What Is a Sway Bar?

Sway bars probably get less attention than they deserve. Control arms, shock absorbers, springs and struts may come to mind when you’re looking at suspension components, but what is a sway bar for?

The History of the Sway Bar

The first cars were barely faster (and certainly less dynamic) than the horses they were intended to replace. More power and more speed, however, required the addition of a more dynamic chassis for greater control and ride comfort. Body roll in corners became a noticeable feature of high-speed driving — around 12 mph. Something was needed to mitigate body roll when cornering, if not to improve rider comfort then at least to keep all four wheels on the ground.

What Is a Sway Bar?

The sway bar goes by several names, including roll bar, stabilizer bar, anti-sway bar and anti-roll bar. It’s a torsion bar, essentially a twisting spring, that limits how much a control arm can move up and down independently of its opposite member. Vehicle dynamics dictate that the vehicle will tend to roll to the outside of the turn, which can affect vehicle control, especially with a high center of gravity or squishy tires, like you might find on an SUV. Without a sway bar, the tires on the inside of the turn may even lift off the pavement.

For example, in a right turn, the vehicle tends to roll to the left, with the left wheels forcing closer to the body and the right wheels falling away from the body. With sway bars loosely connecting left and right sides, the left-side wheels will partially pull the right-side wheels up, pulling the body down on the right and reducing body roll.

How much body roll is reduced depends on the stiffness of the stabilizer bar. Sports cars have stiffer sway bars than off-road vehicles, so they stay flatter in corners to improve control, while off-road vehicles can maintain traction on uneven terrain.

Common Sway Bar Problems

While the sway bar tends to have few problems, the links and bushings are in constant motion under push and pull forces. Eventually, links and bushings wear and loosen, leading to clunking noises on uneven bumps. Straight-on speed bumps shouldn’t agitate a loose bushing or link, but a manhole cover or pothole might. The ears, which are the holes at the end of the sway bar, are particularly under stress and may crack or break off.

In all of these cases, the solution is to replace the affected parts. Sway bar bushings mount to the body or frame, while sway bar links mount to struts or control arms. You can lubricate the sway bar link joints if they’re equipped with grease fittings.

In some cases, you may need to replace the whole sway bar. An OE-type sway bar will restore factory ride quality. In some cases, you can tweak your ride with a non-OE option. A stiffer rear sway bar on a front-wheel drive, for example, tends to reduce understeer, while a stiffer front sway bar on a rear-wheel drive tends to reduce oversteer.

The sway bar isn’t just something that makes noise when the links or bushings wear out — it greatly affects ride quality during cornering. Without it, we might still be rounding turns at 12 mph.

Check out all the shocks and struts available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on what a sway bar is, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.