What are control arms?

Control arms, sometimes called "A arms," are the core of your front suspension system. In simple terms, control arms are the link that connects your front wheels to your car. One end connects to the wheel assembly and the other end connects to the framework of your car.

The upper control arm connects to the uppermost area of the front wheel and the lower control arm connects to the lower most area of the front wheel, with both arms then attaching to the frame of the car. If you have independent rear suspension, the design is similar.

In simple terms, control arms are the link that connects your front wheels to your car.

What are the types of control arm suspensions?

The most common types of control arm suspensions are:

• Control arm type suspension
• Strut type suspension 

Strut type designs have a lower control arm but no upper control arm. In strut designs, the strut becomes the upper control arm and is sometimes connected directly to the spindle or the lower control arm.

How do control arms work?

A. Each control arm is connected to the vehicle frame with two control arm bushings. These bushings allow the control arms to move up and down.
B.The opposite end of the control arm is attached to a steel spindle. The spindle is what the front wheel is bolted to. On non-strut equipped vehicles, the spindle is attached to both the upper and lower control arms with a ball joint. The ball joint is a steel ball enclosed in a steel socket that allows the spindle and front wheel to rotate left and right and allow the wheels to move up and down following the roads surface.
C.Sandwiched between the control arm and vehicle frame, positioned in a spring socket, is a heavy steel coil spring that supports the weight of your vehicle and provides a cushion against bumps.
D.To combine the two opposite motions on each end of the control arm, the arms are tied on the frame side to pivot up and down on the control arm bushings. On the opposite end, the control arm is tied to the spindle and front wheel with upper and lower ball joints. The coil spring supports the weight of the car and dampens the shock of road surfaces.

To ensure that the control arms, bushings and ball joints are in perfect alignment, some control arms include adjustable attachment points at the frame. When necessary, a mechanic can align the front end and keep your car driving straight down the road.