Sway Bars

A sway bar (also stabilizer bar, anti-sway bar, roll bar, or anti-roll bar, ARB) is an automobile suspension device. It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. more...

Home
ATV Parts
Apparel & Merchandise
Automotive Tools
Aviation Parts
Boat Parts
Car & Truck Parts
Air Conditioning and Heat
Air Intake & Fuel Delivery
Brakes
Charging & Starting Systems
Computer, Chip, Cruise...
Cooling System
Decals, Emblems, & Detailing
Emission System
Engines & Components
Exhaust
Exterior
Filters
Gaskets
Gauges
Glass
Ignition System
Interior
Lighting & Lamps
Other Parts
Safety & Security
Salvage Parts Cars
Suspension & Steering
Ball Joints
Caster/Camber Kits
Coil Springs
Control Arms & Parts
Leaf Springs
Lift Kits & Parts
Lower Kits & Parts
Other
Pitman & Idler Arms
Power Steering Pumps & Parts
Shocks & Struts
Steering Racks & Gear Boxes
Strut Bars
Sway Bars
Tie Rod Linkages
Transmission & Drivetrain
Turbos, Nitrous,...
Wheels, Tires & Parts
Car Audio, Video
Manuals & Literature
Motorcycle Parts
Other Vehicle Parts
Personal Watercraft Parts
Racing Parts
Services & Installation
Snowmobile Parts
Vintage Car & Truck Parts
Wholesale Lots

A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction.

Principles

A sway bar is usually a torsional 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 bar just rotates about its mounting points and does not bend. If the wheels move relative to each other, the bar is forced to twist.

The bar resists the bending through its stiffness. The stiffness of an anti-roll bar is based on the fourth power of its diameter, the stiffness of the material, the inverse of the length of the lever arms (i.e., the shorter the lever arm, the stiffer the bar), the geometry of the mounting points, and the rigidity of the bar's mounting points. Some anti-roll bars, particularly those intended for use in auto racing, are adjustable, allowing their stiffness to be altered 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 bar. The stiffer the 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.

In a turn, the sprung mass of the vehicle's body produces a lateral force at the cg proportional to lateral acceleration. Because the cg is usually not on the roll axis, the lateral force creates a moment about the roll axis that tends to roll the body. (The roll axis is a line that joins the front and rear roll centers (SAEJ670e). The moment is called the roll couple.

Roll couple is resisted by the suspension roll stiffness, which is a function of the spring rate of the vehicle's springs and of the anti-roll bars, if any. The use of anti-roll bars allows designers to reduce roll without making the suspension's springs stiffer in the vertical plane, which allows improved body control with less compromise of ride quality.

One effect of body (frame) lean, for typical suspension geometry, is positive camber of the wheels on the outside of the turn and negative on the inside, which reduces their cornering grip (especially with cross ply tires).

Anti roll bars provide 2 main functions:

The first is the reduction of body lean. The reduction of body lean is dependent on the total roll stiffness of the vehicle. Increasing the total roll stiffness of a vehicle does not change the steady state total load (weight) transfer from the inside wheels to the outside wheels, it only reduces body lean. The total lateral load transfer is determined by the CG height and track width.

Read more at Wikipedia.org