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  1. #1
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    Sliding AFDs really necessary for touring boots?

    So for ISO 9523 soles with the rubber soles...I know lots of people jam them into STHs or CASTified pivots even though they're technically not supposed to. What kind of additional risk are they taking on to their knees? I'm assuming there will be lots of varying answers but I'm curious to what they are. Any testing been done, at home or in a "lab"? I'm tempted to try and rig something up that would test this and I'm open to suggestions. Yes, I could solve this problem easily and just got buy some wardens, but what's the fun in that.

    Calling all enginerds...does it make any difference on how the binding releases in a twist scenario? My understanding is that a binding like an STH releases at the toe and a pivot releases at the heel in a twist scenario. Does this change anything because of moment arms and whatnot?

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    Might as well get it out of the way: "Yer gonna die."

  3. #3
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    I suspect that the ability of the toe to release would depend significantly on the mechanics of the fall. The more weight on the toe, the more I'd expect the grippy rubber soul to do it's thing and inhibit a release. But more weight on the toe also implies falling forward, in which case the heal ought to release just fine. I think any "lab" testing would need to run the test in a wide range of situations accounting for more or less weight on the toe / AFD.

  4. #4
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    Quote Originally Posted by toast2266 View Post
    more weight on the toe also implies falling forward, in which case the heal ought to release just fine.
    Consider a twisting fall as you stuff your tips on a mogul. Stuffing the tips puts a lot of "weight" (vertical force) on the toe, but not enough for a vertical release at the heel.

    Quote Originally Posted by toast2266 View Post
    I think any "lab" testing would need to run the test in a wide range of situations accounting for more or less weight on the toe / AFD.
    Yep. And the best study of this I've seen made available to the public if Jeff Campbell's PhD thesis.

    https://digital.lib.washington.edu/r...dle/1773/38177

    https://digital.lib.washington.edu/r...=1&isAllowed=y

    tl;dr: sliding AFDs can bind with touring boots when there's more weight on the toe. When that happens, the release mechanism is now governed by the force to unbind the sliding AFD mechanism rather than the DIN spring. GW/WTR/etc shouldn't suffer these issues but they weren't out when Campbell did his testing. In Campbell's tests, the binding with the most consistent release with AT boots had a static AFD and the toe wings high enough that they didn't interfere with the tech inserts.
    "Alpine rock and steep, deep powder are what I seek, and I will always find solace there." - Bean Bowers

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  5. #5
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    Purely Anecdotal evidence, by I have now heard from 5 different orthopedic surgeons who swear by the sliding AFD, and won't ski anything else, no matter what the boot is (alpine or touring). Of those, 3 of them say they haven't seen a single patient with ACL tears who had the sliding AFD, the other 2 feel the damage they have seen wasn't as bad as they usually see in serious ACL tears..

    I'm guessing having a redundant load path to ensure a boot kicks out of a binding greatly reduced the risk of injury. Imagine gunk/shit under the boot that prevents the boot from sliding on the AFD.. With no sliding AFD, in a wreck, that lack of motion is translated into a twist of your knee... With a sliding AFD, even if your boot doesn't slide on the little Delrin pad, the fact that the pad itself can still translate, helps your boot release and prevent an injury. It makes a lot of sense...

  6. #6
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    Quote Originally Posted by brundo View Post

    Calling all enginerds...does it make any difference on how the binding releases in a twist scenario? My understanding is that a binding like an STH releases at the toe and a pivot releases at the heel in a twist scenario. Does this change anything because of moment arms and whatnot?
    Not an enginerd, but a lateral release in a pivot still comes from the toe. Like toast said, certain scenarios will amplify the friction between the afd and rubber sole, meaning the binding may release fine under some scenarios, but not in others.

  7. #7
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    Quote Originally Posted by toast2266 View Post
    I suspect that the ability of the toe to release would depend significantly on the mechanics of the fall. The more weight on the toe, the more I'd expect the grippy rubber soul to do it's thing and inhibit a release. But more weight on the toe also implies falling forward, in which case the heal ought to release just fine. I think any "lab" testing would need to run the test in a wide range of situations accounting for more or less weight on the toe / AFD.
    Would a pivot vs a STH change this at all? Once again my understanding is that a pivot twists out at the heel and a sth twists out at the toe. So if you were backseat while twisting out there would be a lot of weight on the rubber heel, making it difficult for the heel to slide, which sounds like a bad scenario for a pivot, but maybe since the whole heel is rotating (vs a toe having to slide off in an sth) its not that big of a deal

  8. #8
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    Quote Originally Posted by ExPowderSnob View Post
    Purely Anecdotal evidence, by I have now heard from 5 different orthopedic surgeons who swear by the sliding AFD, and won't ski anything else, no matter what the boot is (alpine or touring). Of those, 3 of them say they haven't seen a single patient with ACL tears who had the sliding AFD, the other 2 feel the damage they have seen wasn't as bad as they usually see in serious ACL tears..
    I personally tore my ACL with a WTR boot on a sliding AFD (pivot 14s). I didn't have any sort of meniscus tear - doctor described it as a clean tear - but I still required surgery and 9mo for recovery (back to moderate skiing at 7).

    Enginerd here, and I don't think it's a good idea to suggest a sliding AFD will help prevent ACL tears. There's no evidence to back this up and doesn't make much sense mechanically. Lateral release at the heel on the other hand...
    ...but then you risk spiral fracture of the tibia.

    Lateral release at the toe and heel might be the only true solution for both, but that sounds both costly and frustrating in regards to prerelease.

    edit:
    all that being said, I am very in on sliding AFDs. The interface of the delrin sliding mechanism with it's guidetrack is always going to be much cleaner and provide more consistent motion than the interface between the boot sole and the delrin on a static AFD.
    aerospace eng with a gravity fetish
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  9. #9
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    Quote Originally Posted by auvgeek View Post
    Yep. And the best study of this I've seen made available to the public if Jeff Campbell's PhD thesis.

    https://digital.lib.washington.edu/r...dle/1773/38177

    https://digital.lib.washington.edu/r...=1&isAllowed=y

    tl;dr: sliding AFDs can bind with touring boots when there's more weight on the toe. When that happens, the release mechanism is now governed by the force to unbind the sliding AFD mechanism rather than the DIN spring. GW/WTR/etc shouldn't suffer these issues. In Campbell's tests, the binding with the most consistent release with AT boots had a static AFD and the toe wings high enough that they didn't interfere with the tech inserts.
    Wow that's a long read, but I'll be sure to give it a skim. Thanks for the paper. That's really interesting that he found static to be more consistent. I would assume there would be no downside to a sliding afd because the afd still has the ability to slide. But maybe the key word here is consistent. Did he say what bindings met this criteria of these high toe wings?

  10. #10
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    Quote Originally Posted by brundo View Post
    Would a pivot vs a STH change this at all? Once again my understanding is that a pivot twists out at the heel and a sth twists out at the toe. So if you were backseat while twisting out there would be a lot of weight on the rubber heel, making it difficult for the heel to slide, which sounds like a bad scenario for a pivot, but maybe since the whole heel is rotating (vs a toe having to slide off in an sth) its not that big of a deal
    I don't think STH vs. Pivot would make a ton of difference. Both of those release sideways at the toe. The Pivots can rotate at the heel, which probably helps release in certain situations, but I don't think that'd be any different on a DIN sole vs. an ISO 9523 sole.

    If I had to guess, I'd think the STH would be better for toe releases since you manually set the toe height. The Pivot toe height automatically adjusts, which means that the binding is putting a pre-determined amount of downforce on the rubber sole / AFD interface. With the adjustable STH toe height, you could maybe run the toe slightly high in order to minimize friction between the sole and the AFD. Of course, all of that is pretty wishy-washy and will almost certainly result in a non-particularly scientific or repeatable release value.

  11. #11
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    Quote Originally Posted by ExPowderSnob View Post
    Purely Anecdotal evidence, by I have now heard from 5 different orthopedic surgeons who swear by the sliding AFD, and won't ski anything else, no matter what the boot is (alpine or touring). Of those, 3 of them say they haven't seen a single patient with ACL tears who had the sliding AFD, the other 2 feel the damage they have seen wasn't as bad as they usually see in serious ACL tears..

    I'm guessing having a redundant load path to ensure a boot kicks out of a binding greatly reduced the risk of injury. Imagine gunk/shit under the boot that prevents the boot from sliding on the AFD.. With no sliding AFD, in a wreck, that lack of motion is translated into a twist of your knee... With a sliding AFD, even if your boot doesn't slide on the little Delrin pad, the fact that the pad itself can still translate, helps your boot release and prevent an injury. It makes a lot of sense...
    This makes sense and from some pretty smart people. I wonder though that the reason they haven't seen as many people with ACL tears with sliding AFDs is because the large majority of bindings don't have sliding AFDs so its just a numbers game if 80% of people don't have sliding AFDs

  12. #12
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    Quote Originally Posted by brundo View Post
    Once again my understanding is that a pivot twists out at the heel and a sth twists out at the toe
    Both release laterally at the toe.

    There are a few bindings that release laterally at both the heel and the toe (knee binding and whatever Howell is working on), there are bindings that release at the heel (many tech bindings), and bindings that release at the toe (most alpine bindings).

    Also, my understanding is toe release saves your tib/fib and heel release saves your ACL in a backwards, twisting fall. There are totally unrelated to static vs sliding AFDs.

    https://www.wildsnow.com/15123/tech-...cl-broken-leg/
    "Alpine rock and steep, deep powder are what I seek, and I will always find solace there." - Bean Bowers

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  13. #13
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    Quote Originally Posted by brundo View Post
    Wow that's a long read, but I'll be sure to give it a skim. Thanks for the paper. That's really interesting that he found static to be more consistent. I would assume there would be no downside to a sliding afd because the afd still has the ability to slide. But maybe the key word here is consistent. Did he say what bindings met this criteria of these high toe wings?
    No, there is definitely a downside to the sliding AFD: it binds up and takes a MUCH higher force to release in certain conditions -- e.g., when the front of the ski is loaded and you need to release laterally at the toe. "Consistent release" means it releases to spec in various conditions. Plenty of people do backyard binding testing, but Campbell's research is the first I've seen made publicly available where different loads are applied to the body of the ski. I'm sure there's much more research to be done, but it's a start.

    Campbell never said which bindings were which. High toe wings and a static AFD pretty much gives it away, though.

    Quote Originally Posted by macon View Post
    all that being said, I am very in on sliding AFDs. The interface of the delrin sliding mechanism with it's guidetrack is always going to be much cleaner and provide more consistent motion than the interface between the boot sole and the delrin on a static AFD.
    Dude, look at Campbell research. The data say otherwise. When the sliding AFD mechanism binds on the guide track, the release is no longer governed by the release spring but by the force to unbind the sliding AFD.
    "Alpine rock and steep, deep powder are what I seek, and I will always find solace there." - Bean Bowers

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  14. #14
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    Quote Originally Posted by brundo View Post
    I wonder though that the reason they haven't seen as many people with ACL tears with sliding AFDs is because the large majority of bindings don't have sliding AFDs so its just a numbers game if 80% of people don't have sliding AFDs
    I'm willing to bet this is the case.
    aerospace eng with a gravity fetish
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  15. #15
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    Quote Originally Posted by macon View Post
    I personally tore my ACL with a WTR boot on a sliding AFD (pivot 14s). I didn't have any sort of meniscus tear - doctor described it as a clean tear - but I still required surgery and 9mo for recovery (back to moderate skiing at 7).

    Enginerd here, and I don't think it's a good idea to suggest a sliding AFD will help prevent ACL tears. There's no evidence to back this up and doesn't make much sense mechanically. Lateral release at the heel on the other hand...
    ...but then you risk spiral fracture of the tibia.

    Lateral release at the toe and heel might be the only true solution for both, but that sounds both costly and frustrating in regards to prerelease.

    edit:
    all that being said, I am very in on sliding AFDs. The interface of the delrin sliding mechanism with it's guidetrack is always going to be much cleaner and provide more consistent motion than the interface between the boot sole and the delrin on a static AFD.
    Sorry about the injury, exactly what I'm trying to avoid. Isn't lateral release at the toe and heel exactly what a pivot is? They're also known as being one of the best in terms of prerelease

  16. #16
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    Quote Originally Posted by brundo View Post
    Isn't lateral release at the toe and heel exactly what a pivot is?
    No. With a pivot binding, the lateral release is only at the toe. The heel pivots but does not release laterally.

  17. #17
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    Quote Originally Posted by toast2266 View Post
    grippy rubber soul
    This is a problem in skiing today. Just let it slide, man.
    PE, Mechanical Engineering
    University of Bridger Bowl Alumnus
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  18. #18
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    Quote Originally Posted by Norseman View Post
    This is a problem in skiing today. Just let it slide, man.
    Heh. And here I thought soul turns required tele bindings.

  19. #19
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    I'm curious about the "jamming in non-MNC or similar bindings"? Will an ISO 9523 sole fit in a pivot 18? I have ISO 9523 soles and have wardens and shift and just assumed with the amount of toe height adjustment it would not even fit let alone release.

  20. #20
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    Quote Originally Posted by GeezerSteve View Post
    No. With a pivot binding, the lateral release is only at the toe. The heel pivots but does not release laterally.
    This. Itís a common misconception that Pivots release laterally at the heel, but try it on a bench and youíll see itís not possible.

  21. #21
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    Quote Originally Posted by MegaStoke View Post
    This. Itís a common misconception that Pivots release laterally at the heel, but try it on a bench and youíll see itís not possible.
    Huh. So what's the point of the pivoting heel?

  22. #22
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    Quote Originally Posted by auvgeek View Post
    Campbell never said which bindings were which. High toe wings and a static AFD pretty much gives it away, though.
    Please decode. STHs? I not as binding smert as many of you. Before this year I just went with the ones I could find on sale.

  23. #23
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    Quote Originally Posted by brundo View Post
    Huh. So what's the point of the pivoting heel?
    A small degree of lateral elasticity at the heel, and the heel piece rotates to follow the boot heel when releasing laterally at the toe, allowing for smoother release.

  24. #24
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    Quote Originally Posted by auvgeek View Post
    Dude, read Campbell's thesis. The data say otherwise. When you bind up the mechanism on the guide track, the release is no longer governed by the release spring but by the force to unbind the sliding AFD.
    I'm looking at it now, but I don't see where in the report says the sliding AFD ever bound. Can you point out to me where this is stated definitively?

    All I'm seeing is that every sliding/mechanical AFD was forced past their limit on the guide track, as is stated in Figure 3.9 (page 84). Additionally, "AFD pressure was poorly correlated to release torque for both Alpine and AT boots in all
    three boundary conditions." Figure 3.7, Table 3.2 (page 75).

    His report provides great analysis, but I'm having trouble understanding where he identified the inconsistency in the mechanical AFD. Then again I've only taken a cursory look at this.

    Unfortunately, the mechanical AFDs used in this report are not the standard delrin/teflon sliding afds that are used now, as stated on page 69 (this study was conducted and the thesis was generated prior to the WTR/Gripwalk industry shift).
    aerospace eng with a gravity fetish
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  25. #25
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    Quote Originally Posted by brundo View Post
    Huh. So what's the point of the pivoting heel?
    Marketing, mostly. Yes, it possibly reduces friction at the interface between the top of the heel lug and the dildo, but that's usually a pretty clean, low-wear area that doesn't have a lot of friction to begin with. Mythology aside, it's not surprising Look dropped it for awhile. The Rockerace heel has a similar short mount, and is probably more precise in every way.

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