A brief introduction to compression damping modes
The before shown two load/velocity diagrams are results of dynometer damper tests. In contrary to springs damping force is mostly triggered by velocity. So damping force does change depending on how fast the piston/rod moves.
Modern damper setups usually feature non-linear characteristics. Mostly a degressive damping mode is desired. Degressive means that the damping force remains more or less constant above a certain (high) fluid velocity. That eliminates too harsh damping effects over very rough roads while still mobilising best handling.
Progressively working dampers seem to be only made for some (slow) 4WD offroad cars. They do benefit from extra comfort but handling suffers clearly.
We have to differentiate between
compression low-speed and
compression high-speed damping.
1. Low speed compression damping addresses mainly the comfort reserves on less bumpy roads. Typically a rather soft damping force is applied in this case.
A relatively high compression damping force at low piston velocities basically promotes handling behaviour (e.g. high speed turns) and reduces body roll and pitch movements. Also nose diving tendencies at hard braking can be reduced considerably applying strong low compression forces. Typically good sport dampers feature sophisticated low speed compression abilities (best handling without being too harsh).
Low speed characteristics can be altered effectively by changing the oil viscosity for instance. If traction suffers or the ride quality tends to be too harsh especially over short-waved surface, the low speed rate is too strong and should be reduced.
2. High speed compression damping on the other hand deals with the ability to optimally handle bad road surface such like cobblestone, manhole covers or unclean expansion joints. So if you encounter bottom-out tendencies, the high speed compression damping capabilities can be too weak and should be increased.
Mostly changing the damping characteristics (setup) both in compression and rebound does have a considerable
higher impact on ride comfort and ride performance than changing the spring rate!