A damper (shock absorber) is an oil-filled cylinder with a piston inside. As the suspension moves, the piston forces oil through small orifices and past flexible shim stacks. This resistance converts the kinetic energy of suspension movement into heat.
The shim stacks are the key: thin steel discs that flex under pressure. Their thickness, diameter, and stacking sequence determine the damping curve — how much resistance the shock produces at different piston speeds. This is what “valving” means.
Compression (bump): resistance when the shock shortens — absorbing hits.
Rebound (extension): resistance when the shock lengthens — controlling the return. Most shocks have more rebound damping than compression — typically a 60/40 or 70/30 rebound/compression split.
The F-V curve is the signature of a damper — a graph showing damping force (N) vs. piston velocity (m/s), plotted for both compression and rebound.
Digressive valving is the standard for off-road: relatively stiff at low piston velocities (body roll control, pitch control), then softening at higher velocities (big hits, fast bumps). This lets the shock manage body control without being punishingly stiff on impacts.
Linear valving produces force proportional to velocity — simple but harsh on big hits. Progressive valving gets stiffer at higher velocities — good for preventing bottoming but harsh for sustained rough terrain.
When comparing shocks, look at three things: the low-speed slope (body control), the knee point where digression starts (transition speed), and the high-speed slope (impact handling). A good desert shock has strong low-speed damping with a clear knee into a flatter high-speed zone.
Twin-tube: Inner and outer tubes with oil flowing between them through base valves. Cheap to manufacture, adequate for road use. Problem: the oil shares space with a gas pocket, and under rapid cycling the gas mixes with oil (aeration), causing damping to fade.
Mono-tube: Single tube with a floating piston separating oil from pressurised nitrogen gas. The nitrogen charge keeps the oil pressurised — preventing cavitation even under rapid cycling. Better heat dissipation (single wall), more consistent performance, but more expensive and sensitive to stone damage.
Monotube is the absolute minimum for any desert use. Twin-tubes will fade within minutes on washboard or whoops.
Bore diameter determines oil volume — and oil volume is directly proportional to thermal capacity. More oil takes longer to heat up.
| Bore | Oil Volume | Application |
|---|---|---|
| 1.5″ | Baseline | Light duty, road only |
| 2.0″ | ~50% more | Entry performance — Stage 1–2 minimum |
| 2.5″ | ~56% more than 2.0″ | Sweet spot — Stage 2 standard |
| 3.0″+ | Maximum | Race trucks — Stage 3 |
Adding a remote reservoir increases total oil volume by 30–50% on top of the bore size. A 2.0″ shock with a reservoir can approach the thermal capacity of a 2.5″ without one — but a 2.5″ with a reservoir is significantly better than both.
Desert whoops cycle shocks thousands of times per minute. Without proper nitrogen charge, oil cavitates (foams) and you lose damping force instantly. Nitrogen charge pressure should be checked regularly — it’s one of the most overlooked maintenance items on performance shocks.