For years, air shocks have been standard in mountain biking. Coil shocks were reserved almost exclusively on downhill mountain bikes. Some believed that air shocks would replace coil shocks completely. After all, if you walk into any bike shop, you’ll notice that pretty much all of the mountain bikes come with an air shock. Thanks to some technological improvements and influence from professional racers, coil shocks have begun making a comeback. Particularly among enduro and trail riders. This guide outlines the differences between the two types of shocks. It also lists the pros and cons of using a coil shock vs air shock for mountain biking. We’ll cover performance, maintenance, adjustability, price, weight, ride quality, versatility, and much more.
Table of Contents
- What is a Coil Shock?
- What is an Air Shock?
- Coil Shocks Vs Air Shocks
- Damping Systems
- Pros and Cons Summary
What is a Coil Shock?
Coil shocks use a wound steel or titanium spring to provide resistance. Coil shocks have a linear spring rate. This means that the amount of force required to compress the spring increases constantly throughout the suspension range. For example, if it takes 500N of force to move the suspension 5cm, it would take 1000N of force to move the suspension 10cm. The total travel of the shock from unloaded to fully loaded is called the stroke length.
The linear spring rate means coil shocks do not provide much bottom-out resistance. For this reason, coil shocks pair best with frames with a progressive spring rate.
Coils are identified with two numbers. The first number is the amount of force required to compress the shock a given distance. This is usually measured in pounds per inch or newtons per millimeter. For example, a coil shock with a 450lb spring will require 450lbs of force to compress 1 inch. Coils are available in 25 or 50 pound per inch increments. The second number is the total travel distance of the coil. Most springs have 2-3.5″ of travel (50-90mm).
To adjust the spring rate of a coil shock, you can swap out the metal coil for a stiffer or softer spring. You can adjust the preload and sag by turning a knob on the shock. This compresses or decompresses the coil.
Coil shocks are popular among downhill mountain bikers. They are making a comeback on trail and enduro bikes. Coil shocks are also known as coil-over.
What is an Air Shock?
Air shocks use the compression resistance of pressurized air for shock absorption. The spring in the shock is provided by compressed air that is sealed in an airtight chamber inside of the body of the shock. The air chamber is called the ‘can’. As the air is compressed, it resists further compression.
Air shocks have a progressive spring rate. This means that the suspension becomes harder to compress as it travels throughout its range. The stiffness increases exponentially. For example, if the shock requires 500N of force to compress 5cm, it may take 1500N of force to compress 10cm. An air shock can be paired with a frame with either a linear or progressive spring rate.
The spring rate of an air shock is adjusted by changing the air pressure inside of the shock. This requires a special high-pressure pump called a shock pump. There is a separate control for adjusting the preload and sag of the shock. Most models also allow you to adjust the progression by using spacers to change the volume inside of the air chamber.
Air shocks are used in all types of mountain biking. They are the most common suspension design, by far. If you look at almost any manufacturer’s line of full-suspension bikes, you’ll notice that almost every model comes with an air shock. They are particularly common on trail and enduro mountain bikes. They are less common on downhill bikes. Air shocks are also known as air-springs.
Coil Shock Vs Air Shock
Air shocks are much more adjustable than coil shocks. They allow you to precisely tune almost every aspect of the suspension’s behavior. For example, you can optimize an air shock for your exact bodyweight, the terrain you plan to ride, and your desired ride feel by adjusting the spring rate, progression, and damping. Air shocks are also much easier to adjust than coil shocks. Coil shocks have far fewer adjustment options. They are more difficult to adjust as well.
Air Shock Adjustment
With an air shock, you can set the exact spring rate or stiffness you desire. This is done by changing the air pressure inside of the shock’s air chamber. Increasing the air pressure makes the shock feel stiffer. Letting air out makes it feel softer. Along with the spring rate, the air pressure also helps to control bottom-out resistance as well as the sag and ride feel of the shock.
You can easily dial in your desired spring rate and sag by changing the PSI in the shock using a shock pump and gauge. This adjustment takes just a few minutes to make. You simply connect the pump to a valve on the shock and push air in or let air out. It’s so easy to adjust the spring rate of an air shock that you can do it before every ride or even stop and do it mid-ride. You can’t do that with coil suspension.
You may want to set your air shock’s spring rate to suit the type of terrain you’re riding that day. For example, if you’re riding a bumpy trail, you might let out a bit of air to soften the shock up. This adjustment also comes in handy if you want to carry some heavy gear on your bike or if you gain weight. You can adjust the spring rate to correct for the weight change.
Air shocks are progressive. As the suspension moves throughout its range, it becomes exponentially harder to compress. You can adjust the level of progression. This is achieved by installing or removing internal plastic volume spacers to change the internal volume of the shock’s air chamber.
This adjustment changes the force required to compress the suspension as it travels throughout its range. In other words, you can fine-tune the spring rate curve to make the shock easier or harder to compress at different points in the suspension range. For example, you can set your suspension so it becomes hard to compress early in the range by adding spacers to decrease the volume of the air chamber. You can adjust the suspension to operate almost linearly until the end of the range by removing spacers to increase the volume in the chamber.
This helps you control the bottom-out resistance and ride feel of the sock. Progression adjustment also allows air shocks to work with a wide range of suspension frame designs with different leverage ratios. Adjusting air suspension progression is easy. You simply let the air out of your shock, unscrew the shock body to access the air chamber (air can), then place or remove spacers.
The ideal progression setting depends on your frame design as well as the terrain you plan to ride. If you are using a frame with a linear suspension design, like a single pivot frame, you would want to set your air shock to be more progressive so it is less likely to bottom out. If your frame has a more progressive design, like a twin link frame, you might adjust the progression of your shock so it operates more linearly.
You can increase bottom-out resistance and change the ride feel by adjusting the progression. If you are riding rough terrain with big drops and jumps, you may want to increase your suspension’s progression to reduce the likelihood of bottoming out during a big hit. Increasing the progression can also make the ride feel a bit more playful or poppy.
A separate adjuster lets you set preload to change the bike’s sag. Many air shocks also allow you to adjust the compression and rebound damping as well.
Coil Shock Adjustment
Coil shocks, on the other hand, are much less adjustable than air shocks. In order to change the spring rate, you must swap out the coil. Coils are typically available in either 25 or 50 lb per inch increments. There may only be 3-4 different spring weights available for your specific shock. It is possible that your ideal spring weight sits somewhere between two sizes.
Springs are identified with two numbers. The first number represents the number of pounds required to compress the spring 1 inch. The second number is the total travel distance. Most coils have 2-3.5″ of travel. Keep in mind, this is not the distance your wheel can travel. Your frame controls that.
Changing a coil isn’t an easy job. To change the spring rate, you have to physically swap out the spring. This involves taking the shock apart. You’re not going to carry an extra spring and swap them out by the side of the trail. You can’t easily adjust the suspension if you gain or lose weight or decide to mount some bikepacking bags.
Coil shocks have a linear spring rate. The stiffness increases at a constant rate throughout the range. There are no progression adjustments on coil shocks. There are progressively wound springs available if you want progressive suspension. If you want to use one of these, you’ll have to swap out your coil.
One adjustment you can easily make on a coil shock is the preload. You can change the preload to set the shock’s sag. This is done by simply turning a dial on the shock. Many coil shocks also allow you to adjust the rebound damping. Some offer a compression damping adjustment as well.
On average, an air shock weighs about 300-500 grams (around 0.66-1.1 lbs) less than a comparable coil shock. For example, an average air shock weighs around 350 grams (0.88lbs) while an average coil shock weighs around 800 grams (1.8lbs). That’s a difference of around 400 grams or about 1 pound. An average-sized rider cycling up a 15% grade for 2 miles at an output of 250 watts will take around 10 seconds longer with a coil shock.
Air shocks are lighter because they don’t have a heavy metal coil. The air in the chamber performs the same function and weighs nothing. A lighter bike allows you to accelerate and climb faster and maneuver more easily because there is less mass to move around. It’s also easier to hop a lighter bike off the ground. In cycling, a pound is a pretty significant weight difference.
Coil shock weight depends partly on the spring rate. Shocks with a higher spring rate require thicker gauge metal to make the stiffer spring. This adds weight to the shock. You can reduce the weight of a coil shock by installing a lighter-weight coil. Titanium coils are much lighter than steel. Of course, they are more expensive as well.
The weight difference between modern coil and air shocks is much smaller than it was in the past. Coil shocks are lighter than ever thanks to modern lightweight steel and titanium alloys used to make the coil. Surprisingly, air shocks are heavier than they were in the past due to advanced systems like piggyback chambers and negative springs. These improve performance but add a considerable amount of weight.
Coil shocks require less frequent maintenance than air shocks. The main reason is that there are fewer internal seals. As a result, coil shocks are less affected by dust, dirt, sand, and other contaminants. Coil shocks also don’t heat up as much during heavy use. This allows the oil and seals to last longer. This allows maintenance intervals to be longer. As an added benefit, the performance remains a bit more consistent.
Most manufacturers recommend that you get your coil shock fully rebuilt once every 100-200 riding hours. For the average rider, this equates to around once every 12-18 months. Of course, if you ride frequently, you’ll have to perform maintenance more often. In addition, you’ll want to perform a basic service every 50-100 riding hours or 1-2 times between full overhauls. You should also clean the shock after every ride. This reduces the likelihood of contamination.
Air shocks, on the other hand, require a bit more frequent maintenance. Many manufactures recommend a full rebuild every 75-125 riding hours. For most riders, that will be every 8-12 months. In addition, you’ll want to do a basic service every 25-50 riding hours. You’ll need to perform about 2-3 basic services between full rebuilds. As you can see, maintenance intervals for air shocks are shorter than coil shock.
This extra maintenance is necessary because air shocks have more internal seals. They can get contaminated with dust, dirt, and grime more easily. The seals are also crucial for the shock to function. If the seals that keep the air chamber airtight were to get contaminated or fail, the air would leak out and the shock would stop working. If the seals get contaminated, the oil can also get contaminated or leak out. This would cause damping performance to fade.
In addition, air shocks create more heat than coil shocks because the extra seals create more friction. The heating and cooling of the oil causes parts to wear more quickly. The oil can also degrade. For this reason, the oil and seals need to be changed more often in air shocks. It is also recommended to top the oil up and clean the seals between overhauls.
A complete shock overhaul for a coil or air shock typically involves taking the shock apart, inspecting all of the parts, replacing all of the seals, and replacing the shock fluid. Most riders either ship their shock to the manufacture or take it to a bike shop for a full rebuild. You can’t really do this service at home because some specialty tools and know-how are required.
A basic service involves inspecting the shock for wear or damage, topping up the fluid, and replacing the air sleeve seals if you’re using an oil shock. You can perform a basic service on your coil or air shock by yourself or take the bike to a shop. You should also wipe down the shock after every ride to reduce the liklihood of seal contamination.
If you don’t properly maintain your shock or you neglect maintenance, it will eventually get contaminated with debris. The seals will begin to leak and the oil (and air) will leak out. Abrasion from debris rubbing against internal parts as they move can also cause unnecessary wear and tear. Your shock will wear out prematurely if you don’t maintain it and keep it clean.
For more info on shock maintenance, check out this great guide.
When a shock continuously compresses and decompresses, friction between the seals and moving parts cause the system to heat up. Excessive heat build-up causes shock performance to degrade. This is known as heat fade. This affects both the spring rate and damping system of the shock. This problem is particularly common while riding down long bumpy descents that take longer than around 20 minutes. Downhill mountain bikers have to be careful that they don’t overheat their shock.
Coil shocks manage heat much better than air shocks. They do not heat up as quickly and they do not create nearly as much heat. As a result, coil shocks generally don’t suffer from heat fade. Performance remains consistent.
The reason coil shocks don’t suffer from heat fade is that there are fewer seals creating friction. The metal coil itself requires no seals and has no moving parts so it stays cool. As a result, the spring rate of the coil does not change during a long descent. Because there are fewer seals, the oil in the damping system of coil shocks stays cooler as well. This allows the damping performance to remain more consistent. For these reasons, most downhill mountain bikers prefer coil shocks. They can ride down long descents without having to worry about their shock overheating.
Air shocks, on the other hand, require tight seals to keep the pressurized air inside. They have more seals as well. The seals create friction in the system, which heats the shock up. This heat also causes the oil in the damping system to heat up. This can change the oil’s viscosity. The fluid becomes thinner, which makes the damping system less effective. The thin oil can more easily flow through the ports in the shock as it compresses and rebounds. This makes the ride a bit more rough and bouncy. That said, modern oils are pretty resistant to viscosity changes.
When air shocks heat up, the air inside the chamber also expands. This increases the pressure, which increases the spring rate. The seals inside can also expand slightly when they get hot, making them tighter. The shock become stiffer as a result and can’t compress as far. This increased pressure changes the shock’s progression as well. For these reasons, air shocks are not ideal for downhill and freeride mountain biking. The heat buildup makes the shock stiff and bouncy.
The heat can be dangerous as well. Air shocks can actually get so hot that they can burn your leg. Feel the body of the shock after a long descent if you currently use an air shock. If it’s hot, you may be better off switching to a coil shock. If you ride in an extremely hot climate, you might also be better off with a coil shock. Outside heat combined with heat created by the shock can cause performance to fade. That said, most recreational riders will never ride hard or fast enough for heat to be an issue. If your shock overheats, you can just take a break and let the shock cool off. For competitive riders, heat build-up can be a serious problem that can affect speed.
Air shock designs have been improved over the years to better deal with heat. Modern models have larger volume air and oil chambers that allow for better cooling. This greatly reduces heat fade. Most modern air shocks also have internal floating pistons (IFP) that move the oil and gas (usually nitrogen) away from the main part of the shock. This allows heat to dissipate more easily.
Piggybacking shocks also have two compression circuits. This splits up the load so less heat builds up in the damping system. Manufacturers are also finding ways to reduce friction so the shock creates less heat to begin with. Modern high-end air shocks deal with heat very well. That said, coil shocks still offer better performance on long descents because they don’t create nearly as much heat.
Small Bump Sensitivity
Coil shocks are more sensitive to small bumps than air shocks. This is possible because coil shocks contain fewer seals. Some of the seals fit looser as well because the shock doesn’t need to be airtight. Fewer seals means there is less static friction or stiction in the system. Stiction is caused by friction from the seals rubbing against moving parts such as the shock shaft.
Sufficient force is required to overcome stiction in order for a stationary shock to begin moving. The amount of force required to break the stiction and make the suspension begin compressing is called breakaway force. Coil shocks require less breakaway force than air shocks. In other words, the impact threshold for coil shocks to begin moving is lower. This allows coil shocks to be more sensitive to small bumps than air shocks.
A coil shock can soak up a small bump that an air shock wouldn’t even react to because the coil shock requires less force to break the stiction and begin moving. When you hit a bump, a coil shock can also react faster. This gives coil shocks a smoother and more supple ride feel. As an added benefit, the better small bump sensitivity of coil shocks allows the damping system to do a better job because it can begin working more quickly and with less force.
Air shocks, on the other hand, aren’t quite as sensitive to small bumps because they have more seals. Some of the seals must fit tighter because they need to hold pressurized air inside the shock in order for it to function. This increases stiction. It takes more breakaway force to get an air shock moving. An air shock may not react to a small bump that doesn’t create enough force to break the stiction. They also can’t react quite as quickly to bumps. This makes the ride feel a bit more harsh. The damping system can’t work quite as well either because it can’t respond as quickly to an impact.
To help solve this problem, newer air shocks feature a large negative spring. This negative spring opposes the air spring when the shock is fully extended in its resting state. The negative spring assists the shock to overcome the static friction so it can provide better small bump sensitivity. In other words, it reduces the amount of breakaway force that is required to get the shock moving.
A well-designed air shock with a large negative spring offers almost the same small bump sensitivity as a coil shock. Some modern coil shocks also have a negative spring. For more info on negative springs and how they work, check out this article.
Coil shocks offer better traction than air shocks. This is possible due to the superior small bump sensitivity. The rear wheel can track the contours of the ground better and more consistently when the suspension is more sensitive to bumps. The linear spring rate curve of coil shocks also makes the suspension feel a bit more responsive. Particularly while riding rough sections of trail. This also helps to improve traction.
Increased traction allows you to take corners harder and faster without having to worry as much about your wheel sliding out from under you. The bike sticks to the trail better. The bike also feels more stable while riding over bumps. The increased traction also allows you to brake a bit harder without skidding your tire. This all inspires confidence. Coil shocks are great for riding trails with loose surfaces or lots of curves.
Air shocks don’t provide quite as much grip. The reason is that they can’t absorb some small bumps due to stiction. As a result, the rear wheel can’t track the ground as consistently. It bounces around a bit more. When the rear wheel is bouncing around, traction decreases. After all, your wheel can’t provide grip when it’s bouncing off the ground. You may not be able to corner quite as hard with an air shock. On rough stretches, you might have to ride a bit slower so you have enough grip.
Bottom Out Resistance
Air shocks provide better bottom-out resistance than coil shocks. The total amount of force it takes to compress an air shock and bottom it out is greater than a coil shock. This is possible thanks to the progressive spring rate of air shocks. As the shock compresses through its range, it becomes exponentially harder to compress further. The spring rate ‘ramps up.’ Toward the end of the suspension range, it takes an enormous amount of force to further compress the air inside of the shock. This reduces the likelihood of the shock bottoming out during a hard hit, large drop, or after landing from a jump.
Air shocks also allow you to easily adjust the bottom-out resistance. There are two ways to achieve this. The first option is to decrease the volume in the air chamber by adding some spacers. This makes the suspension more progressive. The suspension becomes harder to compress earlier in the range and is more resistant to bottoming out as a result. This feature allows air shocks to pair with frames with a linear leverage rate. The shock can provide progression to reduce bottom outs instead of the frame.
The second way to increase bottom-out resistance is to increase the PSI in the air chamber with a shock pump. This increases the spring rate and stiffens up the suspension so it is harder to compress and bottom out. If you plan to ride a rough trail with lots of drops or jumps, it’s a good idea to crank up the bottom-out resistance by increasing the air pressure or progression.
Coil shocks can bottom out more easily than air shocks because spring rate is linear. The amount of force required to compress the metal spring increases constantly throughout it’s range. The total amount of force required to fully compress the shock and bottom out is less than an air shock (assuming both shocks are adjusted for the same rider weight on the same frame).
During a drop, jump, or hard hit, you can fully compress the spring and bottom out a coil shock. You’ll know when this happens because you’ll feel a hard stop and hear a thud when the suspension stops traveling. It is particularly easy to bottom out a coil shock on a frame with a linear leverage rate because neither the frame nor shock provide any progression. Coil shocks pair best with frames with a progressive leverage ratio. I’ll talk more in-depth about this later.
Regardless of which type of suspension you use, chances are you will bottom out once in a while during a particularly hard hit or drop. If you jump your bike, the risk of bottoming out increases. Bottoming out around once per ride is normal. Almost all modern shocks have some type of bottom-out protection built-in to prevent damage to the shock. This is usually a rubber ring that prevents metal on metal contact inside of the shock during a bottom out.
If you bottom out too hard or too frequently, you can cause damage to your shock or frame. Eventually, your suspension’s bottom-out protection will wear out. A particularly hard hit could bend a wheel or even bend your bike’s frame. You want to adjust your suspension so bottom outs are rare. If you’re bottoming out too often, increase the pressure or progression in your air shock or install a stiffer coil to your coil shock. If you never bottom out, you may be able to loosen up your suspension a bit. It may be too stiff.
Coil and Air Shock Cost
Coil shocks are usually slightly more expensive than air shocks. You can buy a mid-range to high-end coil shock for $500-$650. Air shocks cost around $400-$600 on average.
When calculating the cost of a shock, it’s important to consider the maintenance cost over time. Coil shocks require less frequent maintenance. For this reason, they are usually cheaper in the long run. If you ride an average amount, you might save $100 per year on maintenance if you go with a coil shock.
Full shock service generally costs around $150. This involves a complete cleaning and rebuild with all new seals and oil. Most manufactures recommend you get your coil shock serviced every 100-200 hours or once every 12-18 months.
Air shocks generally need to be serviced a bit more frequently. This is because the seals need to be replaced more frequently to keep the shock airtight. Most manufacturers recommend a full service every 75-125 hours or every 8-12 months. The frequency depends on how often you ride and the manufacturer of your shock. The more frequent rebuilds adds to the cost of ownership of air shocks.
Shocks also need basic service between full services. This involves topping up the oil, cleaning or replacing the seals. This service costs around $30-$50. You can do this yourself for a lot less if you buy some basic tools and parts. Coil shocks generally need one basic service between full services. Air shocks might need 2 or 3 basic services between full services. The shorter maintenance intervals of air shocks adds to the cost of ownership.
Neglecting maintenance will increase the cost of ownership over time as well because your shock will wear out sooner. Generally, coil shocks deal with neglect better than air shocks. If you’re buying a used bike, you’ll want to ask the owner how often the shock was maintained.
One extra expense you may have if you ride a coil shock is a new spring. This will be necessary if you want to have the ability to change your shock’s spring rate for riding different terrain. Coil shock springs cost anywhere from $20 to $130 depending on the quality, design, and material they’re made of. Titanium springs are more expensive than steel, for example. If you’re only able to own one bike and you use it for trail riding, bikepacking, and downhill riding, you might need a few different coils. The cost can add up. Of course, you don’t need to buy multiple springs. You can just set your suspension up and leave it as is.
This is an expense that you avoid if you go with an air shock because the spring rate is adjustable. With an air shock, all you need is a shock pump to adjust the spring rate. Shock pumps cost around $20-$50.
This RockShox High-Pressure Bicycle Shock Pump (#ad) would be a good option. It features a built-in gauge and has a max PSI of 300.
Comfort and Ride Quality
Coil shocks offer a more comfortable ride than air shocks. This is possible thanks to the greater sensitivity that coil shocks offer. They can soak up small bumps that air shocks might not react to. This allows for a smoother ride. In addition, the linear spring rate keeps coil shocks more planted to the ground. The rear wheel doesn’t bounce around quite as much after a hard hit. This makes the bike feel a bit less lively. Those with joint or back pain may benefit from the smoother ride that coil shocks offer.
Air shocks, on the other hand, offer a bit more lively ride. The progressive spring rate can make the suspension feel bouncy and playful. Some riders like this and others don’t. The inferior small bump sensitivity also makes the ride feel slightly rougher. How much you notice this depends on the terrain you’re riding.
Coil shocks allow you to ride slightly faster than air shocks. This is possible thanks to the sensitivity of the shock, which allows the wheel to better track the contour of the ground. This, in turn, improves traction, which allows for better cornering and braking.
With a coil shock, you can corner, accelerate, and brake harder without losing grip. This allows you to ride faster. Particularly on trails with loose surfaces and lots of tight corners. In addition, coil shocks offer a smoother ride. You can steer more precisely and control the bike better when it isn’t bouncing around violently underneath you.
If you ride competitively or just like to ride as fast as possible, you may be a bit better off with a coil shock. That said, the difference in speed between a properly set up air and coil suspension system will be very small. On a typical downhill run, you might be able to ride 1-2 seconds faster with a coil shock. If you just ride recreationally, this is insignificant. If you ride competitively, an extra second or two might make the difference between winning or losing a race.
That said, there are some situations where an air shock might allow you to ride faster than a coil shock. For example, air shocks are better for riding trails with lots of jumps, drops, large bumps, and rollers. The progressive spring rate gives the bike more support. This allows you to hit these obstacles a bit faster and harder without worrying about slowing down or bottoming out.
Frame Compatibility for Coil and Air Shocks
Before buying a shock, it’s important to consider the design of the suspension frame you plan to mount it to. Air shocks offer much better frame compatibility. In fact, pretty much all frames are compatible with air shocks. Some suspension bike frames are not compatible with coil shocks.
This is the case because suspension bike frames come with different leverage ratios. They can have either a linear leverage ratio or progressive leverage ratio design. The leverage ratio is the ratio between the distance the rear wheel travels in relation to the distance the shock travels.
Manufacturers can manipulate the leverage ratio by changing the location and number of pivot points and by using linkages. This allows the leverage ratio to change or remain constant throughout the suspension range. This change in the leverage ratio is called the leverage rate curve. It can be represented visually on a graph.
Linear Leverage Ratio Frames
The simplest frames have a linear leverage ratio. On these frames, the ratio between the rear wheel movement and the suspension travel remains constant throughout the suspension range. For example, on a frame with a 3:1 linear leverage ratio, the rear wheel would move 3 inches while the shock compressed 1 inch. The leverage ratio would remain the same everywhere in the suspension’s travel.
The simplest suspension frame design, called single-pivot suspension, operates linearly. The leverage curve will be a flat horizontal line when represented on a graph. These frames pair well with air shocks because the shock can provide progression to reduce bottom-outs.
Progressive Leverage Ratio Frames
On frames with a progressive leverage ratio, the ratio between the rear wheel movement and suspension travel changes throughout the suspension range. The force required to move the rear wheel increases or ramps up as the suspension travels through its range. A high leverage ratio makes it easy to compress the shock. A lower leverage ratio makes it harder to compress the shock.
For example, the leverage ratio might be 4:1 at the beginning of the travel. Toward the end of the travel, the leverage ratio might change to 2:1. This leverage ratio is usually averaged out to 3:1 for marketing purposes. This helps to reduce the likelihood of bottoming out.
On a graph, a progressive leverage curve is represented with a downward sloping line. A few suspension frame designs that offer progression include linkage-driven single pivot, Horst-link, and twin-link.
Choosing the Right Shock for Your Frame
Frames with a linear leverage ratio are typically designed to be paired with an air shock. The linear leverage ratio frame relies on the progression of the air shock to provide bottom-out resistance.
Frames with a progressive leverage ratio pair well with coil shocks because the frame can give the bike all of the bottom-out resistance that it needs. The shock doesn’t need to provide progression.
If you were to pair a linear leverage rate frame with a linear leverage rate coil shock, you may experience harsh bottom-outs because you can blow through your suspension range too easily. There isn’t enough progression in the system to prevent this. For this reason, coil shocks aren’t recommended to be paired with linear leverage rate frames.
To compensate for the lack of progression in the system, you could install a coil with an extra high spring rate or run extra high compression damping. In this case, the suspension would be too stiff for normal use, causing the ride to feel harsh.
Air shocks are compatible with pretty much all suspension frames because the progression is adjustable. If you’re using a frame with a lot of progression, you can adjust your air shock to behave more linearly by removing some volume spacers from the air chamber. If you’re using a frame with a linear compression curve, you can install some spacers to increase the progression.
To complicate things even further, there are also frames with a regressive leverage ratio. These frames work the opposite of progressive frames. The force required to compress the shock decreases throughout the suspension range. For example, the leverage ratio might be 2:1 at the beginning of the range then increase to 4:1 toward the end. On a graph, a regressive leverage ratio is represented with an upward sloping line. Regressive leverage rate frames pair best with air shocks with volume reducers.
To recap, coil shocks work best with frames with a progressive leverage ratio frame. Air shocks work best with frames with a more linear leverage ratio. Some frames are compatible with both air and coil shocks. Pretty much all frames can work with air shocks due to the adjustable progression. Before you buy a new shock or frame, it’s best to check with the manufacture to see which types of shocks they recommend for the frame.
Coil and Air Shock Versatility
Because they are more adjustable, air shocks offer much more versatility than coil shocks. For example, you can easily adjust the shock’s spring rate to match the type of terrain you’re riding. If you want to tackle a trail with lots of big drops and jumps, you can add some volume spacers to increase the progression. If you’re riding a very rough rocky trail, you might let some air out to reduce the spring rate to soften up the suspension.
You can also adjust the shock to accommodate different rider weights. Maybe you want to lend your lightweight friend your bike for the day. You can easily reduce the pressure to make the suspension a bit softer. If you want to mount heavy bikepacking bags on the same bike, you can pump some more air into the shock and increase the spring rate. If you buy a new frame, you can swap your air shock over. It doesn’t matter if the frame has a progressive or linear leverage ratio because air shocks can be adjusted to suit both.
To make these adjustments to an air shock, you don’t need to buy any extra parts or take the shock apart. You can adjust the suspension in a matter of minutes with a shock pump. You could optimize your suspension for every ride if you wanted to.
Coil shocks are less versatile because they are more difficult to adjust and offer fewer adjustment options. For example, maybe you want to use the same bike for fully-loaded bikepacking and trail riding. With a coil shock, you would have to buy different coils with different spring rates, take the suspension apart, and swap them out. You also can’t adjust the progression on coil shocks. This further limits versatility. You can’t as easily use the same bike for multiple types of mountain biking. It just isn’t practical. Coil shocks also aren’t compatible with all frames due to the linear leverage ratio. This can be an issue if you want to upgrade your frame.
Durability and Longevity
Generally, coil shocks are a bit more durable and long-lasting than air shocks. They can also deal better with neglect. Mostly because there is less heat buildup and there are fewer seals so maintenance intervals are longer. There are fewer parts that can wear out or fail. Because coil shocks don’t heat up as much as air shocks, you don’t have to worry about causing damage from overheating. The fluid can last a bit longer because it’s not heating up as much. Modern steel and titanium coils last pretty much forever. Older models would shorten and sag a bit over time.
Air shocks tend to be a bit more fragile. If you don’t keep up on maintenance, the seals begin leaking air. When this happens, you’ll have to pump the shock back up regularly. If the leak gets bad enough, the shock will stop working. Heat buildup can also speed up wear. Excessive heat buildup can even cause internal damage to the shock.
That said, all modern shocks are very reliable and long-lasting. You shouldn’t have to worry about longevity, as long as you stay on top of maintenance. The shock should last many many years.
Frame and Shock Options
These days, most full-suspension mountain bike frames are designed to pair with air shocks. The linkages and pivot points are engineered in a way that optimizes the frame’s leverage ratio for more progressive air suspension. Most complete full-suspension bikes come with air shocks from the factory. In fact, if you go to a bike shop, almost all of the full-suspension mountain bike will have an air shock. You may only see a handful of bikes with coil shocks.
This is the case because air shocks are more adjustable, easier to adjust, and more popular. Bike shops can simply adjust an air shock to fit almost any frame and rider. With coil shocks, they would have to carry a bunch of different springs of different stiffnesses and swap them out. This would take more time and labor. Air shocks make it easier for shops to fit bikes to riders. Most riders seem to prefer air shocks as well. For these reason, you’ll have a lot more bike frame and suspension options to choose from if you go with an air shock.
If you’re sure you want to use a coil shock, you’ll have to seek out a bike with a progressive leverage rate. Most of the major mountain bike brands offer frames that are compatible with coil-over shocks. A few examples include Pivot, Yeti, Santa Cruz, Transition, and Guerilla Gravity. Some manufacturers recommend against using a coil shock with their frames. In some cases, it may be possible to swap out a linkage on your existing bike frame to make it more progressive and compatible with a coil shock. For example, Cascade Components offers this replacement link. Of course, you can pair a coil shock with a linear leverage ratio frame. Plenty of riders do this. It does increase the likelihood of bottom outs.
Coil shocks can be noisy. For example, if the coil is loose because it isn’t preloaded enough, it can knock against the bases of the shock when it’s not compressed. Some longer coils can knock against the side of the damper body when compressed. Most models have some kind of rubber stopper to prevent these kinds of noises. Air shocks operate more quietly.
Some riders prefer the looks of coil shocks. The thick metal coil spring looks pretty cool. You can see the coil compressing as you ride. Coils also come in a range of colors that you can match to your bike’s paint or accent color scheme. Air shocks, on the other hand, are usually just black tubes. They look much more plain. Of course, looks are subjective and don’t affect the performance of the shock.
Coil Vs Air Shock Ride Characteristics
Both coil and air shocks offer different ride charactaristics. Neither is really better than the other.
Coil shocks feel more planted to the ground thanks to the increased small bump sensitivity. Due to the linear spring rate, the bike doesn’t bounce around quite as much. The ride feels a bit more stable and flat, like you’re glued to the ground. The ride is smoother and more plush as well.
Air shocks, on the other hand, offer a more playful ride. The progressive suspension makes the bike want to pop and bounce. This makes it easier to lift the bike off the ground. The bike also feels a bit more supportive. These features make air shocks a great choice for those who like to jump and hop their bike.
The spring ratio curve of the shock, the leverage ratio curve of the frame, and the adjustment of the shock together all play a major role in the way the bike feels while riding. As mentioned earlier, different frame and shock combinations and adjustments can change the progression throughout the suspension travel.
For example, some setups are designed to be soft at the beginning of the stroke then firm up toward the middle then firm up again toward the end. Some setups may be firm at the beginning then soften toward the middle. Others are designed to be linear through the suspension range then firm up at the end to prevent bottom outs. The best setup depends on the terrain you’re riding and personal preference.
As you can imagine, there is an enormous amount of customization you can make to a the suspension ratios between frame designs, suspension designs, and suspension adjustments. This choice comes down to the terrain you ride and personal preference.
A Note About Frames and Suspension Behavior
The frame and shock play a major role in the pedaling and braking behavior of the bike as well as efficiency. Ideally, you want your bike to remain as stable as possible while you pedal and brake. You also want a bike that doesn’t waste energy compressing the suspension unnecessarily.
When you pedal, your weight shifts back and compresses the suspension. This is called ‘squat’. The suspension rebounds back as you finish the stroke. As you pedal along, the bike oscillates up and down a little bit. This is pedal bob. Pretty much every full-suspension mountain bike suffers from some level of pedal bob.
Pedal bob wastes energy by compressing the shock unnecessarily. You’re essentially wasting energy compressing the suspension that could be used to drive you forward. Some suspension setups deal with pedal bob better than others.
Most full suspension bikes feature some kind of anti-squat or anti-bob system to help the bike resist pedal-bob. This is achieved mostly through frame design. Essentially the suspension system is designed to resist compression as you pedal. The swingarm angle, chainline, chain tension, pivot point, suspension type, and driving force of the wheel all play a role in the anti-squat characteristics of the bike.
Ideally, you want your frame to cancel out pedal-bob with anti-squat. This is called 100% anti-squat suspension. If anti-squat is greater than 100%, the suspension extends while you accelerate. If the anti-squat is less than 100%, the suspension will compress while you pedal. The anti-squat characteristics of the frame change as the suspension compresses and decompresses while you ride because the leverage rate of the frame and spring rate of the shock change as they travel through their ranges. This happens with both air and coil shocks. You can’t maintain 100% anti-squat at all times. Some frame and suspension combos do a better job of reducing pedal bob than others.
Modern shocks can reduce pedal bob with a special kind of damping called platform damping. This system only allows the suspension to activate when a specific impact force is reached. Essentially, the suspension ignores any forces below that force threshold.
One drawback to riding a frame with lots of anti-squat is that there can be pedal kickback. Pedal kickback happens when the cranks try to rotate backward when the suspension compresses. This happens because the distance between the bottom bracket and rear axle increases as the suspension compresses. The top of the chain needs more links to make up for the additional distance. This is known as chain growth. The chain tries to pull the chainring backward causing the cranks to rotate backward.
You’ll notice this phenomenon when the cassette can’t spin forward or if the wheel is spinning too slowly. For this reason, pedal kickback is more noticeable while climbing and riding slowly.
Braking and Suspension
Braking also affects the way the suspension behaves. When you brake, your weight shifts forward and the suspension wants to extend. At the same time, force from the rear brake caliper pushing on the swingarm makes the suspension want to compress. The forces somewhat balance each other out to make the bike feel more stable under braking.
The force from the rear brake caliper is called anti-rise. Some frames have more anti-rise than others. High levels of anti-rise can make the frame feel stiffer. For this reason, many companies optimize their frames to reduce anti-rise. At the same time, you don’t want your suspension extending too much during braking. There is a compromise.
For more info on suspension frame designs, check out this phenomenal article from Bike Radar. It explains every aspect of bike suspension in great detail.
A Note About Suspension Coil and Air Shock Damping Systems
Both air and coil shocks have a damping system built-in. Shocks need a damper to prevent them from oscillating after a compression or rebound. The damper smooths out the ride by preventing the bike from bouncing like a pogo stick after it hits an obstacle. Both air and coil shocks use similar damping technology.
Standard dampers work by forcing oil through a small hole or series of holes (called ports) inside of the shock as the shock compresses and rebounds. The hole size controls the rate that the oil can flow. The oil flows faster through a larger hole and slower through a smaller hole. The flowing oil controls the speed that the shock can compress and rebound. There are two dampening circuits in a shock. One is for compression damping and the other is for rebound damping.
Most coil and air shocks allow you to adjust the damping for the terrain and your weight. These adjustments are called rebound damping and compression dampening. These adjustments change the size of the ports in the damping system. This changes the speed that oil can flow through the damper, which changes the speed that the shock compresses and rebounds. The oil flows more slowly through a smaller hole and more quickly through a larger hole.
The amount of damping adjustment that is possible depends on the shock. Some shocks only offer rebound damping adjustment. Some offer both compression and rebound damping. High-end shocks offer different adjustments for both high speed and low-speed compression damping and beginning and end stroke rebound damping. Low-end shocks don’t offer any damping adjustment at all.
Some modern shocks come with a new damping technology called platform damping. This system is designed to eliminate pedal bob. Platform dampened suspension does not compress and rebound under pedaling forces. This makes the bike more efficient because you’re not wasting energy activating the suspension as you pedal.
Shocks with a platform damping system only activate when certain impact force is achieved. The suspension is designed to ignore any forces below that threshold. Under normal pedaling forces, the shock remains effectively locked out. Once you hit a bump that reaches the impact threshold, the suspension will activate. Shocks with platform damping can be adjusted with a dial. They can be adjusted from completely locked out to no no platform damping.
When a shock absorber compresses and rebounds, it creates friction. This friction heats up the oil in the damping system. Generally, air shocks create more heat than coil shocks because they have more seals. Excessive heat can cause the damping performance to fade. More on that later.
Coil Shock Pros and Cons
Coil Shock Pros
- Easier to maintain- Coil shocks have longer maintenance intervals because there are fewer seals. Most models need to be rebuilt every 100-200 hours of use.
- No heat fade- Coil shocks do not overheat on long descents because there are fewer internal seals creating friction. The coil doesn’t heat up.
- Superior bump sensitivity- Because there are fewer seals, coil shocks have less static friction. It takes less force to activate the shock. This allows coil shocks to absorb smaller bumps.
- Better traction- The superior bump sensitivity allows the rear wheel to better track the ground. This improves traction.
- Cheaper- Coil shocks have a higher initial cost but cost less in the long run because they require less maintenance.
- More comfortable- Coil shocks offer a smoother and less lively ride due to the superior bump sensitivity and linear spring rate.
- Faster- The improved traction allows you to corner at higher speeds without losing grip.
- More durable and long-lasting- Because there is less heat buildup and fewer seals, the shock lasts longer. Coil shocks can deal with neglect better as well.
Coil Shock Cons
- Fewer adjustment options- You can’t adjust the progression. To adjust the spring rate, you have to swap out coils.
- Heavier- Coil shocks weigh around 1 pound (400 grams) more than air shocks.
- It’s easier to bottom-out- The linear spring rate makes it easier to blow through your suspension travel and bottom out.
- Coil shocks are compatible with fewer frames- Due to the linear spring rate, coil shocks pair best with frames with a progressive leverage rate. This leaves you fewer options.
- Less versatile- You can’t easily change the spring rate of a coil shock and you can’t adjust the progression. This makes it harder to use the bike for different types of mountain biking.
- Fewer shock and bike options- Because coil shocks are less popular, there are fewer options on the market to choose from.
- Louder- Coils can knock against the base or side of the damper if they’re not adjusted properly.
Air Shock Pros and Cons
Air shock Pros
- More adjustable- You can set the exact spring rate and progression you desire.
- Lighter- Air shocks don’t have a heavy metal coil. They weigh around 1 pound less.
- Better bottom-out resistance- Due to the progressive spring rate, air shocks stiffen up toward the end of their range. This reduces the likelihood of bottoming out.
- Better frame compatibility- Because the progression rate is adjustable, air shocks are compatible with pretty much all frames.
- More versatile- You can easily adjust the spring rate and progression of air shocks to optimize your bike for different types of mountain biking.
- More shock and bike options- Because air shocks are more popular, there are more options on the market to choose from.
- Quieter- Air shocks don’t make much noise.
Air Shock Cons
- More frequent maintenance is required- Air shocks need to be rebuilt every 8-12 months for the average rider.
- Air shocks suffer from heat fade- Friction from the seals rubbing on moving parts causes the shock to heat up. This heats the oil, causing damping performance to fade. The shock can become stiffer as well.
- Poor small bump sensitivity- Air shocks have tight seals which create a lot of stiction. It takes more breakaway force to activate the shock. Air shock may not react to small bumps.
- Less traction- The wheel can bounce around a bit more because the suspension isn’t as sensitive. This reduces grip.
- More expensive- Air shocks cost less initially. In the long run, they are more expensive because they require more frequent maintenance.
- Les comfortable- Air shocks have a bouncier and more lively ride due to the progressive spring rate and inferior bump sensitivity.
- Slower- The inferior traction means you can’t take corners quite as fast. This costs time.
- Less durable- Air shocks are a bit sensitive to contamination. If you neglect maintenance, the shock will leak and fail. Leaks are more common because there are more seals.
Who Should Choose a Coil Shock?
You should choose a coil shock if you ride downhill, enduro, or just like to ride fast. Because less heat builds up, you can handle longer descents without worrying about suspension fade. Those who prefer a smoother and more comfortable ride will appreciate the small bump sensitivity of coil shocks. As an added benefit to bump sensitivity, coil suspension offers better traction. The ride also feels more stable and planted and less lively due to the linear spring rate. This is inspires confidence. You may also like a coil shock if you don’t like doing maintenance often. Most riders will only have to service their coil shock once per year with a minor service in between.
Who Should Choose an Air Shock?
You should choose an air shock if you ride varied terrain, flatter trails, or terrain that includes lots of uphills. Those who like to adjust their suspension often for different terrain, rider weight, and ride feel will appreciate the easy and extensive adjustability of air shocks. You can optimize your suspension for almost any situation. The versatility is a nice feature if you only have one bike. The progressive spring rate of air shocks makes them ideal for those who jump or ride off large drops. Air shocks are less likely to bottom out. Those who prefer a bouncy and playful shock will also prefer the progression of air shocks. If you care about weight and need the lightest possible shock, air suspension is the way to go. It’s also easier to buy a bike if you go with an air shock because pretty much every frame is compatible.
Final Thoughts About Coil Vs Air Shocks
The best type of shock for your bike really comes down to the terrain you plan to ride, your frame design, and personal preference. There is no best shock. The choice between coil vs air shocks is similar to the debate between flat vs clipless pedals or 650b vs 29” wheels. Neither choice is better. There are compromises.
For downhill mountain bikers and those who race, coil shocks are probably the best choice. Coil shocks offer the best performance in most situations. You don’t have to worry about heat fade and traction is superior. Most mountain bikers can ride a bit faster with a coil shock.
For those who ride more casually, air shocks are often the best choice. The adjustability allows you to tune your shock for any situation. Modern air shocks also perform better than ever. Manufacturers are finding ways to reduce friction and heat buildup. Whether you choose an air shock or coil shock, I hope this guide has helped you in making your decision.
Where do you stand on the coil shock vs air shock debate? Share your experience in the comments below!
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