Struts & Suspension Control Arms & Parts Control Arms: What You Need to Know

Your vehicle's suspension system is what keeps the tires in contact with the road, absorbs bumps, and allows you to steer safely. Two critical components in that system are struts and control arms. While they work together, they serve different functions. This article explains what each part does, how they interact, signs of wear, and what to consider when replacing them.

What Are Struts?

Struts are a structural part of the suspension. They combine a shock absorber and a coil spring into a single unit. The strut supports the vehicle's weight, dampens oscillations from road irregularities, and maintains wheel alignment. In many vehicles (especially front-wheel drive cars), the strut also serves as a pivot point for steering.

Types of Struts

• MacPherson strut: Common in front suspensions. It has a single strut assembly that connects the wheel hub to the chassis.
• Coilover strut: Similar but often adjustable for ride height and damping.
• Cartridge strut: The insert can be replaced without changing the housing.

Most modern vehicles use sealed strut assemblies that come pre-assembled with the spring. When they wear out, you replace the whole unit.

What Are Control Arms?

Control arms connect the wheel hub to the vehicle's frame. They allow the wheel to move up and down while keeping it in the correct fore-aft position. Each wheel typically has an upper and a lower control arm (though some setups have only a lower arm). The control arm houses ball joints at one end and bushings at the pivot points.

Parts of a Control Arm

• Ball joint: The pivot that attaches to the steering knuckle. It allows rotation and angular movement.
• Bushings: Rubber or polyurethane sleeves that absorb vibration and allow controlled movement at the frame side.
• Arm itself: Usually made of stamped steel or forged aluminum.

Control arms can be replaced as a complete assembly (with ball joint and bushings already installed) or as separate parts. Full assemblies are easier and faster to install.

How Struts and Control Arms Work Together

The strut and control arm are linked by the steering knuckle. The control arm locates the knuckle laterally, while the strut controls vertical motion and also provides the upper pivot. In a MacPherson strut system, the strut acts as both a shock absorber and a guiding link. The lower control arm supports the bottom of the knuckle, and the strut supports the top.

When either component wears, it affects the other. A worn control arm bushing can cause misalignment, accelerating strut wear. Conversely, a bad strut can transfer extra loads to the control arm.

Signs of a Failing Suspension

Symptoms of Bad Struts

• Nose diving when braking
• Excessive bounce after hitting a bump
• Uneven tire wear (cupping)
• Fluid leaks on the strut housing
• Knocking or clunking sounds on rough roads
• Vehicle sags in one corner

Symptoms of Bad Control Arms

• Clunking or popping when turning or going over bumps
• Steering wander or loose steering feel
• Uneven tire wear (especially on one edge)
• Vibration in the steering wheel
• Visible play in the ball joint (if inspected)

If you notice any of these, have the suspension checked. Neglect can lead to poor handling, increased stopping distances, and damage to other parts.

When to Replace Struts and Control Arms

There's no set mileage for replacement – it depends on driving conditions, road quality, and part quality. However, many manufacturers recommend inspecting struts at 50,000 miles. Control arms can last 80,000 to 100,000 miles or more. But if you drive on rough roads or carry heavy loads, replacement may come sooner.

Should You Replace in Pairs?

• Struts: Always replace in pairs (both front or both rear) to maintain balanced handling. If one is bad, the other likely isn't far behind.
• Control arms: Replace in pairs on the same axle. If the right lower control arm is worn, replace the left as well.

Choosing Replacement Parts

OEM vs Aftermarket

• OEM (Original Equipment Manufacturer): Made by the same supplier as the factory parts. They match exactly but cost more.
• Aftermarket: Many brands offer parts that meet or exceed OEM specs. Some are better (e.g., polyurethane bushings for longevity), others are lower quality. Stick with reputable brands like Moog, AC Delco, or TRW for control arms; KYB, Monroe, or Bilstein for struts.

Loaded vs Bare

• Loaded control arm: Comes with ball joint and bushings pre-installed. Saves time and ensures proper fit.
• Bare control arm: Just the metal arm; you must transfer old parts or buy new ones separately. Not recommended unless you have a press and experience.

Quick Struts vs Strut Assembly

• Quick strut or complete strut assembly: Includes spring, mount, and boot. Easy to install – just bolt in. More expensive but saves labor.
• Strut cartridge: Only the damper; you reuse the spring. Requires a spring compressor. Cheaper but more work.

For most DIYers, a quick strut is the way to go. For control arms, go with a loaded assembly.

Installation Tips

Replacing struts and control arms can be dangerous due to spring tension. Unless you have proper tools (spring compressors, ball joint press), leave it to a professional. If you do it yourself:

• Always support the vehicle on jack stands.
• Replace struts one at a time to avoid spring tension issues.
• Tighten bolts with the suspension loaded (weight on wheels) to prevent bushing binding.
• After installation, get a wheel alignment. Any change in ride height or control arm position alters camber and toe.

Practical Recommendation

If your car has over 60,000 miles and you're experiencing handling issues, inspect both struts and control arms. A complete front suspension overhaul (both struts, both lower control arms, and sway bar links) can restore like-new ride quality. For struts, buy quick struts from a trusted brand. For control arms, buy loaded assemblies. Always replace in pairs and get an alignment afterwards. Prices vary by vehicle, but quality parts cost $150–$400 per corner (parts only). Labor can double that. It's a worthwhile investment in safety and comfort.