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How Your Car’s Suspension Works

Alex Palmeri
June 6, 2018

Maybe your car has a lot of horsepower, or gets excellent gas mileage. None of that would matter if it didn’t drive in a straight line or stop when you want it to. Lurking under every vehicle is an intricate suspension system that makes your ride safe and comfortable. 

Although there are a few different kinds of suspensions, the basic principle is always the same. The suspension is built to provide a comfortable ride on all terrains, provide good handling around turns and, most importantly, assist in providing traction so your tires stay planted on the road at all times.

Let's look at what the suspension does, or you can skip ahead to learn about the parts of the system and the different types of suspensions.

What a suspension system does

Even the best streets aren’t perfectly smooth. Your car’s suspension system is needed to provide a cushion between you and road irregularities like rough patches, potholes, speed bumps and debris. 

When you hit a bump, energy is transferred to your tire and wheel. Some of this energy is absorbed, and some is not. Without the suspension system, a good portion of that energy would be transferred to the frame, causing you to feel it in the driver’s seat. You would be bouncing around all over the place — it would feel like driving a giant go-kart. 

Force is also created when the car turns. In this case, the suspension helps keep the vehicle planted on all four tires. When the body leans to one side, the suspension system can compensate, reducing body roll and allowing the tires to be more effective. 

This is also true when braking and accelerating, since weight transfers either to the front or rear of the car. If you brake hard, the car’s rear will want to lift up, which would reduce the contact pressure of the rear tires and hamper braking power. The suspension minimizes this. 

Let’s go over the individual parts of a vehicle's suspension, and how they work together to make your vehicle safer.

Suspension parts, and how they work together 

The suspension is part of your vehicle's chassis and incorporates the frame, the suspension system, the steering system, and wheels and tires. The major components in every modern suspension system are springs, dampeners and anti-sway bars. 

leaf spring
Leaf spring image courtesy of Wikipedia/Tennen-Gas

Springs

The vehicle’s springs are the foundation of the suspension system. Their job is to hold the weight of the vehicle and its occupants, keep the car high enough so it doesn’t bottom out, and allow the wheels to move up and down without jarring the passengers. Here are a few different types of springs found on modern cars and trucks.

Steel coil spring: This is the most common type of spring, and it’s seen on most cars on the road. The name says it all: a coil spring is a heavy-duty steel bar wound into a coil. It compresses and expands to absorb the impact of irregular roads as you drive.

Leaf spring: Seen on many trucks and even some sports cars, such as the Chevrolet Corvette, a leaf spring consists of several “leaves” clamped together to form one unit. Each leaf is a thin, flat, arc-shaped piece of metal, and they’re stacked on top of each other. The more leaves, the more weight the vehicle can carry without compromising ride height.

Torsion bar: A torsion bar-style spring has been used in everything from large military vehicles to pickups and larger SUVs. A torsion bar is a long, straight piece of metal that mounts to the frame or chassis at one end and a control arm, spindle or axle at the other end. When you hit a bump, the vertical motion of the wheel causes the bar to twist. The torsion resistance of the bar absorbs this energy, providing the same result as the coil or leaf spring.

Air spring: Seen on many luxury cars, an air spring is a cylinder filled with air and positioned between the control arm and car’s body. A compressor fills the cylinder, which is typically made of a high-quality rubber, and this holds the vehicle up. The air then absorbs energy transferred to the wheels and tires from the road. With some of these systems, you can adjust the ride height on the fly with a switch or button inside the car.

Hydraulic spring: These springs are also common on higher-end vehicles and use hydraulic fluid pressurized by a pump. The fluid acts as the cushion between you and road, and in most cases the ride height and ride stiffness are constantly adjusted by computers and sensors. 

strut
Strut image courtesy of Wikipedia/Robert Basic

Dampeners

Because these springs extend and compress at a fast and uncontrollable rate, a dampener is needed to control their motion. There are two types of dampening devices on most vehicles: shocks or struts. Let’s take a look at how each works and how they assist in ride quality and handling.

Shock absorbers: A shock absorbs and controls the compression and rebound of your springs. This helps make sure your tires don’t leave the ground. Shocks are normally located near the spring at each corner of the vehicle. Inside the shock absorber is a piston that moves inside a tube that contains hydraulic fluid. As the shock moves up and down, this fluid is forced through small holes and valves that control the amount of resistance and dampening needed for a smooth ride. 

Struts: A strut is a spring and shock in one assembly. The shock is mounted inside the coil spring and they can be removed from a vehicle as one unit. Struts are used in many cars, light-duty trucks and SUVs, and provide a compact and economical option for automakers. The spring is removable from the strut assembly, so both parts can be replaced individually if needed. 

sway bar
Sway bar image courtesy of Wikipedia/Nick Ares

Sway bar

Sometimes called an anti-roll or anti-sway bar, this part ties one side of the vehicle's suspension to the other to help keep everything stable. The sway bar is connected to the frame or chassis with mounts and bushings. From there, each end of the bar is connected via a link to the control arm or spindle. 

By connecting both sides, the sway bar reduces body roll when you turn. Some older vehicles had either just a rear sway bar or none at all, but automakers now incorporate them front and rear on almost every vehicle on the road.

Active suspension

As with so many car systems these days, computers can help your suspension work even better. Active suspension is a computer-controlled enhancement of the MacPherson struts and shock absorbers on a vehicle. The computer can automatically change the dampening and the ride height characteristics of the struts or shocks in relation to road speed, or the driver can select one or more enhanced or softened suspension presets.

» RELATED SYSTEM: Learn about your power steering system

Types of suspension

There are two basic types of suspensions, dependent and independent. Some cars will have just one type, but other vehicles have both. Let’s take a look at how they function, both on the front and rear of the car, and the pros and cons of each.

Dependent front suspension: Found on many older cars, trucks and vans, a dependent front suspension connects the right wheels to the left ones. On a four-wheel-drive truck, this uses the axle tube housing, while a rear-wheel-drive car with front dependent suspension uses an axle beam.

This style typically incorporates a normal shock absorber with either coil, leaf or torsion springs. This type provides strength, simplicity and off-road capability, but its downfall is a less comfortable ride. Because both wheels are connected, a jolt from a bump will be felt on both sides of the car.

Independent front suspension: The is the most common type of front suspension — it's used on almost every car. An independent front suspension allows each wheel to move on its own because there’s no axle connecting the two. This improves handling and ride comfort, and is more compact and lighter. This type doesn’t have many negatives when used on normal cars that aren’t meant to go off road.

Rear dependent or rigid axle suspension: This type of suspension is mostly used on trucks, vans and rear-wheel drive vehicles. It connects both rear wheels with one solid axle and is typically paired with a normal shock and coil or leaf spring.

Independent rear suspension: Used on many newer vehicles with either front- or rear-wheel drive, an independent rear suspension is basically the same as front independent suspension minus the steering components. 

When a car has this in the front and rear, it’s called "four-wheel independent suspension." This provides the best handling and ride comfort overall because each wheel can absorb road impacts individually. This isolates bumps to one wheel, so they’re not felt throughout the car. Independent rear suspension also provides for the most flexibility when turning, which is why most sports cars use this type. 

» LEARN MORE: Get an estimate for your suspension system repair

Keeping your suspension system working 

Springs, shocks and struts will wear out — but they do this slowly, so you may not notice a drastic change in ride quality over a long period of time. Because of this, it’s important to have these parts inspected periodically for wear. 

When these parts do wear out, your driving experience will get less comfortable. You’ll feel more jolts, the car will feel less balanced around turns, or you may hear rattling or thumping sounds when you turn or go over bumps.

There’s typically not a set maintenance schedule for coils, shocks and struts, but many often need replacement at some point between 50,000 and 100,000 miles. Check your owner’s manual. If you stick to your car’s maintenance schedule, your mechanic can help you identify when it’s time for new parts.

 

Alex Palmeri

About the Author

Alex Palmeri worked nine years as a master technician at Mercedes-Benz of Chicago and is currently the foreman at a large fleet garage. He writes about automotive news, maintenance and racing, and runs a YouTube channel called Legit Street Cars.

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