When shocks and struts are worn, they also have an adverse effect on the steering in a vehicle. They can cause the vehicle to be unable to control the roll of its body when turning, and this reduces the grip of the tires on the road. The steering system will have a longer reaction time and make it more difficult for the driver to steer the car.
When a wheel is connected to a shock or strut that is worn, it tends to bounce and shift excessively while the vehicle is in motion. This gives the driver of the vehicle less traction to work with. The excessive bouncing and shifting can cause other parts of a vehicle to wear out more quickly, such as the tires and the other parts of the suspension.
Struts and shocks are on your vehicle to limit how far the suspension can travel. When struts and shocks are working properly, a vehicle will not bounce continually, even when on an uneven road. This is achieved by taking the movement of the springs and changing them into heat-based energy. The hydraulic fluid in the shocks or struts causes this heat energy to dissipate.
Shocks and struts are generally replaced in pairs -- though this isn't absolutely necessary if only one shock or strut is leaking or has suffered damage at a low mileage.
A strut is basically a shock
absorber mounted inside a coil spring. Struts perform two
jobs: They provide a dampening function like shock absorbers,
and they provide structural support for the vehicle
suspension. That means struts deliver a bit more than shock
absorbers, which don't support vehicle weight -- they only
control the speed at which weight is transferred in a car, not
the weight itself.