Coil vs. Air Shocks: MTB Shocks

Downhillers, enduro racers, and everyday trail shredders are putting coil shocks on their mountain bikes. But are they better than air shocks? Find out what the advantages and disadvantages are.

Coil shocks vs. Air shocks for mountain bikes

Written by
Bruce Lin

Published on

Posted in
Guides

For years, air shocks dominated the mountain bike market, but recently, we've been seeing more coil shocks equipped on enduro, an even trail bikes. Modern mid- to long-travel mountain bikes are incredibly capable, and riders are pushing them harder than ever. Along with that, shock technology has improved to the point where coil shocks are a great option for downhill-focused trail and enduro bikes that still need to be pedaled uphill. 

So is it time for you to try a coil shock on your trail or enduro bike? Let's take a look at the pros and cons of coil and air shocks so you can understand the differences and decide which is the better choice for your bike, terrain, and riding preferences.

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Why ride a coil shock?

Coil shock advantages

  • Supple feel with less stiction (resistance to movement at the beginning of the shock's travel).
  • Consistent performance and resistance to heat that can build up on long and rough descents.
  • More reliable with less-frequent maintenance.

Coil shock disadvantages

  • Heavier weight.
  • Finding the correct spring rate is more involved — you have to replace the spring with a stiffer or softer spring.
  • Less bottom-out resistance on more linear suspension designs. 

Downhill performance

The wound coil spring on a coil shock shocks does not heat up as drastically as a pressurized air spring does on long downhills. There are two key benefits to a cooler shock: The coil shock's damper oil does not heat up as much, so its performance stays more consistent, and the spring rate of a coil will not change during intense cycles. (More on heat fade in a moment.)

Stiction

Coil shocks require fewer seals than air shocks, resulting in less stiction — static friction created by seals against a shock shaft. The amount of force required to break this stiction is called the breakaway force. Because coils have less stiction and a lower breakaway force they have better small-bump sensitivity and a plusher feel.

This increased sensitivity can also improve traction, as it allows the rear wheel to track the ground more consistently. Bikes with coil shocks usually feel more planted in rough terrain.

Maintenance

Fewer seals mean coil shocks generally require less maintenance and aren’t as affected by dirt, dust, and grime. Most coil shock manufacturers recommend a rebuild every 12 months. Though it's not recommended, many recreational riders go several seasons without rebuilding their coil shock. 

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Weight

Coil shocks weigh significantly more than air shocks — on average about one pound more. A metal spring will always weigh more than air. Some coil shocks offer lightweight springs that can narrow the weight gap. Fox, for example, has SLS (super light steel) spring that come in orange. The downside is these lighter springs usually cost significantly more than standard springs. 

Spring rate

It is more difficult to change the spring rate for coil shocks. You have to remove the shock from the bike and swap out the coil spring. Riders may have to buy and experiment with multiple springs to dial in the correct spring rate and achieve the correct sag for their bike, terrain, and weight and there's always the chance that you'll be between spring rates, especially if they're only offered in larger (e.g 50lbs/in) increments. 

Linear vs. progressive spring rate

Another consideration is the coil's linear spring rate. This contributes to the plush and planted feel, but it also means that coil shocks have less bottom-out resistance than progressive air shocks. 

Some bikes are designed around the air shocks and won't play well with coils. The suspension design of these bikes will have a linear leverage rate that relies on an air spring's progression to provide bottom-out resistance. With a coil shock, there might not be enough suspension progression to prevent harsh bottom-outs during big hits. This forces riders to run an excessively high spring rate or excessive compression damping to compensate, which can cause a bike to feel harsh or dead.

Linear vs Progressive spring rate leverage curve mtbThis graph shows how a progressive spring rate or leverage rate helps to prevent bottom-outs. Ideally, either the spring, the suspension design of a frame, or both will be progressive enough to resist bottoming out too harshly or too often.

Coil shocks usually play best with bikes that a more progressive suspension leverage rate. Some bike manufacturers may recommend against using a coil shock due to a frame’s linear leverage rate or particular fitment issues. 

If you're curios if your bike's suspension will work with a coil I suggest checking out Antonio Osuna's Linkage Design blog. He models the suspension leverage curve for many popular bikes, though it's all written in Spanish so you may have to use google translate. If you are ever unsure if a coil shock is compatible with your frame, it's always best to check with your bike’s manufacturer. 

If you're dying to use a coil on a bike with a linear suspension, or just bottoming out too much in general, some manufacturers like Cane Creek and MRP are now making progressive rate coil springs that could be the answer to your wishes. 

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Why ride an air shock?

Air shock advantages

  • Lighter weight — up to 500 grams lighter compared to a coil shock.
  • Easy to tune spring rate by changing air pressure.
  • Better bottom-out resistance.

Air shock disadvantages

  • Greater stiction and breakaway force, sometime leading to a harsher feel.
  • Performance fades or changes due to heat on long downhills.
  • Requires more regular service and maintenance.

MTB Air ShockAir shocks like this Fox DPX2 are reliable, simple, and great for the majority of applications.

Spring rate

Air shocks rely on an air spring created by an airtight chamber in the shock. This chamber is filled using a shock pump. It is easy to change the spring rate of an air shock to suit different bikes, terrain, and rider weights. You can even do so mid-ride.

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The air spring also allows riders to dial in the spring rate more accurately than coil springs. Coil springs are generally available in increments of 25-50lbs/in and there is a chance that your ideal spring weight is between two available springs. An air spring can be set to the exact PSI to provide your desired sag, ride feel, and bottom-out resistance.

An air spring is also more progressive than a coil spring. As the air is compressed through the shock's travel, it becomes harder to compress it further. This helps prevent an air shock from bottoming out and allows it to play well with suspension designs that have a more linear leverage rate. This progression and bottom-out resistance can be fine-tuned with volume reducers or spacers that fit inside the air chamber. This is useful for riders who are pushing the limits of their bike and need more support for bit hits and rough terrain.

Weight

Air shocks are significantly lighter than coil shocks, sometime weighing over a pound less than a comparable coil shock. They also tend to be less active, or bouncy, when climbing. This makes air shocks a better choice for bike and riders that need to do a significant amount of climbing. Most do-it-all trail bikes that need to climb as well as they descend choose air shock for this reason. You'll never see a coil shock on an XC race bike.

Stiction

An air shock needs more seals to create an airtight chamber, which increases stiction. The breakaway force is higher and the rear-end of the bike won't feel as supple or stuck to the ground as it will with a coil. The best air shocks come close to coil plushness, but won't fully match the supple feel and low breakaway force of a coil shock due to those seals.

Maintenance

Stiction will increase as a shock’s seals and oil degrade or become contaminated with dirt, dust, and grime. It’s often recommended that air shocks be serviced at least every season to maintain performance — potentially more frequently if you ride a lot or in harsh conditions.

Downhill performance

Because air shocks are more progressive, they have a reputation for making bikes feel more playful and easier to jump and pop off trail features. 

But as mentioned earlier, air shocks are prone to heat fade on long downhills. When the air spring is subjected to repeated compressions, the entire shock heats up causing the air spring to become stiffer and the damping to speed up or become less effective because the shock oil is thinner at high temperatures. The longer and rougher your downhill runs are, the more this will be a problem.

Bigger, burlier air shocks like the Fox Float X2 and Cane Creek DB Kitsuma Air are aimed at the enduro and downhill market and have made a great deal of progress in recent years. Downhill-focused air shocks like these are designed with significantly larger air and oil volumes to improve fade resistance and provide a supple feel that can come close to the feel of a coil shock.

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Coil vs. Air: What's the best shock for your bike?

Santa Crus Hightower Coil ShockHiking to the top. If downhill performance is more important than how well a bike goes uphill, a coil shock might be for you.

Choose a coil shock if:

  • You regularly ride bike park or gnarly downhill trails and need a shock that can handle long and rough descents without losing performance.
  • Your bike feels harsh or skittish and you want better small-bump sensitivity or traction.
  • You prefer a rear end that feels more planted.
  • You don’t want to maintain or service your shock as much.
  • You think coil shocks look cool.

Choose an air shock if:

  • You do more riding that includes plenty of uphills and flatter terrain.
  • You want to keep your bike light.
  • You prefer a rear end that feels more playful and poppy.
  • You need more progression in your shock to resist bottoming out during big hits.
  • You like to quickly and easily change and tune your spring rate based on conditions, terrain, or riding weight.

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What do riders at The Pro’s Closet think?

The Pro's Closet Coil vs Air shocksThe majority of riders at The Pro's Closet are riding air shocks. The park rats and shredders all have coils though.

We polled the mountain bikers in the shop to see what our own employees prefer when it comes to coil versus air shocks. Around 50 riders ride mid- to long-travel trail or enduro bikes. Of these riders, only 7 are currently riding a coil shock. Everyone else is on an air shock. Interestingly, when asked about what they’d like on their next bike, almost half of the riders said they’d consider switching to a coil shock. Though coil shocks are less common, a lot of riders are curious.

Here are some opinions from a few of the most experienced mountain bikers in the shop:

Spencer, Senior Editor - "Coil is too heavy for me and for my riding style. I don't think it makes enough of a difference in performance."

Bruce, Writer - "I do a lot of lift-serviced downhill riding and a few air shocks I’ve owned in the past have failed, lost damping performance, and even burned my leg after heating up to extreme temperatures. I switched to a coil shock and now ride it everywhere."

Asher, Purchasing Associate - "Air has come a long way in small bump sensitivity, static breakaway force, and heat fade with larger air and oil volumes as well as improved seals. The weight penalty for a coil isn't worth the small and diminishing improvements for me."

Grant, Bike Technician - "Coil shocks are smoother and more sensitive to small bumps. I think coils are also more supportive in the travel when going up and down tech sections, and heat doesn’t affect the performance of the shock very much."

Coil vs. Air shocks: The bottom line

You’ll have to carefully weigh the advantages and disadvantages of each type of shock. In the end, there is no “best” shock option for every rider and every situation. Ultimately it comes down to personal preference, and any shock choice is a compromise. Your ideal shock should be at its best when you need it most. For hardcore downhillers, that probably means a coil shock. For riders who end up earning their turns with long, tough climbs, an air shock might be best.

So which do you ride and why — coil or air? Let me know what you think in the comments!

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