The careless practice of operating tires without the valve cap should not be followed, because, without the valve cap in place, there is usually a slow leak of air from the tire, causing the tire to run in an underinflated condition. If air should leak out around the base of the valve, it will be necessary to install a new tire valve assembly. This is easily accomplished with a special lever-type tool. They suspend the vehicle's frame, body, engine, and the power train above the wheels. These are quite heavy assemblies.
Some cars require stabilizers to steady the chassis against front end roll and sway on turns.
Stabilizers are designed to control this centrifugal tendency that forces a rising action on the side toward the inside of the turn. When the car turns and begins to lean over, the sway bar uses the upward force on the outer wheel to lift on the inner wheel, thus keeping the car more level. A control arm is a bar with a pivot at each end, used to attach suspension members to the chassis. When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear axle housing and the frame to carry driving and brake torque. A-arms are control arms with two inboard pivots, giving strength.