A spring alone makes a poor suspension fork. It can yield when a tire strikes a rock, but the energy stored in that compression has to go somewhere. Without a damper to govern its return, the fork can bounce repeatedly, disturbing the tire's grip and the rider's control.
The spring is the fork's load bearer, not its brake. Whether made from a metal coil or compressed air, it supports the rider and lets the front wheel move upward over an obstacle instead of sending the entire impact through the handlebars. As the fork compresses, it stores energy; as it extends, it releases that energy. That return matters. Between successive bumps, the wheel needs to move back down so it can follow the ground rather than hang above it.
The damper makes that return manageable. It forces oil through restricted passages, converting some of the fork's motion into heat and resisting movement. Rebound damping controls how quickly the fork extends; compression damping resists its inward travel. Too little rebound damping can leave the front end bouncing. Too much can prevent the fork from extending sufficiently between bumps, reducing available travel and grip. Settings are a compromise. A fork must move freely enough to track rough ground yet recover with enough restraint to keep the bicycle composed. On a rocky descent, the result is visible in the tire's quiet pursuit of a restless surface.
