Sway Bar - Purpose and Operation

Purpose and Operation

An anti-sway or anti-roll bar is intended to force each side of the vehicle to lower, or rise, to similar heights, to reduce the sideways tilting (roll) of the vehicle on curves, sharp corners, or large bumps. With the bar removed, a vehicle's wheels can tilt away by much larger distances (as shown by the SUV image at right). Although there are many variations in design, a common function is to force the opposite wheel's shock absorber, spring or suspension rod to lower, or rise, to a similar level as the other wheel. In a fast turn, a vehicle tends to drop closer onto the outer wheels, and the sway bar will soon force the opposite wheel to also get closer to the vehicle. As a result, the vehicle tends to "hug" the road, closer in a fast turn, where all wheels are closer to the body. After the fast turn, then the downward pressure is reduced, and the paired wheels can return to their normal height against the vehicle, kept at similar levels by the connecting sway bar.

Because each pair of wheels is cross-connected by a bar, then the combined operation causes all wheels to generally offset the separate tilting of the others, and the vehicle tends to remain level against the general slope of the terrain. A negative side-effect, of connecting pairs of wheels, is that a jarring or bump to one wheel tends to also jar the opposite wheel, causing a larger impact applied across the whole width of the vehicle. If there are several potholes scattered in the road, then a vehicle will tend to rock, side-to-side, or waddle, due to the action of the bar at each pair of wheels. Other suspension techniques can be used to delay, or dampen, the effect of the connecting bar, as when hitting small holes which momentarily jolt just a single wheel, whereas larger holes or longer tilting would then tug the bar with the opposite wheel.