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.