Buying a control arm for your car can sometimes be a daunting and confusing task. At Sanxin, it is our mission to make that task as easy and painless as possible. This Buyer’s Guide is designed to answer any questions you may have during your search for the right control arms for your car, and how to buy control arms on Sanxin.
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 frame or chassis of your car.
The upper control arm connects to the uppermost area of the steering knuckle or spindle and the lower control arm connects to the lower most area of the knuckle or spindle, with both arms then attaching to the frame of the car.
The most common types of control arm suspensions are:
• Control arm type suspension a.k.a double wishbone
• Strut type suspension a.k.a. the McPherson strut
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.
Control arms may not be common terms for many vehicle owners. You may have never even heard of them, but it is a critical component of your vehicle’s suspension system that allows your tires to smoothly go up and down in a controlled fashion. Without it, your ride probably wouldn’t be very enjoyable or safe.
Most vehicles use either one or two control arms per wheel, on the front, and sometimes on the rear suspension too. Many front-wheel-drive vehicles only use a lower control arm, while trucks and SUVs often have both an upper and a lower control arm. A control arm connects the wheel hub and steering knuckle to the frame of the vehicle. They are typically equipped with bushings on the frame side of the vehicle and a ball joint on the wheel side to allow flex and controlled movement according to road conditions and steering input from the driver. Control arms allow wheels to move up and down while preventing forward and rearward movement.
A – Each control arm is connected to the vehicle frame with two control arm bushings. These bushings allow the control arms to rotate on the bushing axis, thus allowing the other end of the arm to go 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 onto. 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 allows the wheels to move up and down following the road 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 and prevent uneven tire wear.
When control arms go bad you’re going to know it. The car may squeak or make a knocking sound whenever you drive over a bump, or it may pull to one side or the other. You also may notice the tires wearing unevenly. Control arm failure happens due to normal wear and tear, or the bushing on the control arm may have become compromised.
When shopping for your new control arm assembly you’ll want to look for sturdy enough materials at a price within your budget. This part endures quite a bit of stress so you want a durable product.
To make sure you get a good quality control arm assembly, you need to consider the following points:
• Decide on materials. Cast aluminum control arm assemblies are lightweight and corrosion-resistant, however they tend to buckle more easily over rough potholes. Cast iron arms are exceptionally strong and are typically wishbone-shaped. Stamped steel arms were typically used on older cars. They’re less expensive but can easily fall prey to rust.
• Look for OEM (Original Equipment Manufacturer) -comparable pieces if you’re going with aftermarket parts. High-quality aftermarket parts can perform to the same level as OEM parts, just make sure to buy from a reputable seller.
• Choose a control arm assembly that is powder coated or otherwise treated for corrosion resistance.
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