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. 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. I’ll cover handling, adjustability, maintenance requirements, sensitivity, weight, ride comfort, price, versatility, ride feel, and more. I’ll also outline the main differences between coil and air forks. This guide focuses on forks but much of the info applies to rear shocks as well.
Over the years, I’ve ridden both coil and air forks extensively. My first mountain bike had a coil fork. Later, I switched to air forks. Recently, I switched back. In this guide, I’ll share my personal experience.
Key Takeaways
Air forks offer more adjustment options. They are also easier to adjust. This makes them more versatile. In addition, air forks are lighter, provide better bottom-out resistance, lively performance, and more frame options.
Coil forks are more sensitive to small bumps and have more useable range. This gives you better traction and better braking performance and allows you to ride faster. They are also cheaper, more comfortable, more durable, lower maintenance, and longer lasting.
Air forks are ideal for cross country and trail riders, those who value adjustability, those who ride varied terrain, and those who want to reduce the weight of their bike.
Coil forks are better for downhill, enduro, and freeride cyclists, those on a budget, those who require durability, those who ride aggressively on rugged terrain, and those looking for comfort.
Air Forks
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 air 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 shock requires a special high-pressure pump called a shock pump. You simply attach the pump to a valve on the fork and add or remove air. You also adjust the fork preload and sag by changing the pressure. 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.
Coil Forks
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 for a stiffer fork 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 shock. 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. Coil forks are sometimes referred to as spring forks.
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 air pressure inside of the fork’s air chamber. Increasing the air 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 air shock with a shock pump and gauge.
This same adjustment sets the fork’s sag. This adjustment allows you to easily optimize the fork for different terrain, the rider’s weight, and the 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 have two air valves. 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 bicycle 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