Do the inner workings of forks and shocks seem like a dark art to you? If so, read this quick primer. Learning how to adjust the rebound and compression settings on your mountain bike will allow you to better tune your gear to make the most of your time on the trails. If you understand how a coffee French press works, you're already halfway there!
Some suspension basics, explained
In its most basic form, suspension starts with a spring. A spring can be constructed from coiled metal, just like a mattress spring, or from a gas, usually air, inside of a sealed chamber.
A coil spring feels linear, meaning the amount of force required to get it to move is consistent throughout the entire range of travel. Conversely, an air spring becomes progressively firmer as it is compressed. There are various ways in which suspension designers adjust these behaviours to suit their intended purposes, and there are certainly pros and cons to air and coil suspensions, but for now we’ll leave it at this: air and coils are both effective means of creating a spring.
Related: How to set suspension sag
But suspension is not just a spring. A spring plus damping equals suspension. Without damping, your fork and shock would be little more than a pair of pogo sticks bouncing uncontrollably off every rock and root and flipping you over the handlebar. That’s not what we want.
Damping means controlling the movement of a spring. There are two types of damping: compression and rebound.
Why compression damping is a bit like a coffee filter
Compression damping regulates the force that moves a fork or shock through its travel. Compression damping is achieved with fluid, usually oil. This oil circulates through a compression circuit, and by restricting its flow, the suspension can be made firmer and can even be completely locked out.
What’s a compression circuit, you ask? Well the exact mechanics of it will differ by make and model, but in general, a compression circuit is composed of small metal plates, called shims, as well as ports, designed to regulate the flow of oil. Think of the compression circuit as being a French press for coffee. When you apply pressure, the fluid — or coffee — moves through the mesh filter.
If there were more mesh openings you would be able to press down with less effort. Conversely, if there were fewer mesh openings, it would require more force to press the plunger down. Finally, if the plunger didn’t have any mesh openings for the coffee to pass through, it wouldn’t be possible to compress the plunger — you would be “locked-out” of your coffee.
So what does all this coffee talk translate to on the trail?
On many suspension forks and shocks, compression damping takes the form of a dial and a lockout lever. Both Fox and RockShox use blue to denote compression adjustments on their forks and shocks.
Turning these knobs and/or dials will gradually restrict the flow of oil through the compression circuit, thereby making your suspension firmer under compression.
When your suspension is open, the flow of oil through the compression damper is unrestricted and it will compress freely to absorb impacts. (Think free flowing coffee.)
Having your suspension positioned in the open position is useful while descending, and when riding technical terrain, where traction is paramount.
Increasing the level of compression damping is useful for firming up your bike’s suspension for times when you need some suspension, but also don’t want to waste energy to unwanted suspension movement or “bob”. Smooth, rolling trails are an example of a terrain where you might want to consider firming up your bike’s suspension.
And what about the times where you want to be completely locked-out? Well, if you’re looking to keep suspension movement to a minimum while pedaling on the road or climbing smooth trails, consider flipping the lever into the firmest compression setting.
How rebound damping works
So now we’re at the point in the movement where your suspension has compressed, so it’s done half of its job. Remember that your bike’s suspension is more than just a spring. Rebound damping regulates the speed at which your fork or shock recovers, or bounces back, from an impact and returns to its full travel.
Much like a compression circuit, rebound damping relies on oil moving through a circuit to regulate the speed at which the suspension extends after being compressed.
The coffee-as-oil analogy holds true here as well. When the flow of oil is restricted, your fork or shock will slowly return to its full travel. When there’s no restriction on the flow of oil through the rebound circuit, the spring — be it air or a coil — will rapidly “spring back” from an impact. (Remember, you don’t want to pogo down the trail.)
Knowing how to bounce back from bumps
Both Fox and RockShox use red to denote rebound adjustments, although they take different approaches to understanding how to increase or decrease rebound damping.
How to tune RockShox rebound damping
RockShox takes the very user-friendly approach of using a tortoise and a jackalope to tell the rider which way to turn the rebound knob in order to increase or decrease the speed with which their suspension extends after being compressed.
Turning the knob all the way counter-clockwise as indicated by the jackalope will open up the rebound circuit, allowing oil to circulate freely.
On the flipside, going “full turtle” will restrict the flow of oil to the point where your fork or shock sluggishly returns to its full travel.
How to tune Fox rebound damping
Fox, on the other hand, takes an approach that requires the user to be a bit more in-tune with what’s going on inside the fork. The ‘plus’ and ‘minus’ labels on the company’s rebound knobs indicate the addition or subtraction rebound damping, not the speed at which the suspension will recover from an impact. With Fox, plus means more rebound damping (slower return) and minus means less rebound damping (faster return). Got it?
A number of factors influence how fast you want your suspension to rebound: rider weight, speed, riding style and the terrain will all play a role. It’s important to remember that suspension is intended to maximize traction; it does this by keeping your rubber in contact with the ground.
The key to adjusting your rebound is to find the sweet spot, where the suspension returns from an impact quick enough to recover for the next one, but slow enough as to not buck you around or to break traction. Too slow, and the suspension will feel sluggish and can even “stack-up”, meaning that it doesn’t have time to extend between successive impacts. Too fast, and your suspension will bounce off obstacles, thereby breaking traction.
A good starting point is to turn the rebound knob to one extreme (it doesn’t matter which) and count the number of clicks it takes to get to the other end of the range. Most forks and shocks are designed to perform best in the middle their rebound adjustment range, so by setting the rebound dial midway through the range of adjustment you can arrive at a default starting position from which you can increase or decreases your rebound speed to suit your needs. On a section of trail you are comfortable with, play around with the settings and pay attention to how the bike feels.