DICTIONARY OF POPULAR SUSPENSION ERRORS: PART 2
The Bilstein Academy is seeking to clarify technical misunderstandings
Recently, the Bilstein Academy supplied information to clarify and largely dispel some of the popular myths surrounding the suspension.
However, it says there are still more dos and don’ts about shock absorbers and more to be covered and so in this article, Bilstein examines a popular test procedure for radial play on the piston rod, which does not necessarily lead to the desired result.
It also clarifies what spring travel limiters can really do – and what they definitely cannot. Last but not least the Head of the Bilstein Academy, Rainer Popiol, gets to the bottom of the thesis that the “hardness” of a suspension system corresponds directly to its performance like a sports car.
When it comes to checking the suspension, this scene is still widespread in the workshops: the mechanic checks the lateral play on the newly installed – or even old – shock absorber at the extended piston rod.
“This is not a good idea, because there is an extremely long lever arm here, and thus poor support of the piston rod is guaranteed. The almost inevitable diagnosis is therefore too much radial play,” Rainer said.
“In order to correctly determine any radial play that may exist, the piston rod/working piston must be in the design position of the vehicle/suspension.
“This is the main working area of the damper and here the piston rod is guided and supported by both the locking package and the working piston.
“It should be noted, however, that no standardised guide values exist, which makes an assessment difficult.”
Bump stops are also much discussed, but this does not refer to the existing pressure stops/buffers, but rather to components for retrofitting.
In forums, and to some extent also on the part of parts manufacturers, Bilstein notes it is often incorrectly claimed that these protect the suspension and body during the compression process.
“Bump stops take away the necessary spring travel from the vehicle. They prevent the shock absorber from sensibly reducing the dynamic vibrations from the suspension. If the shock absorber rests on the bump stop, the driving behaviour is very hard and ‘bumpy;’ the car can hardly be driven sensibly,” Rainer said.
“Thus, the opposite of the initial statement is more likely to be true: the bump stops do not prevent suspension parts and body from damage; these are rather overstressed and therefore wear out faster.
“Regardless of such misconceived advantages, these components are mainly used in the following case: a vehicle was lowered and then a wider wheel/tyre combination with an unsuitable offset was installed.
“The bump stops are then intended to prevent the tyres from grinding on the lower edges of the mudguards or on the rear side panel. But this motive also produces suboptimal results: for reasons of safety and performance, a fast vehicle should always have sufficient spring deflection.
“Only in this way can the shock absorber do its job well and reduce vibrations.”
Bilstein says there is another myth in the tuning environment: the harder the suspension is, the more it feels like driving a sports car. However, does this thesis really stand up to closer scrutiny?
“The often-quoted rule of thumb simplifies far too much and can therefore be considered wrong,” Rainer said.
“The fact is: even a sports suspension must be balanced. Extremes are often counterproductive.”
Bilstein says however that if the initial statement is put into perspective and supported by further measures, you can still come to terms with the argumentation.
Of course, lowering the suspension can bring advantages for driving dynamics. It is correct that lowering of the vehicle’s centre of gravity, which must be precisely defined, reduces the tendency to roll and improves the driving dynamics with the maximum possible residual spring travel.
When using sports springs, preferably in conjunction with suitable high-performance shock absorbers, a technically reasonable measure must always be taken into account: 40mm lower means 40mm less spring deflection travel at the axle.
Bilstein says sufficient residual spring travel should, however, always remain available. It explains that when lowering the vehicle, the quality and performance of the components used is also decisive, stating that if, for example, the dampers are tuned too hard, this can have a negative effect on tyre traction. Therefore, it says not every car that looks extremely deep and sporty can live up to this promise in terms of handling.
For more information, visit www.bilstein.com
Photo: Copyright Bilstein 2021