Atomic Ski Boot Flex Testing Machine

Post by blogger | February 24, 2017      
Atomic boot flex testing machinery. We need a name for this rig.

Atomic boot flex testing machinery. We need a name for this rig. I propose “Atomic BS Detector.”

I recently enjoyed visiting Atomic headquarters in Austria, lots to write about. For now, in my opinion one of the reasons Atomic usually has ski racers on World Cup podiums is they have a highly technical corporate culture. While doing things by “feel” can be valid, one area where I’d like to to see more documented measurement is in the area of boot flex. The industry throws numbers around (130!) like a coach throwing soccer balls at a grade school field practice. My understanding is quite a bit of that is simply done by employees buckling into the boots and essentially sticking a number on what they feel, most often related to other boots in the same brand rather than an industry-wide standard.

Result, ski boot flex numbering can be a joke. But not if it’s actually measured with standardized mechanicals hooked to a computerized load cell. Our hope is that this scientific measurement done by Atomic — and perhaps certain other boot makers (let us know, happy to publish more) — will eventually work towards an industry agreed standard of instrumentation and reporting. Or, perhaps a third-party will lash up this type of machine and begin publishing results? In the latter case, the ultimate BS detector!

From Atomic, lightly edited for clarity and brevity: This was custom made for us by a local robotics team, it flexes the boot fore/aft to specified degrees/angles and measures how much Nm force it takes to reach those angles. The range we set is very realistic and achieved during normal skiing. When we hook a boot up to it, it provides us with the data you see on the attached chart- maximum stiffness and flex curve. It allows us to see how all of our own boots and competitors stack up against each other. We use this data to find out how stiff our competitors actually are vs. what they claim, and also to align our own boots as consistently as possible. If we see that we are too stiff or too soft for a given flex rating, we can adjust the plastic mixture accordingly. As you know there is no DIN, ISO or any other industry standard for flexes, so this data is incredibly helpful for us to deliver what we think are the truest and more legitimate flexing boots on the market. We like to think that if a standard would be developed for flex, we would be at the top of the list. This is even more crucial in the touring world where lots of lofty flex numbers and promises of progressive flex are made, but appear to sometimes not delivered.

Atomic boot flex measurement tool.

Atomic boot flex measurement tool.

Another view of the rig.  Items of note:

Another view of the rig. Items of note: Some sort of artificial foot is of course essential, in the video you can see they’ve labeled this one as 26.5, indicating they might have different ‘feet.’ Atomic opts to test with the liner installed. I can understand why that might be the case, but it would seem better to test all boots _without the liner_ as well as with it, and create two flex curves. Or, perhaps simply test all boots without liner, since aftermarket liners and customizations are so common. Note how the boot is firmly clamped down, to eliminate variables in binding flex, while the boot is still suspended between two points as with most tech bindings. If the boot is set solidly on AFDs, that would presumably stiffen the flex a bit as the soles of ski touring boots can bow flex quite a bit. This machine resembles others I’ve seen in the industry that were used for cyclic durability testing, perhaps Atomic uses it for that as well.

Machine results, flex comparison.

Machine results, forward flex comparison. Ideal for progressive flex is a curve that has a slight “belly” not a straight line. Though the straight line that climbs is clearly better than the horizontal line you would get in the case of a boot made from steel, with nearly zero flex. Click to enlarge, and you’ll see the Y axis is labeled with Nm (newton meters) which is a measurement of torque. Note in the case of Hawx 130 that the flex curve indeed intersects Nm 130. Thing is, that’s only at one point during the flexing of the boot, so the question arises, at what point do you grab a number to print on the boot? That’ll probably be another thing needing standardization. At the least, kudos to Atomic for relating the published boot flex number to actual measured newton meters, and high praise for actually using a nicely built machine to do so.



19 Responses to “Atomic Ski Boot Flex Testing Machine”

  1. Bill H February 24th, 2017 8:49 am

    Maybe SkiAlper can rent some time on the machine for next year’s issue 🙂

  2. Tom Gos February 24th, 2017 9:27 am

    Lou, I seem to remember that back in the ’80s Ski Magazine (the American one) would measure boot flexes and publish curves similar to what Atomic has sent you. I’m sure they weren’t using a robot at that time, probably some sort of spring type force measuring tool. Maybe you can build something similar in the Wildsnow shop and publish your own flex comparisons?

    Also, this is the first time I’ve read that the boot flex rating number is actually a N-m torque value. Have you confirmed that with manufacturers or is the 130 value on the curve simply a coincidence?

  3. Lou Dawson 2 February 24th, 2017 11:13 am

    From what I know, unlikely all the boot flex ratings in the industry are an actual Nm torque value, but some might be. Even if some of the companies use machines such as this, there is no standardization. In the case of Atomic they are indeed the Nm measured by their machine.

    Thinking this through, I don’t think numbers such as “130” are a coincidence. But study the graph, and you’ll see it is Nm vs angle, so it only hits 130 at one point…

    It looks like the lever on the Atomic machine is about 50 centimeters, obtaining 130 newton meters would mean during boot flex the load cell on the machine would need to measure 260 newtons (26.52 kilos, 58.7 pounds) of “force” with a 50 centimeter arm? Does that sound right? Engineers, help us?

    This is pretty danged tricky, as the lever arm would need to somehow be exactly the same for each boot. Measured from the boot cuff pivots? If they’re using an artificial foot with a fixed pivot that doesn’t quite match the boot pivots, that would skew the results to some degree?


  4. Lou Dawson 2 February 24th, 2017 11:21 am

    Tom, it would be easy to do something crude using a torque wrench on an artificial foot and leg, buckled into a boot, and then pulling the torque wrench to a standardized point in the boot flex range. Sounds like a time consuming thing to set up for iffy results. Instead, I think this is something better left to the pros with budgets, I think Atomic is doing it just fine, and other people probably are as well. Instead of one-of machines, again, we need something standardized. But that’s not saying I won’t fool around with it, as I do have that nice force gauge. Lou

  5. Omekim February 24th, 2017 11:23 am

    Ummm…. The machine looks to be at room temperature. They should probably put it in a freezer, or do they test with changing temperature somehow? From personal experience my Langes flex totally different whether in the house or spring skiing (super soft and sometimes collapse completely) or just below freezing (perfect) or -15C or less (solid like concrete).

  6. Jack February 24th, 2017 12:05 pm

    hmmm. I wonder how hard it would be to instrument the boot liner to measure forces transmitted to the boot during actual skiing? Probably not too hard. Really good repeatability across size ranges would be a bit tough. Might be easier to instrument the anti-friction pads on the binding. One could characterize a test skier’s force inputs, which, I would guess, vary a lot.

    I second Omekim’s comment about temp. Not certain how easy it is to compensate for this from a room temp. measurement.

  7. Carl February 24th, 2017 12:57 pm

    I have found how the boot is buckled has a huge flex impact as well. Boots feel soft when buckled loosely but stiffen up around the sticks I have for ankles. This is a hard test to standardize.

  8. Tom Gos February 24th, 2017 1:37 pm

    Lou, with regard to your torque math you are correct about the 50cm lever arm and the double Newtons (yes, I’m a licensed engineer).

    As for all the factors (like temperature) that would effect the measurement of an absolute value, such is life – any type of measurement reported is for a specific condition. I don’t think the absolute value is what’s of interest, the comparable values for a selection of boots is what is interesting. None of us can relate to an actual torque value, but we can all understand that a brand A boot on one foot is stiffer or softer than a brand B boot on the other. This is why a standardized measuring system would be so valuable. But I suspect the boot manufacturers will never offer up data on how their boot compares to a named competitor (notice that the Atomic table keeps the competitors anonymous). This is why it would be great to see an independent third party perform the tests and report the results.

  9. Lou Dawson 2 February 24th, 2017 2:15 pm

    Thanks Tom, I have fun learning about the tech stuff but definitely don’t have the training. Indeed, comparable values are what’s important, though the bugabear is that some plastics get stiffer when cold, and some don’t… I’d think in the end they’d want to test the boots at perhaps zero C as a standard.

    I’m still fantasizing that I could indeed lash something up. Measuring force isn’t hard for me, the challenge is making the foot-leg that’s fair to the process, as well as combining measured angle or distance with the instrument I’ve got. I’ll wait and see what other guys in the industry come up with. Atomic may have lit a bit of a fire, they sure look good when they say “130” and can back it up with a test rig and Wildsnow blog post (smile).


  10. Jack February 24th, 2017 2:31 pm

    re: foot/leg
    Find someone who repairs/rebuilds prosthetics, or find a MS grad student in some sort of human factors research who needs a project. I imagine both types would be knowledgable and ‘makers’.

  11. Lou Dawson 2 February 24th, 2017 2:55 pm

    More from Matt at Atomic:

    “The Nm rating of 130 is actually just a coincidence. As you mentioned, at what angle should we take the Nm measurement and correlate that to a flex rating? Not so easy… And as you can see, at the end of the flex range we reach a little over 190 Nm with our “130”. Ultimately, when we have a boot that had a good reception as a “real” 130 in the markets, with athletes, testers, etc. we use this as our baseline at least and try to match our boots to it. Same for the other flexes too.

    The video was obviously done at room temperature for simplicity’s sake. We do take room temperature information very seriously though, as almost all boots are purchased at room temperature – aside from shop buyers, very few people actually demo boots. But we also do the same tests at -20°C, -10°C, 0°C, 10°C, 20°C for all boots. We have a huge walk-in freezer that we run our longevity tests in, as well as these tests. As you can imagine, have quite the library built up on flex data.

    In terms of with liner or without liner, it’s a hard call to make. We like to use the boot as it is delivered to the customer. That might be the fairest way to go about it.


  12. Lee Lau February 24th, 2017 6:35 pm

    That is so incredibly cool!

  13. See February 24th, 2017 7:48 pm

    The coolest aspect of this device, in my opinion, is the graph. It looks like it should provide a good representation of the progressiveness of the flex. I would really like to compare graphs for overlap boots, tongue boots, carbon cuff light touring boots, etc..

  14. Tom Gos February 25th, 2017 4:28 pm

    I have to say one of the most interesting aspects of this post (that seems to be overlooked) is the photos of the new Atomic free touring boot. I can’t see how the walk mode bar engages the lower boot shell, it almost looks as if it’s only with the visible gripper teeth but I can’t imagine that being a solid connection. Any insights Lou?

  15. Lou Dawson 2 February 26th, 2017 11:59 am

    Tom, it’s a standard external lean lock, it has a slot that hooks over a horizontal pin at the base of the bar, in position as pictured. It’s quite solid. We favor the external locks, less trouble, very rigid. Lou

  16. See February 26th, 2017 1:18 pm
  17. Lou Dawson 2 February 26th, 2017 1:57 pm

    Thanks See, appreciate the help. Lou

  18. carlos February 27th, 2017 6:13 am

    I heard also Dalbello has a machinery to test boots, maybe if you have contacts with them you can ask for their experience

  19. Jwolter March 8th, 2017 12:16 am

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