Shock absorbers are one of the most important, but also one of the least appreciated elements in the car. They are responsible for maintaining continuous wheel contact with the road and the driving comfort through appropriate suppression of vibrations transmitted to the body.
What is the purpose of shock absorbers?
The shock absorber is the link between the unsprung element (swingarm, steering bridge), and the body, and is designed to reduce body sway and to prevent the wheel from lifting off the ground in potholes. This is accomplished by a jump (rod sliding out) and rebound (rod sliding in). It is the movement of the rod that determines the characteristics of the shock absorber. Without going into the technical description of the amplitudes and frequencies, we should only note that a large damping stroke of the wheel - as in sports cars - is unfavorable for comfort and health (due to the frequent vibration in human organs). Hence, while developing the characteristics of the shock absorber - to provide maximum comfort - we always take into account the type of the car, its suspension and operating conditions.
However, comfort is not the only indicator of proper operation of the shock absorber. The shock absorber is also designed to prevent chatter of the car body during movement, which makes it difficult to maintain stability. A faulty shock absorber reduces the constant wheel contact with the road surface. Simply put, the wheels detach from the road, which increases the risk of slipping and contributes to extended braking distance (research carried out in this direction have shown that the braking path may be extended by up to 30%).
It is also worth noting that worn shock absorbers do not only reduce safety, but also have a negative impact on other aspects of the car's functioning: the tires and chassis components are worn, such as tie rod ends or transverse elements of the steering system.
Shock absorbers - types
Shock absorbers that are used in passenger cars can be divided into two basic types: oil and oil-and-gas - commonly known as gas dampers.
In the case of oil dampers (these are twin-tube shock absorbers), the housing - the external tube - is just a container for hydraulic oil. It is about 70% filled with oil (the remaining compensation chamber is filled with air). Twin-tube shock absorbers have two types of damping valves - piston valve for moving the piston and the bottom valve at the bottom of the housing. When the shock absorber is compressed, bottom valve is responsible for the damping. The principle is simple - the oil displaced by the piston rod flows into the oil chamber, encountering resistance from the bottom valve which inhibits movement. The piston valve is responsible for reflecting the shock absorber.
The advantages of this solution include simple design, relatively low price, very high durability and the fact that rapid damage results (the wheel bouncing on a transverse obstruction while driving fast, and sudden movement of the piston rod damaging the valves) in only gradual loss of function. A disadvantage of the oil shock absorbers is their constant, linear damping force and a change in oil density at different temperatures. The car may feel very hard in the cold (drivers say that it "rattles") and may begin to "float" at high ambient temperatures, when driving on uneven roads.
Master-Sport shock absorbers have greatly reduced this phenomenon through the use of special oil that does not change its parameters due to temperature changes.
In the case of oil-gas dampers (gas), the design of the working part consists of a tube, in which a piston is installed. Apart from the oil, there is also compressed gas (nitrogen) in the shock absorber, separated from the oil by means of a movable partition. This solution makes the gas damper react faster to surface irregularities, which ensures that the wheel better adheres to the road. The characteristics of oil and gas dampers are more hardened than in oil dampers, which are a better option for those driving dynamically and for the owners of sporty cars. There are no problems with a significant change in attenuation due to temperature changes. Unfortunately, the disadvantage of this solution is its delicate structure, a sudden loss of function upon damage (leakage of gas containment chamber) and a higher price.
An alternative to gas dampers are the twin-tube low-pressure oil dampers, in which, instead of air, the expansion tank uses nitrogen at a pressure of 6 to 8 bar. Such a solution, and the work of the bottom valve are adequate to achieve similar damping characteristics.
How to operate the shock absorbers properly?
On Polish roads, a shock absorber should withstand a minimum of 100,000 km, but the drivers themselves often contribute to shortening the mileage. What should we remember?
First of all, the shock absorber must be properly secured. Even slight shifts in mounting mean that in addition to the axial force acting along the rod, there will be lateral forces. This, in turn, would affect and damage the cylinder walls.
Secondly, for safety and to provide additional resistance, additional elastic elements are used, such as: reflections travel stops (in the shock absorber or the lead column) and rebound tops (spring bumpers). After exceeding a certain suspension deflection, they switch to work, preventing the impact of elements on one another on the edges of the operating range. If these elements are defective, it is possible to damage the shock absorber or other car components.
Thirdly, shock absorbers must be checked!!! During its normal operation, the damper performs about 2,500 movements per one kilometer. For this reason, we should drive the car to the workshop at least once a year, in order to check its performance.
Fourthly, the replacement should apply to both shock absorbers on one axis. In the event that one of the shock absorbers fails due to wear, it is expected that the second one on the axle would soon wears out as well (after all, both worked in the same road conditions). Replacement of only the defective one will leave us with uneven damping and the weaker shock absorber will also fail soon.
Choosing the shock absorber
Used shock absorber. When it comes to shock absorbers, you should never buy used variants. You never know what mileage the item previously had and, therefore, when it would be worn; also, that makes it impossible to provide identical replacements for both absorbers on one axle.
How you drive. The first thing we should decide before buying a shock absorber is its type: oil or gas. As previously mentioned, the oil variant is cheaper and more resistant to mechanical damage, but it is "softer", which will result in greater tilting of the car body while turning. In addition, classic oil damper, whose damping is tested at 20°C (operating temperature), may show a 60% increase in this parameter at -20°C and a 30% increase in the rebound strength. However, at a temperature of 60°C (which is the temperature normally achieved by shock absorbers), damping force decreases by 27%, and the rebound strength by 23%. Thus, in our climatic conditions, a shock absorber may be more effective or lose half of its performance properties.
On the other hand, the use of the "hard gas dampers" will give us a fantastic feeling when driving fast on the road (e.g. mountain roads), but this will be at the expense of comfort when driving on worse roads. Also, this solution is more expensive.
The golden mean, therefore, is to purchase a low-pressure oil shock absorber that provides the advantages of both solutions, especially when - as in Master Sport shock absorbers - the impact of temperature changes on the damping range has been eliminated.
Substitutes. Although it is accepted that the most renowned companies such as Monroe, Sachs, KYB, or Delphi are the only viable alternative for factory-made shock absorbers, it is worth paying attention to the quality of other alternatives that meet the products requirements for original equipment (meet the standards of the manufacturers).
A typical example are the shock absorbers made by Master-Sport. These twin-tube low-pressure dampers provide: reduced 25% of vibrations (due to our own design solutions), resistance to weather conditions (due to the oil showing consistent performance in extreme temperatures), and better performance characteristics (compensates unevenness of the road by strict valve control).
Therefore, given the operation values (mileage of at least 100,000 km), the innovative solutions to combine the advantages of gas and oil dampers, and the accuracy of performance, Master-Sport shock absorbers far exceed the quality of the products of other companies.
At the end it is worth paying attention to the correct assembly of products. Doing this unprofessionally, carelessly and without proper assessment of the technical quality of the working components may result not only in a faster deterioration of parts, but also damage other components. Hence, it is worth commissioning the replacement to authorized specialists whose employees are properly qualified.