Are you about to upgrade your fork? Then this is essential reading!
The Basics of suspension components
As mentioned earlier, coil springs are the most reliable system, have a relatively linear spring rate with a small amount of preload adjustment. Springs are incredibly supple “off the top” or at the start of the stroke and remain active all the time, making adjustments to the spring curve will require a new spring. Most brands offer a few different spring weights recommended for riders in a specific weight range.
Air forks are more easily adjusted and can be changed on the trail if required. Typically air springs have a more progressive ramping up/firming up towards the end of the stroke. Air springs require a negative air spring to ensure the “off the top” feel of the fork is supple like that of a coil, the bigger the negative spring the more supple a fork usually is. An air spring's spring curve can be made more progressive or more linear by adding or removing “tokens” which will increase or decrease the volume of the air chamber.
Compression damping controls the rate of which the fork can compress and can be incorporated into a single lockout lever, or as separate High Speed Compression and Low Speed Compression adjustments the separate High speed compression circuit can restrict the forks movement when hitting something at high speed such as a big landing or deep pothole on a fire road that you didn’t see. The low speed compression circuit takes care of things like pedalling induced bob small braking bumps and initial diving of the fork on lower speed impacts. Without compression damping suspension can feel mushy and have a tendency to dive on descents and into corners.
Rebound damping controls the rate of which the fork rebounds or returns, too fast and your bike will feel like a springbok and too slow and it will never come back out before you hit the next bump. Typically forks only have one rebound adjustment, but some newer DH forks and Enduro forks have separate Low and High speed rebound adjustments. These adjustments do the exact same thing as the above but rather restricts the oil flow as the wheel travels back out.