A shock absorber is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the energy of the shock into another form of energy which is then dissipated. Most shock absorbers are a form of dashpot, pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston, one design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid, in hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, in general terms, shock absorbers help cushion vehicles on uneven roads. In a vehicle, shock absorbers reduce the effect of traveling over rough ground, leading to improved ride quality, while shock absorbers serve the purpose of limiting excessive suspension movement, their intended sole purpose is to damp spring oscillations. Shock absorbers use valving of oil and gasses to absorb energy from the springs. Spring rates are chosen by the based on the weight of the vehicle. Some people use shocks to modify spring rates but this is not the correct use, along with hysteresis in the tire itself, they damp the energy stored in the motion of the unsprung weight up and down. Effective wheel bounce damping may require tuning shocks to an optimal resistance, spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars are used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers, as only store. Vehicles typically employ both hydraulic shock absorbers and springs or torsion bars, in this combination, shock absorber refers specifically to the hydraulic piston that absorbs and dissipates vibration. Now, composite suspension system are used mainly in 2 wheelers, in common with carriages and railway locomotives, most early motor vehicles used leaf springs. However the amount of damping provided by leaf spring friction was limited and variable according to the conditions of the springs and it also operated in both directions. Motorcycle front suspension adopted coil sprung Druid forks from about 1906, and similar designs later added rotary friction dampers and these friction disk shock absorbers were also fitted to many cars. One of the problems with motor cars was the variation in sprung weight between lightly loaded and fully loaded, especially for the rear springs. What was called for was damping that operated on the rebound, horock came up with a design in 1901 that had hydraulic damping, it worked in one direction only
Miniature oil filled Coilover shock components for scale cars.
Diagram of the main components of a twin-tube and mono-tube shock absorber