TECH TALK: Air Shocks Versus Coil Shocks, What's Better? 26

All of your questions answered! We discuss one of the hottest tech topics in mountain biking with the guys making rear shocks for a living.

TECH TALK: Air Shocks Versus Coil Shocks, What's Better?

Should you switch to a coil shock? It's a question many are asking, and today we're excited to bring you some valuable insight into the world of mountain bike rear suspension. Listen in as we chat with RockShox Rear Shock Product Manager, Chris Mandell, and World Cup downhill racer turned SRAM PR Coordinator, Duncan Riffle, for an in-depth discussion about their thoughts and experiences with both air and coil shocks. Chances are very good that you'll learn something interesting.

Highlights & Key Takeaways

  • 00:57 - What type of bikes work best with a coil shock?
  • 02:14 - When a bike isn't progressive enough, what happens?
  • 03:53 - What are the benefits of switching to a coil?
  • 04:26 - Explanation of the adiabatic process and its impact on air shocks
  • 05:30 - Are coil shocks more consistent than air?
  • 06:24 - Can the adiabatic effect be minimized, or is it beneficial?
  • 07:06 - When switching shock types, is there a difference in where you ride in the travel?
  • 08:11 - What are the downsides of switching to a coil?
  • 08:36 - Does weight or heat come into play at all?
  • 09:23 - Do air shocks suffer from fade compared to a coil?
  • 10:33 - Does Chris Mandell prefer coil or air? Why?
  • 11:16 - What about Duncan Riffle with his history in World Cup downhill racing?
  • 12:18 - Duncan discusses how not every bike will be ideal for one or the other, and how RockShox is trying to bring the two worlds closer together.
  • 13:17 - Why are air shocks "poppier" than coils? More about the adiabatic process

Thanks for tuning in! What has your experience with coil shocks been? Join the discussion in the Vital MTB forum.

You can learn more about the RockShox Super Deluxe Air shock in this in-depth feature, or hit up the RockShox website for a complete overview of their lineup.


Full Transcription

Vital MTB: How does Spomer say it? Welcome, mountain bikers. This is Vital MTB Product Editor, Brandon Turman. In today's Tech Talk we're going to cover a hot topic in the mountain bike world right now, and that's air shocks versus coil shocks. If you follow racing at all, you've likely seen a big push within the Enduro World Series, with many top Pros making the switch to coil. It's even beginning to trickle down into bike specs, here and there. So, which one is better? What type of rider is each best for? Is it worth making the switch? Today we're going to chat with RockShox Rear Shock Product Manager, Chris Mandell, and Duncan Riffle, a former World Cup racer turned SRAM PR Coordinator about their thoughts and experiences with coil and air. We're going to dive deep today in the Tech Talk, covering everything from what type of bikes work best with the coil to the pros and cons of each, and even touch on some very interesting details about how something called the adiabatic effect impacts air shocks. Bike nerds rejoice!

So, Chris, you're pretty educated on this topic. I imagine you've done a bunch of experimenting yourself. What type of bikes have you found work well with a coil?

Chris Mandell: Yeah, good question. So, there's a component of the bike and then there's a component of the individual rider style that works into there. Generally, one of the things we definitely see that lends itself towards a bike that's going to work better with coil, is one that has a higher rising rate. And that's just a way of describing how progressive the bike is. And so, based on the way that we calculate it, bikes that have 10-12% rise on a trail bike are going to give you the kind of support that you need and bottom-out control that you need. With that being said, there's other bikes out on the market that have a little bit lower than that that still ride really well with coil just because of other aspects of their kinematics. And then, when it comes to the downhill bike side of things, kind of 18% and higher. Sometimes for World Cup athletes they're looking to get above 30% rise when it comes to when a coil starts really working well for them. 

Vital MTB: So when you're under those numbers, what type of things happen?

Chris Mandell: You tend to get bottom-out a little bit quicker, or you tend to crush bottom-out. It's the nature of the spring. So, an air spring is going to have a curve that ramps up, depending on how it's set up. When you take all the tokens out of our current air spring system, we have a pretty flat, pretty linear curve so you can get fairly close to how a coil spring is going to behave. It's when you start adding those tokens into the system that you start changing the angle of that curve. It starts changing at sag, but the changes at sag are pretty imperceptible. It really kicks in at about 50% of stroke – that's when a rider can really start telling the difference with the addition of a token. And then, towards bottom-out you're getting a pretty massive change in terms of the air pressure at bottom-out. 

So, with more tokens, you'll have higher air pressure at bottom-out. The less tokens you'll have lower air pressure at bottom-out, so less bottom-out resistance at that point. A coil spring is going to be perfectly linear, so you're going to move straight across that curve. If you have a bike that's relatively linear with that coil spring that's relatively linear, it's going to be really easy for you to get to the bottom-out bumper on the coil spring shock. But if your bike is relatively progressive, your bike kinematics are going to resist the linear nature of the coil spring and make it a little bit harder for you to get to bottom-out. 

Vital MTB: Okay. So assuming you have a bike that is progressive enough, what are some of the benefits that you guys are seeing from making the switch to a coil?

Chris Mandell: So, I would say...and this is kind of where, you know, rider preference comes into that. You're going to get a lot of, like, really smooth, consistent feel from the coil spring side of things, where really it's going to be...the spring is always going to behave in the exact same manner, no matter what shaft speed you hit. 

So one thing that happens with air springs is they have what's called the adiabatic process, which is super complicated. I can't explain the math on it, but it has to do with air spring systems. When you pressurize air, there's a temperature change that accompanies the change in making the volume smaller. However, if you do a shaft speed change that's super fast, like say 100 inches per a second, there's no time for that energy to change into a temperature change, so it results in an increase in air pressure. What we believe is that one of the reasons why air springs tend to have a poppier, more playful feel, is that adiabatic process aiding the air spring to give a little bit more support when you have faster shaft speeds, and behaving a little bit more like a coil spring at slower shaft speeds.

Vital MTB: That's very interesting. Some of the benefits might include a more consistent feel, is that what I'm getting?

Chris Mandell: Yeah. I don't mean consistent in that the air spring is changing in some kind of a negative way. I mean that if you hit a coil spring at 100 inches per second, it's going to behave the same way as if you hit it at 20 inches per second, whereas the air spring is going to respond differently to that 20 inch per second than it does to the 100 inch per a second. So, for some riders, they prefer to have that consistency in the way the spring is responding to their inputs. Other riders prefer to use that air spring to jump off of things and get further down the trail, leverage the fact that the air spring is changing based on their inputs to it.

Vital MTB: So as suspension designers, are you guys working to change that adiabatic effect? Or is it something that you guys feel is beneficial?

Chris Mandell: Well, first of all, we definitely feel it's beneficial. We feel that's one of the differences between air springs and coil springs. It's okay that there's differences between the two of them. They're two different ways of solving the same problem. If we could change the adiabatic process, we would probably switch industries and go swimming in Olympic-sized pools of money.

Vital MTB: All right, something to shoot for! Okay, so as you're riding down a trail with the coil shock or an air shock, is there a difference in where you ride in the travel? It's likely dependent on the bike...

Chris Mandell: Yeah, so that's going to be dependent on the bike, it's going to be dependent on...it'll be a little bit on the rider to make sure that they set the bike up with equal amounts of sag between the two shocks. That's obviously something we place a lot of emphasis on with our coil shocks, and that's why we have sag gradients on the shaft to make it a lot easier to set the sag. But again, that's really going to be dependent upon the rider setting those two shocks up really similar. One nice thing for us is that with the Super Deluxe RCT reservoir, which is a two-position reservoir with a low-speed compression ingest, air-to-coil it's going to provide you with the same damping characteristics. It's just the spring that's changed in that situation.

Vital MTB: So what are some of the downsides of making the switch to a coil?

Chris Mandell: If you're a rider who likes to smash into things super hard and you're on a bike that's relatively linear, you're probably going to end up having to run such a stiff spring to avoid bottom-out that you'll be losing some of that off-the-top performance that people like so much in coil. 

Vital MTB: Okay. Does weight or heat come into play at all?

Chris Mandell: You know, weight is always a discussion. You've picked up my bikes before, so it's definitely...you know it's not on the top of the list that I have. But weight is definitely something that goes into that. We see a lot of people who are super weight-conscious, but we also see a lot of people who are...they wanna save weight in critical places like wheels, tires, saddles, and handlebars. Then when it comes to their suspension they wanna focus on the performance that they want to have on the bike, which is why they're willing to do something like put a coil shock on their bike, because they prefer the way that coils ride. I mean, just putting a piggyback shock on your bike is heavier than the option of putting an inline shock on your bike.

Vital MTB: Right. So a modern mountain bike air shock, like the Super Deluxe, does that suffer from fade over time versus a coil shock?

Chris Mandell: So, it's a little bit of a hard one to kind of really get into because there's kind of a lot going on there. In terms of damping, the air shock and the coil shock are going to be consistent along the same lines. We do a lot of heat testing. In fact, we were out with Sam Hill and Dave Camp – who works on the Rear Shock Team and is pretty quick in his own right – doing heat testing a couple of weeks ago. What we see from those guys, who are pretty fast and hard on their shocks and bikes in general, we don't see them getting the shocks up to temperatures that significantly impact the damping performance of coil or air shocks. 

Vital MTB: Okay. There you have it. You have to ride harder than Sam Hill or Dave Camp. 

Chris Mandell: Both really hard things to do. And I definitely noticed that Dave Camp riding with Sam Hill is faster than Dave Camp normally.

Duncan Riffle: Go figure.

Vital MTB: Okay. So gents, both of you, I'm curious. Are you a coil guy or an air guy?

Chris Mandell: I'll go first. I actually go both ways. It's interesting, my preference is to ride air, but...and I couldn't do this this year, but at the Andes Pacifico, which is a blind race in South America, I really wanted to ride a coil because I found with blind racing there's something about the way the coil works. The fact that you're kind of riding super ginger there, I want to ride a coil when I'm riding blind. But then when I'm riding my home trails or smashing laps in Whistler, my preference is to ride air.

Vital MTB: Okay. And Duncan, coming from that World Cup background, what's your preference?

Duncan Riffle: Yeah, it's interesting because like you said, with my background in downhill racing, it was always a coil. We never actually had that option for air in a long-travel bike. Downhill air shocks were just really not a thing, and if they were a thing they wouldn't last. It's kind of like a pipe dream, you know? We would run it for certain courses that we would try and get the weight down, but at that point we were nowhere near the technology and advancements that we have and are capable and achieving in our long-travel air shocks now that we were then. So, that being said, I'll be right there with Chris when he said I always preferred an air. Just the feeling and the liveliness of it, I think that's just more my style of riding. Having long-travel coil shocks was obviously just a smash device, really, and was a lot more capable. So I think I definitely am going to kind of echo Chris's sentiment there and say that I like to ride both.

I think the reason that we're actually here all talking at this point is for what I'm about to say, and that's the sense that each bike is different. What we really want to convey is that not every bike or every situation is going to be ideal for a coil or ideal for air, and that having that option nowadays is what we really are striving to do – kind of bring the two closer together, right? So, coil has lived on one end of the spectrum and air has lived on another entirely different end of the spectrum. What we're doing is bringing those a lot closer so you can really achieve the best ride for your terrain or your style of riding.

Vital MTB: Right. It was fun to do some back-to-back testing. A lot of my personal findings echoed what you guys are saying. It was very interesting to put the coil on and then go back to an air shock after several runs and feel out some of the differences. Honestly, I haven't even heard of the whole adiabatic thing, which is very interesting. 

Chris Mandell: It's definitely something that we're super aware of. That's the best explanation for why we feel like air shocks have that poppier, livelier feel than a coil shock is going to have.

Vital MTB: Is some of that also due to the fact that they're inherently progressive in their design, versus the coil, which is linear? 

Chris Mandell: If we take the volume spacers out of one of our air shocks, we're getting pretty close to the linear system. We're close enough that we don't actually think a rider could properly tell the difference. There's differences on the dyno, but we don't think that they're so far apart that a rider could tell. But when a rider rides the two, they can parse out which one's which. And we...I cant go too deep into it, but we've done some things and built some shocks that isolate the springs. So we've had the opportunities to basically trick the human rider in ways that we wouldn't normally be able to with the current shocks that are available on the market.

Vital MTB: Interesting. All right, there you guys go! That's air versus coil with RockShox. We covered some pretty heady details with Chris and Duncan, and I hope that the takeaway is that it's really a matter of preference. Not only is it highly dependent on the kinematics of your bike and whether it's progressive or not, but how that plays in your riding preferences and style may vary from person to person.

What's the bottom line? It's best to go do some back-to-back testing on your own and experiment if you can. Cheers, all! Keep the rubber side down, and thanks for listening in.

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26 comments
  • pdon

    11/15/2017 7:45 AM

    Soory, late to the game on this one.

    I think rider weight is an enormous factor. I am 6'2" 195-200 lbs with riding gear.
    Before the volume spacer thing really took off a few years ago, I was airing up a RS Monarch + shocks to 210 to get the appropriate sag on my Nomads and Devinci Spartan. That shock just cannot function long-term with that air pressure. I've learned in the past 3 or so years to run a lower air pressure like 185ish and run a hefty amounts of volume spacers.

    Moral of the story, air shocks can be really tricky for the folks that are 200+ as I have heard they are tuned for the 160lb(?) rider from the factory.

    When they function right, they are great.

  • Brandongoebel96

    11/15/2017 8:17 AM

    Not sure if the pressures are different but I weigh 175-180lbs and have been running 210psi in my rs deluxe with the max spacers(3). It still bottoms out more than I would want so I have to raise the pressure more occasionally. This makes me think my bike(Commencal Meta AM V4.2) is less progressive than I thought. I would love a coil and see the coil run on ews race bikes but not sure if it will be enough. Anyone have any input? It is only the deluxe and not the super deluxe but I don't think there is a difference in bottom out resistance in the two. I could be wrong though.

  • Losvar

    10/18/2017 12:59 AM

    I prefer coil, because fade on air shocks is real, the RS Monarch on my trusty old Mega got so hot that it hurt to touch it after a long run.

  • Mudmandh

    10/14/2017 6:44 PM

    in the past air shocks was so bad but now days watching Gwin winning WC with air shock shows that air shocks are working great

  • chrisingrassia

    10/15/2017 12:15 AM

    Is that your frame of reference?

  • TEAMROBOT

    10/16/2017 11:45 AM

    Great analysis and insight.

  • jefedelosjefes

    10/13/2017 2:32 PM

    All that talk and no mention of durability and maintenance? Sure, brand new air shocks feel great out of the box, but beat on them for 6 months and then run your comparisons. Air shocks always have this slow degradation of their performance, sorry rockshox, there's nothing your new fancy technology can ever do about this. Coil springs run more consistent for their whole life; no degradation of the spring performance... ever. No friction, no air leaks, no maintainance, no problems. I'll take a 200g weight penalty for that peace of mind and consistent performance any day. My preference has absolutely dick to do with their performance out of the box and more about me wanting to grab my bike and just ride.

  • erik2k10

    10/13/2017 4:24 PM

    100% Agree! Only racers with a mechanic rebuilding their shocks after every race should prefer air. Plus air shocks fade, even the large air can ones on a long run. I have coil on my Nomad v4 and the kinematics are perfect for coil. I'm never running air again. The tiny little bit of extra pop from air shocks is not better than the plushness and predictability of coil, end of story

  • adrennan

    10/13/2017 10:50 AM

    what an awesome time to be a mountain biker. so much crazy awesome technology available

  • jeff.brines

    10/13/2017 7:14 AM

    I learned something. Never knew about the adiabatic process. Makes sense. EDIT: @David Camp call out!!! Yes! (though they missed talking about how leverages ratios could impact damping quality as well) EDITX2: I agree the coil is better for blind riding.

  • TEAMROBOT

    10/14/2017 5:38 AM

    I don't understand. If the adiabatic process occurs at high shaft speeds, why would that affect a low shaft speed moment like pushing into a jump face? By poppy I assume we're talking about jumping. Similarly, small bump impacts are high shaft speed moments, so by this same process wouldn't an air shock always be rougher on small bumps?

    Not saying they're wrong, and it sounds like their blind testing indicates riders can always tell a difference between air and coil. Just saying it doesn't make sense. Maybe pushing into a lip is a high shaft speed moment?

  • kleinblake

    10/14/2017 8:04 AM

    All bumps pass through the low speed circuit into the high speed circuit

  • TEAMROBOT

    10/14/2017 8:33 AM

    We're not talking about damping circuits and oil here, we're talking about the relative reactive-ness of the different spring materials. What Mandell said was that steel reacts equally at all shaft speeds, air does not.

  • boaz

    10/14/2017 9:28 AM

    I’m wondering the same. based on what they said it seems like air will always suffer on really fast rough sections; shaft speed is way higher there than on a jump face. i recently got a dpx2 on my 160mm rig and it feels amazing in high speed rough - like nearly on par with the coil on my dh bike so maybe i’m (we’re) misunderstanding their explanation

  • kidwoo

    10/15/2017 11:19 AM

    Under the description header in that wikipedia link "A process that does NOT involve the transfer of heat or matter into or out of a system, so that Q = 0, is called an adiabatic process, and such a system is said to be adiabatically isolated.[4][5] The assumption that a process is adiabatic is a frequently made simplifying assumption. For example, the compression of a gas within a cylinder of an engine is assumed to occur so rapidly that on the time scale of the compression process, little of the system's energy can be transferred out as heat to the surroundings. Even though the cylinders are not insulated and are quite conductive, that process is idealized to be adiabatic. The same can be said to be true for the expansion process of such a system." So essentially under high shaft velocities the heating has little/no/less time to occur whereas lower velocities experience heating....and presumably a higher rate of pressure gain through the stroke. So basically the opposite of the heating process occuring at higher speeds.

  • TEAMROBOT

    10/16/2017 12:12 PM

    After some reading, adiabatic is a fancy word for "air spring element heats up under use."

    The question is: what causes heat build up? Obviously lots of rock smashing for tens of minutes will cause heat build up, but everyone already knows this and it's not what Mandell and Dunc-Dawg are talking about here. After a little more googling, the adiabatic process is a consistent element of all air springs at ALL shaft speeds. It's the big, scary word that hides the reason why air suspension is progressive in nature. As positive spring chamber volume is reduced during compression, rising pressure creates heat, and that new heat increases spring pressure. More importantly, air pressure goes up by a greater rate than volume goes down. If volume goes down by X percent during a compression cycle, air spring pressure goes up by X+Y percent, where Y is a function of heat build up. I haven't read this next bit anywhere, but I'd be willing to bet that as an air spring rebounds to full length, air pressure goes down and with it temps do too, returning to somewhere near the original ambient temp. Otherwise a fork or shock would be hot after a parking lot test. So heat and pressure build up during a single cycle is purely adiabatic, and heat build up after 14 minutes of smashing Garbonzo downhill runs is qualitatively different.

    Steel springs don't operate on pressure, so heat build up wouldn't significantly affect spring rate. So that's all a really long way of saying what we already know: air springs are naturally progressive, and coil springs are naturally linear. All we're adding with the word "adiabatic" is the nuance that the progressive nature of air springs is a product of heat build up from pressure changes.

    If that's all true, then what Mandell and Dunc-Dawg said is "Progressive air springs feel more progressive because they're progressive." This would represent a not-so-big insight, hiding behind a big, scary, science-y sounding word.

  • Serge-W

    10/16/2017 7:22 AM

    The simplifying assumption is that the process is well and truly adiabatic (no process is in reality).

    The adiabatic effect is the heating up of air during compression. The effect that they describe is that the heat stays mostly in the air at high shaft speeds.

    This is because the compression and release cycle is so fast at high shaft speeds, that there is very little time for heat dissipation into the surrounding metal aircan. However, when an airshock is compressed rapidly, the momentary heat essentially causes a higher, effective pressure of the air, compared to when you slowly compress the shock and let the heat dissipate.

    So the point is that at high shaft speeds the shock becomes more progressive than what the shock's air pressure and settings would suggest.

    For me, the feeling of air shocks in rock gardens is harsh at the right pressure or bottom-out when at lower pressures. Coil + rising rate fame FTW, more than enough pop

  • Brandongoebel96

    10/13/2017 6:27 AM

    How can you know or figure out the progressivity of your bike? Also why don't suspension companies have demo days for their product. I'd love to try other suspension on my bike and feel why I need it

  • Roots_rider

    10/13/2017 9:25 AM

    http://linkagedesign.blogspot.com/search/label/Young%20Talent

    Try here. List of bikes on the right of the page. May or may not be on here.

  • LLLLL

    10/13/2017 10:46 AM

    Just get your shock serviced, remove the tokens and add more air and rebound.

  • jeff.brines

    10/13/2017 10:51 AM

    What LLLLL and Roots said.

    Its extremely hard for most companies to do a demo day for a rear shock specifically. Way too many eye-to-eyes and baseline tunes to make it a reasonable thing. I do think companies like Push could do a "30 back money guarantee" or something.

    LLLLL nailed it with how to make your air shock feel like a coil. Lol. And for a lot of riders, they'd be smart to give this a try, especially before springing (get it?) for a coil.

    As far as figuring out how progressive your bike is, linkagedesign is great. That said, there are bikes that are progressive but don't work well with a coil. So YMMV.

  • app-uncture

    10/13/2017 7:40 PM

    Did this recently on my Transition Patrol, which is already progressive and comes stock with 2 tokens, yes its "poppy" which some might say is fun, but I wanted more plush, was close to buying a coil, but tried no tokens first, and it feels much more like I want it, might try one back in to see how that feels.

  • MTBrent

    10/13/2017 5:35 AM

    I could listen to this stuff for days. Good stuff, Brandon!

  • zuman

    10/13/2017 4:40 AM

    What does higher rising rate means?

  • DhDork

    10/13/2017 7:35 AM

    The amount of leverage needed to compress the shock rises as it goes through the travel. aka: progressive. Falling rate is the opposite, leverage rate decreases. Falling is ideal only with an air shock, as it will create a "linear" rate with the natural progression of an air shock.

  • Primoz

    10/13/2017 9:13 AM

    Actually a rising rate (rate of shock movement at constant rear axle movement) coincides with a falling leverage ratio. The force needed to compress the shock for 1 mm is higher at 1:1 ratio than is at 2:1 ratio. Which also means the shock moves faster at the 1:1 ratio given a constant axle movement than at the 2:1 ratio, since it moves 1 mm vs. 0,5 mm for every 1 mm movement of the rear axle. Therefore rate (of change).

    I hope i didn't make a blunder in there

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