Measuring Release Values — Salomon-Atomic U-spring bindings

Post by blogger | September 13, 2018      

We published this last spring. People missed it. Useful infos so we reup. The point of the exercise is you don’t want to be making assumptions about binding release and retention values. At the least, a hand check on workbench, better, actually measure. Exception being skiers who simply crank all settings to the maximum, as testing those rigs often requires excessive force, and they provide little to no injury protection needing verification. In other words, a binding set on release value 13 is about staying on your feet, not coming off.

And by the way… when you do your bench testing, be aware of gotchas such as the Fritschi Evo/Tecton offerings needing the boot toe actuation of binding toe opening during a forward release. Easy to check on the bench, major problem if this does’t function correctly.

'Twist' testing.

‘Twist’ testing. (Binding shown is a Dynafit, while the binding we cover in this article is the Salomon-Atomic.

This project used a Vermont binding release checker. While this tool is designed for toe-wing (alpine) binding release checking of TUV certified DIN/ISO standard systems, it correlates well when used to evaluate lateral (twisting, side) release and retention of classic tech bindings. To verify, I checked a set of Dynafit Speed Radical I’ve got mounted up for my current Cosmos 3 boots, as well as testing with my quite used TLT-6 boots. Dynafit binding set on 8, checked out with release value (RV) of 7.5/8 on the torque wrench using my boot choices, other experiments showed good results as well. Thus knowing the Vermont instrument would give me usable results (at least for comparisons), I then played around with the Salomon-Atomic U-spring bindings.

Lateral, twisting, results (informal averages of several test cycles):

7 with the “Women” spring using Cosmos, and 6 with the TLT-6 (makes sense, see below for info about testing with no heel spring).

8 with the “Men” spring, Cosmos, 7 with TLT-6.

10 with the “Expert” spring using Cosmos, 9 with TLT-6.

(Vertical, forward release is challenging to measure accurately with the Vermont device due to the limited elasticity of tech bindings, but the numbers I got seemed fairly consistent with the TLT-6 lateral results. The “Expert” spring took so much force I was afraid of breaking the ski, so I didn’t get a measurement at that extreme, I’d imagine it’s at least 11.5. The “Men” spring measured 8.5 and the “Women” was 5.5. I only measured vertical force with the TLT boots, as rear Dynafit boot fittings are usually close matches across brands, and operate more simply than the toe system.)

Women spring has cutaway to reduce tension.

“Women” spring has cutaway to reduce tension, interestingly it made little difference as opposed to releasing the boot with the heel unit disengaged, thus depending entirely on the toe unit.

Interestingly, when released with NO rear spring, I still got around RV 7 with the Cosmos and RV 6 with the Dynafit TLT-6, indicating how strong the Salomon-Atomic toe springs are in comparison to the weakest “Women” heel spring. More, and sadly, the toe fittings in my Cosmos test boots tended to catch during the release cycle and cause a spike. That’s an all too common problem you should always check for on the bench. A “sticky” boot is perhaps a non issue for skiers using higher RV settings (and might even be beneficial in terms of accidental release), but could be a factor if you’re seeking a smooth release at lower settings.

My testing indicates that no matter what, you won’t get a lateral release setting below about 6/7 for this binding (though that could vary depending on boot toe fitting action). Smaller folks take note. Since my testing indicates the various springs are actually providing a fairly limited range of values, there is no reason for more springs within the range. That explains why these bindings work well for so many people. In other words, if you’re seeking a an RV value setting in increments of around 1 or 2, you get that with the three available springs. On the other hand, an additional super-high value spring could be a good addition. Conversely, if you desire torsional release values below 6/7 a different spring won’t help, you instead need a different brand-model binding.

Huge caveat with all this is your boot fittings are part of the binding, and can significantly change your release values. Thus, as I’m always harping on, if you desire accurate settings it’s necessary to test each specific boot-binding setup. Otherwise your are engaging in guesswork or at best trial and error (i.e., set binding low, ski it, eject, dial up, repeat) Brakes are a factor as well, if you use brakes they may change your settings and the ski should be testing with the brakes, since this project is about comparing strength of springs and getting an approximation of release values, I did not test with brakes.

Torque scale.

Torque scale.


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36 Responses to “Measuring Release Values — Salomon-Atomic U-spring bindings”

  1. Dabe May 7th, 2018 11:55 am

    Unrelated to post but what, if anything, do you use to plug up the holes left from removing the vestigial buckles?

  2. Lou Dawson 2 May 7th, 2018 12:45 pm

    I put a square of Gorilla tape on the inside, then fill with a gob of silicon caulk. Works fine. Lou

  3. jbo May 7th, 2018 1:01 pm

    Hi Lou, you should use the A/T adapter for the Vermont device when testing most tech bindings. It moves the axis of rotation above the toe instead of the heel. But then again you have the torque arm coming out to the front instead of the rear which is typical when measuring alpine bindings. Also, you shouldn’t clamp the ski down for a twist test as you can unwittingly introduce off-axis force. Did you get a DVD with your kit?

    Further, you should be clear whether you’re testing with brakes since the results can be very different (I don’t see them in the photo?). Finally, you should mention the BSL when backing into “RV” from Nm since the ranges are lumpy.

  4. Chris May 7th, 2018 2:17 pm

    A real world data point…I skied the Salomon/Atomic pin binding all winter (80 days?) and never once released. I should also say there was never a point where I felt I should have released.

    I’m 6’ and 190 pounds. Like steep/aggressive terrain but am a fairly smooth skier and don’t ski that fast. I used the Man spring with a 317 BSL Atomic Backland Carbon. I skied skis 95-107 wide. I’ve skied some very firm snow with my toe unlocked with no issues. Also I tour with the toe unlocked in soft snow which is a nice bonus. As Lou says the toe springs are pretty strong.

  5. Lou Dawson 2 May 7th, 2018 2:40 pm

    Hi JBO, everything I’m doing worked, am aware it can be tweaked. Main goal of my process is comparison between binding/boot combos, but it does measure the RV accurately enough in my opinion. Clamping the ski down is mandatory for what I’m doing, otherwise someone would have to hold it, same thing. Good point about brakes, no testing with brakes at this time. I’ll add verbiage about that. Thanks, Lou

  6. See May 7th, 2018 8:00 pm

    Hmmm… different boots yielded smaller range of measured rv’s with the Dynafits than with the Salomon/Atomics. Super stiff toe springs make toe socket dimensions more critical?

    I don’t totally get how clamping the ski can introduce “off-axis force” but a peg in front of the toe and behind the heel would seem like a reasonable approximation of the official VT Safety rig without requiring anyone to hold the ski.

    I’d really like to see a post that looks at how brakes (with and without afd’s) effect lateral and forward release values.

  7. Lauren DeLand May 7th, 2018 8:24 pm

    Thank you for the insights. I tore my MCL and PCL in a forward twisting fall using these bindings this year. If I had fully understood the limitations of this binding design, or the significant force require for this particular toe piece, I would have switched to a more consistent releasing binding like the Vipec (what I ski now). All U-spring bindings have limits but this binding in particular has me pretty concerned for skier health and safety after three months of rehabilitation.

  8. See May 7th, 2018 8:33 pm

    I’m guessing taking care to keep the wrench in plane with bindings minimizes “off-axis force.”

  9. See May 7th, 2018 9:29 pm

    “(M)ore consistent releasing binding like the Vipec” meaning what? High toe spring tension is good for reducing prerelease which is good for skier health.

  10. Crazy Horse May 7th, 2018 9:31 pm

    Talk about a blast from the past!. I used to have one of those analog torque wrenches about 40 years ago, but its a digital world now. “Vermont” must have found a bunch of these antiques buried in some farmer’s barn for 25 cents each.

    If a device like this were to actually calibrate release torque it should have a bearing or collar holding the shaft in a constant position relative to the ski. Otherwise it measures torque plus off axis wobble as See noted .

  11. jbo May 7th, 2018 9:33 pm

    See – Exactly re: off-axis force. Unsurprisingly the brakes affect the softer springs more than the stiff ones.

    Lauren – Sorry to hear of your injury! Always sucks to miss out on ski time.
    Unfortunately I don’t think you can conclude a different binding would have protected your ligaments.

  12. Bruno Schull May 7th, 2018 11:51 pm

    I injured my MCL and possible ACL as well this season with a forward twisting fall with Vipecs and Scott Cosmos boots. I think, but do not know, that catching/friction between the toe pins and the sockets contributed to a catchy release, and to my injury. As Lou has frequently emphasized, I will from now on be checking my boots/bindings carefully.

  13. XXX_er May 8th, 2018 1:44 am

    Since you got this tool i am curious how a rad or vertical with brakes or other fully functioning adjustable bindings tests test out on a boot with a real dynafit fittings?

    My opinion of fixed release/no brake bindings is they are for real rando dudes whom are dripping with lycra, otherwise the concept of compromising a binding that wasn’t that safe to begin with is silly

  14. Lou Dawson 2 May 8th, 2018 7:27 am

    Thought I should emphasize the unlike a ski shop, I’m not using this tool to verify exact “DIN” settings for individual setups. Thus, so long as my results are repeatable it’ll suffice for comparing different bindings, evaluating the differences between U-springs, and that sort of thing (yes, including the influence of brakes). Rule of thumb with brakes, for our family, is they subtract 1/2 of a release value number in vertical retention, and add 1/2 in lateral due to friction and other types of mechanical resistance. I’d imagine in real life that might vary quite a bit per individual setup, and as Jbo say, the lower your settings the more influence the brakes will have.

    As for measuring individual release values for a given shop customer’s boot/binding setup, the Wintersteiger Safetronic is clearly what you’d want, not some primitive system of levers and torque wrenches found “in a farmer’s barn.” (SMILE)

    Another thing: The best way to test is to have the “foot” and leg shaft fixed to a rigid metal frame, and move the ski, but such a setup is probably beyond the scope of what we could do here at Wildsnow. For example, I’ve seen the testing setup at Marker, G3 and Fritschi among others and they all use a large cubical frame with a fixed foot, with a ski and binding attached. Sometimes they’ll have a Wintersteiger as well.

  15. Lou Dawson 2 May 8th, 2018 7:43 am

    Regarding ACL/MCL and other soft tissue injuries, perhaps the Knee alpine binding does more to protect, but to the best of my knowledge ski bindings in general do little to nothing in terms of preventing such injuries by every mechanism with which they might occur. Regardless, touring bindings should be skied at the lowest settings possible without incurring accidental release, along with bench testing, and skiers should avoid falling as much as is possible… Personally speaking, I’ve had three knee ligament injuries while skiing. None required surgery but I’ve got one knee that’s not exactly 100%. One injury on early Marker alpine bindings that were locked up with ice (requiring one of my two Cascade toboggan rides), one on nordic racing skis while doing something stupid (something like “here, hold this while I try that”), and one on Silvretta 404 bindings during which I didn’t fall but simply twisted the wrong way while standing around in deep snow with a heavy pack. Lou

  16. Lou Dawson 2 May 8th, 2018 8:05 am

    Xer, the Cosmos has “real” Dynafit fittings, what goes on is that fittings vary, even Dynafit certified ones, thus the importance of bench testing as well as knowing that wear on the toe fittings can perhaps make them operate more smoothly but may also lower the release values. Lou

  17. See May 8th, 2018 8:27 am

    Sorry if I sounded curt, LDL. Obviously you’re saying that you believe the Vipecs release more consistently. But I’m wondering if there is evidence, anecdotal or otherwise, that supports claims of superior release performance with Vipecs. Also, I am very interested if the U-spring system is causing people to ski with their bindings at suboptimal release values, perhaps too high in your case? For example, if I use the M springs on the mtn/backlands, my bindings will (theoretically) be at the same release values as Chris (above), who is bigger, younger, stronger and more skilled than I. (My boots are a lot smaller, so there is that.) I’m glad the rehab apparently went well and you’re back in action.

  18. TimZ May 8th, 2018 10:05 am

    I’d be interested if you could make some measurements on the new Black Diamond(ATK) bindings when they come out. In particular the fixed release/replaceable spring bindings like the Trofeo. I’d like to know if the numerical RV’s correlate to dynafit adjustable numeric values

  19. XXX_er May 8th, 2018 1:12 pm

    Non dynafit fittings got garmont/scott in trouble back about yrs ago, we compared a buddies cosmos and there was a very real difference

    ,I always arrive at my binding setting by turning them up till they stop falling off

    Dynafit din like settings end up being about the same as my din alpine setups

  20. Lou Dawson 2 May 8th, 2018 1:41 pm


  21. Lou Dawson 2 May 16th, 2018 8:45 am

    Hey all interested in this, I should mention that as was alluded to above, how the ski is clamped does influence release values, especially vertical. For example, if the ski is fairly flexible and clamped in a way that allows it to flex, the boot pulls a few mm forward on the heel pins as the ski flexes during a forward release, thus reducing the release values.

    I mention this as I want to emphasize that any testing I’m doing is to simply determine the ball-park release values, and how they compare between brands and swapped springs. It’s debatable, but I believe the Vermont system is not adequate for determining *exact* value under the DIN/ISO standard, for example if serving a ski shop customer. A Wintersteiger machine is clearly what you’d need for that.


  22. See May 16th, 2018 9:32 am

    Seems to me that if you place the clamp close to the heel piece for vertical testing, the problems posed by ski flex would be minimal. And I am not aware of any other source of this sort of transparent, measurement based information available to those of us who don’t have access to expensive shop equipment. If you’re lucky enough to have access to a shop that is up on this stuff, that’s great. But I suspect such shops are rare. Thanks again, Lou.

  23. Lou Dawson 2 May 16th, 2018 10:04 am

    Indeed… main point is that bench measurements may not be the same as real life, and also that classic tech bindings have more than one flaw as to their release-retention characteristics. As someone said “they’re a ski touring binding, not a ski binding…”

  24. See May 16th, 2018 7:11 pm

    All the more reason to learn about the strengths, weaknesses, quirks, etc. so as to reduce the risk of having an equipment related bad day.

  25. Lou 2 May 17th, 2018 7:09 am

    Agree! Perhaps part of the reason exists (smile). Lou

  26. jbo May 18th, 2018 1:18 pm

    Hi Lou, the Vermont tool can be fairly accurate if you keep it calibrated and use the Vermont vise. But the machines are more fun. With your hands free you can record releases, slow down the video and see some interesting behavior!

    The Wintersteiger isn’t my favorite for tech bindings fwiw. You have to put the ski in backwards for lateral tests and there isn’t a calibration to adjust for the vertical axis of rotation being further forward in tech boots.

  27. Lou Dawson 2 May 18th, 2018 1:48 pm

    Jbo, which machine do you think is best? Thanks, Lou

  28. Lou Dawson 2 May 19th, 2018 4:16 pm

    Hey Jbo, can you give me a center to center measurement for the add-on “pivot change” bar that’s supposed to be used for AT bindings? I can’t afford to by one, but I have a welder and some old tool junk laying around, so I’ll cobble one up so I can eliminate the variable of my not using it. Thanks for any help. Lou

  29. jbo May 19th, 2018 6:14 pm

    No problem Lou, it is 10 3/4″.

  30. Matus September 14th, 2018 1:40 am

    Lou, what about testing the horizontal stiffness of the heel springs only (i.e. the front of the boot is rotating free).

    I would say that the heel springs do not matter very much when it comes to horizontal forces. In my view, the heel part rotates too easily when I think of my 90 kg and 30-50 km/h speed (I use a man spring in Atomic/Salomon binding).

  31. Lou Dawson 2 September 14th, 2018 9:23 am

    Hi Matus, the side (lateral) retention/release of a classic tech touring binding depends as much on the toe springs tension as the heel, and of course the heel is adjustable. Thus, measuring the heel independent of the toe serves no value I can see. As we’ve focused on for years, three things are important:
    1. Strong toe springs.
    2. Measured release values close to numbers printed on binding.
    3. Smooth movement of boot within range of release/retention.

  32. Al September 16th, 2018 9:53 pm

    Hi Lou
    Do you know of anecdotal/personal experience (besides the one unfortunate incident from above) regarding the atomic/salomon bindings? Are people, ok men, pre releasing with the “m” springs or not releasing in any consistent way? The reviews are good, but I think many people are like me and don’t stress them much. I skied them all spring and really liked them (light, easy to use) on the m spring, but I’m so easy on equipment I’m thinking of taking my chances on the lighter spring this year.

  33. Lou Dawson 2 September 17th, 2018 7:21 am

    Hi Al, there is no mystery, the heel operates the same way as any other classic tech binding in terms of being spring loaded in side retention-release. The M spring sets that at one value that is not adjustable, around 8 according to my evaluations. The W spring brings that down do around 7 for lateral BUT around 5 or 6 for the vertical, since classic tech bindings lack vertical elasticity and often must be run at higher release values for vertical, dropping down to the sexist , err I mean “W” spring might indeed risk accidental release considering the lowered vertical tension.

    The proper way to figure this out is to have a set of your bindings tested to determine what values you normally ski with, along with checking your recommended “DIN” levels according to the standard chart. Then test the setup you are questioning and see how it compares. Or else, as 95% of ski tourers do, guess, crank ’em up a bit higher and carpe skium.

  34. DAVID DODGE September 17th, 2018 9:57 am

    Lou – the Vermont Calibrator is a very good calibration device if used properly. As a lot of commenters have mentioned off axis loads can affect it though. It is important not to clamp the ski because the most common error introduced by clamping is a roll moment on the ski. If you don’t have the special vice the best way to prevent this is to put c-clamps beside the ski, not on top of it when doing twist releases. Fully clamping the ski tail is necessary for forward releases.

    Notice I said “very good calibration device”. It is not a good binding evaluation device. It is good at and intended to be used to set binding release values properly. The numbers on the bindings are only initial indicator settings and should be confirmed and tweaked with a calibrator such as the Vermont system. The reason for this, as you know, is that boot sole length and other boot/binding variations affect the release value.

    The reason calibration devices are not good binding evaluators is that they usually only provide a “moment of couple” (pure torque) to the boot/binding system. When skiing, it is very rare and difficult to apply an moment of couple. Imagine hanging from a harness under a helicopter and having it drill you into the ground. That’s the equivalent of using a torque wrench or most other calibrators. Almost all skiing injuries are the result of a moment of force. In other words, a force acting at or resolved to a single point on the ski with the body of the skier’s inertia providing resistance to that force. This a very different loading condition and introduces potentially large errors in release depending on how far the binding’s kinematic pivot axis is from the vertical tibial axis (twist) or horizontal boot top axis (forward). Errors with pin/tech binding can be in excess of + AND – 100% under some circumstances due the large distance between the vertical pivot axis and the tibial axis for twist release and the increased distance toward the toe of the boot for the horizontal pivot axis in forward release.

    Most pin/tech bindings are very good for their intended purpose if people are aware of their shortcomings. I always tell people to lock out the toe in “die if you fall” conditions and in other downhill conditions to keep the speeds down. The dangerous leg breaking forces are within 45cms of the boot toe. If you are going fast your inertia will create twisting moments at release of +100%. However, if you are going slow enough large forces close to the boot sole will cause your body to rotate and you will just flip over and land on your back before dangerous moments can break your leg or destroy your knee.

  35. Lou Dawson 2 September 17th, 2018 11:10 am

    Thanks David, your take always valued, I’ll mess around with the calibrator regarding roll and clamping, now that I understand the issue. Lou

  36. AndRand March 24th, 2019 6:13 am

    Have you tried with vertical forces acting on toe (as during landing leaning back or stepping/jumping hard with one edge on hard snow)? It looks like no matter where the axis of the jaws pins still grab them up.

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