owners of swaying travel trailers figure sway is the "nature of the beast" and just live with the reduced enjoyment of RVing that it produces. But travel trailers can and should handle well. The causes of sway often are not analyzed correctly, if at all. The step-by-step procedure described here can be the key to safe, enjoyable towing.

Weight and Balance
Sway is a fishtailing motion of the trailer, caused by external forces that set the trailer's mass into lateral motion with the trailer's wheels serving as the axis or pivot point. The motion is a sideways seesaw. All conventionally hitched travel trailers will sway slightly in response to crosswinds or the bow wave of an 18-wheeler overtaking from the rear. The good ones will need little correction by the driver and will quickly restabilize. Only poorly set-up trailers will continue to sway after the force that caused the instability has ceased. In fact, in poorly balanced trailers, the sway motion may increase until control is lost. Unfortunately, most evaluations of sway problems focus on the hitch or the tow vehicle, but the trailer's weight distribution often is the primary cause.

Following are points on how to tell a well-behaved travel trailer from a poor one, and how to correct a problem in a trailer that you may already own.

Trailer Checkup
A trailer's inherent stability is part of its design, based on the amount of weight in front of the axles vs. the amount of weight behind. The difference between these two weight masses is the amount of weight on the trailers hitch, which is called the hitch weight or tongue wight.

Trailers with insufficient hitch weight have two deficiencies: The percentage of weight (mass) behind the axle(s) is too high, so when set in motion it acts as a pendulum; and the distance between the hitch ball and the trailer axles is insufficient.

Simply stated, trailers with a high proportion of hitch weight to gross weight usually have more of their length ahead of the axles, and they handle better. The generally accepted industry standard is that hitch weight should be approximately 10 percent of gross weight. In fact, that is a bare minimum, and some trailers with 10 percent hitch weight do not handle well. Hitch weights of 12 percent or higher (up to the weight limits of the hitch and vehicle beings used) assure proper handling.

In marginal situations, the owner's ability to handle and unstable trailer will depend on the inherent stability of the tow vehicle, which is yet another variable. A truck or van with a long wheelbase, a relatively short rear overhang and stiff springs often will at least partially make up for a trailer's lack of inherent stability, whereas if the trailer is towed by a softly sprung vehicle with a long overhang, the trailer's shortcomings will be more obvious.

How a Trailer Should Handle
Many trailerists become accustomed to being uncomfortable or even frightened by trailer sway when they encounter strong crosswinds, trucks overtaking from the rear, or mountainous roads. They think it's normal - the way all trailer's handle. Not so! Properly designed, well-matched tow vehicles and trailers have positive control and good road manners and are fun to drive.

Strong crosswinds may tend to push the tow vehicle/trailer combination laterally, and it may end up wandering out of the traffic lane a bit if the driver isn't paying close attention. But steering should be predictable, and the driver should be able to use corrective steering measures without fear of sway. Likewise, it should be possible to drive a mountain road aggressively while being able to keep the tow vehicle in the proper position on curves.

Speeding 18-wheelers present hazards to conventionally hitched trailers that don't handle well, particularly while descending mountain grades. A tow vehicle/trailer rig is most susceptible to destabilizing forces while descending a grade at highway speeds, and such conditions are the true test of inherent stability. It's natural for the bow wave (air pressure) of a speeding 18-wheeler to have an effect on a tow vehicle and trailer - an effect that requires steering correction. But the effect should not be destabilization that makes the tow vehicle feel like steering control is minimal and therefore unpredictable.

However, it is always necessary to monitor one's rearview mirror and anticipate the effects on an 18-wheeler overtaking from the rear. Drivers of marginally stable vehicles who are caught napping usually are the drivers who have control problems.

The four important keys to good road manners while towing a travel trailer are:

1. Proper trailer-weight distribution;

2. Proper hitch adjustment;

3. Use of effective sway-control equipment;

4. Anticipation of adverse driving conditions.

Weight Evaluation
If you notice significant trailer sway during normal driving and an occasional uncomfortable situation, your rig is not set up properly, and that should be corrected. The first step in evaluating a trailer for correction of stability is a trip to the scales.

Commercial scales are accessible in most communities at rental yards, moving and storage firms, and grain elevators. Gross weight and hitch weight should be recorded with the trailer loaded for travel. Gross weight is recorded with the trailer unhitched on the scale.

Hitch weight is determined by recording two trailer weights. For the first, weigh the trailer, unhitched, itched on the scale. Hitch weight is determined by recording two trailer , unhitched, on the scale. For the second, position the tongue jack off the scale (trailer unhitched and tongue height same as when towing) to weigh only the trailer wheels. Subtract the two figures for hitch weight. Weighing the trailer wheels with the trailer hitched and spring bars in use will give a false hitch weight reading.

If hitch-weight percentage is down around 10 percent or less, it can cause unstable trailer behavior. If hitch weight is 10 to 12 percent, towing stability still could be a problem if the tow vehicle is marginally stable. If hitch weight is 12 to 15 percent, the trailer should handle well and should not be a contributor to any instability problem.

IT's important that hitch weight not exceed the rating of te equipment. Ratings of conventional hitches typically range between 800 and 1000 pounds, although they are available up to 2000 pounds. Ratings are stamped on hitch components.

Let's examine a couple of examples of trailers that have very different weight distribution:

Example 1
Total trailer weight 5400 pounds
Hitch weight 650 pounds
Hitch weight percentage: 650 / 5400 = 12%

In this example, hitch weight is a good margin of total weight. This trailer should handle well.

Example 2
Total trailer weight 6200 pounds
Hitch weight 560 pounds
Hitch weight percentage: 560 / 6200 = 9%

This example involves a trailer that clearly has insufficient hitch weight, and it undoubtedly is prone to sway. The only solution is to move weight forward. This may be accomplished by moving some supplies or a rear-mounted spare tire.

The worst place for a tire, or anything else that's relatively heavy, is on the back of a travel trailer that has marginal hitch weight. Carry it in the tow vehicle unless it can be mounted on the trailer's A-frame (in front). Another possibility is the battery; if carried in the rear, it could be relocated forward to the trailer A-frame.

The freshwater tank should not be located behind the trailer axles. This does occur, however, whenever designers don't pay proper attention to rroadworthiness. If a rear water tank can be replaced by one of a different shape that will fit under a sofa in the forward section of the trailer, for example, the positive effect on stability will be dramatic. Ideally, the water tank should be located over the axles, so it's varying content does not effect hitch weight significantly. Of course, it's wise to empty holding tanks before traveling, to minimize weight in the rear.

Suffice it to say that a trailer with insufficient hitch weight can be towed successfully by combining a very stable tow vehicle with very conservative driving habits, but such a rig can get out of control in an emergency situation.

Proper Hitch Adjustment
Another important factor in tow vehicle/trailer stability is proper adjustment of a conventional load-distributing hitch. Proper adjustment means that the trailer is level and that the tow vehicle was level before hitching, it should remain at that angle after hitching.

The concept of a properly operating load-distributing hitch is that it should distribute hitch weight to all axles of the tow vehicle and the trailer. Here's how to make it happen:

1. Measure the tow vehicle at reference points on the front and rear bumpers with the vehicle loaded for travel, but prior to hitching.

2. Hitch the trailer and adjust spring-bar tension, so weight appears to have been added to the front as well as the rear of the tow vehicle.

3. Measure front and rear reference points again. If, for example, the rear of the vehicle has dropped one inch and the front has only dropped a quarter inch, add more tension to the spring bars, which will raise the rear and lower ther front. Continue adjustment until the measurements are approximately the same. If a discrepancy is unavoidable, the rear of the vehicle should drop slightly more than the front.

If the spring bars cannot be adjusted tightly enough to achieve similar or identical vehicle-height reduction, stiffer spring bars may be needed. The spring bars should be rated for at least the amount of hitch weight of the trailer, plus about 200 pounds if the tow vehicle is softly sprung.

If, after proper adjustment of tow-vehicle attitude is achieved, the trailer is not level, the ball mount should be raised or lowered. Bolt-together ball mounts permit ball-height adjustment. If the ball mount is welded to the shank, replace it with a ball mount that can be adjusted. (Such mounts are available at hitch shops.)

Importance of Sway Control
Assuming hitch weight of a poorly balanced trailer is raised to at least 12 percent (but not more than the rating of the hitch) by redistribution supplies or equipment, use of an effective sway control is another important element in the towing stability formula. Two types of sway controls are available, the friction-type controls from Reese and Eaz-Lift, and the Reese Duo Cam. Both types are effective, but the Reese Duo Cam depends on adequate hitch weight for its effectiveness. Thus, it's most suitable to trailers with high hitch weights.

A sway control should be utilized, no matter how good trailer stability appears to be. The sway control dampens or slows the pivoting motion of the trailer coupler on the ball, and is very valuable during emergency maneuvers to prevent driver steering overreaction, not to mention its role in helping the tow vehicle and trailer feel like they are in concert with each other.

To properly adjust a friction-bar sway control for maximum effectiveness, tighten the control until you notice that the tow vehicle doesn't quite straighten out after completing a sharp turn at slow speeds. Loosen the control slightly, so the vehicle will track straight after the turn. If your sway control cannot be tightened enough to cause the tow vehicle to "dog-track" after a slow-speed turn, the unit probably needs service (cleaning, light sanding of friction surfaces). If that still does not created the desired effect, add a second sway-control unit on the opposite side.

The PullRite Hitch
So far, we have focused on conventional hitches, in the interest of helping you retain equipment that may already be in place. However, the most effective sway control actually is a very unconventional hitch called the PullRite. The unique feature of this hitch is that it relocates the tow vehicle/trailer pivot point from its usual location behind the bumper to a point immediately behind the rear axle. The trailer no longer pivots on the hitch ball, so it's necessary to visualize the trailer A-frame having been, in effect, extended about five feet underneath the tow vehicle to the pivot point.

With the trailer, in effect, lengthened and tracking much like a fifth-wheel trailer, a certain amount of maneuverability is sacrificed. The PullRite also functions as a load-distributing (equalizing) hitch.

The PullRite can dramatically improve towing stability. Even an inherently unstable trailer can be cured of its bad road manners. The principle is similar to that of fifth-wheel hitching, although the applications differ widely. The fifth-wheel hitch pin normally is positioned a couple of inches ahead of the rear-axle centerline, topside in the bed of the truck, while the PullRite pivot point is underneath the vehicle, a few inches to the rear of the axle housing.

PullRite hitches are available in two models, one rated for 10,000 pounds maximum trailer weight and 1000 pounds maximum hitch weight, and another rated at 20,000 pounds maximum trailer weight and 2000 pounds maximum hitch weight. The PullRite is available for full-size trucks, vans and sport-utility vehicles.

Evaluating the Tow Vehicle
Tow vehicles come in all shapes and sizes and with varying inherent stability for trailer towing. Their manufacturers rate them for specific trailer-weight limits, which should not be exceeded.

Factors that affect stability include wheelbase length, rear overhang, steering characteristics and center of gravity. The most significant factor is the proportion between wheelbase and rear overhang. A longer wheelbase makes a vehicle respond more slowly to steering input. A short rear overhang gives the trailer less mechanical advantage over the tow vehicle.

Typically, short-wheelbase sport-utility vehicles, such as the Ford Broncos, Dodge Ramchargers and pre-1992 GM Blazers/Jimmys are not as stable as vans, trucks and Suburbans built by the same manufacturers. It's possible to tow successfully with sport-utility vehicles, but they are less forgiving of poor trailer balance and/or improper hitching and sway control.

If sway tends to be a problem even though the trailer has a good proportion of hitch weight vs. gross weight and hitching is proper, it may be necessary to raise the trailer's hitch-weight proportion still higher. The sway-control device being utilized should be very effective.

For the tow vehicle itself, use maximum air pressure (stamped on tire sidewalls) in rear tires to stiffen sidewalls and follow the vehicle manufacturer's recommended pressure in front. Use effective shock absorbers, which tend to keep the vehicle in better control on uneven road surfaces. A friction-type sway control adjusted to a stiff setting is especially important for comfortable towing with short-wheelbase vehicles.

Corrective Driving Techniques
When stability is in question under exceptionally bad driving conditions, despite good trailer balance and proper equipment, the driver must compensate. In any marginal driving situation, reduce speed, which will slow the reaction of your vehicles to external forces, while also giving you more time to react.

If sway occurs, the single most valuable technique for counteracting it is independent actuation of trailer brakes, even though it requires removing one hand from the steering wheel for a moment.

The location of the brake controller is a critical safety consideration. If it's positioned far under the dash and is hard to reach, relocate it to a better position accessible to the hand you can most comfortably remove from the steering wheel, typically the left hand. The Moore Sway/Brake Control (see this product evaluation on page 89 in this issue) provides trailer-brake control from the steering wheel.

With a properly balanced rig, you probably won't need to use the manual brake-control lever. But being capable of using it as a natural defensive maneuver is your insurance policy against loss of control in an emergency situation.

If severe sway occurs, don't step on the tow vehicle's brake pedal unless you're in danger of hitting something. Just lift your foot from the accelerator pedal, and apply trailer brakes sharply via the hand control. During adverse driving conditions, such as severe crosswinds, reduce speed and anticipate terrain that can produce sharp wind blasts. Be prepared to use trailer brakes if necessary.

The driver who is vigilant about monitoring driving conditions and the scene in his rearview mirror typically will have better capability to use defensive techniques than the driver who is caught napping by a sudden change in driving conditions.

By following the recommendations outlined here, tow vehicle and trailer road manners can be greatly improved, providing safe, enjoyable travel.


Eaz-Lift Spring Corporation, P.O. Box 489, Sun Valley, California 91353-0489, (800) 636-9412; PullRite/Pulliam Enterprises Incorporated, 13790 E. Jefferson Boulevard, Mishawaka, Indiana 46545, (800) 443-2307; Reese Products, P.O. Box 1706, Elkhart, Indiana 46515, (800) 326-1090.

As printed in Trailer Life, February 1994.