<P> In automotive suspension, a control arm, also known as an A-arm, is a hinged suspension link between the chassis and the suspension upright or hub that carries the wheel . </P> <P> The inboard (chassis) end of a control arm is attached by a single pivot, usually a rubber bushing . It can thus control the position of the outboard end in only a single degree of freedom, maintaining the radial distance from the inboard mount . Although not deliberately free to move, the single bushing does not control the arm from moving back and forth; this motion is constrained by a separate link or radius rod . </P> <P> This is in contrast to the wishbone . Wishbones are triangular and have two widely spaced inboard bearings . These constrain the outboard end of the wishbone from moving back and forth, controlling two degrees of freedom, and without requiring additional links . </P> <P> Most control arms form the lower link of a suspension . A few designs use them as the upper link, usually with a lower wishbone . The additional radius rod is then attached to the upper arm . </P>

What is a lateral arm on a car