This week’s Suspension Tech looks at the evolution of the rear shock, specifically why the coil shocks are seeing a resurgence. The development of full-suspension mountain bikes over the last couple decades has seen more and more capable designs switching more and more to lightweight air shocks. Then, in the last year or two, coil springs have made a comeback. And it’s not just long travel bikes, coil shocks are creeping back into trail riding segments too. So why now?

Why coil shocks are making a comeback

There are really a few separate issues at play here, so we reached out to industry insiders, including the product manager at Cane Creek – who produces both coil & air shocks (as well as coil & air forks.) We also chatted with Stefan Sack who does suspension R&D work with X-Fusion and spec’s both air & coil shocks on Bionicon bikes.

Weight

Cane Creek DBCoil IL inline rear shocks

Weight had been an original driver of the switch to air shocks, as we were all clamoring to lighten up our mountain bikes to better enjoy trail riding. Cane Creek’s Sam Anderson reminds us that it’s “common for 160mm travel bikes to weigh in a 28-35lb (12.5-16kg) range now, where not too long ago it was common to be pedaling around on a 35-40lb (16-18kg) pig.” Bike designers were shaving weight wherever possible, and the coil was an obvious target.

But now carbon frame manufacturing and more efficient alloy forging & machining has made frames both lighter and stiffer. That let bike designers add a couple hundred grams back to something like suspension without a big overall weight penalty. Sam tells us, “the gain in performance outweighs (literally) the weight gain.” In fact, now many new coil shocks are even lighter than some comparable high volume air shocks.

Shock Leverage Curves

Another key point is the more advanced leverage rate curves being engineered into modern mountain bike frames. With more advanced virtual pivot-style suspension designs, and even linkage-driven single pivots, bike designers are incorporating progressive leverage curves into the physical design of the frame’s kinematics.

That’s actually a really big deal, because previous generation designs relied on the shock to provide most of the bottom-out protection. Air shocks work well for that, because they are inherently more progressive as they compress.

Supple, Friction-Free Feel

ND Tuned DH zxRC3 worlds lightest weight coil shock for downhill mountain bikes

Coils shocks on the other hand are more linear. Sam said, “if the frames are being more progressive, it allows more opportunity for a linear damper to be used to get that super supple feel that can only be achieved with a coil.”

Stefan calls it just a more “consistent feeling” where you can hop on the bike and the suspension just starts moving right away. When you get your spring preload set up correctly, coil shocks are less affected by the seal stiction that air shocks exhibit, letting coil suspension eat up even the smallest of bumps. A big part of that is just that coil shocks have fewer and smaller seals to overcome.

More Travel

One thing we tie to that progressive air vs. linear coil argument is also that what we now call a “trail” bike keeps growing in travel. What was considered gravity-level travel a decade ago, might be your run-of-the-mill trail or light enduro bike now.

The longer travel a bike is, the more riders might prefer a more linear feel to the rear wheel travel, which a coil shock provides. Building a long travel trail bike – say longer than 160mm – with an air shock means that the frame suspension designer has to compensate for the progressive curve of the shock so you don’t end up with a bike where you feel like you never get to use the last 40mm or so of your bike’s travel.

Ease of Use & Durability

Cane Creek DB Coil CS enduro coil-over rear shock for mountain bikes

Cane Creek thinks the biggest reason of all to put a coil shock on your trail bike is to just set it and forget it. “People don’t want to mess with their bikes. Service is inevitable… but by having a coil shock, there is more longevity, and the maintenance interval can be prolonged relative to air springs.” By replacing an air spring with a physical coil spring, there is just one less element to worry about. That can sometimes also mean some cost savings as well, especially helpful on the OEM side to hit a desired pricepoint with a new bike.

It’s always possible that you might break a coil spring, but it seems much less common than having the air spring collapse because you didn’t maintain it well enough. Sam says, especially for riding far from home, “the coil shock can be the extra confidence that some riders are looking for.”

Consistency & Reliability

Beyond regular service, another big issue for air shocks (and the reason they’ve never really taken over in the gravity segments) is that with quick, repeated impacts the air spring heats up. And that changes the air spring rate. Now that trail bikes are getting ridden on more aggressive descents, especially as we crossover towards Enduro, the more consistent performance of a physical coil spring often becomes a more ideal, robust solution.

Stefan summed it up with the thought that all things equal, he would probably prefer to design & ride trail bikes with a coil shock. You start with a proper frame suspension design optimized to work with the linear coil shock, then dial in the correct spring rate, save weight elsewhere on the bike, and get a bike designed for “maximum fun down the hill”.

Most modern riders don’t seem to mind a few hundred extra grams, especially if they’re used to dial up the fun-o-meter. Case in point, we’ve all fully accepted adding weight back to our trail bikes via dropper seatposts to better enjoy the ride. So it looks like we can expect to see more trail bikes popping back up with coil sprung suspension.

 


The fun never ends. Stay tuned for a new post each week that explores one small suspension tech, tuning or product topic. Check out past posts here. Got a question you want answered? Email us. Want your brand or product featured? We can do that too.

SaveSave

SaveSave

SaveSave

23 COMMENTS

  1. one issue with air springs is that damping rate does not rise in tandem with the spring rate. Thus, what might have been overdamped in low compression could be underdamped at high compression. Since coil spring bikes are relying on a progressive rate at the mount, the damping moves in tandem with the spring load. One drawback of coil spring dampers is you cannot change the spring rate without changing the coil. The only thing you can change on trail is the preload, which may lead to some compromises on trail. Air springs change their rate throughout the travel. Good article.

  2. All of the listed reasons for a “come back” are all the reasons coils have always been better. Everyone that has ridden a coil knows that they are better. Can anyone name one suspension product that has ever been better than coil? Are there any vehicles that use only air springs?

    The weight thing? That wasn’t really why air shocks became a thing, that was just the marketing jargon used to SELL air shocks. I doubt anyone really was looking at their bike and said, “Everything is great, but those suspension components are sure heavy! I’ll gladly pay for an inferior product that weighs less! 800g tyres? Perfect! 1kg crankset? Exactly what we need!”

    Air shocks became a thing because like press fit bottom brackets, they are cheaper to manufacture. Fox et al. don’t have to produce a bunch of different springs for each model of shock. Changing the air pressure is much more simple than swapping a spring and air is free(ish). Air cans only have one benefit; we can all basically ride the same one.

    • There are a tremendous amount of vehicles using air springs for their suspension systems. A lot of luxury vehicles opt for air springs to match spring weight to vehicle load. Additionally nearly all trucks use them for the same reason.
      The push for air springs was due weight and adjustability. In order to adjust a coil spring, you have to remove the shock and replace the spring, preload adjustment doesn’t change the spring rate, it just compresses the spring, if you have too much preload then you risk coil bind.
      Air shocks require a significant amount of engineering and incredibly tight tolerances. If the coil shock was the superior choice regardless of the application, then the r&d for air shocks wouldn’t have occurred.

        • Read above, luxury, not performance: Mercedes Benz, Rolls Royce/Bentley, Porsche, Lincoln, Land Rover/Range Rover, Audi, Cadillac. My 2000 Ford Crown Victoria had rear air suspension. Jeep also uses air assist. I believe Tesla also uses air suspension. I also believe there are a couple Subaru models that have optional air suspension.

        • Lest we forget, F1 was on air suspension in the early 2000s until it was outlawed, and desert racing has been using nitrogen as its spring for years.
          And I’d venture that a Porsche Panamera Turbo and a SLS AMG are pretty performancey too.

      • I’d argue that except at the very basic level comparing automotive suspension and bike suspension is apples and oranges. Especially considering that the high-performance auto suspension has a lot more going on than a high performance bicycle suspension.

  3. The biggest reason for a comeback of coil shocks is the climbing platform switch. Without that you would not see such wide acceptance. That is something that was exclusive to air shocks for the longest time.

    • ehh not quite “exclusively”. Once upon in the early 2000s Fox released ProPedal on it’s DHX coil shocks. in 2007, Marzocchi put TST compression dampers in their Roco coil shocks. and to boot, Marzocchi produced that _same_ shock with the same compression damper up until 2016.

      Not saying early versions of pro-pedal were good, but they did exist. TST on the other hand actually would pretty much lockout. I know this because I actually still own one.

  4. Coils are amazing if they are a good fit for the suspension.
    But they also have some issues:
    – minor sag adjustments = different springs (super loaded packpack for long adventure vs. short quick ride with no back pack)
    – exact sag is hard to achieve, are you in between #50 rates?
    – due to the bottom out bumper, they are very progressive at end stroke.
    – hard to find if you are using full stroke

    • Sag is not very important. This article failed to say that. Running the minimum preload for a given airing rate is ideal. As long as you’re close to the give sag design, your fine. Your body position on the bike affects sag the most, you rarely ride in the perfectly centered position in the real world, you shift your weight back, you’ll sag deeper, forward, the opposite. Here’s an example; on my nomad 3 with 11/6 shock and a 500lb spring for my 200lb rider weight, I run my saddle slammed forward, I get about 20% sag seated while climbing, when I’m standing in my DH body position, I get just a hair under 30%. Factor in compression damping and rebound in the fork keeping thing high in the travel, and my dynamic sag (while moving) while descending is over 40%. I never bottom harshly, and my efficiency is good enough that my enduro bike keeps pace with shorter travel bikes on the climbs and flats, and dusts them on the downs due to the traction to hold the corners.

  5. I like the way a coil shock feels but I am concerned about the rearward axle path of the instant center and its objective relation to the contact patch of the rear wheel. When I ride a bike that rides great, I still fear that the mid-travel plushness might be overridden by a leverage rate that exceeds the anti-squat capabilities of driveside chainstay. Furthermore, when coupled with the anti-growth forces that arise from a large-volume air can with a stroke of less than 88.4mm you start…

    Hahahahahaha, just kidding, I am just writing gibberish that a lot of people get into instead of just riding the f-ing bike and determining whether not it’s good. I’ve known anal retentive types that have ridden a bike, liked it, then hated it because “I read the instant center is not right for my style of riding.”

    I bet these are the same people that dumped an old boy/girlfriend because she didn’t score correctly on the Myers-Briggs Type Indicator test.

    Just ride. Leave the “kinematics” to real engineers, stop copy-pasting what you read on Wikipedia.

  6. As far as a higher-end rental fleet goes, air shocks are still king for being able to setup each customer with the perfect sag. Having a library of coils in various lengths, rates, and IDs is expensive, and swapping springs is time-consuming. That said, I really like having a dialed coil on my personal ride.

  7. So we are at this part of the cycle now? So – next year “New Brand X Air Shock – totally like coil shock now”

    Coil shocks have been making a comback for so long now, that I almost think they never went away 🙂

  8. Weight penalty…..not really
    I recently swapped my CCDB air (525g.) for a CC Inline with Ohlins spring (565g) on a 150mm travel BMC ridden cross country.
    A major improvement in suppleness

  9. tradeoffs.. coil isnt always better. pick your poison. for a lot of descending, little maintenance coil is great.
    for the rest, air is just better… everything else is bike fashion statements

    • This. Coil is better for some things but lacks some of the ease/low cost adjustability of air springs. I’m guessing a lot of the popularity is style based on emulating pro enduro set-ups to look serious on the trailhead

  10. The F1 comparison is not applicable because Fi cars have a fairly low range of suspension movement. The reason airsprings are not allowed is because F1 does not allow adjustable ride height (the main reason), moveable aero pieces (lowering the car will lower the skirts and increase the downforce), moveable side skirts, etc. You won’t find air springs on any purpose built race car because coil springs are superior in many ways. Another problem no one mentioned is that when the damper is an air spring combo device, that leaves much less room for the damping oil. Running 60 or 70% less damping oil has significant penalties and will lead to damping fade very quickly. The cars that use air suspension are doing so to achieve a variable ride height foremost, variable tuning of the ride comfort secondary, performance is not a real consideration on any vehicle using air springs.

  11. The weight issue is there, a coil adds one pound to a bike. And then there is the spring rate, you simply cannot beat air in terms of adjustability …

  12. I went from a Cane Creek DB inline air (used for 2.5 years) to the Cane Creek inline coil 4 months ago. This is on a SC 5010cc. Not to mention I dumped the FOX Evol 2016 34 fork…. for the Cane Creek Helm coil. Why… because air “sprung” suspensions are simply trying to do what a coil suspension does naturally…. but failing. And rides like a dream. Nothing rides like a SPRING!

COMMENT HERE: (For best results, log in through Wordpress or your social media account. Anonymous/fake email comments may be unapproved or deleted. ALL first-time commenter's posts are held for moderation. Check our Comment Policy for full details.)

This site uses Akismet to reduce spam. Learn how your comment data is processed.