Control Arm Definition

June 4, 2021

A control arm is the part that forms the link between the suspension of a car and the chassis. Although control arms come in different shapes and sizes, they are easy to recognize or spot. They are the visible metal structures that run from the vehicle body to the wheel assembly.


On the chassis side, a control arm mounts by means of bolts. It hinges on rubber or polyurethane bushings called control arm bushings. The wheel assembly end of the control arm features a ball joint. That way, the component moves on both ends.


You will mostly find control arms in the front axles where they attach to the steering knuckle. Some heavy and high-end vehicles will have control arms in the rear axle as well. Most control arm car parts are broad at one end and narrow at the other. They can be an “A” or “L” shape, but some feature a simple shaft.


The number of control arms on a single wheel varies depending on the type of vehicle. Some have two control arms on either side- an upper and lower one. These can be seen attached to the wheel assembly through ball joints while the other ends bolt to the vehicle frame. This type of suspension system is called double “wishbone suspension,” and for reasons we will see shortly.


Modern, inexpensive cars mostly have a single control arm at each wheel- a lower control arm. These are vehicles that use the MacPherson strut suspension. This type of suspension supports most of the weight on a strut, and the reason for the lack of an upper control arm. It has its advantages and disadvantages (we will see about that in a minute).


Control arms feature three main parts: bushings and sleeves, main body, and ball joint. Control arm bushings help to reduce friction and vibrations while the control arm ball joint forms the pivot at the steering knuckle or wheel assembly. The main body is the control arm link that connects the component to either end. It can be stamped steel, cast iron, or aluminum.