If you’ve ever wondered what do struts do on a car, you’re not alone. Struts are vital components that do more than just absorb bumps; they integrate a shock absorber with a spring to support the vehicle’s weight and control its motion. Understanding them is key to grasping how your car handles the road.
This guide will explain everything in simple terms. You’ll learn how they work, why they’re so important, and how to spot when they need replacing.
What Do Struts Do On A Car
At its core, a strut is a major structural part of your vehicle’s suspension system. It’s a single unit that combines two critical jobs. First, it acts as a damper, controlling the up-and-down movement of the springs. Second, it provides structural support, often serving as a pivot point for steering.
Without struts, your car would bounce uncontrollably after hitting a bump. They keep the tires firmly planted on the pavement, which is essential for safety, comfort, and control.
The Core Functions Of A Strut Assembly
A strut assembly performs several interconnected functions every time you drive. These are not separate jobs but parts of a single, integrated system working to keep you stable.
Support Vehicle Weight And Maintain Ride Height
The coil spring wrapped around the strut’s main housing is responsible for supporting the weight of your car. It compresses and expands to absorb the energy from road imperfections. This spring determines your car’s ride height, which is the distance between the axle and the chassis.
Dampen Oscillation And Absorb Impacts
Inside the strut housing is a shock absorber filled with hydraulic fluid or gas. When the spring compresses and releases, it wants to bounce. The shock absorber’s job is to dampen this oscillation. It converts the kinetic energy from the bounce into heat energy, which is then dissipated, stopping the bouncing motion quickly.
Provide Structural Support And Steering Pivot
Unlike a simple shock absorber, a strut is a load-bearing component. It is typically mounted to the vehicle’s body or frame at the top and to the steering knuckle at the bottom. This rigid structure helps maintain wheel alignment. In many front-wheel-drive cars, the strut also serves as the upper steering pivot, crucial for turning your wheels when you rotate the steering wheel.
Key Components Inside A Strut Assembly
To fully understand how a strut works, it helps to know what’s inside. A complete strut assembly is made up of several key parts that work together.
- Strut Housing: This is the strong, cylindrical outer body that holds all the internal components and attaches to the steering knuckle.
- Coil Spring: Wound around the outside of the housing, it supports the vehicle’s weight and absorbs large impacts.
- Shock Absorber (Internal): Sealed inside the housing, this piston-and-cylinder unit filled with fluid controls the spring’s movement.
- Strut Mount (Bearing Plate): Located at the top, this component connects the strut to the vehicle’s body and allows for rotation during steering.
- Bump Stop/Jounce Bumper: A rubber or polyurethane cushion that prevents metal-to-metal contact if the suspension compresses fully.
- Spring Seat/Perch: The platform that holds the coil spring in its correct position on the strut housing.
Struts Vs. Shock Absorbers: Clearing The Confusion
People often use the terms “strut” and “shock” interchangeably, but they are different parts with different roles. Knowing the distinction is important for maintenance and repair discussions.
- Struts: Are a structural part of the suspension. They replace the upper control arm and serve as a steering pivot. You cannot remove a strut without supporting the vehicle’s weight separately. They are generally more expensive to replace.
- Shock Absorbers: Are non-structural damping devices. They work alongside separate springs (like leaf or coil springs) and control bounce. They do not support vehicle weight or affect steering geometry. They are typically simpler and less costly to replace.
In short, all struts contain a shock absorber, but not all shock absorbers are part of a strut. Your car will use either a strut-type or a shock-type suspension at each wheel, and some vehicles use a combination, like struts in front and shocks in the rear.
How Worn Struts Affect Your Car And Safety
Struts wear out gradually, so you might not notice the slow decline in performance. However, driving with bad struts has serious consequences for your vehicle’s handling, tire wear, and overall safety.
- Poor Handling and Body Roll: The car may feel loose, floaty, or unstable, especially during cornering, lane changes, or on windy roads. Excessive body lean or “nose-diving” during braking is a classic sign.
- Longer Stopping Distances: Worn struts reduce tire contact with the road. During hard braking, the front end dives excessively, lifting the rear tires and reducing overall traction, which can increase stopping distance by a significant margin.
- Uneven and Accelerated Tire Wear: Without proper damping, the tires can “bounce” or “cup,” leading to uneven, scalloped wear patterns. This forces you to replace tires long before their normal lifespan is up.
- Increased Wear on Other Components: Bad struts transfer more impact force to other suspension and steering parts, like ball joints, control arm bushings, and even the chassis, leading to more expensive repairs down the line.
- Reduced Comfort: You’ll feel every bump and vibration more harshly. The ride becomes jittery and uncomfortable, with the vehicle bouncing multiple times after hitting a bump.
Recognizing The Symptoms Of Bad Struts
Being able to identify failing struts early can save you money and keep you safe. Here are the most common symptoms to watch (and listen) for.
- Excessive Bouncing: Push down firmly on each corner of your car and release. A good strut will allow the car to bounce back and settle immediately. If it continues to bounce two or three times, the strut is likely worn out.
- Unusual Noises: Listen for knocking, clunking, or rattling sounds from the wheel wells when driving over bumps or rough pavement. This often indicates worn strut mounts or internal damage.
- Fluid Leaks: Visible oil or hydraulic fluid leaking down the side of the strut housing is a clear sign the internal seal has failed and the strut is losing its damping ability.
- Uneven Tire Wear: Regularly inspect your tires. Look for bald spots, cupping (scalloped dips around the tread), or significantly more wear on one side of the tire than the other.
- Steering Problems: The steering may feel vague, loose, or harder to control. You might notice the car pulls to one side or wanders on the highway, requiring constant small corrections.
The Process Of Replacing Struts
Strut replacement is a significant maintenance item. While some experienced DIYers tackle it, it often requires special tools like a spring compressor, which can be dangerous if used incorrectly.
Professional Replacement Steps
- The vehicle is lifted and the wheel is removed.
- The brake line and anti-roll bar link are disconnected from the strut assembly.
- The strut tower bolts at the top (under the hood or in the trunk) and the bolts at the steering knuckle at the bottom are removed.
- The entire strut assembly is taken out as a unit.
- Using a hydraulic spring compressor, the old spring is transferred to the new strut assembly, or a complete pre-assembled unit is installed.
- The new assembly is fitted back into the vehicle and all bolts are torqued to the manufacturer’s specification.
- A wheel alignment is absolutely necessary, as replacing struts will alter the vehicle’s suspension geometry.
Many mechanics recommend replacing struts in pairs (both front or both rear) to maintain balanced handling. Complete, pre-assembled strut units are popular because they are safer and faster to install, as the spring is already correctly mounted.
FAQ About Struts And Suspension
How Long Do Struts Typically Last?
Strut lifespan varies widely based on driving conditions, vehicle type, and load. A general range is between 50,000 and 100,000 miles. If you frequently drive on rough roads or carry heavy loads, they may wear out sooner. Regular inspections are the best way to gauge their condition.
Can I Drive With A Broken Strut?
It is not safe to drive with a completely failed strut. A broken strut compromises vehicle control, increases stopping distance, and puts extra stress on other components. You should have it repaired as soon as possible. Driving even a short distance can be risky.
What Is The Difference Between Struts And Coilovers?
Coilovers are a performance-oriented type of strut. The name is short for “coil-over shock,” and they allow for adjustment of ride height and sometimes damping stiffness. While all coilovers are struts, not all factory struts are adjustable coilovers. They are common in motorsport and aftermarket upgrades.
Do New Struts Improve Ride Quality?
Yes, significantly. Replacing worn struts will restore your car’s original ride comfort, stability, and handling. You will notice a immediate reduction in bouncing, noise, and vibration. The car will feel tighter and more planted on the road.
How Much Does Strut Replacement Cost?
The cost depends on your vehicle make and model and whether you use OEM or aftermarket parts. For a typical sedan, replacing a pair of struts with labor can range from $600 to $1,200. Using pre-assembled quick-struts often reduces labor time. Remember, a wheel alignment (usually $75-$150) is a required additional cost after the work is done.
Struts are fundamental to your car’s safety and performance. They work silently in the background, but their role in keeping your tires on the road and your car under control cannot be overstated. By recognizing the signs of wear and addressing them promptly, you ensure a smoother, safer, and more predictable driving experience for you and your passengers. Regular checks by a qualified technician during tire rotations or oil changes are a smart way to monitor their condition.