Suspension 101:

Complete Guide to the Basics of Bicycle Suspension

There are few things as mystifying to the average rider than suspension. While most get the gist of what suspension is supposed to do, an endless sea of terms like damping, piggyback, stiction, high speed this, and low speed that can have a lot of us simply nodding along when the discussion gets into the weeds. Our goal is to unravel the mysteries by providing a basic understanding of how bike suspension works, defining some of the more confusing terms, and providing some best practices so that you can make the most out of the squishy bits on your bike.

Suspension Fundamentals

One of the biggest misconceptions is that suspension is just a spring. The problem with that is springs alone make for a pretty terrible riding experience. Springs are great at absorbing impacts but what happens to all that absorbed energy is just as important. With no way to control the kinetic energy of an impact, a spring will just return it all back as quickly as it came in and your bike is now just an expensive pogo stick. That’s where dampers come in – the spring is all about absorption while a damper is all about management and control.

Most modern bike suspension will have both a spring and a damper but there are lots of ways to accomplish the same things. This next section will dive a bit deeper into how both springs and dampers work and the different kinds you might see on your bike.

Spring Rates, Progression, and Leverage Ratios

In the bike world, springs come in two main flavours – coil and air. While coil springs use the elasticity of metal to store energy, air springs use the properties of pressurized air. They both serve the same basic function, but each has its own benefits and drawbacks. To understand the differences between different springs, it’s important to understand the concept of spring rates, progression, and leverage curves.

Got that straight? Well on a bike’s rear shock, things get further complicated by adding in the rear linkage and suspension kinematics of the frame. Rear suspension on a bike is basically just a large lever and the leverage ratio of that system is an important factor to take in when trying to understand spring rates and progression. The leverage ratio of a bike is the relationship between how much the rear wheel moves versus how much the rear shock is compressed – so if the rear wheel moves 30mm and the shock is compressed 10mm the leverage ratio is 3:1.  

Just like springs, the leverage ratio of the rear linkage can be linear across the travel or progressive (and in rare cases even regressive) and is most useful to us when we look at it in the form of a graph. Most bike manufacturers will put this information either online or in the owner’s manual. Controlling the leverage ratio curve is one of the keys ways in which bike manufacturers can change the way a bike handles and feels. It’s also an important factor to take in when discussing coil versus air springs since putting together the wrong combination of shock and leverage ratio can lead to major downsides on your ride.

Ultimately it’s all about balance – if you combine a linear shock with a linear leverage curve, you might create a bike that blows through its travel, feels dead and sloppy, and doesn’t provide enough support while pedaling. On the other extreme, if you combine a progressive shock with a progressive leverage curve, you can create a bike that struggles to use all its travel while feeling harsh and uptight. In general, progressive leverage bikes work best with coil shocks and linear bikes work best with air shocks.

Coil Springs

An additional feature of coil shocks has to do with stiction – which is the effect of static friction that you need to overcome before you can get your suspension moving. Because coil-sprung suspension doesn’t have as many sealing and sliding surfaces, stiction isn’t a major factor and coil suspension is more sensitive and easier to activate.

This combination of low stiction and a linear spring rate can make coil-sprung bikes feel plusher and more sensitive while giving the sensation of endless travel. The biggest downsides to coil springs are their higher weight and lack of adjustability – if you want to change the spring rate for a different rider or terrain then you’ll need to replace the spring with a different one.

Air Springs

To help deal with this, the pressure in the negative air chamber balances the pressure in the positive chamber and keeps the piston floating between the two, ready to react. This helps to smooth out the stiction point as the negative air chamber pushes down with the incoming force and makes the spring much more sensitive to small impacts. Without a negative air chamber, the minimum amount of force needed to start compressing the spring would be much higher leading to a much harsher ride. In most modern suspension designs, you only need to pressurize one of the chambers and then the spring automatically self-equalizes both chambers for the most balanced feel. 

Air springs tend to be much lighter than their coil siblings but by far the biggest benefit to air springs is their adjustability. By changing the amount of pressure you can change the spring rate of the system. This means you can change how your suspension feels on a whim, allowing you to dial in your bike exactly how you like it and then change it to suit different terrain just as easily. The other main feature of air springs is that they are inherently progressive. This can be useful to some riders and riding styles as it helps keep you from bottoming out your suspension. The progressive nature of air springs, along with their stiction issues, is also the main drawback of these types of springs – they can make air-sprung suspension feel harsher and make it difficult to use the full range of travel. While you can limit some of these issues with proper setup and adjustment, all of that adds another layer of complexity when you’re trying to dial in your ride.

Damper Basics

Now that we’ve figured out how the spring side of the equation works, we can talk about the damper portion of a suspension system. To recap, we know that a spring’s main job is to absorb impacts and store kinetic energy. The control and management of all the stored energy is called damping and the damper is the part of the suspension system tasked with the job. To do this, dampers focus on two main phases: compression and rebound. We’ll get into more of the details later, but the basics are that the compression phase is what happens as the system absorbs an impact and moves into its travel while the rebound phase is what happens after the impact and all that energy is released back.

Dampers are usually the most complex part of a suspension system, and their inner workings can be a mystery to even the most seasoned riders. We won’t try and explain all the engineering and physics involved but the most important concept to understand is that most dampers are effectively a circuit filled with oil, and impeding or releasing the flow of that oil helps to manage the energy absorbed by the suspension system. This is done in several ways depending on whether you’re looking at a shock or a fork, what brand, and what model of suspension is involved. You might hear about parts like shim stacks, valves, and bladders but the important thing to know is that these all deal with how oil moves through the damper circuit.

Another thing to note is heat affects damper performance. As the oil temperature in the damper circuit changes, this changes the viscosity and other physical properties of the oil and can make a major difference in the performance of the damper. Heat is created anytime you use your suspension, but is also affected by the type of spring used. Coil springs create less overall heat due to their simple design while air springs create more overall heat due to added friction from O-rings and sealing surfaces. This is especially an issue with rear shocks as their overall size, oil volume, and thermal capacity is significantly smaller than a fork.

Compression

So now that we have a very basic understanding of how dampers work, let’s take a closer look at the two main phases of suspension damping – compression and rebound. 

So how does that affect your bike? In the most basic sense, when you open or speed up your compression, you will have a more supple and comfortable ride and when you close or slow down your compression, you’ll have a stiffer, more supportive ride.

Rebound

In general, faster riding over rough, rythmic terrain calls for faster rebound so that your shock can keep up and get ready for the next impact instead of getting bogged down in its travel. While slower speeds and smoother terrain calls for slower rebound to prevent unnecessary bounce and bucking when encountering obstacles.

High-Speed vs. Low-Speed

See the section about fine-tuning rebound and compression near the end of this guide to get more advice on how to adjust these settings for the best ride.

Sag Adjustment

Now that you have a basic understanding of how suspension works and some of the terms involved, we can apply that knowledge and get your suspension dialed-in for your specific style of riding. Keep in mind that everything to follow is a general guideline or baseline to start from, but every bike and rider is different and will want different things from their suspension.

The biggest external factor that affects how your suspension behaves is rider weight. This is because the weight of what you’re trying to suspend (which in our case is you and your gear) affects how deep into your travel your suspension sits – we call that the sprung weight and the sag respectively. Most bike suspension is designed to compress about 20-30% of its travel when you sit on the bike so that the system is active and ready to get to work. The recommended sag differs by brand and component, so it’s best to reference your owner’s manual or lookup the recommended settings for your bike online.

If you have a coil shock, the easiest way to get a baseline is to use one of the many spring rate calculators available online to find the recommended spring rate for your weight. Like we mentioned before, one of the biggest downsides to coil shocks is having to completely change out the spring to change the spring rate so you might have to try a few springs before you find the perfect setup.

If you have an air spring, fortunately you can adjust the sag to your weight by increasing or decreasing the air pressure with a shock pump. Most manufacturers will have a weight-to-pressure chart for their specific models and our recommendation is to use those as your baseline. In either case, you always want to test and check that the recommended pressure or spring rate works for you and your bike. To help mark and measure sag, most forks and air-sprung rear shocks will have a rubber O-ring that sits around the stanchion which will show you the furthest point your shock has compressed. 

To find your current sag, the first thing to do is make sure all your compression adjustments are set fully to open. Once that’s done, have a friend hold your bike while you get on it with both feet on the pedals and your body in an active riding stance. Once you’re in position, use your body to load up the suspension a few times to free up any stiction then let your bike come to a natural resting point while you maintain that active riding position. Get your friend to slide down the sag ring against the wiper seal before you carefully get off your bike, being sure not to compress your suspension any further. Now that your bike isn’t compressed, the sag indicator will show you how deep into the travel your bike got.

On some manufacturers (namely RockShox) the travel increments and recommended sag are marked directly on the stanchion itself which makes finding the correct sag much easier. For any shocks or forks that don’t include the marks, the easiest way to measure is by finding the total travel or stroke length (usually written on the part or in the manual) and then doing some simple math to determine how much of that you want to be using for sag. Once you have a number, you can use your sag indicator and a ruler or tape measure to compare where you’re at to where you want to be.

What about coil-sprung rear shocks that don’t have a sag indicator? If your shock falls in that category, you can use the rubber bottom out bumper to do the same job as a sag indicator. One downside to this is that getting inside the coil to measure the sag can be tricky so another way to find the right sag is by measuring the distance between the shock eyelets unloaded and loaded and use that as your reference.

Compression and Rebound Adjustment

Now that we’ve got the sag set, we can move on to adjusting compression and rebound. This advice is probably starting to sound old, but every rider and shock is different. After riding and getting a feel for your bike, you may want to make changes – but the recommended settings from your bike or shock manufacturer will give you a neutral starting point.

As you turn your adjuster knobs, you should be able to feel the individual clicks as you turn them in either direction. The knobs should turn easily and once they don’t then you’ve reached the end of the adjustment range. Most manufacturer recommended settings will translate to the number of clicks from the fully open position (or spun as far counterclockwise as possible).

Once you’ve got everything set to a recommended baseline – make sure to note what your settings are currently at so you can change or come back to them. Before making any more changes, the best advice is to get out and ride your bike to get a feel for how everything’s working at the baseline settings. With a couple of rides under your belt, you might find certain scenarios where your suspension isn’t working quite the way you’d like. In the next few sections, we’ll try and go over some of the main scenarios and how you can dial in your settings to get the most out of your rides.

Volume Spacers

One of the main factors in dialing-in a suspension setup is balancing the sag and start of your travel with the progression ramp and bottom-out protection. In an ideal scenario, your suspension is supple enough at the beginning of the travel to soak up smaller hits and trail chatter while having enough capacity to keep you from constantly bottoming out. Depending on your riding style and the terrain you encounter most, the manufacturer recommended settings might not be able to provide both things.

If you have a coil spring, then your options are to change your coil or add/remove compression until you’ve reached the right balance. If you’re bottoming out often, adding a few clicks of compression might not make a big enough difference and you’ll need to switch to a coil with a higher spring rate. Luckily, coil springs don’t usually have as many issues on the other side of the extreme since there aren’t as many seals or as much stiction preventing the fork or shock from getting started. On the chance that your coil suspension still feels too harsh, try opening or speeding up your compression before switching out to a new spring-rate.

A less known scenario is the exact opposite, where lighter than average riders tend to bottom out their suspension when set to the recommended sag, especially if they ride bigger terrain with lots of jumps, drops, or high-speed corners. This has to do with stiction and the physics of speed, weight, and overall force. Lighter riders are using more of their weight to overcome stiction even though the overall forces created during riding aren’t as directly impacted by rider weight. This usually leads to running excessively low pressures just to be able to sag the suspension and that low pressure not having enough capacity to support the rider and prevent bottom-outs. In this scenario, a more progressive spring rate curve created by adding volume spacers (and reducing volume) helps by increasing bottom-out protection while making little difference to that minimum activation force since the overall air pressure is still quite low.

One important thing to note – just because you’ve bottomed out once during a ride, doesn’t necessarily mean you should make changes. In an ideal setup, you want to be using as much of the travel as possible and some of the biggest hits may mean using every last millimeter. If you never come close to bottoming out, there’s a portion of the travel that’s not being utilized and you should look to either reduce your air pressure or remove some volume spacers to make your suspension more linear or move to a lighter spring rate on a coil spring.

Compression and Rebound Fine-Tuning

Once you’ve reached a balance with the sag point and dialed in your spring rate and progression curve you can look at making smaller changes with your compression and rebound settings.

If the rebound is too slow, the effects are especially noticeable during high-speed, high-frequency scenarios like washboard and trail chatter as your suspension can’t get back to sag before encountering the next impact. This can make the ride feel generally harsh and uncomfortable and cause a loss of suspension and traction in the worst-case scenario. Slow rebound can also lead to a general lack of pop and liveliness.

In general, compression settings on the bike have more to do with how the bike handles and feels than what happens during and after impacts. These are generally what would be classified as low-speed scenarios and are the most common compression adjustments available on most models of suspension. Some of those may only have presets that you can switch between (e.g. climb, trail, descend) and the specifics of those can only be adjusted during servicing.

For a rear shock, you may want to increase low-speed compression if you get excessive pedal bob, the ride feels too loose, or the back end bucks off of jumps and other bumps. No matter what you choose to do, our recommendation is to make small changes, remember to write down your settings, and ride some more until you’ve reached the ideal setup for you.

Suspension Maintenance

A 50-hour or basic service most importantly deals with the stanchion(s), spring, and internal lubrication. For forks this is usually called a lowers service or an air-can service when talking about a rear air shock. The stanchion is the external friction surface that slides in and out during use and the wiper seal is what holds all the lubricating oil inside the shock and keeps the dirt, dust, and debris on the outside. As these parts see the most movement and most contaminants – getting inside to clean everything while replacing worn out seals and lubricating oil is integral in keeping your suspension as smooth and buttery as possible while limiting long-term damage. Keep in mind, this is generally not needed on a coil rear shock but still important for coil-sprung forks.

A 200-hour or factory overhaul service usually means doing everything involved in a 50-hour service but then also disassembling and servicing the damper. This can be serviced less often than the wiper seals and spring because the damper is much more protected from the outside world and any contaminants. Doing a complete overhaul is also necessary if you notice any changes to your damper performance. This is generally seen as a loss in either compression or rebound adjustments but can also be heard in the form of “slurping” which indicates a loss of oil or air pressure in the damper.

In general, a basic 50-hour service is something that can be done in a home workshop environment with the right tools and knowledge, but a 200-hour overhaul is best left to specially trained suspension technicians as dampers are significantly more complicated internally.

Glossary

Fork: Connects the front tire to your bike frame and handlebars allowing you to steer and control the bike. Can be either rigid or suspended (in which case is sometimes referred to as front suspension). 

Shock: Rear suspension that connects the rear wheel and triangle to the rest of the bike frame through a set of linkage arms. 

Stroke: The length that a suspension part can compress. This measurement will be the exact same as fork travel but is not directly correlated with rear wheel travel. 

Travel: The distance the rear wheel can move under compression. This will be the exact same measurement for fork stroke but is not correlated with rear suspension stroke. 

Spring: The part of suspension system which absorbs impacts and supports the rider’s weight. On bikes, these can be either air pistons or coil springs. 

Damper: The part of the suspension system that helps control and manage the kinetic energy absorbed by a fork or shock – this process is called dampening. 

Compression: The first phase of suspension as the system is compressed by an incoming force. 

Rebound: The second phase of suspension as the system rebounds or decompresses and releases absorbed kinetic energy back into the environment.? 

Stiction: The force of friction (from seals and sliding surfaces) keeping a suspension system in a static state. Stiction means there is a minimum threshold of force before a suspension system is able to react.? 

High-Speed: Refers to the shaft speed of your suspension system. High-speed scenarios are usually associated with impacts. 

Low-Speed: Refers to the shaft speed of your suspension system. Low-speed scenarios are usually associated with bike feel and handling maneuvers?(e.g. brake dive, pedal bob, etc.) 

Sag: The resting position of your bike and your suspension when compressed by your body weight and gear. Bikes and suspension are designed with a specific amount of recommended sag for the best performance. 

Air Volume Spacers: Also known as volume adjusters or tokens. They’re used to affect the progression of air shocks to provide specific ride characteristics for different riders. 

Preload: The amount a coil spring is compressed in the suspension system without any external factors like rider weight or terrain. Can usually be adjusted to help dial in sag on coil-sprung bikes. 

Bottom Out: Occurs when you’ve compressed a suspension part the complete length of its stroke usually during the largest hits, impacts, and landings.?Most suspension systems will have a bottom out bumper made of hard rubber to help soften the blow. 

Stanchion: The external sliding surface of the suspension system. 

Wiper Seal: The rubber gasket surrounding the stanchion(s) which helps keep contaminants out of and lubricating oil inside of the suspension internals.

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