Suspension Damping
Damping is the hydraulic system inside of your fork or shock that in the most simple terms controls how quickly your suspension can compress or extend. These circuits typically consist of channels for oil to run through with ports (holes) of (often) adjustable size, disk shaped springs called shims, and rods which change the size of the ports or the spring tension of the shims. All forks and shocks found on mountain bikes will have some form of damping, typically getting more adjustable and complex as you get to the higher end products.
Compression Damping
Your compression circuit controls how quickly the fork or shock can compress independent of the spring. If your suspension has a lock out or "Firm" lever, it is usually part of this circuit as well. Reducing your compression damping allows your suspension to compress more quickly which makes it feel "plusher" but will decrease the stability of your bike. Increasing your compression damping will slow down how quickly your suspension will compress, spreading impacts out over a longer period of time. This can add a lot of stability to your bike but can make the suspension feel harsh if you increase the damping too much.
Low speed compression controls how quickly your suspension compresses under low speed events such as weight shifts, small bumps in the trail surface, or when you are braking. This is usually controlled by a small disk inside the fork with some holes in it allowing oil to pass. The size of the hole changes the rate at which oil can pass through those holes, the smaller the hole, the less oil can pass through in the same amount of time. Think of holding your thumb over the end of a garden hose. On many suspension systems, the size of these holes is adjustable with a dial or lever and if you block the holes off completely, your suspension will not be able to compress at all.
High speed compression controls your suspension compressing at high shaft speeds that would be created by larger or faster impacts such as hitting a G out or landing a drop. High speed compression is typically controlled by shims which are disk shaped springs often stacked in a certain order to tune the rate at which they flex, similar to the leaf springs used in the suspension of large trucks. Tuning the flex of these springs allows you to control how much force is required for the damping fluid to push past these springs which are often right behind the low speed circuit. This means that at low oil speeds (small or slow impacts) the oil goes through the low speed circuit and then, not having enough force to flex the shim stack, continues through small ports to bypass the high speed circuit. Under high oil speeds (larger, faster impacts) however, the oil has enough force to flex the shims creating larger openings for the oil to go through, allowing the suspension to compress at a higher speed and allowing your wheel to move out of the way of whatever you have hit more quickly. If your fork or shock has adjustable high speed compression, turning the dial will increase the amount of force required for the oil to flex the shims, keeping the oil going through the low speed circuit for higher speed impacts and limiting flow through the damper.
It is common for riders to change their compression damping for different trails or riding areas that have different features than what you typically ride. For instance, it is common to increase your compression damping when visiting a lift access bike park, where trail speeds are often higher and there are many features with larger impacts.
Rebound Damping
Rebound damping is essentially the same in function as compression damping, but in reverse. So it controls how quickly your suspension is able to extend rather than compress. Rebound damping is generally set to counter the force of the coil or air spring in your suspension extending, so the higher your spring rate, the more rebound damping you will need.
Low speed rebound controls how quickly your suspension extends when there is low spring force extending your suspension. Having too much rebound damping will cause your suspension to not extend fully between impacts which can cause your suspension to feel harsh as you will be sitting at a part of your shock stroke with a higher spring force and your suspension will not compress as easily. Having too little rebound damping can cause your bike to feel unpredictable and could even cause your wheel to lose contact with the ground in certain conditions. Finding a balance is critical to having your bike feel balanced and predictable while also having good traction and compliance.
High speed rebound controls the extension of your suspension when there is very high spring force acting on the damper, typically near the end of the stroke. One scenario where having adjustable high speed rebound is extremely beneficial would be for a rider who uses both a high spring rate and a large amount of volume tokens which would create very high spring pressure when the suspension is fully compressed which could overwhelm a non adjustable circuit.
What if my suspension doesn't have some (or any) of these adjustments? For many riders, your suspension not having many external adjustments will not affect your experience significantly as it just means that the manufacturer has pre-set all of the damping circuits to reflect what they have determined, through extensive testing, to be as close to ideal as possible for most riders. This allows you to set your spring rate and rebound damping to your desired setting and go ride without having to think about it too much.
Here at Black’s Cycle, we can help you understand the way in which these adjustments affect your ride as well as how you can adjust them to get your bike riding the way you want it to!