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Can I install springs and shock absorbers myself? Can you feel when the shock absorbers are worn out? What is the difference between high-quality and cheap spare parts? When it comes to the chassis in particular, motorists have many questions. On the other hand, a lot of half-knowledge and blanket statements are communicated. The experts at the BILSTEIN Academy, who normally primarily impart specialist knowledge to workshop employees, have now taken on typical consumer questions.
What do shock absorbers do in the vehicle?
Unlike the springs, which are really responsible for the suspension of the vehicle, the term "shock absorbers" is somewhat misleading. Actually, one should speak of vibration dampers, because they reduce the vibrations generated during compression and rebound in a controlled manner. If there were no shock absorbers, a car would bounce for quite a long time and in extreme situations it would oscillate more and more.
This would result in extremely unstable driving behavior, especially on a wavy or winding road, and contact with the road could break off again and again. Consequently, shock absorbers have long been used in automobile construction. However, in order for them to retain their full effect, shock absorbers, as typical wearing parts, sometimes have to be replaced. Since there are no fixed intervals for this, their function should be checked regularly in the workshop.
Which types of shock absorbers are primarily used today?
The design of the telescopic shock absorber that is common today goes back almost 100 years with various intermediate steps. A piston with valve openings moves in an oil bath, which effectively slows down the vibrations generated by the suspension. In the case of the classic twin-tube damper, displaced oil flows off into a reservoir via additional valves. Disadvantage: If the shock absorber is repeatedly strongly stimulated, part of the oil and the air bound in it turn into foam. Since this, unlike liquid, can be easily compressed, there is a risk of a loss of damping force of up to 35% in the worst case. BILSTEIN therefore pioneered the gas pressure principle back in 1954.
In the monotube gas pressure shock absorber, which was then ready for series production, a highly pressurized nitrogen cushion prevents the oil from foaming. This means that the damping force always remains the same and the driving behavior is predictable - this is also referred to as "identification stable". Gas pressure shock absorbers are therefore standard almost everywhere in current vehicles. BILSTEIN also allows many older vehicles to be retrofitted. Gas pressure shock absorbers for sporty applications are often also available in monotube technology. Here, all work processes are combined in a single tube, which offers various technical advantages for this application.
How is the development currently going?
Gas pressure shock absorbers are still state of the art, but they are increasingly being combined with active electronic control. It is possible to vary the damping force at the touch of a button, so that the chassis acts more sportily or more comfortably. Alternatively, an automatic adjustment based on sensor or camera feedback or by evaluating the driving profile is often possible. Technically, this is achieved by changing the resistance exerted by the oil. This is done by regulating the flow at the valves. Air suspension systems can be found again and again, especially in high-quality vehicles. Instead of the steel spring, an air spring is used here, which can be combined with a wide variety of shock absorber variants.
Do you also have to have the chassis checked separately for cars that have had their checkbooks maintained?
As part of the routine general inspection, only a visual inspection of the chassis components takes place - the same applies to inspections. A thorough chassis check should therefore be carried out in the workshop at the latest every 20.000 kilometers. In everyday life, on the other hand, chassis problems often go unnoticed by the driver. Shock absorbers wear out gradually and the whole drama often only becomes apparent in practice in extreme situations: for example when suddenly swerving when the vehicle suddenly swerves. In addition, the braking distance increases by up to 20 percent and the risk of aquaplaning increases. Incidentally, ABS and ESP can only compensate for this effect to a limited extent, as their effectiveness is significantly reduced by heavily worn shock absorbers.
Can I carry out work on the chassis myself?
Replacing chassis components is routine for workshops. Well-trained companies also know air suspension systems, active dampers and the set-up of sports suspension systems inside out. However, due to the enormous stored forces, extreme caution is required when handling suspension springs - this applies in particular to non-professionals! If you work without the right spring compressor and the necessary caution, you can seriously injure yourself. Lifting platforms are also not without problems: the car must stand absolutely securely on it so that it does not slip down. When lifting or lowering, no one should be in the danger area.
Hobby screwdrivers should also consider that work on the chassis must be carried out 100% correctly, after all these are safety-relevant components. In the worst case, errors or carelessness during installation can lead to an accident. Installation videos from the Internet can offer a certain orientation, but by no means all show all processes correctly. You should therefore only fully trust reputable sources. Anyone who dares to approach air suspension should definitely know what they are doing. Because certain "careless mistakes" quickly damage the new components irreversibly. For example, when you lower the vehicle onto springs that are still unpressurized.
In the case of adjustable sports suspensions, in addition to correct installation, the right set-up is crucial in order to achieve the desired driving characteristics. In order to avoid risks, BILSTEIN designs the compression and rebound settings of its coilovers in such a way that all combinations can be driven. Anyone who installs a new chassis, lowering springs or shock absorbers in a car must always have an axle measurement carried out. This is the only way to ensure that all chassis parameters are correct. Failure to do this can result in a wide variety of negative consequences: from a lack of directional stability to problems with steering to tires that are worn on one side.
Where can I get advice on shock absorbers?
Basically, you should not choose shock absorbers at random, but inform yourself in detail. Especially if you don't just want to buy a simple spare part, but want to change the driving behavior of your vehicle for the better, you should definitely go to a qualified specialist company. In addition to the pure installation, the workshop also understands the corresponding set-up. It is important to inform the employees of the company in advance of your exact wishes.
The right product can then be selected on this basis. More expensive and more complex does not necessarily mean better. It depends on what properties and features you expect from a chassis. Workshops can also get advice from BILSTEIN at any time in order to provide their customers with the best possible support, even in particularly complicated cases: BILSTEIN Technical Support can help by telephone on +02333 791 4222-XNUMX or by sending an email to technik@bilstein.de. Interested parties can also find additional basic knowledge and information on training courses at workshop.bilstein.com.
If all shock absorbers work on the same principle, are they equally good?
The underlying physical principle is the same for all modern shock absorbers, regardless of whether they are large pick-ups, agile sports cars or comfortable SUVs. Nevertheless, there are big differences in the details, after all the vehicles differ enormously in terms of size, weight, wheelbase, loading conditions, etc. The final tuning of shock absorbers is very small in the truest sense of the word: their character can be fine-tuned by combining tiny spring washers. In addition to the particularly important dimensions and this set-up, there is a wealth of other details that are important for the performance of a shock absorber as a spare part. These are finely tuned systems where small variations in design make big differences in handling.
In the case of off-road shock absorbers in particular, these are, for example, large external reservoirs. If the vehicle is originally equipped with active dampers, it also needs the appropriate spare parts so that this feature continues to work. Air spring struts in particular are often replaced by remanufactured old parts. What many do not consider: The integrated shock absorbers are also used in this case and are still in their original condition, with an uncertain mileage. In addition, the solenoid valves are sometimes shut down, so that an active air suspension becomes a passive one. For the reasons explained, BILSTEIN always relies on brand-new goods in all areas, which attain 100% the level of the original series part and support all factory functions.
What risks do drivers take when buying cheap shock absorbers?
In addition to the aspects already mentioned, such as missing features in active dampers, there are also deficits in the quality of the materials and the manufacturing precision. If everything is not as it should be, the handling can deteriorate compared to the original condition. In addition, inferior materials lead to leaks or corrosion much more quickly, which in turn impairs driving safety. In short: Cheap shock absorbers often don't last as long and sometimes wear out faster. For this reason, a vehicle with standard gas pressure shock absorbers should not be retrofitted with cheaper oil shock absorbers. BILSTEIN is of the opinion that spare parts should be at least original equipment quality. After all, shock absorbers are safety-relevant components, which means that any step backwards is, so to speak, automatically ruled out.
What can drivers optimize in terms of shock absorbers "depending on the terrain"?
If you often drive on bad roads, regularly tow a trailer or drive with a full load, you can switch to the BILSTEIN B6 gas pressure shock absorber, for example. With its plus in damping power and many other positive properties, it stands for the "improved" standard replacement option. It is also ideal for a significantly better driving experience in SUVs, minibuses and other vehicles with a high center of gravity due to their design. For the driver with sporty ambitions, there are of course the classic sports chassis. With a low center of gravity and a "harder" spring-damper combination, they offer a lot of driving pleasure.
By the way, BILSTEIN advises against simply installing shorter springs, since the interaction with the series dampers is not optimal here. If you want variable height adjustment, you can also use a coilover kit. More exclusive products also offer an adjustment option for compression and rebound. The set-up can be changed at any time, just like in racing. Last but not least, it is even possible to retrofit an active chassis. If you belong to the small group of off-road fans who are extremely keen to convert, you can also think about a special lift kit. Appropriate chassis offer a lot of ground clearance for uneven terrain or deep snow and extra-long suspension travel. Photo credit: ThyssenKrupp Bilstein GmbH
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