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Do bellows help or hurt uphill efficiently?

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  • Do bellows help or hurt uphill efficiently?

    In the comments on Wild Snow's recent Telemark article -- and in other places I've seen recently -- there's been a debate on whether boots with bellows are more efficient for skinning than rigid boots (like all modern AT offerings). Are there any data on this? Or a legit, overwhelming consensus from pro racer types?

  • #2

    It seems pretty likely that the primary reason bellows went away for AT boots was because of their propensity to release unsafely, and it was too much of a liability for the manufacturers. I'm less convinced that it has to do with uphill performance.

    For one, Dynafit's flexi-toe AT boots were in 2 of their lightest, raciest models at the time, the D.Y.N.A. and the TLT5. In other words, it wasn't done for beginners' comfort; Dynafit had reason to believe it made for faster skinning (for folks to whom it really matters).

    Obviously, classic XC boots are used primarily on flatter ground, but they have fairly flexi soles. If fully rigid soles were faster, they could be made that way, like skate boots. (Yes, I know part of the reason for flexi soles was to help set the grip wax pocket in the snow. Is this the same with zero skis?)

    The argument against bellows is that it sops up energy every time you flex them. This is undoubtedly true in 75mm tele boots with the duckbill clamped down. It's more complicated in a 2-pin tech-toe setup. Since the boot can pivot freely, any flex in the boot is primarily to get the foot/ankle in the kinesthetically ideal position for a powerful push-off -- not necessarily because it's required to lift the heel off the ski. Do the losses outweigh the gains, or vice versa?

    Anyway, the real answer is probably "It all depends." Mostly upon biomechanics and upon terrain. For folks like me who are relatively inflexible, the more points in the chain that can accommodate some flex, the more natural my stride can be (for some folks, this also applies to skiing downhill in free-heel gear vs locked-heel gear). Of course some uphillers look totally smooth in rigid-soled boots. Lucky bastards.

    On steep pitches, where gravity reduces glide to nil, I've noticed that my bellows stay quasi-permanently flexed, almost as if the push were coming more from the ball of the foot. It reminds me of running up a steep hill in trail runners, choppy steps on deeply-flexed soles.

    Of course every reason I've given is circumstantial and/or anecdotal. And I could be flat-out wrong. Does anyone know of better proof one way or another?

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    • #3
      All I can say is that the flexible bellows allows for a more natural stride and is far more comfortable if you're out for several days with nothing but ski boots.

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      • #4
        Certainly feels natural. (Never used AT) On flatter terrain you are using your foot muscles to give a kick, better than a fixed sole shuffle. Whether it is more efficient, who knows, guess not that significant. Of course going steep you are on heel raisers, so everyone is shuffling.
        I think the dropping of the bellows was to give a stiffer, lighter boot, more about the downhill.

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        • #5
          Conversely, can you Tele in AT boots?
          The cuff would not be locked, though may need some elastic resistance to give better toe pressure. The overall forward lean is similar if not better than a Tele boot.
          (Please ignore my failed mk1 TTS)

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          • #6
            On steep ground with heel riser activated, a bellowed boot sinks over the bellow when you put your weight on it - not much, but noteable, and losing a few millimeter in vertical gain each step adds up. On the other hand the bellowed boot have a clear advantage in the kick&glide. So to conclude I think that bellowed boots are better in the end, and that the demise of bellowed boots from skimo racing are more influenced by other reasons such as weight, releasabilty and keeping the boot simple and rigid.

            On a sidenote, I rarely use heel risers on boots with decent ROM so the collapsing bellow is less of a problem for me.

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            • #7
              BTS,

              As you said, "it depends." I don't think there is any clear evidence it is superior. As dschane pointed out, and telemarkers know, the stride is a whole lot more natural with the bellows. But, I think the concept was dropped by Scarpa because a bellows demands pebax, which is heavier than Grilamid. In racing, weight matters. And, the current state of the art in skimo boots allows for WAY more cuff ROM than any bellowed boot, which compensates for the stiff sole.

              I suspect part of the hold up with Scarpa's next gen tele-boot is to create something that will translate into the skimo arena and deliver a clear advantage that will give tele a boost in the media's eyes and help spur new interest. Maybe. 110% speculation there.

              ain't no turn like tele!

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              • #8
                I think the bellows reduces efficiency if you are climbing. It may be more comfortable to wear over the course of the day and be an advantage generating a kick for gliding on the flats, but I think it makes stair stepping less efficient because your energy goes into bending the boot or using a greater range of motion in your stride to overcome the extra travel distance caused by the boot bending on every step.

                For all of us pinheads, I think we know better than most that a flexible boot is better on the flat terrain with the appropriate skis. Asking some hardcore AT skiers who've skied both bellowed and non-bellowed boots if they think one style is better than the other for climbing, you might get a split opinion or maybe a unanimous one. It would be interesting to know if AT skiers who tried both clearly prefer one over the other, and why...
                the fall line is your friend.... resistance is futile

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                • #9
                  I have a lot of time hiking with non bellowed AT boots both heavy and light as well as plenty of time hiking with tele gear both heavy and light. I think that once skins are on and are hiking on wild BC type snow there isn't much glide so it comes down to stride length and IMO, Tech AT has a longer stride so more distance covered with each step. Now, I am not comparing Tech Tele as I have never toured with anyone on those but regular NTN and free pivot tele seem to have a shorter stride and either have to pick up the pace or fall behind or the AT skier slows down a little. So, in my experience, This is more of a difference than bellows or maybe weight. WTBS, I think bellows and tele skis in general have a advantage with K&G on the flats and slogging with skins off. New school, Tech AT boots have a lot of ROM and with buckles thrown open has enough flexibility to not need bellows even for a race course advantage.

                  For me, I would not want bellows on my AT boots even if there was some sort of advantage. Of course you need bellows on tele boots but I think the experiment of bellowed race AT boots is over or at least over for moving that to the recreational market.

                  Want to gain performance? Improve fitness and strength to speed up pace.
                  "Just say no to groomed snow"

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                  • #10
                    my guess is that the "it depends" really depends on a lot of factors and in the end, same boot, same skier, the answer is yes, no, shmaybe, depending on terrain.

                    If the bellows was perfectly elastic/ frictionless/zero damping, and had zero droop, and zero impact to mass, i think the answer would be yes, it is more efficient. But none of those things are true. compressing the bellows takes energy, energy that is not all returned. the droop, as mentioned, requires energy to recover the lost elevation. And the including a bellows implies certain materials need to be used, which ends up impacting mass with today's materials/designs.

                    take the above, and on flats where there is glide, long strides, and no elevation change, bellows are likely better. on steeps where glide is zero, stride length is shorter, and there is elevation gain, likely not. in between, shmaybe, probably depends on the individual's style/biomechanics.

                    for most of us, it is probably a e of one or ln(1) of the other. (dweeb math joke, e is defined as the natural log of 1)

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                    • #11
                      Originally posted by telemarkmark View Post
                      Conversely, can you Tele in AT boots?
                      The cuff would not be locked, though may need some elastic resistance to give better toe pressure. The overall forward lean is similar if not better than a Tele boot.
                      (Please ignore my failed mk1 TTS)
                      I can, sort of tele with my La Sportiva Spectres, with the cuff unlocked. This boot (unlike other AT boots) doesn't have a lot of cuff travel to the rear, when you unlock the boot cuff, but lots of flex forward, in the cuff.. Boot heel is still locked down..So I can tele on low angle slopes with soft snow. The only scary thing is, if you fell, with the cuff unlocked, not sure if you would generate enough twisting force for a safe release.
                      Last edited by chamonix; 6th October 2019, 06:46 PM.

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                      • #12
                        I think it's a specious argument because in my opinion, ROM confers a much greater advantage in terms of stride length than a flexible but still pretty stiff tele boot takes away in terms of climbing efficiency given a tech binding in both cases. That's why I wish even more for greater ROM than a weight reduction in my tele boots. A little weight loss would be nice but the ROM is the more significant deficit for me.

                        And I wonder if anyone else finds it amusingly ironic that conventional tele wisdom used to be that a short stride was more efficient in skinning and now almost everybody agrees that a longer stride is much faster and more efficient. A short stride was all we could do without going anaerobic before we got free hinging bindings.

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                        • #13
                          I tend to "scoot" skin with short strides with looses boot buckles so I don't think it makes much difference. Maybe at longer strides on steep up hills, but it's pretty minimal. The flex is for tele when all the buckles are tight.

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                          • #14
                            With no physical evidence, it seems to me bellows are slightly less efficient on average, and Cesare is correct, ROM is more noticeable, and of course weight is a big deal. But that doesn't mean I tour on 65mm waisted Ski Mo race skis. Having fun is the key.

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                            • #15
                              Originally posted by cesare View Post
                              And I wonder if anyone else finds it amusingly ironic that conventional tele wisdom used to be that a short stride was more efficient in skinning and now almost everybody agrees that a longer stride is much faster and more efficient. A short stride was all we could do without going anaerobic before we got free hinging bindings.
                              Do other's agree that a longer stride is considered more efficient? All the ski mo racer beta that I have read says shorten your stride for efficiency. I don't know why tele would be different.

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