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mechanical properties of tele springs

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  • mechanical properties of tele springs

    I'm sure one of the engineers on here knows this. Is there a good table of properties of the various springs currently used in tele bindings, such as different Voile cartridges, etc...?

    In particular, the spring constant and the amount of travel that the spring has from the position where it generates no force (fully uncompressed) to whatever is the maximum compression possible (for a compression spring, there is a hard limit on travel, while for an expansion spring there is some maximum amount you can expand it before it distorts). I assume the springs are generally all being used in a linear regime, at least until you hit limit of travel? Also interested in typical preload force on springs in typical setups, i.e., force when the heel is flat on ski. In an ideal world, I'd love to know these measurements for all different kinds of things: 75mm bindings, TTS (presumably fairly similar to 75mm since the same cartridges are used in most cases), and NTN.

  • #2
    originally, heel cables were not involved in generating leverage in tele. Cables were used because the 3 pin connection between the boot and binding got sloppy fast, so the addition of sprung cables driving the boot forward into the wedge shape of the binding made a longer lasting solid connection between boot and binding. Side mounted cables on the boot actually helped break the bellows when the skier lifted his heel.... Later, Mike Miller invented the underfoot cable binding which created the modern leverage relationship of binding heel retention and generated ski tip pressure.

    ...But in spite of the discovery of a mechanical leverage in tele bindings (and stiff boots to use as a lever in those bindings) the essential ideas of technique are still there, just in different proportions because the mechanical advantage of powerful bindings allow for a much wider range of technique.

    The first NTN bindings were so neutral in their mechanical design, I learned to ski without a lot of spring tension or binding activity. It made me have to use more balance, timing and skier intuition rather than use leverage in a power technique... You can go down the power technique road. The Hammerhead binding obliterated other binding manufacturers because of it's powerful leverage capabilities. If you had no technique or very little experience, you could set a HH up to be very active and your skis would react more quickly to your input. It helped a lot of people learn tele pretty quickly,... and of course every tele freeride contest podium was occupied by 3 guys in T1 boots and hammerhead bindings for a lot of years because of how powerful that combo was...

    If you can learn to ski well without a lot of spring tension, you will compensate by learning the basics of good technique rather than learning to control powerful binding generated forces in a power oriented technique... In some ways it doesn't matter which way you go, because when you are on your gear, the technique you develope works. I think the less powerful binding oriented technique helps you if you switch to light weight XCD gear where you don't have binding leverage... but that's not a huge compromise.

    It's good to be aware of the element that comprise your tele experience. It's always good to try one and compare it to the other...

    ... springs?? I don't know... Back in the early 2000's I skied HH's on 4 a few times without a lot of preload, and it felt like a heel piece to me (and I'm a bigger person) I guess if I had originally learned on powerfully sprung bindings, I might prefer it now. I feel like powerful gear helped elevate my skiing performance to a point, then more powerful spring settings beyond that just felt like a heel piece....
    Last edited by tele.skier; 6 September 2020, 07:00 PM. Reason: Because I never write anything clearly the first time
    the fall line is your friend.... resistance is futile

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    • #3
      tele.skier, I think I have fairly similar feelings on technique and activity to you, but I don't think any of that's relevant here. I've got a pair of skis with 3-pins that I use sometimes (not counting my classic XC and skate XC skis), but other than that every tele binding I have has springs in it, and I'm guessing most of your bindings have some kind of spring in them too. I think you've said you've never skied a tech toe tele binding, but you can't ski tech toe tele without some kind of spring.

      Actually, the reason I'm asking is that I've got some ideas for a really lightweight, really neutral TTS binding and I'm trying to get some ballpark estimates for what is the minimal spring constant and travel I'd need.

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      • #4
        Originally posted by xmatt View Post
        I've got some ideas for a really lightweight, really neutral TTS binding and I'm trying to get some ballpark estimates for what is the minimal spring constant and travel I'd need.
        Sweet! I'll give ya the cliff notes of what I've learned from many attempts at doing the same thing. Forgive me if any of this is old news to you, perhaps there are other budding tinkerers out there with some brilliant ideas.

        (First, if you haven't already, go thru the Tele Tech Chronicles articles that Dostie put together for Telemark Skier Magazine. This one has links to all the others. One of them lists the spring travel for a bunch of off-the-shelf options. jasonq may have mentioned having recorded some spring rates at some point.)

        The number one thing I'd suggest is to design in a wide range of adjustability, not worrying so much about lightweight on the first iteration. It HAS to ski well first. I've found it hard to predict things like activity settings until I'm on the snow. Once you find the values you really like, then move forward with paring things down and dropping weight.

        If you're going to be using non-telemark-specific springs, Lee Spring and Century Spring have good online catalogs. They list Spring Rate (lb/in) rather than the Spring Constant. Having the springs on one foot add up to 130-150 lb/in seems like a good ballpark place to start. The perfect value can of course vary wildly based on binding geometry, the boots you're using, skiing technique, etc.

        If you're going to the trouble of designing something from scratch, I'd shoot for at least 50mm (2.0") of spring travel. Compressing a spring until it limits out every turn is bad for many reasons, including for the life of the spring. The extended length and solid length are listed on the catalog pages as well.

        I try to make my prototypes have activity options (distance the cable pivot point sits aft of the toe pins) of 40-80mm. If you know you really like neutral, maybe go 20-70 or something. I wouldn't consider myself a lover of super active bindings, but my TTS sweet spot usually ends up around 72mm. I believe Cesare is in the same boat. Distance down from the pins also plays a role. Folks say that every 1 mm down equals 2 mm back. There's a good list of binding pin heights here.

        And if there was to be one golden rule of TTS building, the further back you put the cable, the more spring travel you need.

        ​​​​​​​Keep us updated on your build!

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        • #5
          As BTS mentioned, I listed what I could find at the time in my article on Spring Size Matters for the Tele Tech Chronicles.

          ain't no turn like tele!

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          • #6
            Xmatt. You usually need a certain amount of tension to hold the boot into the tech toe. The shoulders of the boot sockets being wider at the back ( I guess you know this already, but someone here kindly pointed it out when I first thought about tech toes....that should not work) Perhaps on tech toes specifically designed for tele this is not the case?

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            • #7
              telemarkmark, yep, I do know that and that is a great point. Actually, one of the things I'm wondering is how much forward force is needed to stay in the toe. BTS says 130-150 lb/in spring constant on each foot. A spring probably isn't compressed that much, maybe 1/2 inch, with heel down? I should measure how much preload I use. If so, that's about 70 lbs needed of forward force.

              I don't really have a design yet, but just fooling around with some ideas. One thought is to think about the requirements in terms of force needed when heel is down (exactly what you were talking about) and also in terms of total energy that needs to be stored. Do I really need to store as much energy as a 140 lb/in spring with 2 inches of travel, i.e. E=1/2 k x^2? Probably not. That 140 lb/in spring compressed 2 inches is probably creating much more force than I actually need or want when the heel is up that much. I really think that I only want travel to avoid breaking things; I don't need to generate lots of force when the spring is highly bent. So, I'd be happy with something that generates enough force to stay in the tech toe when heel is down and generates enough resistance to heel lift to make it possible to balance and bend my bellows without rotating on the toe, and it is ok if the resistance doesn't ramp up much more or even decreases at higher heel angles. My guess is that jorider's Tt2 effectively does something like this by moving the pivot forward once the front starts to pivot, but I am trying to understand.

              My other thought is that I want a really light simple binding with a lot of freedom. I think Meidjo and existing TTS (I use Moonlight) perform pretty awesome, and actually aren't all that heavy (same weight as a lot of midweight AT bindings) but I feel like there is something missing on the really light end, something really free, even if it doesn't quite rip downhill as well.

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              • #8
                Xmatt, look forward to seeing what you come up with.
                My Skimo Tele binding uses a Dynafit Speed toe, a multi leaf carbon leaf spring, short simple springs. Weighs in at 460g, including heels and screws. A lighter toe and heel could probably knock 150g off that. It has taken sometime to get used to it and get the tension right, but before lockdown I was really starting to enjoy it. I use it with F1 Race boots

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                • #9
                  telemarkmark That latest iteration is looking pretty slick. Shaving off 150g would make it extra impressive. You should share it in the Tt2? thread, your bindings and those are very similar, using two stages to tailor the flex and address spring limits. Nice work!

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                  • #10
                    nice telemarkmark! Lighter toe, lighter heel certainly. And do you need that solid metal behind the springs? Since it is just cord in front of the springs, would there be any performance loss in using something flexible behind? And is that really bungee cord??? I thought about spectra and I'm amazed bungee works. And would a usual heel throw instead of that toe throw save some weight?

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