What is a Control Arm on a Car? Control Arms Explained

The control arm is a crucial part of car suspension that is rarely discussed. It joins the wheels to the chassis, stabilizing the vehicle and making it steerable. So, you always want it in good condition, or your car may need to be safer to drive. Here’s more about the part and why it’s so crucial.

What is a Control Arm on a Car?

A car control arm (also popularly called an “A” arm) is the component that forms the structural connection between the wheel hub assembly and the chassis. It typically pivots on the wheel side using a ball joint and hinges on the chassis using a rubber/polyurethane bushing or bushings.

That way, the wheels operate independently of the frame, rotating from side to side while allowing vertical movements. Here are some other facts about this suspension part.

• Traditionally, the arm has been A-shaped and commonly called a wishbone. The modern type is available in various designs, including L-shapes and straight shafts.
• Older vehicles with conventional double wishbone suspensions have two arms on each front axle wheel. These are known as the upper and lower arms.
• Most modern cars use the MacPherson suspension. In these vehicles, the upper control arm is replaced by a suspension strut, with only a single lower arm on either side of the axle.
• Some vehicles have this part in the rear axle as well. These include SUVs and trucks.

What Do Control Arms Do on a Car?

As its name suggests, the primary function of a control arm is to keep the vehicle under control when on the road. It joins the frame to the suspension, allowing the two to move together in unison.

The ball at one end of the assembly allows the steering knuckle to rotate the wheel, letting you conveniently guide the vehicle.

The bushings at the other end dampen the body vibrations, ensuring smooth rides. They also allow the body’s controlled up/down movement and keep the tires on the road for improved stability.

Do Control Arms Come With Ball Joints?

Not necessarily. Some do, and some do not. It depends on the specific design and if it’s an earlier model for older cars or an arm for newer vehicles.

Most control arms manufactured today have pre-installed ball joints. As a result, you can only replace them as a single unit and not separately.

Older vehicles may have the ball joint separate from the arm. These allow you to change the ball joint if it gets damaged.

How Control Arms Work

They connect to the wheel assembly using ball joints and the chassis with rubber or polyurethane bushings. That way, they have free motion on either end of the assembly.

The ball joint allows up/down and lateral movement to make steering the vehicle possible. On the chassis side, the bushings allow an up-and-down motion while dumping vibrations.

Control Arm Components

The control arm of a car typically comprises the body, a ball joint on the end that mounts to the wheel hub assembly or steering knuckle, and bushing where it attaches to the chassis.

Arm Body

The body is the main section between the mountings on either end of the assembly. Various materials are used to make the arm body. They include steel, aluminum, and cast iron.

Bushings

The bushings are located where the arm mounts on the vehicle body. They reduce friction by preventing metal-to-metal contact between the arm and the chassis.

The bushings also dampen chassis vibrations when the vehicle moves up and down for smooth rides. Some bushings are replaceable; some are not.

Ball Joint

The ball joint links the wheel assembly and the suspension to the body. It allows the suspension to move up and down and the steering knuckle or spindle to rotate.

Like the bushings, the ball joints are either replaceable or built into it. Some come greased for life, with polymer inserts in the socket to prevent metal and metal contact.

Types of Control Arms

These suspension components are classified by their location and whether their length can change. They include the upper and lower, front and rear, and adjustable types.

Upper and Lower Arms

The upper types attach further up the suspension and frame. Only cars with conventional double wishbone suspension use them. In most modern vehicles, the upper arm is absent. Instead, a strut suspension takes its place.

The lower types attach to the lower section of the wheel assembly. They bear most of the weight and are used by virtually every vehicle, including newer models with strut suspension.

Front and Rear Arms

The front types attach to the front axle or suspension. A double wishbone suspension has two on each side of the axle, while a MacPherson suspension only has one.

Rear control arms are mainly found in heavy-duty automobiles like SUVs and trucks. In these vehicles, having the arms in the front and rear enhances handling and comfort.

Adjustable Arms

These allow you to customize their length as desired using a threaded section. They are famous for allowing car owners and repair technicians to set tire camber. If you just replaced the arms and needed an alignment, these arm types would make that easier.

Control Arm Material

This suspension part is typically made using stamped steel, cast iron, or stamped aluminum. The type of material used depends on the required level of sturdiness, weight or cost savings, and ability to resist wear or corrosion, among other factors.

Stamped Steel

Steel is a good material. In addition to being sturdy, it easily flexes and won’t easily break or crack under the vehicle’s weight or impact. Steel arms also cost less to manufacture, which makes them an inexpensive option.

But steel is susceptible to rusting. In wet or salty driving conditions, the component may eventually rust. Manufacturers usually cover the steel surface with a protective coat to prevent rusting.

Cast Aluminum

Aluminum weighs comparatively less and will not introduce unnecessary weight. It also does not rust and can last longer in wet or salty conditions. It also absorbs vibration better than the other materials.

Cast aluminum can support much weight, too. However, it does not flex and can break or crack if subjected to excessive force. It also wears fast owing to its soft nature.

Cast Iron

Cast iron is more rigid than steel and aluminum and can support heavier loads. Cast-iron arms are, therefore, mainly used in heavy-duty vehicles like trucks.

Like steel, cast or forged iron is susceptible to corrosion over time. So, the material is usually coated to protect it against damage if you drive in wet conditions.

How Much Does a Control Arm Cost?

The price of control arm assemblies ranges from 50$ to 250$. The exact cost depends on several factors, such as the specific material used to make them, the arm design, and the vehicle make or model.

For instance, an aluminum type is more expensive. Stamped steel is more affordable and will suffice in most situations, especially mild driving conditions. You only need to ensure it’s coated to extend control arm lifespan.

Designs include A and L shapes or straight and adjustable constructions. Make sure the construction suits your vehicle type and suspension.

You can also go for aftermarket type rather than OE arms. They cost less and are often built using better materials and features.

Conclusion

Your car’s handling depends on one less-talked-about component: the control arm. It plays a crucial role in making your rides smooth and safe, but only if it’s up to the task. Are you looking for a reliable control arms manufacturer and supplier?

WanTuo is your one-stop source. We build our suspension arm to weather the harshest conditions, ensuring outstanding performance, durability, and, more importantly, your safety. Upgrade to a WanTuo arm today!