If you own, or have even driven, a motorhome, there's a good chance you are familiar with sway. We define sway as a leaning or rocking motion. It's caused by pulling into/out of a driveway, a sudden blast of wind, a passing truck, a sharp corner or driving over uneven road surfaces. Sway can also be experienced when parked by the side of the road when it’s windy, or even when someone steps on board.
It’s not so much a matter of the components in the chassis being responsible for sway, but rather, the components that can be replaced or updated to help prevent it. Weak springs (leaf or coil) or a lack of anti-sway bars can contribute to excessive sway. On an air bag-equipped chassis, it can be the very act of the air entering/exiting the bags. We use anti sway bars and shock absorbers to control sway. Replacing only the shock absorbers (if they are in good condition) won’t have as great an effect.
A spring’s rate is very important. A spring “rate” is the amount of force it takes to compress a coil spring, or deflect a leaf spring by one inch. If you increase the rate too much, sway will be reduced, but the ride will be too harsh. A suspension is a system, and each part plays a part in the collective whole. When you get it right, you fall right into that "sweet spot" of optimum handling and ride.
An anti-sway bar functions by pushing down on the wheel inside the turn that’s trying to lift, keeping the vehicle flat in a curve. The bigger the anti-sway bar, the more torsional resistance it generates. When you increase the diameter of the bar 1/8-inch, for example, it creates 20-30% more torsional resistance. Although, more is not always better. Too much resistance can cause a harsh ride on some vehicles, and can create mounting and/or clearance issues.
When we get a customer complaining of sway, one of the first things we’re going to look at is the sway bars. Does the coach have them? On the Ford F53 chassis, we add an additional sway bar to the rear, and install a larger one on the front. Some air suspension coaches don’t have sway bars at all. For example, the Monaco 8 and 10 bag chassis. We can add sway bars to those for greatly improved handling. Workhorse W Series chassis (W16 to W24) don’t use traditional anti sway bars either. They use a square piece of tubing that attaches from one leaf spring to the other. We recommend a traditional anti-sway bar, which attaches from the frame to the axle. In our opinion, this design does a much better job of controlling sway.
For coaches that ride on air and have no provisions for mounting sway bars, we can install our SuperSteer Motion Control Units. These are a good option if you are looking for a simple, less expensive way to control sway. They control the airflow into and out of the bags, therefore reducing sway. MCU installation takes about 45 minutes per axle on most coaches, and we offer them in various degrees of control. If your coach has weak or worn shock absorbers, installing MCU’s may reduce sway, but could cause another phenomenon known as “porpoising”, (or front-to-rear bounce). By replacing your shocks, you will avoid this issue.
Besides improving the overall handling of the coach, another reason to consider reducing sway is fuel economy. That’s right—improving the handling of your coach can save fuel. Think about it. If you are constantly correcting the steering wheel, you aren’t driving in a straight line. You’re effectively driving further to cover the same distance. Also, as you move the steering wheel back and forth, you are scrubbing off speed. This reduces fuel efficiency and increases tire wear. Finally, if you are constantly slowing down for curves because the coach doesn’t handle well, you’re on and off the gas more frequently, which means burning more fuel. Controlling sway on your coach is a worthwhile investment. It will make your coach more enjoyable, affordable, and safer to drive.