Mountain Bike Suspension 101
Learn everything you need to know about suspension - from key terms to how to set it up - in this handy explainer by cycling expert Isaac C.
Full squish or half squish, suspension on mountain bikes provides necessary traction over rough sections of trails. Suspension technology has improved greatly over the last five years. While new suspension has become more affordable and more capable, a proper suspension setup is still crucial to get the most out of your bike. When setting up your suspension, there are three main adjustments that can be made. The guide will focus on Fox and RockShox suspension. The process for setting up other brands such as Marzocchi, DVO, or Suntour will be the same, but the descriptions may vary.
The main settings that can be adjusted easily are the following:
The spring rate determines how much force is required to compress the fork or shock, with a higher spring rate requiring more force to compress. This setting compensates for the rider’s bodyweight. With an air shock or fork, the spring rate is adjusted by adding or removing air using a shock pump. The air valves on forks are on the top left side of the fork, and on a rear shock, look for a small schrader valve similar to what you would see on a car tire. For a coil shock, the only way to adjust the spring rate is by purchasing a new spring and replacing the spring.
The compression setting influences how much resistance there is to the fork or shock compressing (going from extended to compressed). Oh high-end forks and shocks such as the Fox Factory series, Rockshox Ultimate, and DVO suspension, there are both high and low speed compression adjustments. High-speed compression applies to high-speed impacts such as hitting rocks or landing drops. For most riders, high-speed compression should be left as soft as possible. Low-speed compression applies to slow compressions such as the compression forces from braking. Low-speed compression can be tuned to provide more support under braking or cornering. Shoot for a setting that doesn’t feel harsh but provides the desired support.
Rebound controls how quickly your suspension returns to its uncompressed state. The main objective of rebound is to find a balanced setting where the suspension rebounds fast enough to be ready for the next impact, but doesn’t rebound so quickly that the rider gets thrown around by the suspension. Rebound knobs are the red knob found on most suspension brands.
Progressivity is an increase in spring rate as the shock compresses. At the end of the stroke, the shock or fork becomes very difficult to compress further. All air shocks and forks act in a progressive manner, which prevents a harsh bottom out of the suspension when sustaining very large impacts. The progression of the shock can be changed using volume spacers inside the air spring. More volume spacers make an air spring more progressive. Coil springs are linear and will not ramp up to prevent harsh bottom outs.
Air Shock or Coil Shock?
The two types of shock and forks available are air shocks and coil shocks. Most bikes will come stock with an air shock. Air shocks are lighter weight and more tunable. Air shocks provide easy ways to change both the spring rate and the progressivity of the shock. Coil shocks have a fixed spring rate with no adjustability and have a linear spring rate with no progressivity. This means that some bikes are not compatible with coil shocks because their leverage curve is not progressive enough. Running a coil shock on these bikes will result in harsh bottom-outs. However, coil shocks have fewer seals than air shocks which results in a lower activation force and coil shocks feeling smooth like butter. Coil shocks are often used by downhill and enduro racers, while most other bikers will opt for an air shock.
This setup guide will focus on air shocks since they are most common.
How to Set Up Your Suspension
- Shock pump
- Ruler/calipers/tape measure
- A friend
When setting up suspension, take notes. Take notes of air pressures, rebound, and compression adjustments. These notes will prove to be invaluable as you change settings to tune the suspension.
For both full-suspension bikes and hardtails, the initial setup of the mountain bike suspension fork is an easy process. Most forks have a chart on the back of the lower leg. This chart is a great place to start when setting up your suspension. Based on your body weight, the chart will recommend an air pressure and rebound setting.
To adjust the pressure in the air spring, remove the air cap on the top on the left upper leg and attach your shock pump to the schrader valve. DO NOT use a floor pump meant for tires.
Rebound settings are measured in ‘clicks from closed’. On RockShox suspension, the turtle denotes fully closed and on Fox suspension, the plus denotes fully closed. Once you have set the fork to the recommended settings, go for a couple of rides and if necessary, fine tune the suspension. Pay close attention how the suspension feels. If you seem to be using too much travel for small bumps, add a couple of pounds of air pressure. If you feel like you’re being thrown around by the fork when you go through bumpy sections, move the rebound a click or two back towards closed.
Rear suspension is a more involved process because every bike has a different rear suspension design which drives the suspension differently. These different rear suspension designs influence aspects of the bike’s performance such as anti-squat, anti-rise, pedal kickback, and a lot of other characteristics which would warrant their own suspension 201 article.
Because of these more complicated characteristics, rear suspension is set using sag - that is, the amount of travel that is used when the rider sits on the bike. To measure sag, sit on the bike in a normal seated position. Without bouncing on the bike, push the o-ring up against the shock body then dismount the bike without compressing the rear suspension. This is where a friend can be helpful to help hold the bike still and move the o-ring. Measure the distance between the o-ring and the shock body. Divide this length by the shock stroke (the length of the stanchion/shiny bit on the shock). This number is your sag percentage. Most bikes behave best with 25-30% sag.
Adjust sag by adding or removing air from the shock. For cross-country riding, aim for lower sag percentages. The rear suspension has adjustable compression and rebound similar to the front suspension. To set rebound, find a curb or small drop and ride off while seated. The shock should be set to the fastest rebound setting (towards the -) that allows the shock to return to its starting position and not ‘overshoot’ (go past the initial point then bounce back and forth until settled). Again, fine adjustments should be made if the suspension settings aren’t working correctly on the trail.
Tire pressure can greatly influence the performance and feel of the suspension of your bike. Having your tire pressure too high can make the bike feel harsh and bouncy, even when the suspension is correctly set up. Most riders prefer tire pressures ranging between 20 and 30 psi. The perfect tire pressure is elusive and depends on many factors such as whether a tire is tubeless, terrain and trail conditions. Fast rolling hard pack will require different tire pressures than rough terrain. Tire pressure is also something that should be experimented with and noted when setting up your bike.
Setting up suspension is an important part of bike setup. Remember to start with the basics and tinker to fit your suspension to your needs, there is no magic setting.