Every vehicle that have shock absorbers need a specific calibration of damping to obtain maximum performance. In this episode we will see together how is possible to achieve certain damping characteristics (Force-Velocity graphs) and the correct shim stack choice or dedicated components designs.
Damping force is created by generating fluid pressure inside the shock absorber. To generate fluid pressure generally metal discs are used. They are typically stamped out of spring steel with different diameters and thickness. This metal discs are known as shims.
The shims, that are positioned on the face of the piston, resist opening, creating fluid pressure through this restriction. In order for oil to flow through the piston, it has to bend the shims up to create an opening. If the shims are thin the oil can easily bend them open very far, allowing a lot of oil to move through the piston to creating very little damping effect, if the shims are thicker will create more damping.
In the pics below we can see how is possible to find a hydraulic specifications via shims.
As described above number of shims indicate different damping behaviors. Many shims (with the same shim thickness) means more hydraulic force developed. Furthermore thicker shims (less quantity) mean increased damping and thinner shims less damping. Keep in mind thinner shims are always less stiffer than a thicker shim.
The shim stack profile affecting the shock absorber behavior as described below.
Keep in mind that on the C profile (Horn) the shims nearest the piston are less influenced by the higher ones and are freer to open up.
In addition to shim stack there are other components such as the top plate. This affect the graph gradient.
Furthermore Annular shims can create preload on shims and increase low speed indipendence range, to create digressive system with linear style piston design.
This system can create digressive curve.
In opposition to the Annular shims, Sandwich shim generate linear force to create high flow in low speed and while keeping high forces in high velocity.
Design piston shape can generate a genetic damping curve as Linear, Digressive or Progressive to be manipulate for specific damping value with different shims layout.
Special piston designs can affect also the damping graphs.
