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A control arm is a piece of a vehicle's suspension. There are several different types of control arms used in manufacturing a vehicle's suspension. Both front and rear control arms are used in four-wheel, independent suspension designs. Some types of control arm pieces are used to turn the wheels in the steering gear, while others are used to control wheel hop and bounce. Perhaps the most recognizable control arm is found on a vehicle's anti-roll bar.
A vehicle's suspension is a complexity of geometry and leverage. The front suspensions in most vehicles manufactured today not only steer the vehicle, but also drive the vehicle. Front-wheel drive designs rely on a control arm to counteract the engine's torque. By placing an engine torque limiter arm between the engine and the vehicle's chassis, the vehicle is able to be easily steered while applying power to the engine. Without this arm, the vehicle would be nearly impossible to steer when a driver applies power to the wheels.
Modern suspensions use a strut system of shock and upper control arm. By placing an arm at the bottom of the strut to control forward and rearward movement, the strut is able to work unassisted from the top of the suspension in controlling wheel movement. In earlier designs, both a top and bottom control arm were used with a spring sandwiched in between them. This type of suspension drastically limited the amount of wheel travel a suspension could have. This created a much rougher ride, as the suspension was forced to bottom out against rigid bump stops instead of traveling smoothly through the bump.
Placing suspension pieces on the sub-frame instead of requiring a full frame allows for safety enhancing crush panels to be engineered into the vehicle's chassis. These panels absorb energy in the event of a collision and dissipate the energy throughout the chassis and away from the passenger compartment. The use of these crush panels is made possible through the use of control arm suspension.
Many of the control components are manufactured of cast or machined alloys. Creating suspension components from lightweight materials reduces the un-sprung weight of the suspension. This reduces the effects felt from encountering bumps and rough roads. Technology in the advancement of shock absorber design has shown that reducing the weight of the suspension components—such as control arms—has a great deal of influence on the quality of the vehicle's ride. Lighter and softer springs also can be employed by using control arm technology to take advantage of the leverage of the arm.