Control Arm

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In automotive suspension, the control arm (also known as the A-arm) is the articulated suspension link between the chassis and the suspension uprights or hubs that carry the wheels.

The inboard (chassis) end of the control arm is attached by a pivot, usually a rubber bush. Thus, it can control the position of the outboard end in only a single degree of freedom, maintaining a radial distance from the inboard mount. Although not intentionally free to move, a single bushing does not control the arm to move back and forth; this movement is constrained by a separate link or radius rod.

This contrasts with the wishbone. The wishbone is triangular and has two inboard bearings that are widely spaced. These constrain the lateral end of the wishbone to move back and forth, control two degrees of freedom, and require no additional linkage.

Most control arms with arm bush make up the lower link of the suspension. Some designs use them as upper links, usually with a lower wishbone. Then attach additional radius rods to the upper arm.