Suspension Compression Tuning Basics
The compression circuit of your MTB suspension is one of the more misunderstood adjustments you have at your disposal. A good reason for this is frankly MTB suspension tends to be over compressed for the average rider. “I run my shocks completely open” isn’t an uncommon answer, particularly with stock suspension.
The compression circuit is designed to slow, well, compression forces. Compression forces literally compress the suspension. The Compression circuit is the opposite of the Rebound circuit, which controls the shaft’s return to equilibrium (just picture all of the things we’re going to go over in reverse for Rebound).
Suspension Compression Tuning Basics
Let’s look at the GIF for a super simplified damper representation. Hydraulic dampening is based around a couple pretty simple principals. To start, essentially you can’t compress a liquid. That means you can more easily control flow rate and consistency.
In this image you see that the piston with the least amount of flow rate (smallest orifice, in this case because of the least holes) will have the most “dampening” effect. Because the oil must displace through a smaller ports which slows the compression down.
Conversely the left image has the most holes and therefor is less efficient at slowing the shaft speed when a force is introduced.
More compression provides increased support per pound input at the cost of some subtly. Too little compression control means the air spring is completely controlling ramp rate.
The video below illustrates hydraulic dampening basics. On the left is a “fast” setup with multiple ports allowing fluid flow. On the right is a single opening which only allows “slow” fluid transfer. The middle splits the difference…
Ok. Pretty easy to get the idea right? The more clicks of compression you turn in the smaller the flow rate – and the more dampening effect.
Remember, for rebound it’s the opposite – the dampers are designed to control the suspension’s extension, not compression.
Of course your top of the line, ultra sophisticated, how many dials can I tune suspension controls high and low speed shaft speed with the ability to fine tune performance with external controls.
Rather than a piston with a series of holes expect to see shim stacks, bypasses,springs, ifp chambers, etc, etc, etc…
Here’s the control section of the latest Fox Grip2 damper as an example.
Tuning with Compression
So the real trick is balancing compression with air spring for the ultimate in support and small bump compliance.
BikeCo Pro Tune’s allow lighter and less aggressive riders to modify the compression tune range for improved eternal controls. Lessening the sticktion between fork upper and lowers as well as improving damper bleed, flow rate and hydraulic properties reset the performance band from “everyone” to “you”.
Even heavier or more aggressive riders will appreciate the compression tune’s reset. Rather than having a knife edge setup a click here or there is an adjustment – not a sentence to handpump!
Particularly on forks, a couple clicks of low speed compression should provide a bit of support, keeping your weight higher on the bike for steep terrain – not create a bike that no longer sticks to the ground for lack of small bump compliance… A couple clicks of low speed compression on a rear shock should help the bike ride taller in the travel – not skip out in every direction change.
Suspension that offers low and high speed compression allows riders to fine tune both low and high shaft speeds externally. Low speed is typically used for support while high speed assists with bottom out control.
Stock suspension comes out of the box capable of working for the lightest to heaviest riders across a wide speed range.
Light riders guess who suffers on this one? Out of the box suspension has to work for a 300lb rider who’s going to find every single hole down the trail. Are you 160lbs (I’m not so don’t think that’s a knock heavier riders!) and smooth? Well chances are you suffer some small bump as well as tracking issues with your suspension. Add compression? Forget it in that situation, you’re going to completely compromise small bump compliance.
Ideally with the performance window in an appropriate setup a click or three of low speed compression gives riders better support without completely compromising tracking.
High speed compression can be used to assist bottom out resistance allowing less volume spacing for a more linear mid stroke suspension tune as desired.
Tuning in the Real World
Are you hands on? Need to feel it?
Grab a pen and paper and count out your compression clicks. At BikeCo we suggest going from completely open (count as you back out the clicks) although Fox does it the opposite way. Long and short – remember which way you chose to do it! Write down your setup and then spin the dial dramatically while riding in front of your house to see what compression controls actually change.
If you decide to change compression settings on a test ride start by only changing compression. Changing compression and air pressures at the same time work if you’re an experienced rider but can create havoc for the less experienced.
Low speed compression will resist slower shaft speed inputs. As you pedal the bike may feel locked out. Remember on trail that may compromise traction – it’s important to balance support with tracking.
High speed compression resists higher shaft speeds which can be harder to test. Think about smashing straight into a curb at speed. Does your fork easily bottom? Do you need more support in those situations? That’s when High Speed comes in.
Want more info on BikeCo Pro Tune Suspension? Riders all over the globe reset the performance window of their suspension for their bike suspension design, rider weight, aggression, ground speed and terrain. Check out BikeCo Pro Tune Advantages Here! Whether you’re brand new to the sport or an expert rider having dialed suspension is more fun and faster on trail.