A control arm, or sometimes known as an “A-arm” is a suspension component that links the chassis to the wheel assembly of the vehicle. The control arm attaches to both coil spring and leaf suspension components. The “inboard” or chassis connecting end of the control arm is attached by a single pivot. This allows the outboard end to have a certain level of freedom to travel independently but not much.
In a double wishbone suspension there are two control arms, upper and lower. This type of independent suspension system allows for greater control of the coil or leaf spring through it’s movement range and greater adjustment for camber values also.