Skiing 201: How Ski Bindings Work

[Editor’s Note: There’s still a lot of confusion about bindings, and this 201 article is intended to give a general background on how tech and alpine bindings work. Much of this article is taken from Marshal Olson’s review of the Dynafit Beast 16, and we always intended to give this information its own dedicated space. So now, let’s talk about elastic travel, release values, and more.]

A Little Background on Elastic Travel and Release Value

The elastic travel of a binding is the single most important aspect of a ski binding’s ability to retain or release a skier from the ski.

Elastic travel is the amount of distance a binding can move before the boot clears (i.e., “releases from”) a binding. So, for example, if a binding has a 38mm elastic travel value, it can move 37mm and still retain the boot. In a 20mm travel binding, you can only move 19mm before your boot will release from the binding.

The weight of the binding spring will control how much work it takes to displace the binding a given distance. For example, if you have a 200 pounds-per-inch spring, it would require 200 pounds of force to compress the spring 1 inch, or 25.4mm.

Release Value

You can then further tune the binding’s functionality by adjusting the “Release Value” of the binding—i.e. adjusting your binding up from a setting of, say, 8 to 10.

(Note: “Release value” is often mistakenly conflated with “DIN setting.” A DIN setting of “8” is a release value, but not all bindings are “DIN”—Deutsches Institut für Normung—certified.)

The release value of a binding is a measurement of the amount of “spring preload”—the amount of force required to move the binding initially.

Adjusting the spring preload does not affect how firm a spring is through its travel. The spring constant (lets say 200 pounds per inch) is exactly that—a constant for a spring.

So adding preload—e.g., cranking your bindings up from 8 to 12—simply means that the spring requires a higher force to initially compress it. It does not mean that the spring itself just got 50% stiffer.

In a binding with low elasticity, one must run a higher release value to compensate for the short release action of the binding to prevent unwanted release. By running a high release value on a low-elasticity binding, you are simply preventing the binding from entering its motion as naturally.

Doing this will certainly help to keep you in the binding, but it also introduces a higher likelihood of injury. In other words, cranking up the release value on a low-elasticity binding is a pretty sketchy fix.

A highly elastic binding allows a skier to use the binding at a lower release value, since they are relying on the travel (i.e., elasticity) in the binding to prevent unwanted release.

There is then less need to jack up the preload tension, because more elastic travel can occur, increasing the skier’s ability to recover from an awkward situation before (pre-)releasing. This promotes controlled support for recovery through the range of motion of the binding’s elastic travel, but also promotes a smooth release that is unimpeded by an overly firm initial resistance.

The Ideal Binding Trifecta

In a perfect world, then, one would ski a relatively heavily sprung binding with a minimal release value setting, with maximum elastic travel. This enhances the binding’s ability not only to release the skier from its hold, but also to retain a skier if recovery is possible.

Tech Toe Pieces vs. Alpine Toe Pieces

Bindings 101, Blister Gear Review.
Dynafit Vertical ST

Traditional tech bindings such as the Dynafit Radical or Dynafit Vertical function very differently than alpine race-heritage bindings, and this difference is apparent on-snow.

Most tech bindings utilize a rigid connection between the toe piece of the binding and the boot tip.

Bindings 101, Blister Gear Review.

Since the toe piece only has a few millimeters of elasticity (it doesn’t house a release spring), it can only tolerate a few millimeters of travel before release occurs. And since this inelastic connection between the boot and binding is also a metal-on-metal connection, tech binding toe pieces tend to transmit a massive amount of feedback to the skier.

(A few new bindings, which we’ll be reviewing soon — the Dynafit Radical FT 2.0, for example — feature some elastic travel in their toe pieces, but this is still relatively uncommon in the world of tech bindings.)

Bindings 101, Blister Gear Review.
Anti-Friction Device (AFD)

The toe of a typical tech binding is analogous to riding a fully rigid mountain bike frame: there is no elastic travel to absorb feedback, it offers no controlled support, it doesn’t smooth the ride.

An alpine race-heritage binding has a lateral spring in its toe that controls the motion of the boot relative to the binding/ski, with the boot gliding across an anti-friction device (AFD). In this way the toe of an alpine binding is analogous to a mountain bike with a front shock. The binding offers a much smoother ride without sacrificing any control over the shovel of the ski.

To combat the negligible lateral elastic value in a typical tech binding, many people opt to ski with the toe locked out, or the heel release value cranked far higher than they would on an alpine binding. Either practice artificially inhibits the binding from releasing per the manufacturer’s intentions.

Tech Heel Pieces vs. Alpine Heel Pieces

An alpine binding’s heel piece exerts both forward pressure and downward pressure into the heel of the boot. All alpine bindings have vector forces in both forward and downward directions, even if they are not independently adjustable (e.g. Rossi FKS).

The downward pressure in an alpine binding controls the release of the boot from the binding in a forward fall. This downward pressure prevents either upward or downward free play of the boot relative to the binding and ski by constantly pressing the boot tightly into the binding and brake assembly.

The forward pressure in an alpine binding manages the pressure of your boot into the toe piece of the binding and allows the heel piece to clear out of the way when you have a twisting fall. It also maintains a controlled connection between the boot, binding, and tail of the ski when the ski becomes deeply flexed.

These two forces combine to remove lateral and horizontal free play in the boot and binding system by keeping them under tension—not to mention the obvious safety release functionality.

To use the mountain bike analogy again: an alpine heel piece is the equivalent of adding rear suspension to your bike.

Tech Heels

A tech binding only has spring resistance against upward boot motion. In order for the binding to release vertically, you have to overcome the retention spring by opening the two pins enough for the fitting on the heel of the boot to clear them and release. There is not any downward tension or forward tension present in a tech binding at the heel piece.

There is a 5.5mm gap between the heel fitting of the boot and the binding itself. When downward pressure is applied to the heel of the boot, the pins simply slide deeper into the heel fitting and close the gap between the boot and the binding. This free play prevents a skier from accessing the the tail of the ski, and creates a vague and disconnected sensation compared to how an alpine binding feels and behaves.

To compound this issue, the part fit between the pins of the binding and the tech fitting of the boot are imperfect. Since these parts are not held under spring tension, the pins and heel fittings can freely move relative to one another. This creates a further disconnect between skier and ski relative to a conventional alpine binding. On the workbench, you can twist the heel of the boot with the ski held flat and see the boot heel and pins moving relative to one another.

To finish the mountain bike analogy: a traditional tech binding effectively functions like a fully rigid mountain bike with a flat rear tire squirming all over the place. Conversely, an alpine binding functions like a finely tuned, full-suspension trail slayer: smooth, controlled motion on both ends.

NEXT PAGE: So What Does This All Mean On-Snow?

21 comments on “Skiing 201: How Ski Bindings Work”

  1. Excellent article – returning from the side country, I took a nasty inbounds fall at mach speed on hard pack last winter in my Dynafit bindings. For weeks I couldn’t get over how a) easily my binding released b) how easily my knee was tweaked (I rode the patrol sled down the mountain for the first time.) My question is about other rando/AT binding such as the Marker Duke’s and this article. The Duke’s are my inbound binding of choice (I have swappable binding plates) but are they analogous to the classic alpine bindings and their release characteristics or is their a third option (not tech, not classic alpine) not mentioned in the article?

    • Hi John!

      Late answer and maybe known facts already?!
      Learned after a season on Dynafits that one should always wiggle and slam the ski down a couple of times after attaching the toe, BEFORE attaching the heel, to make sure the pins are well in and no snow or ice is in the way. Foe me this has made a great difference and the nasty fake releases on high speed icy groomers are a thing of the past. To be clear ,:my Look PX din 18 are much preferred on all downhill terrain but Dynafits are still usable when attached “correctly”

  2. Excellent article that helps to clear up some long held misconceptions about bindings. Question for you though, at what level in the DIN range do you think a heavier spring binding becomes necessary, assuming the binding is reasonably well designed w decent elastic travel? For example at a DIN of 10 is a binding such as a Marker Baron acceptable or would you think it necessary to upgrade to the Duke. Ignoring any structural differences such as metal vs plastic, etc.

    • hey ben,

      basic engineering principles dictate that as you increase preload on a spring (i.e. add din). you are making it harder to move INITIALLY. the spring rate (k) is a constant.

      generally if you need or want more than 1-2 turns of preload on a spring, you would be better off swapping to a higher stiffness spring.

      my hypothesis is that making a boot harder to move initially in the bindings travel makes it more likely to cause injury. DIN means is that it takes the same amount of force to release. it does not account for the spring stiffness and the amount of travel in the release… higher spring stiffness + more travel = less preload needed = smoother initial travel of the binding = less likely to injure oneself.

      in binding speak, IMO a duke 6-16din binding would be best served being skied by someone in the 6 to 9-10 din range (the lower 1/3 to 40% of its range). i fully realize that flies directly in the face of conventional wisdom in ski land, but well… you asked my opinion ;)

      one should not be married to a DIN value. every binding is different. there are a few variables: spring stiffness (k), spring preload (p) and elasticity/travel (d). i personally ski at a 13.5 on a marker duke, but a 12 on a salomon 920 (12-20 range), and have equal ability to retain in the binding, but more faith in the 920 not hurting me since the motion is so much smoother.

      hope that helps?

  3. The article implies that tech bindings do not offer the same level of safety as a standard alpine binding, but it seems to assume that tech bindings also will be run as a higher release value. What do you think of the relative safety of both systems if they are adjusted at similar and conservative release values? Will the safety of the tech system be relatively close to an alpine binding and primarily compromise ski retention and control?

    You note that forward pressure ‘allows the heel piece to clear out of the way when you have a twisting fall’. Does this apply to both alpine and tech bindings? Several of the new systems like the G3 Ion are starting to offer systems similar to forward pressure but the main advantages highlighted by G3 seem to be better ski retention in situations where the ski is flexed dramatically.

    Thanks and great article!

    • great question kevin,

      a binding’s ability to “retain or release” is described from a physics standpoint as “work done”. this is proportional to Force x Distance. Tech bindings have significantly less elasticity (i.e. less distance), so for comparable work done (i.e. equivalent release values) on the release, you need significantly more force in the spring (i.e. heavier spring), so the spring is much harder to move initially,and this is why inures are more likely.

      forward and more specifically downward pressure on the heel makes the ski feel more contacted and less vague while skiing. traditional pin heels only have upward resistance, so there is control if you are doing a bunch of nose-butters, but the ski moves relative the boot with n control when bending, loading, and driving a ski on firm snow. The pins just slide around in the recess of the boot.

      anyhow, all just my .02

  4. The pre-load idea is a little misleading. Consider a 4 inch spring with a 200 lb/inch spring rate. You need 200 pounds of force to compress it by an inch, and 400 pounds of force to compress it by 2 inches. Now if you preload the spring by compressing it an inch, it will still take 400 pounds of force to compress it another inch. By preloading the spring, you are effectively increasing the spring rate.

    • Spring rate is the slope of a Spring curve, let’s assume an ideal spring and -kx (hooke’s law) applies.

      A stiffer spring has a steeper slope (larger k value)

      A softer spring with lots of preload keeps the same slope (k value) as if it had no preload, but is harder to move initially because you are overcoming the preload displacement (restorative force), and the spring rate.

    • Or to put it another way, preload is simply shifting where on the x axis along the spring curve the motion is starting. You go from 1600lb of spring potential to 1200lb due to going for 4″ useable to 3″ useable spring travel with a 400lb spring rate. But you still have to overcome the stored potential energy created by the preload to move the spring initially.

      • Hi marshal,
        I think that your model assumes that no matter what setting, the elastic travel in binding will always reach maximum compression of the spring.
        In stating that you only shift the start of motion on the X axis, you may be ignoring that the end of motion before release may be shifted as well. To demonstrate the idea, let’s say that there is limit of elastic travel length that is shorter than the spring. In other words that the releasing part of binding traveled to position where it no longer fixes the boot in the binding, while the spring was not yet fully compressed.
        By pre-loading the longer spring, you would use different section of the X-axis e.g. instead of 50-150 lbs you would use 100-200 lbs on spring that goes from 0 to 250 lbs before reaching it’s designed range of motion.
        Now the manual on my Marker TC14 binding say that only ranges up to DIN10 are according to DIN norm and anything higher is on own risk. It might be, that at DIN 10 is like reaching 150-250lbs and any further preload would decrease the range of motion (like 200-250lbs).

        Please note that I do not speak from point of authority or certainty. This is just combination of logical deduction of what was posted here and intuition. But I think it still may provide some value.
        Also note that example values in lbs are arbitrary just to show general principle on some kind of example.

        • hi jan, i am sorry but i don’t follow.

          i am talking about stored kinetic energy within the spring. this is defined as the surface area under the curve, or the integral of the spring rate — high school newtonian physics.

          at the origin, there is no preload, and no stored energy. the more preload, the further along the spring curve, and the more surface area under the curve, so the more stored energy you need to move against.

          one can do thought experiments with a mountain bike — consider a 8″ and a 4″ travel bike. if they are the same spring rate, you would need way more preload on the 4″ bike to not bottom out. or you would need a way higher spring rate on the 4″ travel bike to have the same useable travel. the 8″ bike will be far smoother through its travel either way. one can also have an 8″ travel bike with too soft a spring, crank in a ton of preload, but then the bike is harsh on small bumps, and still bottoms out easily.

          applied to ski bindings, think of the “travel” above as elasticity value, “spring rate” as the DIN range (i.e. 10din has softer spring than 18din binding), “bottom out” as pre-release, and the preload as the amount of turns into the DIN range one goes from the lowest value (i.e. 4min on the 10din, 8min on the 18din).

          if a skier has 9DIN, then they are applying 5x the preload on the 10din max binding, (from 4 min value), as the 18din max value binding (i.e. from 8 min value).

          hope that helps.

  5. To better understand this, draw a simple graph. X axis with 4 1″ marks, the y axis is force. Then draw a line at a 45 degree angle from the origin. this is the spring rate (k value/slope of the line). connect the 4 1″ marks on the x axis with your 45 deg line. Each of these areas under the spring rate line is the amount of kinetic energy required to achieve the displacement of the spring. Integrating force -> kinetic energy. Ke= 1/2 * -k * x^2. Sooo… By adding preload to a spring you must input significantly more KE to move the spring initially, but you are not changing the slope and not changing the spring rate. You are overcoming the stored energy within the spring and overcoming the spring rate at the same time, vs a spring with no preload.

  6. great review on the general characteristics between the tech and alpine bindings. marshal, you obviously feel that the typical dynafit type tech binding gives a clearly inferior skiing experience to the alpine binding. what are your thoughts on the kingpin concept? marker has stated that the kingpin is essentially equivalent to their alpine bindings. do you feel that the complex interaction between the pin toe piece and the alpine rear binding can mitigate the ride of a “fully rigid mt bike frame”? i know your opinion would be pure conjecture without skiing on them, but others have stated (with limited testing) that the kingpin rides similar to the beast.
    btw, i just purchased the wailer 99 and the new 112s, partly based on blister’s reviews. i ski 60-70% resort (family with 2 small kids) and the rest backcountry. the kingpin concept is very appealing with giving the potential solid alpine downhill feel without the fing garbage underneath the foot when hiking (ie duke). obviously, im not going to wait until midwinter for the kingpin to be fully tested before purchasing bindings. currently i have dynafit bindings on all my old skis. thanks again for the great info! rod

    • hey rod-

      i have yet to even see the kingpin in person, but i have a few questions before i get excited:

      1. is there both forward and downward pressure from the heel, like an alpine binding?
      2. if so, how much? comparable to a griffon? or more like a squire / jr binding? (the beast’s forward pressure is minimal, and has no downward pressure)
      3. how many mms of lateral elasticity? (the beast has 2x that of a tech binding, but 1/2 that of a good alpine binding)
      4. how many mms of vertical heel elasticity? (beast has 2x that of a tech binding, but 1/2 that of a good alpine binding)

  7. Marshall- I graduated from UW-Madison in ’78. I was reading your bindings article and could use some help.
    I am 58, 6′ and weigh 208 (lost 50 lbs) in last 1.5 years.
    I ski 2-3 times a year in colorado for a few days. I am an intermediate skier , don’t like moguls and mostly ski blue and groomed black runs at aspen/snowmass.
    I have a new pair of salomon BBR 8.9 skis 176 cm.
    what bindings would you recommend for me?
    Thank you for your help.

  8. Marshall- I graduated from UW-Madison in ’78. I was reading your bindings article and could use some help.
    I am 58, 6′ and weigh 208 (lost 50 lbs) in last 1.5 years.
    I ski 2-3 times a year in colorado for a few days. I am an intermediate skier , don’t like moguls and mostly ski blue and groomed black runs at aspen/snowmass.
    I have a new pair of salomon BBR 8.9 skis 176 cm.
    what bindings would you recommend for me?
    Thank you for your help.

  9. Hi Marshal,

    (My question might appear twice, I submitted it and now I don’t see my original post)

    If elastic travel is such an important metric, I find it frustrating that it’s not listed with any of the tech specifications for bindings online. Even when you go to the manufacturers website.

    Why do you think that’s the case?


  10. Thanks for the shoutout on the recent podcast. I read the above article and comments a few times and I’m still a bit confused. If elastic travel is the most important factor, is there any way to find that for popular alpine bindings? Why doesn’t Blister do reviews of more alpine bindings? I also see in the comments above that if I’m running at a release value of 9 then I will be better off with a 16+ DIN binding rather than 13ish? All the physics talk is way over my head and I’m still a bit lost. Thanks.

  11. Hello, I have such a question: I work at a ski resort. Is it necessary to completely empty the springs in the ski bindings after each winter season? If it stays at full tension, could this cause the springs to fail over time? Thanks in advance.

  12. I know this is an old article, but it’s some pretty important safety-related info, so I thought it was worth commenting to clear up some technical errors.
    The release value is NOT the force required to initially compress the spring from preload. It is the peak force achieved prior to release – i.e. at peak displacement which is the same figure as the max elasticity. I think Marshall is misunderstanding the role of a spring constant. As you increase preload, you do also increase the peak force at max displacement. You just do so linearly as a function of the spring constant. So yes, the spring doesn’t get a stiffer constant, but the range of the spring that you are utilizing is in a “stiffer” part of the curve.
    So his rationale for elasticity is working from the wrong end of the curve. Bindings with higher elasticity are able to *absorb/store more energy in the spring before hitting that peak/release force*. For folks visualizing, there’s more area under the force/displacement curve in the high-elasticity binding, and that area is the energy the spring can store. It’s analogous to mountain bike suspension travel (ignoring the damper) – you can set up a 100mm XC fork and a 200mm DH fork to bottom out at the same peak force, and the DH fork will absorb much more energy through the travel, so an impact with the same energy may be dissipated before the DH fork bottoms, while the XC fork bottoms, despite being set up for the same peak force.
    What this means for us as skiers is a few things. Generally, more elasticity is better and safer, not just when we release, but when we don’t. Arguably more elasticity is less precise because you may spend less time perfectly centered in the preload, but I have yet to hear anyone complain about precision in high-elasticity bindings. Second, is that running a high-DIN binding at the low end will actually ski “softer” than a low DIN binding at that same setting – this is because the stiffer spring (i.e. higher coefficient, i.e. steeper force/displacement curve) is preloaded less to achieve the same peak value, so it’s starting point (i.e. preload) for displacement is *lower than the low DIN binding.* The high-DIN binding will offer better “suspension” but will actually absorb/store less energy on the path to peak force/release value. Up to you to decide which you value more.

  13. Marc:
    Your comments are really good. The statement “Elastic travel is the single most important aspect…..” has always bothered me and has always been wrong. Elasticity is one aspect of binding design, but it is possible to have a very elastic very soft binding with a lot of easy early movement that I personally don’t think I would trust. I’d love to see see force displacement curves released by each binding manufacturer or perhaps someone out there will take the project on.
    I haven’t been comfortable with comments that say a 12 or whatever number on one binding is different than a 12 on another. It certainly isn’t supposed to be that way. The whole purpose of the Release Chart is to standardize release values. However, differences in binding design, such as stiffness certainly affect how each binding functions for individual skiers.

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