Welcome back at EXT tech corner. On the first episode we went deep on damping definition and we looked at the main components of a shock absorber. We see how force works on a damper and how energy is dissipated. In this second episode we want to explain how force on a damping system born and how they can be represented by graphs.
When track conditions cause the vehicle suspension to move, the damper piston will attempt to move through the damper oil. In order for the piston to move, oil must flow from one side to the other one of the piston. This movement generate forces that can represented by graphs.
Look at the pic below where there are shown the two different phases of a damper while working: rebound and bump (compression).
Tips & Tricks: not all know that most of the shock’s manufacturer has distinguished the colors of the two different adjuster for a simple reason: BLUE Bump – RED Rebound.
The rebound shims are located on the upper parts and restrain oil when it goes through piston. As you can see shims bend itself due the fluid pushing its. Depending on the combination of shims, the rebound shim stack opens at a certain pressure. This provides a direct pathway for the oil, allowing to pass through the stack to the other side of the piston.
On the piston is present a Bleed Hole, this is affected only at the low speed of the shaft (and obviously piston). It is always a fixed orifice type.
On the drawing below the same representation as above but for the Bump (Compression) phase. The compression shims are located on the lower part of the piston.
On the graphs you can see how is possible to represent the two phases of damping by velocity and force, and how orifice (bleed) and shim stack influence the damping system.
Nowadays all shock absorbers have adjuster to regulate damping forces. Depending on the number of adjusters the industry classified dampers in X-Way, where X represents the number of adjustments.
Now you can see how this adjuster affect damping forces from full open to full closed.
In the first image you can see how the low speed rebound adjuster (in a mono tube damper design) works. This consist of: an adjuster and a needle. The combination of this act to the orifice and let it pass more or less oil. On the graph you can see difference from open to close.
Same thing happen on the low speed compression side.
On high speed compression the shims present on the valve can be preloaded in this way more or less force will be needed to let oil pass through.
Tricks & Tips: the whole industry counts click from full closed position. The reason is “full hard” is always an absolute position. “Full soft” will vary depending on tolerances. Normally the first click and/or detent is counted as “zero” position. Just remember maximum clockwise is “full hard” for all adjusters.
We refer you now to the next episode of this tech corner where we talk about curves measurements. Stay tuned!