Anti-roll bars reduce a car's tendency to "roll," or lift on one side and dive on the other during cornering by creating a link between the two wheels at either the front or the rear. By controlling the transfer of load from one wheel to the other, cornering is improved.
Also called anti-sway bars or simply sway bars, most anti-roll bars take the form of a U-shaped rod connected to either the front or the rear of the vehicle's wheel, axle or suspension components on each side. When one wheel experiences heavy load, the anti-roll bar twists, reducing the other wheel and side of the car's tendency to lift.
Once the domain of high-performance and luxury cars, anti-roll bars today make up a common suspension component of even some mass-produced sedans. Modern racing and sports car anti-roll bar systems are often adjustable, either manually or through the suspension system's electronic control unit, allowing a driver or technician to change the car's tendency to roll, understeer or oversteer.
An anti-roll bar also functions as an effective and relatively affordable way to increase a car's cornering performance through aftermarket equipment. Adding an anti-roll bar at either the front or the rear (or both) can alter a car's cornering characteristics and reduce body lean.
However, adding an anti-roll bar with too large a diameter or too much stiffness causes a vehicle to become jumpy over rough pavement, or to have undesirable understeer or oversteer characteristics. For this reason, some automakers tend to leave them off cars designed more for comfort than performance. Anti-roll bars fitted to mass-market cars are usually smaller in diameter and composed of softer material with less torsional rigidity.