Your mountain bike’s suspension fork plays a major role in the handling and comfort of your bike. For years, air forks have been standard in pretty much all disciplines of mountain biking. If you walk into a bike shop, you’ll notice that almost all of the mountain bikes come with an air fork. Thanks to some performance improvements, coil forks have begun making a comeback. Particularly for enduro and trail riding. This guide outlines the pros and cons of using a coil fork vs air fork for mountain biking. We’ll cover handling, adjustability, maintenance requirements, sensitivity, weight, comfort, price, versatility, ride feel, and much more.
What is an Air Fork?
Air forks use the compression resistance of pressurized air for shock absorption. The spring in the fork is provided by compressed air that is sealed in an airtight chamber inside of the fork arm. This part is called the air spring. As the air is compressed, it resists further compression. Air forks are used for all types of mountain biking including trail riding, downhill, cross country, enduro, and freeride.
Air forks have a progressive spring rate. This means that the fork becomes harder to compress as it travels throughout its range. At the beginning of the range, the suspension is soft. As the fork is compressed, it becomes exponentially harder to further compress. For example, if the fork takes 500N of force to compress 50mm, it might take 1500N of force to compress 100mm.
The spring rate of an air fork can be adjusted by changing the pressure inside the air chamber. Increasing the pressure increases the spring rate (makes the fork stiffer). Decreasing the pressure reduces the spring rate (makes the fork softer). Adjusting the spring rate of an air fork requires a special high-pressure pump called a shock pump. You simply attach the pump to a Schrader valve on the fork and add or remove air. You also adjust the fork preload and sag by changing the pressure. There are no preload dials like you would find on a coil fork. Most air forks can also be locked out so they do not compress
Most air forks also allow you to adjust the progression by changing the volume of the air chamber. This is achieved by adding or removing plastic spacers inside of the air chamber. Adding spacers decreases the volume inside of the air chamber and removing spacers increases the volume. Reducing the volume of the air chamber makes the fork more progressive or harder to compress earlier in the range.
Air forks also have a damping system. This smooths out the ride and prevents the fork from bouncing around after a compression or rebound. Most models allow you to adjust the compression and rebound damping.
What is a Coil Fork?
Coil forks use a metal coil spring to provide resistance. The coil is made from either steel or titanium. Coil forks have a linear spring rate. This means that the force required to compress the spring increases constantly throughout the fork’s range of travel.
For example, if it takes 500N of force to compress the spring 50mm, it would take 1000N of force to compress the fork 100mm. The total amount of distance that the fork can compress is called the travel. This typically ranges anywhere from 80-200mm depending on the type of mountain bike.
To adjust the spring rate of a coil fork, you can swap out the coils for stiffer or softer options. You can set the fork sag by turning a dial on top of the stanchions. This changes the preload on the springs by compressing or decompressing the springs. Increasing the preload compresses the spring, which makes the fork stiffer and reduces sag. Most coil forks also have a lockout function to prevent them from compressing.
Fork coils are identified with two numbers. The first number identifies the amount of force required to compress the fork a given distance. This is measured in either pounds per inch or newtons per millimeter. For example, a 40lb/in spring would require 40lbs of force to compress the fork 1 inch. Coils are typically available in 5 lb increments. The second number indicates the total travel distance of the coil. For cross country or trail bikes, you might only need 100-120mm of travel. For downhill mountain bikes, you might need 180-200mm of travel.
Coil forks also have a damping system, just like air forks. The damping systems for coil and air forks function in the same way. I’ll talk more in-depth about damping later on.
Air Fork Pros
1. Air forks allow you to set the exact spring rate
You can dial in the precise spring rate or shock stiffness you need by changing the pressure inside of the fork’s air chamber. Increasing the pressure makes the suspension stiffer. Letting air out makes it softer. You can easily set the exact spring rate by changing the PSI in the shock with a shock pump and gauge like this GIYO High Pressure Shock Pump.
This same adjustment sets the fork’s sag. This adjustment allows you to easily optimize the fork for different terrain, rider weight, and ride feel. Coil forks, on the other hand, can’t be set as precisely. You need to swap out the coils to change the spring rate.
2. Air forks allow you to adjust the progression
As mentioned above, air forks are progressive. This means they become exponentially harder to compress throughout their range of travel. You can set the progression of your air fork by adding or removing spacers in the fork’s air chamber. These spacers change the volume of the air chamber. Adding spacers reduces the volume of the air chamber, making the suspension more progressive. Removing spacers increases the volume in the chamber, making the suspension more linear.
This feature allows you to tune the spring rate curve. In other words, you can control how the force required to make the suspension move changes throughout the range of the suspension. For example, you can add spacers to make the fork harder to compress earlier in the travel. You can remove spacers to make the fork operate almost linearly. More progressive forks are less likely to bottom out. They also give the bike a bouncy and lively ride feel. You cannot adjust the progression of a coil fork. They operate linearly.
3. Air forks are easier to adjust
To adjust the spring rate, you simply add or remove air from the fork. This is done with a special high-pressure pump called a shock pump. You simply attach the pump to a Schrader valve on the fork and pump air in or let air out. Shock pumps have a built-in gauge which allows you to easily set the exact pressure. The adjustment takes just a few seconds to make.
Most modern air forks have one valve to adjust both sides of the fork. Some older forks require that you pump each side separately. In this case, you’ll want to make sure both sides have the same pressure to ensure that the fork compresses evenly.
Because air forks are so easy to adjust, you can change your spring rate and sag before each ride or even mid-ride if you carry a shock pump with you. This may come in handy if you want to tackle a particularly gnarly trail. You could let a bit of air out to soften up the ride. If you want to mount some heavy gear or bikepacking bags on your bike, you might increase the pressure a bit.
It’s also easy to adjust the progression of an air fork. You simply check the starting pressure, let the air out, then unscrew the top cap to access the volume spacers. You can then add or remove spacers as needed. The spacers typically just screw or snap into place on the inside of the top cap. You then screw the cap back on, then pump the fork to your desired PSI, and you’re good to go. For more info on changing the volume spacers, check out this guide.
4. Air forks are lighter
On average, you’ll save around 300-500 grams (0.66-1.1 lbs) by choosing an air fork over a coil fork. Air forks tend to weigh around 1500-1900 grams (3.3-4.2 lbs). Most coil forks weigh over 2000 grams (4.4 lbs). For cycling, a pound is a pretty significant weight savings.
Air forks are lighter because the spring is provided by air, which weighs nothing. Coil forks, on the other hand, have heavy steel coil springs. The lighter weight at the front of the bike makes the steering feel faster and more responsive. It’s also easier to lift the front of the bike up and hop.
A lighter bike is also easier to accelerate and climb with. For example, an average-sized cyclist riding up a 15% grade for 2 miles at an output of 250 watts will reach the top about 10 seconds faster with an air fork than they would with a heavier coil fork. If you climb often or ride long distances, this may be significant.
5. Air forks provide better bottom-out resistance
This is possible thanks to the progressive spring rate that the air spring provides. As the fork travels through its range, it becomes exponentially harder to compress. Near the end of the range, it takes a huge amount of force to further compress the air inside. The total amount of force required to compress an air fork and bottom it out is greater than a coil fork. This is assuming that both are set for the same rider weight. This reduces the likelihood of the fork bottoming out during a big drop, hard hit, or after landing from a jump.
Air forks also allow you to easily adjust the bottom-out resistance by changing the spring rate or the progression. Increasing the pressure in the air chamber stiffens up the suspension, making it harder to compress and bottom out. Decreasing the volume in the air chamber by adding spacers makes the fork more progressive. This makes the suspension harder to compress earlier in the range, making it harder to bottom out.
This feature is important because bottoming out too hard or frequently can cause damage to your bike. For example, bottoming out particularly hard could bend a wheel or frame. You want to adjust your suspension so bottom outs are rare.
6. Air Forks are more versatile
The adjustability of air forks makes them much more versatile than coil forks. For example, you can easily adjust the spring rate to match the type of riding you plan to do for the day. If you plan to ride a rough trail with lots of drops and jumps, you can add some spacers to increase the progression to reduce the likelihood of bottoming out during landings. If you loan your bike to a lightweight friend, you can let some air out to reduce the spring rate to make the fork softer. Maybe you want to load your bike up with bikepacking bags and go camping. You can increase the PSI to make your fork stiffer so it can handle the extra weight.
To make these adjustments, all you need is a shock pump and a few minutes of time. You could optimize your suspension for every ride if you wanted. Being able to easily change the spring rate before a ride makes air forks much more versatile. You can use the same bike for multiple types of mountain biking. For example, you could easily use the same bike for trail riding, bikepacking, enduro, and cross country riding with some minor adjustments. To make the same adjustments to a coil fork, you would need to take the fork apart and swap out the coil springs.
Air forks operate very quietly as long as they are properly maintained. You won’t hear any clunks or creaks unless you bottom out, which is rare.
8. More fork and bike choices
If you walk into a bike shop, you’ll notice that most new mountain bikes come with air forks these days. There are more air forks on the market as well if you want to buy a new fork for your existing bike. You simply have more options to choose from if you decide to go with an air fork.
This is the case because air forks are more adjustable, easier to adjust, and more popular. It’s easier for bike shops to sell bikes with air forks because they can simply adjust the fork to fit any rider rather than having to carry a bunch of springs and swap them out. It’s easier to fit riders to bikes. Most mountain bikers seem to prefer air forks as well.
Lively ride characteristics
Due to the progressive spring rate, air forks offer a bit more lively ride. The bike wants to pop and bounce. This makes it easier to lift the bike off the ground. It also makes the bike feel a bit more supportive while landing. The lively ride characteristics make air forks a great choice for those who like to jump, hop, and ride rolling terrain.
Air Fork Cons
1. More frequent maintenance required
Air forks have more seals than coil forks. These extra seals are required to hold the pressurized air inside of the air spring. Because there are more seals, air forks are more likely to be affected by dirt, dust, and other contaminants than coil forks. The seals can get contaminated and the air or oil can begin leaking out, causing the fork suspension to stop working.
In addition, air forks create a bit more heat due to friction from the tight seals. While this heat doesn’t affect performance, it may speed up the degradation of the seals and fork oil. For these reasons, air forks require more frequent maintenance than coil forks.
You will need to service your air fork every 3-6 months, depending on how often you ride. Most manufacturers recommend that you perform a basic service every 25-50 riding hours. This involves cleaning and inspecting the stanchions and fork lowers and replacing the lower seals and dust wipers. You may need to top up the oil as well. You will have to do this basic service 1-3 times between full rebuilds.
Every 75-100 hours, you should have your forks fully rebuilt by a professional. For most riders, this will be around once per year. A full rebuild involves replacing all seals and oil and thoroughly cleaning all components and inspecting them for damage.
To compare, coil forks can usually go for longer intervals without maintenance. They can go 50-100 hours between services and up to 200 hours between rebuilds. If you neglect maintenance, performance will degrade. You can also cause unnecessary wear and tear. For more info on maintenance, check out this great guide.
2. Air forks are less sensitive to small bumps
Because they need to hold pressurized air inside, air forks have more seals than coil forks. Some of these seals need to fit tighter as well. The seals rubbing against moving parts creates friction in the system. As a result, air forks have more static friction or stiction than coil forks. Sufficient force is required to overcome the stiction for the fork to begin moving.
The amount of force required to overcome the stiction is called breakaway force. Air forks require more breakaway force than coil forks. This makes air forks less sensitive to small bumps. For example, riding over a small root may not create enough force to break the stiction on an air fork. That bump could be transmitted through the fork into your arms. That same small root may create enough force to break the stiction of a coil fork and be absorbed. The ride may feel a bit rougher when you use an air fork for this reason. In addition, air forks can’t react quite as fast when you hit a bump. The damping system also can’t work quite as well because it can’t respond as quickly to an impact.
There are a couple of ways to improve small bump sensitivity. You can reduce the spring rate. When you do this, the fork tends to blow through most of the travel then ramp up quickly at the end. You can also choose an air fork with negative springs to help overcome stiction and improve small bump sensitivity. This negative spring opposes the air spring to help reduce breakaway force. A good negative spring system can make air forks almost as sensitive to small as coil forks but not quite.
3. Air forks don’t offer as much traction
Because air forks can’t absorb some small bumps due to stiction, they don’t provide as much grip. The reason is that the front wheel can’t track the ground as consistently when it can’t absorb small bumps. The bike may bounce off of some roots, rocks, and bumps instead of absorbing them. Your tire can’t provide as much grip when it’s bouncing around.
The progressive spring rate can also make the fork feel a bit less responsive. As a result, you may not be able to corner quite as hard with an air fork on some surfaces. The front wheel can wash out more easily. Braking performance can suffer as well.
4. Less comfortable ride
Air forks feel a bit more lively than coil forks. Due to the progressive spring rate, the fork feels a bit more bouncy. Some riders enjoy this feel and others don’t. In addition, the poor small bump sensitivity of air forks can make the ride feel a bit rougher on some surfaces. For these reasons, air forks may not be ideal for those with back or joint pain. The ride is a little bumpier and less comfortable.
5. Air forks are slower
Because air forks don’t offer as much traction due to inferior bump sensitivity, you may not be able to corner or brake quite as hard without losing grip. In addition, the bouncier ride of air forks can make the bike a bit harder to control on very rough terrain. For example, if your bike is bouncing around under you violently, it’s hard to steer. As a result, you may maintain a slightly slower average speed with an air fork.
That said, the difference in performance between a modern air and coil fork is pretty minimal. It might slow you down by a second or two on a typical downhill run. Having said this, there are some situations where air forks allow you to ride faster. For example, air forks can be better for riding trails with lots of jumps, drops, and rollers because they provide more support. This extra support allows you to hit these obstacles faster and harder without having to slow down or risk bottoming out.
6. Air forks are less durable and reliable
Air forks have more parts that can wear out or fail. They usually don’t fail catastrophically but they can develop a leak if you don’t keep up on maintenance. For example, there are more seals inside that can get contaminated and begin leaking. The Schrader valve on top could leak or fail. You may have to add a bit of air before a ride. If you’re riding far away from civilization, it’s a good idea to carry a shock pump with you. Even when your fork is well maintained and in good condition, you may have to add some air every month or so.
Because maintenance intervals are shorter, it’s easier to neglect your fork and cause premature wear and tear. Having said this, modern air forks are incredibly reliable. They are highly unlikely to leave you stranded if you properly maintain them.
7. Air forks are more expensive to run
In general, air forks cost more than coil forks over the course of their lifetime. The initial price difference is pretty minimal. In fact, air forks often cost a couple of hundred dollars less than comparable coil forks. Where air forks become more expensive is in maintenance. Because air forks require more frequent maintenance, it might cost an extra $100 per year to run an air fork for the average rider.
An air fork usually requires a full rebuild every 8-12 months while a coil fork may only require a full rebuild once every 12-18 months. A full factory rebuild costs $150-$175. Between full rebuilds, forks need basic service on fork lowers. An air fork may need 2-3 basic services between full rebuilds while a coil fork may only need 1 basic service. A basic service costs $30-$50. You save some money by doing the basic service by yourself. You will have to buy some parts and tools.
Coil fork maintenance costs about the same but the intervals are longer. All of this additional maintenance adds up. You’ll spend more money maintaining an air fork in the long run. If you neglect maintenance, your air fork becomes even more expensive. For example, new stanchions could cost over $500 if your originals get scratched up due to lack of maintenance.
8. Brake dive can be a problem with air forks
Air forks tend to be softer at the beginning of the travel and through the mid-stroke. When you brake hard, the front of the bike can dip down far into the mid stroke. When you dip down so far, it can be hard to steer. Worst case, you could fly over the handlebars.
There are a few ways to solve the problem of brake dive. You can add some air to increase the spring rate. You can also increase the low speed compression damping if your fork offers that setting. The problem is that these adjustments can reduce small bump sensitivity. Good technique can also help reduce brake dive. When you have to brake hard, try to shift your bodyweight back as far as you can.
9. Some of the suspension range may be unusable
Because air forks are progressive, the force required to compress the springs increases throughout the range. Toward the end of the range, it takes an incredible amount of force to further compress the fork. This makes the final part of the suspension’s travel pretty much useless. The end of the travel will only be used in rare situations where the fork is taking a particularly large hit and bottoming out.
To make more of the suspension usable, you can lower the PSI to reduce the spring rate. When you do this, you’ll blow through most of your suspension when you hit a small bump. When you reach the end of the travel, the progression ramps up quickly. There may still be some unused travel. If you increase the spring rate, the suspension progression ramps up in the middle of the range. This leaves you with even less usable range and less sensitivity. The suspension can’t do its job as well when some of the suspension remains unused.
Coil Fork Pros
1. More sensitive to small bumps
Coil forks have fewer seals. The seals that exist can fit looser because the shock doesn’t need to be airtight. There is less friction in the system because there are fewer moving parts rubbing against one another. This means coil forks have less static friction or stiction to deal with. As a result, the breakaway force is lower. In other words, the impact force required to make the coil forks start moving is lower. This allows for greater small bump sensitivity.
Coil forks can absorb bumps that air forks wouldn’t even react to. Coil forks also react slightly faster when you hit a bump. Additionally, the sensitivity of coil forks allows the dampers to do their job better. All of this gives the bike a smoother and more supple ride feel.
2. Coil forks require less frequent maintenance
Most riders will have to perform maintenance on their coil fork every 6-9 months. To compare, air forks require maintenance every 3-6 months for the average rider.
The main reason coil forks require less frequent maintenance is that they have fewer seals. This makes the fork less sensitive to dirt, dust, and other contaminants causing wear or damage. Because there are fewer seals, coil forks also create less friction when they operate. This means coil forks don’t heat up as much. As a result, these components don’t degrade as quickly. The oil and seals can last a bit longer. For these reasons, coil forks have longer maintenance intervals than air forks.
When the time comes to service the forks, there are fewer parts to clean or replace. To keep your coil fork operating smoothly and efficiently, most manufacturers recommend that you have the fork rebuilt every 100-200 riding hours. That’s once every 12-18 months for most riders. This involves replacing all seals and oil and inspecting the dampers and springs. You should have the rebuild done by a professional.
Every 50-100 riding hours or once between full rebuilds, you should service the fork lowers. This involves replacing the foam rings, dust seals, and topping up the oil. After every ride, you should wipe down your forks to keep them clean. It is particularly important to keep the stanchions clean so they don’t get scratched.
3. Coil forks offer better traction
Coil forks are more sensitive to small bumps because they create less friction when they operate. This allows the front wheel to more consistently track the contours of the ground as you ride. The front tire stays planted on the ground instead of bouncing around.
The linear spring rate curve of the coils also makes the suspension feel a bit more responsive. This is particularly true while riding rough trails or rocky sections. These features help to improve traction.
The improved traction allows you to corner harder without having to worry as much about your wheel washing out. You can brake a bit harder as well. The extra traction makes the bike feel more stable and planted. This inspires confidence and allows you to ride faster. Coil forks are great for riding trails with loose surfaces like gravel or sand as well as trails with lots of tight corners.
4. More comfortable ride
Coil forks soak up small bumps that air forks might not react to. You’ll also feel less chatter and fewer vibrations while riding on a rough surface. This is possible thanks to the superior bump sensitivity. This makes the ride feel smoother and more comfortable. Your hands and arms won’t fatigue as quickly because there are fewer vibrations.
The linear spring rate of coil forks also makes the bike feel more planted to the ground. After a hard hit, the fork travels in a more controlled manner. This is possible because there is less friction in the system. The damping system can do a better job. Coil forks feel a bit less bouncy, as a result. Those with joint pain or back pain will appreciate the smoother and more comfortable ride quality of coil forks.
5. You can ride faster with a coil fork
Most riders are slightly faster on a coil fork than an air fork. The main reason is the superior bump sensitivity. This allows the front wheel to better track the contours of the ground, which improves traction. This, in turn, allows for better cornering and braking. With a coil fork, you can corner and brake harder without your front wheel washing out.
Coil forks also make the ride a bit smoother. You can control your bike better when it’s stable and not bouncing around under you like a bucking bronco. You may be able to steer slightly more accurately with an air fork.
These are all marginal gains but they can add up. Many competitive riders prefer coil forks for these reasons. You may be able to cut 1-2 seconds from an average downhill run by switching from an air fork to a coil fork. One exception may be trails with lots of drops and jumps. The linear spring rate means coils sometimes don’t offer enough support. You may have to hit some obstacles slower or risk bottoming out.
6. More of the suspension range is usable
The linear spring rate of coil forks allows you to utilize the entire suspension range. This is possible because the force required to compress the suspension remains constant throughout the range. It doesn’t ramp up. When you can use the entire range, the suspension can do a better job of absorbing large bumps.
7. Better braking performance
The linear spring rate of coil forks allows for better mid-stroke support. When your brake hard, the bike doesn’t want to dive quite so much. This allows you to brake harder. You also don’t have to worry as much about going over the handlebars during heavy braking.
As an added benefit, you can use less compression dampening. To compare, air forks can feel too very soft at the beginning and mid-stroke causing the bike to dive during heavy braking.
8. Coil forks are more durable, reliable, and long-lasting
Coil forks have fewer moving parts that can fail. For example, there are fewer seals inside and there is no air valve. This means there are fewer parts that can get contaminated. There is no air chamber. You don’t have to worry about air leaks. The coils always work.
Coil forks also deal with neglect better than air forks. If you don’t do your maintenance as often as you should, you can usually get away with it with a coil fork. They can take a beating without failing. If you’re planning to ride far into the backwoods, a coil fork might be a slightly safer and more reliable choice. It’s less likely to leave you stranded.
9. Coil forks are cheaper
Coil forks are slightly more expensive than air forks initially. They generally cost less over their lifetime because they require less frequent maintenance. For example, if you keep your bike for 10 years, you might only need to service your coil fork 20 times. You might need to service an air fork 30 times during that same 10 year period. The longer maintenance interval might save you $100 per year over the lifetime of the fork.
A full fork service costs around $150. A basic service costs around $50. The less often you have to perform maintenance, the more money you’ll save. Of course, you never want to neglect maintenance or you’ll end up spending more replacing your entire fork sooner if it wears out prematurely.
One extra expense you might need to add in for coil forks is buying different coils. If you want to change the spring rate of your fork, you’ll need to buy a new set. A set of coils usually costs $30-$100 depending on the material. Titanium coils cost more than steel. If you’re happy with the way your forks are set up, you’ll never have to worry about replacing the coils. They last pretty much forever.
Coil Fork Cons
1. Coil forks are less adjustable
In order to change the spring rate of your coil fork, you must replace the coils with firmer or softer models. Coils are typically sold in 5 or 10 pound per inch increments. There may only be 3 or 4 different coil options that are compatible with your fork. Your ideal spring rate coil could sit between two sizes. You can not dial in your exact desired spring rate like you can with an air fork.
If you buy a new mountain bike with a coil fork, you might have to replace the coils right off the bat. Most mountain bikes are sold with coils that are the ideal stiffness for average-weight riders (around 160-180 lbs.) If you’re a heavy or lightweight rider, you’ll probably have to replace the coils to achieve the proper spring rate. You might want to take this into consideration when buying a new bike.
Also, you can not adjust the progression of coil forks. They operate linearly. You can fine-tune the sag by adjusting the preload. Most coil forks allow you to adjust the damping. Sometimes you can only adjust the rebound damping. Higher-end models allow you to adjust the compression damping as well.
2. Coil forks are harder to adjust
In order to change the spring rate of a coil fork, you must swap out the coils. This involves taking the fork apart. It’s a pretty big job that requires some tools and mechanical know-how. This means you can’t easily adjust the spring rate to different trail conditions or rider weights.
If you’re riding a difficult trail or if you want to mount bikepacking bags, you’ll have to use your current setup or take the time to swap out the coils. If you gain or lose weight, you’ll have to buy new coils and swap them out. You’re not going to want to adjust your spring rate before every ride. You can’t easily make adjustments by the side of the trail like you can with an air fork. You can easily adjust the preload and sag of your coil fork by turning a dial.
3. Coil forks do not have progression adjustment
Metal coil springs operate linearly. In other words, the force required to compress the coil increases constantly throughout the range of travel. There are no progression adjustments to make. It is possible to make progressive coils by using two separate springs of different stiffnesses. When the softer spring bottoms out, the firmer spring would effectively increase the spring rate. These types of progressive coils are available for motorcycles but I am not aware of any commercially available progressive fork coil options for mountain bikes.
4. Coil forks are less resistant to bottom outs
Bottom outs happen when your coil fully compresses. Coil forks bottom out more easily because they have a linear spring rate. The force required to compress the suspension increases constantly throughout the range of travel. It doesn’t ramp up. For this reason, the total amount of force required to fully compress a coil fork is less than the total amount of force required to fully compress an air fork. In other words, it’s easier to bottom out a coil fork during a hard hit or when landing from a jump or large drop. This is assuming both forks are set up for the same rider weight. You’ll know you bottomed out when you hear a thud and your fork suspension stops moving.
Bottoming out isn’t the end of the world. Most forks have bumpers built in to prevent damage during a hard bottom out. This is a rubber ring that prevents metal-on-metal contact when the spring fully compresses. If you’re bottoming out too hard or more than once per ride, your fork coils probably aren’t stiff enough for your body weight and the type of riding you do. In this case, you should replace your coils with stiffer models to increase the spring rate. Hard or frequent bottom outs can wear out the bottom out protection and eventually, you can damage your fork. A particularly hard bottom out could even damage your wheel or frame.
5. Coil forks are heavier
On average, a coil fork weighs 300-500 grams (around 10-18 oz) more than a comparable air fork. A lightweight coil fork weighs around 2100 grams (4.6 lbs). while a lightweight air fork weighs around 1600 grams (3.5 lbs).
Coil forks weigh more because they use heavy metal coils to provide resistance while air forks use weightless air to provide resistance. The weight difference also depends on the spring rate of the coils. Typically, coils with a higher spring rate weigh more because thicker gauge metal is required to make the stiffer coil. This adds weight.
The heavier weight of coil forks can make the steering feel a bit slower and less responsive. It’s also harder to pop the front wheel off the ground. The added weight also makes the bike a bit harder to climb with and accelerate. It takes more energy to move more mass around. You can reduce the weight of a coil fork by installing lighter springs. For example, titanium coils are quite a bit lighter than steel. Of course, they are more expensive as well.
6. Coil forks are less versatile
Because they are so much harder to adjust, you can’t easily optimize your coil fork for every ride. You also can’t easily adjust the fork for different types of mountain biking. This makes bikes with coil forks a bit less versatile.
For example, maybe you want to use the same bike for trail riding and bikepacking. You would want softer coils for trail riding and firmer coils to support the extra weight of your gear while bikepacking. You would have to buy different sets of coils with different spring rates, take the fork apart, and swap them out in order to optimize the bike for different types of riding. Most riders don’t want to bother with this regularly. It’s not practical.
For this reason, you can’t as easily use the same bike for multiple types of riding. You for sure wouldn’t want to go through this for every ride. With an air fork, you can easily adjust the spring rate or progression with a shock pump. You could even make adjustments mid-ride.
7. Flat ride characteristics
Coil forks tend to hold the bike on the ground. They offer a smooth and plush ride. For some riders, this makes the ride feel a bit boring and flat. The bike doesn’t want to pop or hop. When landing from a drop or jump, coil forks can lack support. Some riders like the flat and stable ride characteristics. Others prefer the more lively and bouncy ride characteristics of air forks.
8. Coil forks can make some noise
It is possible for the metal coil to hit the inside wall of the fork body during compression. When this happens, you’ll hear a clunk sound. If the spring doesn’t have enough preload, it can hit the base of the fork and make some noise. Worn-out seals can cause the fork to make some noise as well. If your coil fork is properly maintained and adjusted, it should operate quietly.
9. Fewer fork and bike choices
If you walk into a bike shop, you’ll notice that very few bikes come with coil forks these days. If you go shopping for a new coil fork to install on your existing bike, you’ll notice that options are somewhat limited. Most forks have air springs. This is slowly changing. Riders are noticing the smoother ride, sensitivity, and superior traction. Some are switching back to coil forks.
A Note About Fork Damping Systems
Both air and coil forks have damping systems built-in. These systems prevent the spring from oscillating after compressing or rebounding. This smooths out the ride so the bike doesn’t bounce up and down like a pogo stick after hitting an obstacle. Air and coil forks use the same damping technology.
The damper works by forcing oil from one chamber to another through a small hole or series of holes. These holes are called ports. As the fork compresses, oil flows one way. As it rebounds, oil flows the other way. Forks have two damping circuits. One for compression damping and one for rebound damping.
The hole size controls the rate that the oil can flow through. Oil flows faster through a larger hole and slower through a smaller hole. This determines how fast the fork can compress and rebound. Smaller holes slow down the movement of the fork and larger holes allow it to compress or rebound faster.
Most forks allow you to adjust the damping for the terrain you plan to ride as well as your weight. These adjustments are called compression damping and rebound damping. When you adjust your fork’s damping, you’re changing the size of the ports to allow fluid to flow through faster or slower. This changes the speed that oil can flow through the dampers, which changes the speed that the fork can compress and rebound.
The amount of adjustment that is possible depends on the fork. Some models only allow you to adjust the rebound damping. Some forks allow you to adjust compression damping as well. High-end forks allow you to set both high and low speed compression damping as well as beginning and end stroke rebound damping. Low-end forks may not offer any damping adjustment at all.
Most air and coil forks also offer a lockout function. This is a mechanism that locks the fork in it’s resting position so it can’t compress or rebound. This is useful while riding on road or climbing. The lockout prevents the fork from compressing unnecessarily and and wasting energy. A lockout fork can increase efficiency. There is usually a small lever on top of the stanchion that allows you to easily switch the lock out on and off. Some forks also allow you to mount a lever on the handlebars to control lockout.
A Note About Coil and Air Fork Ride Characteristics
Coil and air forks each give the bike a slightly different feel when you ride. They have their own unique characteristics. Neither is necessarily better than the other. The choice mostly comes down to personal preference and the type of mountain biking you do.
Coil forks tend to feel a bit more planted to the ground. The wheel doesn’t bounce around quite so much. This is possible thanks to the small bump sensitivity of coil forks. The ride feels a bit more stable and flat. Many riders find that this inspires confidence. Others may find that the ride feels a bit boring.
Air forks, on the other hand, have much more lively and playful ride characteristics. The progressive spring rate of the air fork makes the bike want to pop and bounce. This makes it easier to jump and hop your bike. Some riders prefer the feel of a livelier fork. For others, the ride is too bouncy.
The spring rate curve of the fork also plays a major role in the way the bike handles. The spring rate curve is the way the spring rate changes throughout the fork’s range of travel. Remember, coil forks are mostly linear. The spring rate increases in a constant manner throughout the travel. Air forks, on the other hand, are more progressive. The spring rate increases at an increasing rate throughout the range of travel.
Coil forks tend to feel more supported in the mid-stroke. By that, I mean the bike doesn’t dive so far during a large hit or landing. This also makes the bike more resistant to brake dive. When you brake hard, the fork doesn’t compress too much. The drawback is that coil forks don’t ramp up at the end of the travel so bottom outs are more likely.
Air forks tend to feel very soft in the beginning of the travel. When you hit a decent sized bump, you might blow through half of your fork’s range before the progression ramps up. This behavior is known as wallow. The bike can wallow during heavy braking as well. The solution to this is to increase compression dampening. The drawback is that this will reduce small bump sensitivity. As you can see, the are some compromises to make when considering the ride characteristics of your fork.
Heat Buildup in Coil and Air Forks
When a fork continuously compresses and rebounds, friction in the system causes heat to build up. This friction comes from both the damper working and seals rubbing against moving parts inside of the fork. Generally, forks don’t heat up enough to affect performance.
Rear shocks, on the other hand, can overheat and the performance can fade. This happens most commonly on air shocks. The pressurized air can also heat up and expand, increasing the spring rate slightly. The seals can also expand slightly. The heat may cause the oil viscosity to decrease, causing the ride to become a bit rougher. Luckily, this isn’t a worry with coil or air forks. For more info on shocks, check out my coil vs air shock guide.
There are a number of reasons that forks don’t overheat. First, the spring rate is lower so less energy goes into the damper. This is possible because forks have more travel than rear shocks. Forks also have more volume than rear shocks. Both the air and oil volume are greater. This creates a larger area where heat can dissipate. On a long downhill run, there may be some heat buildup in an air fork but it’s not enough to worry about. Air forks do not suffer from heat fade as air shocks can.
Suspension Fork Travel
Fork travel is the distance that your fork can compress. The amount of travel that you need depends on the type of mountain biking that you do. Ordered from least fork travel to most fork travel, the different types of mountain bikes include:
- Cross country mountain bikes have anywhere from 80-100mm of fork travel. This is the least amount of travel that you’ll find on a modern mountain bike. These bikes are designed for riding bike paths, gravel roads, and some easy single track. They climb well and ride efficiently.
- Trail bikes and most hardtail mountain bikes tend to come with a fork with around 120-140mm of fork travel. These bikes are designed for all-around mountain biking. They can climb and descend well and handle a variety of obstacles well. This is also enough travel to handle some smaller jumps and drops. This is a nice mid-range between cross country and downhill mountain bikes. If you’re just getting into mountain biking, this is a good place to start.
- All-mountain bikes usually have 130-160mm of fork travel. These bikes are designed to handle pretty much any type of mountain biking. They can handle downhill runs, single track, bike paths, gravel, and jumps and drops. They have enough travel to handle it all. In addition, they are also designed to be light and efficient enough to handle some long-distance riding.
- Enduro mountain bikes typically have 150-180mm of fork travel. This large travel allows enduro racers to quickly descend hills. Enduro bikes are still light enough to ascend hills.
- Downhill mountain bikes tend to have around 180-200mm of fork travel. These bikes are designed to handle rough downhill trails quickly. They can also handle large drops and jumps. Pedaling and climbing efficiency is less important.
Generally, for shorter travel forks (80-140mm) either air or coil models work fine. For longer travel forks (140+mm), coil forks are preferable. This is mostly due to the extra mid travel support and smoothness that the linear spring rate offers. Of course, either air or coil forks can work fine for any type of mountain biking. Most professionals still use air forks these days.
Another Option: Air/Coil Hybrid Forks
There are a couple of companies that offer hybrid fork springs. These offer most of the benefits of coil springs with very few drawbacks. They basically coil forks with an air spring that activates toward the end of the travel. The idea is that the air spring provides some progression to reduce the likelihood of bottoming out. Performance wise, hybrid air/coil forks are ideal.
The drawback is that air/coil forks add weight and complexity. They are heavier than air or coil springs. They also have all of the seals of an air spring fork. The cost is higher too. Options are also more limited.
For more info, you can read about this hybrid coil/air spring system.
Who Should Use an Air Fork?
Air forks are ideal for those who ride varied terrain, such as cross country as well as trail riders. They are also a good choice for those who jump their bike. Those who like to use their bike for multiple types of riding can also benefit from the adjustability of air forks. The easy and extensive adjustability allows you to set your suspension up for riding different trail conditions and carrying different amounts of weight. You can optimize an air fork for pretty much any situation.
Some riders also enjoy the progressive spring rate of air forks. This is a nice feature for those who like to jump their bike, ride off drops, and ride rolling terrain. Air forks reduce the likelihood of bottoming out and provide good support during big hits and hard landings. Those who prefer bouncier and more lively ride will enjoy the ride characteristics of air forks. If you care about the weight of your bike, you’ll also appreciate the lighter weight of air forks. You can save a pound or so by going with an air fork over a coil fork. Air forks are a bit easier to buy as well because there are more options on the market.
Who Should Use a Coil Fork?
Coil forks are ideal for those who ride downhill, enduro, rough trails, or just like to ride fast. The superior small bump sensitivity creates a more comfortable ride on rough trails. As an added benefit, the bump sensitivity increases traction by keeping the front wheel planted on the ground. This, in turn, allows you to corner a bit faster.
Coil forks also make the bike feel a bit more stable and planted due to the linear spring rate. This inspires confidence. Coil forks are also great for those who don’t like doing maintenance often. Most riders will only have to service their coil fork once per year. That’s half as often as an air fork.
Final Thoughts About Coil Forks Vs Air Forks
This choice comes down to the type of riding you do, how much adjustability you require, and your personal preference. For general trail riding or cross country riding, air forks are generally the better option. The ability to easily adjust the fork for different types of terrain is a nice feature to have. It makes your bike much more versatile.
For those who ride downhill or ride their bike hard and need a lot of travel, a coil fork is probably the better option. The linear spring rate and minimal stiction give the bike excellent performance. The sensitivity, smoothness, and extra traction make coil forks a joy to use. The performance inspires confidence as well.
Whichever type of fork you decide to go with, I hope this guide has helped you in making your decision.
If you’re trying to decide which type of rear shock to go with, check out my guide: Coil Shocks Vs Air Shocks.
Where do you stand on the coil fork vs air fork debate? Share your experience and tips in the comments below!
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Thursday 16th of June 2022
Good article, but I noted two errors.
Firstly, air is light, but it doesn’t weigh “nothing”, especially when compressed. That said, I realize the air volume in a fork will not weigh much.
Secondly, forks that have only one valve usually have one air chamber on one side, that is, the air is not somehow passed to the other fork tube, contrary to what the article implies. Most often, the damping system is on the other side.
Monday 20th of June 2022
Good info, thanks.