Air vs. Coil Shocks

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To help you understand the benefits of each and what's right for you, we break down how the shocks differ in four key categories.

You might not know it from browsing most brands’ offerings, but there are two styles of shocks for mountain bikes. The air shock is, by far, more popular and you will find on most mountain bikes.

As the name describes, this shock's spring is compressed air. The other, and less popular shock is a coil-spring (also called coil-over) shock. And as its name makes clear, it employs a wound metal spring.

The coil-over shock is more typical of downhill bikes, but it is gaining in popularity among enduro and trail riders. And though the spring material is different, air- and coil-spring shocks work the same. But there are pros and cons to each.

Choosing the right one, however, is not always obvious; even some of the bike and suspension designers we talked with admitted to being surprised by the results of their testing. To help you understand the benefits of each, and which may be the right option for you, we broke down how the shocks differ in four key categories: performance, weight, tunability, and serviceability.

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If evaluated on performance only, a coil shock wins more than 9o percent of the time. That's because an air-spring shock requires tight seals to capture pressurized air. A coil, however, operates without seals because it doesn't have to hold air under high pressure. Fewer seals means less friction, which makes the shock more sensitive. It can react faster to impacts and terrain and feels smoother and more supple.

This is important because when the spring (coil or air) successfully does its job, the damper—the hydraulic system that controls the rate at which the spring compresses and rebounds—can effectively do its job.

"As the reaction time to compression and rebound forces improves, [coil-over shocks] are able to follow the contours of the trail more closely, providing better traction, bump absorption, and braking," says Noah Sears, MRP's vice president of business development. Another downside of air shocks: The friction created by their seals can overheat oil in the damper, especially on long descents that exceed 20 minutes, and that can "cause things to loosen up a bit," says Allan Cooke, Specialized's senior mountain bike marketing specialist.

That's often called fade, and it causes the shock to become bouncier and less controlled. And it's not just the damper that's affected by heat. Extreme heat can also alter the air spring's performance in undesirable ways.

Here's an easy way to tell if you’re overheating your air shock: At the end of a long descent, (carefully) touch the shock body. If it's very hot, you might be a candidate for a coil-over shock. For the same reasons, a coil shock may be better in hot environments.

The Bomber uses a monotube design—a simpler, cheaper system with fewer external-adjustment options and less range. But when tuned properly, it provides a great ride.

A remote lockout lets the rider switch between modes on the fly. Shreddy riders who harbor an inner XC geek, this is for you.

This USA-made shock has two separate valves, each of which can be independently tuned to a desired compression feel. A lever lets the rider toggle between them on the fly.

The IL has no external reservoir: This is a lighter and smaller design, but potentially can't manage heat as well as a piggyback shock. Still, it offers four-way adjustment and a climb switch.

Coil shocks are much heavier. Heavier equates to slower bike speeds, especially when climbing.

An example: A RockShox Deluxe Ultimate+ air shock for an Evil Following weighs 341 grams; a Push ElevenSix coil-spring shock for the same bike weighs 789 grams. That is a difference of 448 grams (a pound). Based on a 165-pound rider putting out a steady 250 watts on a 2-mile climb with a 15 percent grade, that extra pound adds 10 seconds to the rider's climbing time.

A coil has a linear spring rate, meaning it becomes stiffer at a constant rate as it's compressed. An air spring is progressive: When it compresses, its stiffness increases exponentially.

Dialing in a coil shock for a rider's weight requires a handful of different rate coil springs, plus at least partially (sometimes completely) removing the shock from the bike. And with a coil-over shock, end-of-travel progression typically is not adjustable and dictated by the bike's leverage ratio.

Meanwhile, an air spring is easier to set up because all you need is a shock pump to make it stiffer or softer. And it's easier to fine tune because you can change its progression by adding or removing and plastic volume spacers to the air can. With an air shock, you can easily alter the behavior of your rig for a day in the bike park, and just as easily change it back to your everyday trail riding tune.

If you prefer a more playful setup, you are more likely to get that from an air shock. "Friction may actually aid in the poppy, playful, supported feel of an air shock," says Ryan Thornberry, Yeti's product manager.

That added support might also make the bike faster in some situations, says Pivot's president, Chris Cocalis. "We were originally planning on running a coil on the new Phoenix 29 [downhill race bike], but in testing with Fox, the times with the air shock were just faster, and it is lighter and more tunable. Air is better at holding the bike up and carrying more speed down the back sides of jumps, smooth rollers, and larger bumps."

So while it's not always clear which shock type makes a bike faster, it's inarguable that nothing feels as buttery as the ride of a coil-over shock. There's more traction in the situations where you need it, and the bike feels smoother, rides quieter, and sticks to the trail better. If you like sensitivity, a plush ride, and that feeling of being planted, a coil-over shock is probably more your speed.

Coil-over shocks require less maintenance. For one, they’re more durable. That added heat on air shocks mentioned earlier accelerates wear on an air shock's internals. As MRP's Sears points out, [air shocks] require more work to keep them performing at their best. "The shortcoming of air springs is amplified as time from service increases and lubrication diminishes—and, thus, coil wins on consistency, too."

All of this begs the question: If a coil-over shock has so much going for it, why do most bikes come with an air shock?

The biggest reason: They make life easier for manufacturers and dealers by simplifying bike assembly and setup. An air spring is almost infinitely adjustable. Tuning one for different rider weights is as simple as adding or subtracting air with a shock pump. A coil-over requires removing the shock to change out the spring for one that is softer or firmer. "Selling a bike with a coil shock requires carrying additional spring inventory for each weight range," says Kevin Walsh, CEO of Evil Bikes. Plus, coil springs come in only a few rates with somewhat large jumps between each.

An important note: Be be careful about pairing a coil shock with a rear suspension system that uses a clevis (AKA: yoke). This mounting style amplifies the side loads on the shock, increasing wear. Inherent in an air shock's design is increased shock body support and stiffness because of the larger diameter shaft and air sealing system. Without this added support, a coil shock bears the increased side load from the clevis mount almost entirely on its damper shaft [Jump to 8:54 in the embedded video].

Air-shock makers—most notably Fox and RockShox—have drastically improved the performance of air-sprung suspension, primarily by reducing friction. Coil-over shocks still have less friction and run cooler (and always will), but the gap is narrowing, and modern air shocks are more sensitive and consistent than they’ve ever been.

That means air versus coil conversation is much like 27.5- versus 29-inch wheels or flat- versus clipless- pedals. It's not about one being better than the other; it's about rider preferences.

Air shocks are lighter, easier to set up, and easier to tune. Their ride is crisper, poppier, and feels more efficient. Coil shocks are more durable and require less maintenance. Their ride is plusher, more sensitive, and can be more consistent on long and demanding descents.

If you’ve come to the conclusion that you’re best served by an air shock, you’re in luck: Most bikes come with, and are optimized for, air shocks.

If you feel the call of the coil, and are not in the market for a new bike, you’re choosing a tougher road. There are fewer bikes that are truly coil-over compatible. That's because most bikes are designed to work with an air shock. Engineers use the suspension linkages to create a leverage rate on the shock that's optimized for an air spring's more progressive nature—install a coil-spring shock on one of these bikes and you’ll use too much travel too easily, reducing the effectiveness of the suspension.

But with some research, you can find bikes with a progressive-enough leverage ratio—the amount of movement at the rear wheel relative to the amount on the shock shaft—for a coil-over shock. Core mountain bike brands like Yeti, Transition, Pivot, Evil, Guerrilla Gravity, and Santa Cruz offer coil-friendly bikes. The aftermarket is your friend, too: Cascade Components offers replacement links that can make some bikes that (in stock form) are not coil friendly progressive enough to work with a coil-over shock.

The air-spring shock may rule the market for its lighter weight, ease of setup, and infinite adjustability, but that doesn't mean a coil-over is inferior. For many riders, it may be the better-performing, more reliable, and more enjoyable shock to ride.

A gear editor for his entire career, Matt's journey to becoming a leading cycling tech journalist started in 1995, and he's been at it ever since; likely riding more cycling equipment than anyone on the planet along the way. Previous to his time with Bicycling, Matt worked in bike shops as a service manager, mechanic, and sales person. Based in Durango, Colorado, he enjoys riding and testing any and all kinds of bikes, so you’re just as likely to see him on a road bike dressed in Lycra at a Tuesday night worlds ride as you are to find him dressed in a full face helmet and pads riding a bike park on an enduro bike. He doesn't race often, but he's game for anything; having entered road races, criteriums, trials competitions, dual slalom, downhill races, enduros, stage races, short track, time trials, and gran fondos. Next up on his to-do list: a multi day bikepacking trip, and an e-bike race.

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