In principle, suspension struts consist of 2 main components, the springs and dampers. Combining both elements results a system, which in physics is called spring-mass-damper-system and can be calculated with complicated differential equations.
The spring component generates a force as soon as it is compressed. Completely independent of movement, this force is constant as long as there is no dynamic in the system. So staying in the same position means that the force applied by the spring remains the same. There is also non-linearity for springs. This means, for example, that a double deflection does not necessarily also generate double the spring tension. The characteristics of the spring therefore also have an effect on driving behaviour.
Spring characteristics are mainly distinguished in 3 relevant dimensions. Hardness, preload and behaviour. The hardness describes the increase in force per section of compression, by pretensioning (4) smaller differences in spring force are achieved between the two states'spring-in' and'spring-out' and the behaviour can vary between progressive (1) via linear (2) to degressive (3). Special geometries also allow spring characteristics, such as those to be seen in line 5. The following table shows to what extent the various options have a qualitative effect on the driving behaviour of an RC vehicle.
|Hardness||increase||Rear axle ||oversteer|
|Preload||increase||Front axle||Understeer (harder), more compatible with higher frequency* terrain|
|Preload||increase||Rear axle||Oversteer (harder), more compatible with higher frequency* terrain|
|Preload||decrease||Front axle||Oversteer (smoother), more compatible with low-frequency** terrain|
|Preload||decrease||Rear axle||Understeer (softer), more compatible to low frequency** terrain|
|Behaviour||more degressive||Front axle|
|Behaviour||more degressive||Rear axle|
|Behaviour||more progressive||Front axle|
|Behaviour||more progressive||Rear axle|
In principle, an optimal configuration can be calculated, but many assumptions have to be made in the physical model. For example, it would be extremely difficult to specify the terrain, but to simulate this in a functional image, if one really wants to represent the reality of the expected driving task. For this reason, only the qualitative effects of certain changes are described here. It is then recommended to tune the RC vehicle so that it works as well as possible.
The hardness is changed by the choice of spring (material, turns, wire thickness), the preload by adjustable spring plates and the behaviour by the explicit geometry of the spring (inhomogeneous distribution of the turns).
The damper component generates a force as soon as it is set in motion. If the spring-mass-damper system is at rest, the damper does not contribute anything to the force that counteracts the movement of the body. However, the faster the system is moved, the greater the counterforce. The size of conventional RC dampers depends only on the viscosity of the damper oil with which the damper is filled. The higher its viscosity, the stronger the damping increases when the movement of the system is increased. Here, too, a table will describe the qualitative effects on driving behaviour.
|Viscosity||increase||front axle||more compatible to higher frequency* terrain|
|Viscosity||increase||rear axle||more compatible to higher frequency* terrain|
|Viscosity||decrease||front axle||more compatible to low frequency** terrain|
|Viscosity||decrease||rear axl||more compatible to low frequency** terrain|
* more in the direction of gravel or asphalt
** more in the rough terrain
The combination of possible settings results in a very large number of configurations. Not only pragmatic aspects such as terrain or speed play a role here, personal criteria are also important for the personal sweet spot. One could say that one prefers to adjust what one feels best about. Getting to know your own vehicle and frequent handling are therefore essential for successful tuning of the suspension struts.