What should you know about shock absorbers?

Why does a car need shock absorbers?

Shock absorbers dampen the body oscillations caused by road bumps and ensure a more comfortable ride. Together with tires and brakes, shock absorbers are one of the three primary components ensuring your car’s safety. Shock absorbers play a key role in vehicle handling, braking, and road holding. They control the vertical forces acting on the tires and the movement of the suspension, keeping the car’s wheels in constant, secure contact with the road. Under normal driving conditions, a shock absorber piston completes 1,200 strokes for every kilometer driven. As a result of this heavy work, shock absorbers wear out. Worn shock absorbers reduce the safety of your vehicle. It is recommended to have your car’s shock absorbers checked every 20,000 km.

How do shock absorbers work? Shock absorbers themselves do not support the weight of the vehicle body; that is done by the springs. The job of the shock absorbers is to dampen the oscillations of the vehicle body. Today, cars generally use telescopic gas or hydraulic shock absorbers. Their operation is based on flow resistance, which occurs as oil moves from one chamber of the shock absorber to another. The piston at the end of the shock absorber rod works against the oil filling the pressure chamber. As the suspension moves up or down, oil is forced through small holes in the piston, which restricts oil flow and thus prevents the free movement of the entire suspension. This achieves control over the car’s suspension system.

Over time, vehicle suspension designs have evolved, leading to several different types of shock absorbers. By their construction, shock absorbers can be: • Standard/conventional design (eye-to-eye mounting), • MacPherson type strut / complete shock absorber, • MacPherson type suspension cartridge shock absorber, • Spring-seat / coil-over shock absorber, with various mountings possible (eye, pin/stem, crossbar, etc.).

The most common hydraulic (oil) shock absorber consists of a housing that also forms the outer pressure vessel (cylinder), a bottom valve system, an inner cylinder, a piston with a piston rod, and a piston rod guide with a sealing system. Both the outer and inner cylinders are filled with oil. Oil moves from one cylinder to the other through the bottom valve system at the base of the inner cylinder. When oil moves through the valves extremely fast, it begins to foam, causing the shock absorber to stop functioning properly. To prevent foaming, the interior of the shock absorber is pressurized with gas at 2.5 to 5 bar. This creates a gas-charged shock absorber. If you remove the outer cylinder from a twin-tube shock absorber and insert a floating piston to compensate, you get a single-tube (monotube) shock absorber. This floating piston separates the oil from gas pressurized at 25 to 30 bar. Monotube shock absorbers operate more efficiently than twin-tube ones, but they often cannot be used due to space constraints in the car’s suspension system.