Using a replacement sway bar

A sway bar is a torsion bar mounted laterally on a suspension and is designed to reduce side swaying. This bar attempts to accomplish this by transferring movement from one side of the suspension to the other. This is done through the connection of a torsion bar to each side of an axle by flexible links.

A sway bar is usually a torsion spring that resists body roll motions. It is usually constructed out of a U-shaped piece of steel that connects to the body at two points, and at the left and right sides of the suspension. If the left and right wheels move together, the sway bar just rotates about its mounting points and does not bend. If the wheels move relative to each other, the sway bar is subjected to torsion and forced to twist.

The sway bar resists the torsion through its stiffness. The stiffness of an sway bar is based on its diameter, the stiffness of the material,the inverse of the length of the lever arms, the placement of the mounting points, and the rigidity of the sway bar mounting points. Some replacement sway bars are adjustable, allowing their stiffness to be changed by increasing or reducing the length of the lever arms. This permits the roll stiffness to be tuned for different situations without replacing the entire sway bar. The stiffer the sway bar, the more force required to move the left and right wheels relative to each other. This increases the amount of force required to make the body roll.

Because the sway bar connects wheels on the opposite sides of the vehicle together, the sway bar will transmit the force of one-wheel bumps to the opposite wheel. On rough or broken pavement, the sway bar can produce jarring, side-to-side body motions which increase in severity with the diameter and stiffness of the sway bar.

Excessive roll stiffness will cause the inside wheels to lift off the ground during hard cornering. This is only possible if the regular spring rate actually allows the outside wheels to handle the much increased load. This can be an advantage, many front wheel drive production cars will lift a wheel when cornering hard, in order to overload the other wheel on the axle, thus limiting understeer.