In automotive suspension

Suspension (vehicle)

Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

, an automobile's control arm or wishbone (aka. A-arm or A-frame) is a nearly flat and roughly triangular suspension member (or sub-frame), that pivots in two places. The broad end of the triangle attaches at the frame and pivots on a bushing

Bushing (isolator)

A bushing or rubber bushing is a type of vibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension systems, where a bushing made of rubber separates the faces of two metal objects while allowing...

. The narrow end attaches to the steering knuckle and pivots on a ball joint

Ball joint

In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles.More specifically, a ball joint is a steel bearing stud and socket enclosed in a steel casing. The bearing stud is tapered and threaded. It fits into a tapered hole in the steering knuckle. A...

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The upper control arm can clearly be seen at the top portion of the suspension components in the attached photo, where it is the silver part horizontally attached to the frame inside the red body portion and connecting to the steering knuckle near the side of the tire's wheel rim. Note the roughly A-shaped design with the top of the A near the tire and the bottom two points connected to the frame inside the body's space. In the photo, the A-shape is reinforced with a solid triangular plate near the top of the A.

Two such devices per wheel make up a double wishbone suspension

Double wishbone suspension

In automobiles, a double wishbone suspension is an independent suspension design using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control...

, while one control arm per wheel makes up a part, usually the lower part, of a MacPherson strut

MacPherson strut

The MacPherson strut is a type of car suspension system which uses the axis of a telescopic damper as the upper steering pivot. It is widely used in modern vehicles and named after Earle S. MacPherson, who developed the design.-History:...

suspension or of various other configurations.