An sway bar (anti-sway bar, anti-roll bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction. The first stabilizer bar patent was awarded to Canadian inventor Stephen Coleman of Fredericton, New Brunswick on April 22, 1919.
Anti-roll bars were unusual on pre-war cars due to the generally much stiffer suspension and acceptance of body roll. From the 1950s, production cars were more commonly fitted with anti-roll bars, especially those with softer coil spring suspension.