Damping
At its most basic, suspension is just a spring (whether it be air or coil) that is configured so that you can bolt it to a bike. But just bolting a spring to your bike will leave you with a horribly bouncy ride—the spring’s movement needs to be controlled somehow. This is where the damper comes in.
The damper is, in essence, a series of holes that oil is forced through as the shock compresses and rebounds. The damper slows down the movement of the shock so as to make it more controlled.
The quality of the damper is a large part of what you are paying for when you buy a high end shock—higher end dampers do a better job of effectively controlling the suspension, and they also tend to be more adjustable to suit a given rider’s needs.
A discussion of damping can get complicated really quickly, but for the purpose of this article, here’s the basic idea:
The damper is separated into two distinct functions: (1) control how quickly the shock compresses, and (2) control how quickly the shock rebounds, or returns to its uncompressed state.
Compression Damping
Compression damping is used to prevent a number of undesirable bike handling characteristics. For example, in a rear shock, you might get some of that pedal-induced bobbing mentioned above. The right amount of compression damping can help prevent that, while still allowing the suspension to move when it needs to.
Compression damping can also be used to help keep the shock from blowing through its travel on a hard impact. By increasing the compression damping, you can provide additional resistance without having to increase your spring rate or add more air to your shock. This is beneficial because it allows the shock to remain soft and supple so as to absorb smaller impacts, but still prevents the shock from getting completely crushed on a hard impact.
Rebound Damping
Rebound damping controls the return stroke of the shock. A shock with very little rebound damping will feel, to use a technical term, pogo-sticky. A shock with a lot of rebound damping will be very slow to return, which can make it feel sluggish.
In a more practical sense, too little rebound damping can make the bike feel uncontrolled; it will tend to “buck” the rider. Too much rebound damping and the suspension will tend to “pack up” on successive bumps—the shock can’t return quickly enough to absorb the next bump, so each bump pushes the shock farther and farther into its travel.
Virtually all suspension on modern mountain bikes has damping inside of it. The only exceptions are the low end full suspension bikes sold at Walmart—those shocks generally don’t have any sort of damping at all. Generally speaking, the higher end suspension will have more refined damping that is also externally adjustable.
Many modern shocks will have externally adjustable rebound damping, meaning that there’s a knob that allows you to fine tune the rebound adjustment from “lots” to “very little.”
These shocks will also have compression damping, but it’s not always externally adjustable. On some suspension (particularly on forks), the damping may be internally adjustable, but that involves some fairly advanced mechanic-ing that’s beyond the scope of this article.
Externally adjustable compression damping takes a few different forms. On many of the common rear shocks, the compression damping is adjusted via a two or three position lever. This basically means that the shock has two or three pre-set levels of compression damping for use in different situations.
Usually, one setting will have a lot of compression damping in order to make the suspension more firm for climbing, while another setting will have less compression damping to allow the suspension to move more freely for rough descents. A third position might offer some middle ground between those settings.
Companies don’t always label these settings as compression damping adjustments (for example, Fox simply calls it “CTD” on many of their shocks), but regardless of labels, that’s what they are.
Sometimes, particularly on forks, external compression adjustments will be a dial, offering a full range of adjustment, from lots of compression damping to very little compression damping, and everything in between.
High Speed & Low Speed Compression Adjustments
Top of the line suspension (both rear shocks and forks) will usually have separately adjustable high speed and low speed compression adjustments. This essentially means that you can fine tune the compression damping characteristics for low intensity suspension movement separately from the compression damping for high intensity suspension movement.
An example of this is comparing pedal bobbing (a low intensity movement of the suspension) with smacking a big rock at high speed (a high intensity movement). With separately adjustable low speed and high speed compression damping adjustments, you can independently adjust how the suspension will react for each situation.
Lockouts
The benefits of lockouts are fairly straightforward—they make the suspension very firm so as to make the bike feel like it has little or no suspension. While this somewhat defeats the purpose of suspension from the bump compliance perspective, it can make a suspension bike much more efficient when pedaling on smooth ground.
Very few shocks or suspension forks these days come with a “true” lockout—there might be a lever that makes the shock quite stiff, but there is almost always a “blow off” that will allow the shock to compress when you hit a big bump.
These lockouts are essentially just a large amount of compression damping. Some forks and shocks have an adjustable lockout where the “blow off” threshold can be fine tuned to make the shock feel more or less firm when locked out.
So there you have it—the various parts that make up a suspension system. Now it’s time to learn how to adjust this system to get the suspension dialed on your bike. See our next article in this series, Suspension 201: Basic Setup