There are three main controls you’ll see on MTB suspension: preload, rebound, and compression. The latter is sometimes split into low- and high-speed compression on top-end shocks.

Preload

Preload is the resistance the fork gives against your weight. So the heavier you are, the more preload you’re going to need. For a shock with a coil spring this would equate to having a heavier, or thicker spring but for an air shock it’s simply a case of pumping in more pressure.  

Compression damping

Compression damping comes from the internals of the shock and works by regulating the flow of oil through small holes. Compression damping only affects the shock when it’s compressing – this doesn’t affect the preload but can appear to have a similar effect on the rear suspension.

The more compression damping you dial in (+) the slower the fork will move through its travel. This is good if you want a bike to pedal without bobbing, but the negative effect will be the limitation of the suspension’s movement when you hit a bump, making it feel a bit like it’s locked out (see below). In fact, suspension lockout out is simply an extremely high amount of compression damping.

Rebound damping

Rebound damping is a similar internal system to compression and only affects the shock when it’s returning to its natural position after an impact.

As you dial in more rebound damping (+) the fork will return to its natural position more slowly after an impact. A slower return – or more rebound compression – is required if the bike feels like it’s trying to buck you off, especially after corners or when you land a jump, but if repeated hits are causing the suspension to feel like it’s ‘packing down’ and not returning to it’s natural position, you’ll need less damping.