To understand why you need a shock absorber, try driving without it...
In order for the car not to perceive all the unevenness on the road, some elastic element is necessarily used in the car suspension. Usually a spring is used. In addition to the spring, a leaf spring can be used, but this is already completely archaic. Other alternatives to the spring are the Citroen air suspension or the Rover hydropneumatic suspension, which operate on compressed gas. But let's get back to the spring. When driving on the road, the car begins to swing, and this is unacceptable. The main task of the shock absorber is to dampen these vibrations.
All shock absorbers work on the following principle: inside the shock absorber cylinder there is a rod with a piston, which "walks" in oil. When the shock absorber is working, the oil flows through a special hole in the piston. This creates the necessary resistance to the movement of the rod. The shock absorber must also have a capacity (compensatory chamber) with compressed gas (air or nitrogen). A piston moves inside the shock absorber and displaces excess liquid, causing the gas to compress.
When air is used as a gas, this shock absorber is called hydraulic ("Soviet" shock absorbers "SAAZ"). The disadvantage of air is that it "foams the oil" with constant shaking, and with stronger shaking, low-pressure bubbles can appear, which significantly reduces the efficiency of the shock absorber.
Instead of air, nitrogen is often used. Sometimes it is pumped under low pressure of several atmospheres. Such shock absorbers are called low-pressure gas-filled. But low-pressure nitrogen does not solve the fundamental problem of "oil foaming" and cavitation (that is, the formation of low-pressure bubbles).
The solution was found when the French engineer De Carbon pumped nitrogen into the compensating chamber under pressure of more than 20 atmospheres and separated the nitrogen from the oil with a piston gasket, which does not allow the nitrogen and oil to contact each other. This eliminated the problem of oil foaming and cavitation. Nitrogen under high pressure allows the piston valves to operate silently and quickly, and also creates additional force on the rod. Such shock absorbers work efficiently and accurately.
Gas-filled shock absorbers are not recommended for use on small cars, as the additional force exerted on the body by such shock absorbers is harmful for the "crumbs".
Recently, new developments have appeared. For example, the company "Koni" produces shock absorbers with adjustable stiffness. The most "tricked out" one allows you to do this directly from the salon. Such "coolness" is installed on the Maserati car. In turn, the company "BOGE" has developed a system of automatic ground clearance regulation (the "Nivomat" system). Its meaning is that when the car is loaded, it "sags" and its ground clearance (clearance) changes. As soon as the car is loaded, the vibrations of the wheels during movement activate the pump built into the shock absorber design. This pump restores the necessary ground clearance after several hundred meters. After unloading the car, the pump automatically adjusts to the old value of ground clearance.
The shock absorber is that part of the car that you don't think about until it breaks. As soon as the shock absorber "breaks down", we realize how bad it is without it and how good it is with it.
Information copied from the website mercedesman
A car with non-working shock absorbers after driving over any bump starts to swing dangerously, you can even catch your belly on the asphalt. The shock absorber can jam, then the car turns into a "stool". If this happens, then even a baby understands - the shock absorbers need to be replaced or repaired.
But usually shock absorbers wear out gradually and the driver does not notice it. According to Western experts, in Europe about 30% of cars older than 5 years drive with damaged shock absorbers. And what is happening with our roads in the CIS countries is completely unknown.
But shock absorbers affect not only comfort, but also traffic safety. Here it is appropriate to cite the results of the work of an independent research organization "Tuv Rheinland", which conducted an examination of the impact of the shock absorber on traffic safety.
When braking at 50 km/h on a dry road with one shock absorber worn out by 50%, the braking distance of the car increases by two meters. Whether this is a lot or a little is up to you to judge. But how often exactly these two meters are not enough to avoid a tragedy.
When a car with 50% worn shock absorbers drives into a puddle with a 6 mm layer of water, the aquaplaning effect (when the car "floats" above the surface and becomes uncontrollable) occurs at a speed of 81 km/h. With normal shock absorbers, this speed is 85 km/h. In addition to the above, "killed" shock absorbers increase the risk of skidding on sharp turns. Also, worn shock absorbers disable many parts of the car: tires, springs, wheel suspension, ball joints, etc.
Often, motorists think about replacing the shock absorber only when oil starts leaking from it: "the struts are leaking - I'll have to replace them somehow." But this is the last stage of life (or rather, already death!) shock absorber. It is not recommended to bring the car to this state. And to check the operation of the shock absorbers, it is not necessary to go to special stands. You just need to "squeeze" each corner of the car and, if after rocking there is more than one full oscillation, then the shock absorbers "will not withstand". They need to be replaced.
Manufacturers recommend checking the condition of the shock absorber after every 20 thousand km of vehicle mileage.
So, you have decided to replace the shock absorbers. But how to choose? Remember that shock absorbers largely determine the nature of the car's handling. By replacing the shock absorber, you can turn a soft suspension into a sporty one. If you are irritated by excessive body swing at high speeds, for example, on an "eight", our advice: buy shock absorbers of a sporty nature (Koni, Bistein, etc.), but be aware that the suspension will probably be firm, and the road profile will be transmitted in detail to those sitting in the cabin.
"Soviet" shock absorbers are, of course, cheaper than foreign ones. And the owners of "our" cars can choose. You can buy SAAZs, or you can buy products from foreign companies.
Owners of foreign cars have a choice between "original" shock absorbers, that is, those that are supplied directly to the conveyor of the manufacturer, and products of companies working in the secondary market. There are shock absorbers specifically for used cars. Such products are usually much cheaper than "original" ones, and the quality and characteristics of such products are no worse, and sometimes even better, than factory ones.
But replacing shock absorbers is not such a simple matter. There are many subtleties and tricks. And therefore many companies provide a guarantee only if they are installed correctly at service centers.
Now about the guarantees. A normal guarantee in the city should be 1 year, regardless of the mileage. We would recommend buying shock absorbers in brand stores, not in markets. Of course, it is cheaper in markets, but then the struts can be changed every six months. As they say, a miser pays twice.
Let us describe the main manufacturers of shock absorbers whose products can be purchased.
SACHS is the European leader in the supply of shock absorbers to the conveyor. It is installed serially on BMW, Audi, etc.
BOGE – produces hydraulic and gas shock absorbers. Supplied to BMW, Saab, Volvo.
MONROE – ranks first in Europe in terms of sales of shock absorbers to the secondary market. Manufactures hydraulic and gas-filled low-pressure shock absorbers. Supplied to Volvo.
GABRIEL is an American company. Second place in Europe in terms of sales of products on the secondary market. It produces hydraulic and gas shock absorbers.
KAYAVA is a Japanese company. Its products are supplied to many conveyors of Japanese automakers. Shock absorbers for European cars are also produced.
DE CARBON is a French company that was the first to produce high-pressure gas shock absorbers for Mc Ferson suspension.
BILSTEIN – sports shock absorbers. Supplied to some German cars, such as Mercedes-Benz.
KONI – elite Dutch shock absorbers. Supplied to Ferrari, Porshe. They are used in Formula 1, IndyCar racing. Shock absorbers of this company are also used in front-wheel drive VAZs.