How Stock Car Suspensions Work

Stock car suspension.
Stock car suspension.

­The driver of a stock car gets all the attention after a big win, but he or she would never be able to take home a trophy if not for the team that constantly tweaks and fine-tunes the car. Throughout the preparation and during the actual race, pit crews and mechanics stand by to make any necessary alterations to improve the car's capabilities.

You might not think the suspension of a stock car has that much to do with success on a flat, smooth track, but don't be mistaken. Rarely is a track's surface perfect, considering how roughly it's driven on, so suspension is actually an area of primary focus to many teams. Depending on the demands of a specific track, the driver's past performance there and the car's balance in different conditions, the suspension may need to be completely rebuilt for each racetrack. That kind of precision takes a lot of time and effort.

The suspension system consists of a variety of components, including the springs, shock absorbers, sway bars, steering assembly and chassis.

­In this article we'll learn about the role and importance of the steering bushings, brackets and knuckles in stock car suspensions and a brief history about them. We'll also talk about sway bars and how they're chosen based on the track and driver needs.

Shocks and springs are an ever-important part of a suspension system. This article will reveal how they work, and why their role in maneuvering high-speed stock cars is so crucial.

Even wonder about the governing rules for stock car chassis components? In this article we'll explore how the entire framework is laid out and put together.

For now, sit back and enjoy the ride while we examine the fine points of stock car suspension.

Stock Car Brackets and Knuckles

­One part of a stock car's suspension that takes quite a beating is the steering assemblage. Steering brackets and knuckles, which hold the steering assemblage together, get a constant workout and can knock a driver out of a race should they fail. That makes sense -- proper steering and control is an obvious necessity for a sport involving cars traveling at high speeds.

­The steering wheel is connected to the suspension and wheels via the steering knuckles. The knuckle connects the steering wheel to the rest of the car, allowing the driver to direct the vehicle. Two control arms link the chassis and the front suspension, while trailing arms connect the chassis to the rear suspension. Tie rod ends connect to the steering knuckles, which directly control the wheels [source: Burt].

The control arms are connected to the frame with pivoting mounts and steering bushings. Ball joints connect them to the steering knuckle. As the driver turns the wheel, motion is transferred down the steering shaft to the steering gear.

Because knuckles can and do fail, they're connected to the frame with steel cables to prevent the wheel assembly from flying off during a crash [source: Burt].

­Turning during high speeds puts tremendous pressure on the steering assembly and chassis. Throw in a couple of bumps, and a race car can spin out of control. What helps a car maintain control while the driver navigates a turn? The shocks. Next we'll learn about the importance of shock absorbers on the stock car circuit.

Stock Car Shocks

No track is smooth as silk -- without shocks, a stock car would bounce all over the place each time it hit a bump or dip. Shocks and springs are an important part of controlling the car.

As the stock car makes its way around the track, the springs compress and expand when they hit imperfections. The shocks absorb the energy of the spring, keeping the tires on the ground as much as possible. Stock car racing teams spend much of their time configuring and fine-tuning shock-spring combinations for each track to ensure their driver has the best possible control over his or her car [source: Burt].

How the car handles turns depends on which shocks are used and how resistant they are to motion. To control the movement, or energy absorption rate, of a shock, a team might tweak the piston, shims and oil inside a shock.

­As a car hits a bump, a shaft is driven upward in the oil that fills the shock. The piston inside the shock regulates how quickly the shaft moves up (compresses) and down (rebounds). By tweaking the compression and rebound for each specific track, the driver is able to better maneuver the car. To keep the oil from foaming and losing its ability to compress and rebound, a shock is pressurized with nitrogen [source: Diandra].

NASCAR has strict guidelines regarding how much nitrogen, or pressure, can be in each shock. Rear shocks can have no less than 25 pounds of pressure per square inch (psi) (11 kilograms per 6.45 square centimeters), and no more than 75 pounds (34 kg) of pressure psi [source: Diandra].

­ You got some of the basics done, but head to the next page to look at some of the finer details of car suspension.

Stock Car Bushings

So far we've learned about the major components of the suspension system of stock cars. Now we'll move on to bushings, which are little pieces of the puzzle that can make a big difference in how the major components of the suspension system react to turns and straightaways.

Bushings are small, flexible, generally cylindrical rubber pieces that are found between pivot points and moving arms in the chassis and suspension assembly. In normal cars they're designed to soften the ride. Most stock car drivers prefer a stiffer ride, with bushings made of varying densities of polyurethane or solid polymers [source: Orijin Motorsports].

Suspension bushings are placed between springs, mounts and the control arms on the front of the car and in the trailing arms of the rear axle. They're also found in sway bar connections and in various other places on the car. Worn bushings slow down the response of the suspension, causing the driver to experience wobbling [source: Orijin Motorsports].

­Sway bars may look like crowbars, but their job is quite different. Next we'll learn about where to place stock car sway bars and what their purpose is.

Stock Car Sway Bars

When a car goes around a corner, its weight shifts from side to side. Anyone who's ridden in a car has felt that effect, when your body is pulled in the opposite direction of the turn. It's such a common experience that most people wouldn't notice it in an average car ride -- not unless their driver is going a little too fast.

­As stock cars race around oval tracks at high speeds, they deal with an extreme version of this effect. This body roll affects tire grip and performance. How well a tire grips the track depends on the weight pushing the tire into the track. When weight shifts off a tire during a turn, it has less grip and therefore less speed. And anytime parts of the tire leave the track, the driver has less control over the vehicle.

A sway bar helps prevent weight transfer. It connects the suspension of the car, the chassis and the body. Because each racetrack requires a different sway bar with varying stiffness, prepared teams often keep many sway bars in stock [source: Burt].

The stiffer the sway bar, the tighter the connection between the suspension and chassis, which minimizes body roll during a turn. But it's important to remember that sway bars that are too loose or too stiff could also present problems.

Sway bars twist when one of the tires goes over a bump. If both tires go over the bump evenly, the sway bar does nothing, but if one tire goes over a bump the sway bar counteracts the movement to keep the weight of the car from shifting [source: Diandra].

­ The chassis plays an important role in stock car suspension, too. Read on to learn more.

Stock Car Chassis Harnesses

The days of converting production cars to race cars are gone. Stock car racing teams build their own cars with the track in mind. In fact, many teams build different cars for different tracks. One area of the car that they often experiment with is the chassis. The chassis is the steel frame of the car that holds the body and the motor.

The chassis is almost always rectangular, but teams often tweak its minute geometry, moving suspension mounting points depending on the track and the needs of the driver. Offset chassis are not permitted, so they have to build parallel frame rails. Chassis rails are built to strict guidelines of weight, length and thickness [source: Burt].

The chassis includes a main frame (frame and side rails) and front and rear subframes, which are connected by cross members. Every connection that holds the frame together is welded.

­Suspension fittings are added to the frame in varying positions, which the builders determine for specific tracks. After everything else, small flanges are added to strengthen all connections [source: Burt]. It's crucial that the chassis be strong enough to handle the weight of the car on top of the intense racing conditions. So they have to add every piece of support that adds security without weighing down the car and decreasing speed.

The roll cage is part of the chassis and adds strength and security to the car. Side bars are installed to protect the driver during side impacts, and all roll bars that are accessible to the driver are padded. Before the chassis travels down the assembly line, the roll bar framework is completed, passing through the floor boards and firewall, and connected to the frame rails [source: Burt].

A stock car team constantly tweaks and adjusts a car's suspension, from the chassis to the steering column. It takes more than just a gifted driver to win a stock car race; it takes the dedication and creativity of the whole team.

Learn more about how stock car suspension works by checking out the resources on the following page.

Related HowStuffWorks Articles


  • Burt, Bill. Burt, William M. "Stock Car Race Fan's Reference Guide." MotorBooks/MBI Publishing Co.
  • Burt, William. "The Stock Car Race Shop." MotorBooks/MBI Publishing.
  • Diandra. "Juan Pablo Montoya's Shocks." Stock Car Science. (Accessed 01/06/09)
  • Diandra. "The Science of ...Front Sway Bars (Roush Fenway and Others." Stock Car Science. (Accessed 01/06/09)
  • Island Racing. "Stock Car Racing Association Rules 2009." Island Stock Car Association. (accessed 01/06/09) +car&hl=en&ct=clnk&cd=22&gl=us&client=firefox-a
  • Orijin "Solid Control Arm Bushings." (Accessed 01/06/09)
  • The Class Journal Company. "The Automobile." Vol 26. June 6, 1912. (Accessed 01/05/09) lpg=PA1292&dq=stock+car+steering+knuckle&source=bl&ots=xEKhP3i47v& sig=SbS7XRcvTjHc4bC1iNUOxqj-kmI&hl=en&sa=X&oi=book_result& resnum=1&ct=result#PPA1292,M1