Coil vs air shocks: A buying guide for MTB suspension

You may have heard riders debating air vs coil suspension? In the gravity-fed parts of mountain biking, it is a debate going back almost as far as the first suspension bikes. If you are not sure what they mean by this, then this guide should cut through all the jargon and complex technical language to help you understand what air and coil suspension are, the drawbacks and advantages of each, and which might be right for you.

Coil suspension was the original type of mountain bike suspension. Coil springs were a well-known technology from motorcycles and are simple and reliable. This made it relatively easy to put a spring inside a tube, or mount it onto a frame. For the formative years of the sport, all mountain bike suspension was coil-sprung. The downside of coil-sprung suspension is that big, metal springs tend to be quite heavy, and when you are using legs to get to the top of the hill, rather than a petrol-fuelled motor, the extra weight makes it harder work.

In the early years of mountain biking, the problem with air springs was the sealing: Keeping the air inside the shock. Good sealing requires a delicate balance of tightness. If your seals are too loose, then all the air gets out, and your suspension stops working. Make your seals too tight, and you may be able to keep the air inside, but the friction those seals create will make it hard for the suspension to move through its stroke, which won’t feel good out on the trail. Over the years, mountain bike suspension companies poured huge amounts of time and money into the problem, and today, air suspension is so good that most mountain bikes are sold with it rather than coils.

The simplest way to think about mountain bike suspension is as attaching springs to your bike, one in the fork and one at the rear for full-suspension bikes. This is the mechanical part of the suspension. If you have a small spring to play with at home, you might notice that it compresses very easily, then fires back to full length very quickly. Having your suspension spring back so quickly would be quite scary out on the trail. This is why good suspension adds a second part to the equation, an oil-filled damping cartridge that helps control the speed at which the spring compresses and snaps back, or rebounds as we call it. This is called the hydraulics. By using a combination of the mechanical spring and the hydraulic damper, suspension engineers can fine-tune how your suspension compresses and rebounds.

There are two types of springs that are commonly used on mountain bikes - air and coil. Coils are the most instantly recognisable, as they look like a big spring. They are large, metal springs that help provide resistance to the suspension. Air springs are essentially sealed tubes that use the resistance as you compress the air to create support for the rider’s weight, rider input and impacts on the trail.

Air and coil springs behave a little differently. Coil springs are described as being linear, which means that the amount of force you need to compress the spring remains the same all the way through the stroke. This creates a very consistent feeling. Air springs need an increasing amount of force to compress the spring as you go into the stroke. This is because the air in the chamber is sealed in and being squeezed into a smaller and smaller space as you compress it, which means you need more and more force as the air is squeezed in. This is described as being progressive.  

There are a few reasons why a rider may choose a coil or an air spring:

Coil springs are a little more sensitive and comfortable than air springs; riders would describe them as feeling plush. This is why riders looking for maximum damping performance might choose a coil spring, and why our World Cup downhill team opted for coil shocks on our Sender downhill race bike. In the past, the performance difference between air and coil suspension was much greater and modern air shocks are very sensitive and comfortable. Today, only the most demanding riders are likely to feel a big difference.

The difference between a progressive and a linear shock is one of the big reasons to switch between air and coil suspension. Things get a little more involved here because, in choosing a shock for your bike, you need to consider the kinematic or suspension design of your bike. Having some degree of progression in the kinematic is very important, but this needs to be balanced. If the bike is too linear, you would use all your suspension travel too easily, and if it is too progressive, it can become very harsh and unforgiving. This means that you need a shock whose progression matches the kinematic of your frame to maintain this balance.

With the natural progression in an air spring, many bikes that are designed for air springs tend to have a less progressive kinematic to compensate for this. This often means that they are too linear to work well with a coil spring.

With a big, metal spring around it, there is no getting away from the fact that a coil spring is going to be heavier than an air spring. This is why most weight-conscious riders opt for air springs; you would struggle to find a cross-country racer running a coil spring.

In theory, there is little difference here. Where you may find a difference is that some coil shocks do not have lockouts, which means they cannot be stiffened up for climbing.

It is much easier to set up an air shock than a coil-sprung one. With an air shock, you simply need a shock pump (which all our bikes are shipped with) to inflate and deflate it. This means that they can be set up to suit different riders and riding styles very simply. For a coil, you would need to purchase a new spring for a new setup. Springs are rated in pounds, which refers to the amount of force required to compress the spring, and you should be able to get stiffer or lighter springs compared to the one you currently have to make the suspension harder or softer.

To change a spring, you will need to remove the coil, which means either opening the fork or removing the shock from the bike and replacing it. This is part of the reason why we equip most of our mountain bikes with air shocks, so that riders of all weights can get out and ride from day one, while a rider who is outside the recommended weight range would need to buy a new spring first to get the most out of their bike.

One area where air shocks can fall a little behind coil shocks is on long descents. As your suspension moves, it creates small amounts of friction. In an air shock, this friction causes the air to heat up and expand, making the shock stiffer and less reactive. The metal of a coil spring is not affected by heat in the same way, so it will offer the same performance all the way down the mountain.

The terrain you ride on can play a big part in deciding whether a coil or air spring is better for you.

This is where coil shocks shine, with the extra sensitivity and consistency they can offer an edge over air springs.

If the trails you ride tend to be smoother, the extra progression of an air spring can be an advantage. It will give the bike a bit more pop, allowing you to create speed along the trail.

This depends on the kinematic of your frame. If you have a less progressive frame, then it will be better to use a more progressive air shock to prevent harsh bottom outs when you land.

If climbing is your main focus, we would recommend an air shock. While the extra traction of a coil shock would help, the weight penalty of the metal spring is a deal-breaker for most avid climbers.

We do not make a mountain bike that comes with coil-sprung front suspension. Even at the highest levels of downhill racing, it is accepted that an air-sprung fork is the best choice. Some budget bikes may have come with a coil fork in the past, but today, even our entry-level Grand Canyon models have an air fork.

Because of the difference in ease of setup, most of our mountain bikes come with air rear suspension as we think they make the bikes much easier to live with for most people. That said, we see that in the gravity-fed segments of mountain biking, we think that these riders will be happy to live with a coil shock. This is why our Sender downhill bike and some of the Torque and Torque:ON e-MTB models come with coil shocks.

You can fit a coil shock on most of our current models, yes. The outliers are our Lux World Cup and Lux Trail ranges. Aside from the fact that we cannot imagine a cross-country rider fitting a coil shock, there simply is not enough clearance in the frame for a coil shock. After that, most of our mountain bikes can accept a coil shock and have kinematics that would work well with a coil shock. For instance, our gravity-biased trail bike, the Spectral, would work really well with a coil shock.

The one outlier here is the Neuron, which, although it can fit a coil shock, has a very linear kinematic that may make it hard to get a good setting. It also has what is called a yoke-driven suspension design; the shock is attached to the frame by a small yoke. This kind of design can put more stress on the main shaft of the shock, so you need to make sure you choose a shock built for this kind of suspension design and not all coil shocks are.

Sometimes, a simple pros and cons list is the best way to make a tough decision:

It may seem counterintuitive to include linear and progressive performance as both pros and cons, but whether these are a benefit to you will come down to your bike, your suspension preferences and your riding style.

The bottom line of air vs coil suspension comes down to how you prioritise convenience vs outright downhill performance. Do the small differences justify the extra complication of living with a coil shock for you? We think that for most riders, especially those new to the sport, the simplicity of living with an air shock is the best way to go. However, for some riders, there is something about the feel of a coil shock that can’t be beaten. At the end of the day, providing the shock you choose is well-matched to your frame, there is no right or wrong answer - just what you enjoy the most.

If you are new to the sport and would like to dive deeper into the differences between various styles of riding and mountain bikes, we have created a series of buyer’s guides to help you. If you would rather skip the technical details and be matched to a bike, our bike finder tool will take you through a series of simple questions that will match you to a bike that suits your preferences and where you ride.

Whether you choose air or coil for your suspension, we can’t wait to see you out there shredding the trails.