Sliding AFDs really necessary for touring boots?

[PeachesNCream]

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 correlatedto Release Torque for all load cases including Front Preload Twist (right)." Figure 3.7 (page 75).

His report provides great analysis, but I'm having trouble understanding where he identified the inconsistency in the mechanical AFD. Unfortunately, the mechanical AFDs used in this report are not the standard delrin/teflon sliding afds that are used now (this study was conducted prior to the WTR/Gripwalk industry shift).

I think this may have a pretty substantial impact. You're just adding the sliding afd feature and not removing anything. I don't see how this could make it worse

[auvgeek]

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 correlatedto Release Torque for all load cases including Front Preload Twist (right)." Figure 3.7 (page 75).

Bottom of page 83, he says:

"The worst load case for mechanical AFDs occurs in Front Preload Twist releases, when a
preload is applied to the fore-body of the ski significantly increasing the pressure between the
soft AT boot sole and AFD. As a lateral load is applied to the ski, softer AT boot soles stick to
mechanical AFD as the binding moves away. During this phase, the spring-loaded cam in the toe
piece, which normally controls release torque, is overcome. Here the boot settles into a local
minima 5-10° past the point when an Alpine boot would have released (Figure 3.10). Internal
friction retains the boot in the ski and the boot must overcome a second energy barrier to finally
release. This final energy barrier is simply a function of the internal friction of the system and is
no longer controlled by the spring-loaded cam intended to control the release torque."

I could be wrong, but to me that says "mechanical AFDs bind."

His report provides great analysis, but I'm having trouble understanding where he identified the inconsistency in the mechanical AFD. Unfortunately, the mechanical AFDs used in this report are not the standard delrin/teflon sliding afds that are used now (this study was conducted and the thesis was generated prior to the WTR/Gripwalk industry shift).

You are correct about WTR/GW, as I mentioned above, and Campbell stated elsewhere that he would not be concerned about using a mechanical AFD with GW/WTR soles. But not all boots are WTR/GW. And other than the photo of a non-delrin sliding AFD, I'm not sure where you see that NONE of the mechanical AFDs had delrin/teflon...?

[XXX-er]

This is a problem in skiing today. Just let it slide, man.

In addition to the slidey bits consider the heel of an AT boot is thicker, my DIN sole is 29 mm while my Vulcan is another 4mm and I'm sure i've measured AT soles being thicker still so I'm not sure if there is a standard for AT?

So the Alpine heel piece is designed/optimized for that DIN thickness so when you step in the binding goes over center to properly to clamp the heel, with a thicker heel shelf an alpine binding doesn't clamp the same but all that might happen is your heal might pre-release

while your toe is sticking ... what could go wrong eh ?



10 yars ago at Olympics there were 800 course workers on mosytly alpine boots but some were wearing AT ( mostly garmont adrenilen or endorphin ) boots in alpine bindings but they werent really skiing just cycling thru on skis carrying stuff

the course slippers doing the real skiing pushing huge berms of wet smoo were all using real alpine boots & bindings

[macon]

Bottom of page 83, he says:

"The worst load case for mechanical AFDs occurs in Front Preload Twist releases, when a
preload is applied to the fore-body of the ski significantly increasing the pressure between the
soft AT boot sole and AFD. As a lateral load is applied to the ski, softer AT boot soles stick to
mechanical AFD as the binding moves away. During this phase, the spring-loaded cam in the toe
piece, which normally controls release torque, is overcome. Here the boot settles into a local
minima 5-10° past the point when an Alpine boot would have released (Figure 3.10). Internal
friction retains the boot in the ski and the boot must overcome a second energy barrier to finally
release. This final energy barrier is simply a function of the internal friction of the system and is
no longer controlled by the spring-loaded cam intended to control the release torque."

I could be wrong, but to me that says "mechanical AFDs bind."

Ah I didn't see this section, thanks. This give me a couple other questions however.

1: If you look at Figure 3.10, you'll see the plotted binding with a sliding/mechanical AFD has substantially more lateral elasticity at 5 degrees (designated by degrees in the plot and not mm) than the binding with the static AFD at 2-3 degrees. I'm curious how the results would have changed if the test of the mechanical AFD would have been performed on a binding with only 2-3 degrees of elasticity, as it then would not have reached that perceived local minima.

2: I'm also curious what it is that causes the mechanical AFD to create that local minima in the torque curve. My initial thought is that it's the soft rubber on the AT boot lugs coming in contact with static hardware that is not part of the sliding mechanism on the mechanical AFD. This thought is further reinforced by Figure 3.6 (page 72), where the pressure sensitive film shows a much larger contact patch than the rectangular AFD.

I concede that the static AFD has a more consistent torque curve, but I'm not convinced that this curve is because its using a static AFD, whether or not the AT boot lugs are coming in contact with static components on the sliding afd, or if it's just because it's delrin/teflon and not some sort of PU.

You are correct about WTR/GW, as I mentioned above, but not all boots are WTR/GW. Campbell stated elsewhere that he would not be concerned about using a mechanical AFD with GW/WTR soles. Other than the one photo of a non-delrin sliding AFD, I'm not sure where you see that NONE of the mechanical AFDs had delrin/teflon...?

I don't see definitively where the sliding AFD wasn't made of delrin/teflon, however, I'm not aware of any pre-2016 sliding AFDs that were made of delrin/teflon. Additionally he makes the distinction that the static AFDs are often made of teflon on page 68, and I'm not sure he would have done that if the same applied to mechanical.

"Mechanical AFDs consist of a sliding, spring loaded plate that slides with the
boot as it releases in pure twist. Static AFDs are a low-friction surface, often made from Teflon.
Bindings with mechanical AFDs, were coded AFD = 1, and AFD = 0 for static AFDs." (page 68)

And the photo on page 84 shows a non delrin sliding afd.

[auvgeek]

Sounds like we need follow up testing both GW/WTR soles and sliding AFDs with teflon/delrin. Frankly, I wasn't aware that there was a shift in mechanical AFDs from non-Teflon/Delrin to Teflon/Delrin in the past few years.

[macon]

Agreed. All of it definitely needs further analysis.

My understanding is that most, if not all, sliding afds from Amer (salomon, atomic) and Rossi (look) are sliding AFDs made of teflon.

[turnfarmer]

Regarding knee injuries,
Howell has stated that the wings of turntable bindings(pivot is one of these) put the knee at higher risk due to the metal wings preventing any ability of the boot to slide out laterally at the heel.
As said above,I think the short take from the Campbell study is the downward loads bind the mechanical afd. IIRC many of the mechanical afds were destroyed by this mechanism. He used ASTM tests which are much more stringent than din tests.

[ExPowderSnob]

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).

.

By sliding AFD, i meant the mechanical sliding ones like Atomic's MNC type binding... I don't think Pivots have that do they?



THis is what the docs were referring too..

These allow the boot to slide on the delrin plastic as one mode of lateral movement, and then if the boot and plastic pad are stuck together, the whole mechanism allows for lateral movement as well.. it is a double redundancy for release...

[macon]

By sliding AFD, i meant the mechanical sliding ones like Atomic's MNC type binding... I don't think Pivots have that do they?



THis is what the docs were referring too..

These allow the boot to slide on the delrin plastic as one mode of lateral movement, and then if the boot and plastic pad are stuck together, the whole mechanism allows for lateral movement as well.. it is a double redundancy for release...

Yes I am aware.
Pivot 14s have teflon sliding AFDs, very similar to the Shift/STH MNC AFD like you posted. You're right in that P15s and P18s have a static teflon AFD.


hard to see in the pic but that's a sliding afd.


Sorry, but I simply don't believe those doctors have a reasonable enough sample size or have done an in depth study to make a truly honest judgement call like that. Like I said earlier, there's virtually 0 non-anecdotal evidence to back up the assertion that a sliding AFD helps prevent ACL tears.

[PeachesNCream]

Pivot 14s have teflon sliding AFDs, very similar to the Shift/STH MNC AFD like you posted. You're right in that P15s and P18s have a static teflon AFD.


hard to see in the pic but that's a sliding afd

So then why aren't they iso 9523 compatible?

[macon]

So then why aren't they iso 9523 compatible?

It doesn't drop low enough to the touring norm. It only goes down far enough to accept WTR or GW.

edit: Additionally, Rossi/Look don't have any hybrid touring bindings (based on Thor Verdonk's comments, I don't think they intend to make them), and Rossi/Lange only offer Alpine/WTR/GW boots (no true touring soles). So true ISO 9523 compatibility is not really needed for their product line.

Also my guess is that it might interfere with the MNC trademark/licensing in some way but don't know for sure.

[1000-oaks]

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...

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.

X2. Don't forget the thick grease between the sliding elements in the AFD mechanism, which lubricates movement even under heavy load. Greased movement between two clean, flat surfaces is a hell of a lot more consistent than a dirty, roughed up boot sole on a (possibly worn) Teflon pad.

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.

Didn't read the research, but am assuming the ski is securely clamped in place in the test fixture, and the boot toe is pressed downward on the sliding AFD throughout it's travel, even after the toe lug has cleared the binding toe wing. So yes in this particular test there is "binding" between the boot and the sliding AFD at the end of its travel, but in most real world situations the ski would probably rotate a tiny bit (due to the boot pressure on the extended sliding AFD "lever") and any pressure or friction would instantaneously be relieved and the boot free to exit. If the test was repeated with pins on the ends of the ski, mounted in bearings, the friction results at maximum sliding AFD extension would probably be different.

[macon]

@1000-oaks - agreed. Def read the rest of the thread too, certain elements might pique your interest.

--

@auvgeek: I had another thought this morning with respect to the torque curve. Was this test conducted using a constant force increasing linearly or a constant displacement increasing linearly? Based on the graph my suspicion is that it's constant displacement. In which case the local minima, while bizarre, would not be indicative of the sliding AFD "binding", instead, it just shows a location along the track where the AFD is also stable under the right forces. A saddle point if you will. If this is the case, it doesn't lead me to believe the AFD is compromising the safety of the binding at all.

I don't have the plot in front of me right now and I can't look at the ASTM specifications for these tests right now as I'm not in the office, but I'm thinking this might not actually be a "bind" as previously described.

Anyway, saturday morning thoughts.

[stuckathuntermtn]

1 thing of note is generally how imprecise the system is. Even with a worm drive heel, which not every binding has, there's still a given range for realese settings, not a very specific height or weight or boot sole length. Even with adjustable toe height, pushing or pulling backwards on the boot seems to change it. There can be a little snow, ice or dirt in there. Quite remarkable, really.
And a pivoting heel is nice but not necessary. It doesn't pivot to release it just helps the boot exit cleanly. I felt it happen earlier this month when I tried to open it up at Lost Trail in powder but it was still thin. Something just yanked my ski right off. I have older Tyrolias with the heel that can pivot a little on the way out. I could feel it do it's thing, but I don't think any other binding would have made a big difference. You can tell because they've mostly dropped it, I think.

Wait, is it heal or heel?

[MagnificentUnicorn]

Most of you dorks wouldn’t have to worry about injuries so much if you set your release values correctly.

Thinking a Pivot releases laterally at the heel is retarded, they pivot so the boot clears when the toe releases laterally. They’re no safer than any other TUV certified binding

[1000-oaks]

Even with a worm drive heel, which not every binding has, there's still a given range for realese settings, not a very specific height or weight or boot sole length.

Don't forget about loads changing wildly depending on ski flex. For most bindings (race bindings with connector straps excluded), if you g-out into an unseen ditch, there's going to be a large forward pressure and AFD pressure spike when you drop in and ram the far side. Conversely, if you catch an edge, hook a bush, or catch a tip doing a daffy, there's going to be less forward pressure than usual and no pressure on the AFD, and instead a load on the underside of the toe wings.

AT boots on fixed AFD's are probably fine if you always fall backseat (no load on AFD), but the ditch scenario would likely spiral a tib-fib if you don't come out at the heels in time.

[auvgeek]

am assuming the ski is securely clamped in place in the test fixture, and the boot toe is pressed downward on the sliding AFD throughout it's travel, even after the toe lug has cleared the binding toe wing.

Why are you assuming this?

I'm pretty sure he applied a pressure to the fore body of the ski, 45cm forward of the skis midpoint.

[1000-oaks]

Figured either the boot is clamped in place or the ski was, and they were fixed on the same plane. How else could there be load on the sliding AFD at full extension? I'll have to take a look at the research, and stop talking out of my ass, lol.

[stuckathuntermtn]

Don't forget about loads changing wildly depending on ski flex. For most bindings (race bindings with connector straps excluded), if you g-out into an unseen ditch, there's going to be a large forward pressure and AFD pressure spike when you drop in and ram the far side. Conversely, if you catch an edge, hook a bush, or catch a tip doing a daffy, there's going to be less forward pressure than usual and no pressure on the AFD, and instead a load on the underside of the toe wings.

AT boots on fixed AFD's are probably fine if you always fall backseat (no load on AFD), but the ditch scenario would likely spiral a tib-fib if you don't come out at the heels in time.

Yup, those old, garbage Salomon foam core skis + stupid Z bindings = after 1 season you can walk out of the skis because they are so noodily and the bindings have so little hold on your boot. Seen it.
Was pushing down on Guardian AFD last night to see if it would bind much moving sideways, and not really. There's a lot of teflon grease in there too.

[ExPowderSnob]

Sorry, but I simply don't believe those doctors have a reasonable enough sample size or have done an in depth study to make a truly honest judgement call like that. Like I said earlier, there's virtually 0 non-anecdotal evidence to back up the assertion that a sliding AFD helps prevent ACL tears.

Maybe... maybe not. I texted to see how many knees they have repaired, but over a few years, and several surgeries a week, that number won't be small. Until then, I am going to listen to some very smart people, who are subject matter experts on repairing torn ligaments and tendons, who also ski a metric fuck ton, (And 2 of them are damn good skiers), who for themselves, won't ski bindings without that mechanically sliding AFD.

It's a fool who doesn't learn from their own mistakes, and an complete moron that doesn't learn from the mistakes of others...

Is it 100% effective? probably not... If some yahoo skier that cranks the DIN on their bindings to the max because it makes them feel cool during their go-pro youtube edit,, nothing it going to keep that knee connected...

[Cocximus]

Because doctors use them... most doctors care about image more than park rats....

Don't sliding AFDs have teflon pads on top?

[DGamms]

As a doctor and a park rat, I am doubly amused by the above comment

As someone who was torn his own ACL (albeit not on skis), I would love to see the original study redone with the modern Teflon sliding AFDs and with GW/WTR boots included.

As someone who works in a ski town hospital that does 300+ ACL repairs per year, I can assure the TGR crowd that we have seen ACL tears from people using fixed AFD, sliding AFD, and tech bindings. No comment on the overall safety of any the systems, as I suspect the total number of skiers using fixed AFD bindings far exceeds the total number of skiers in the other two groups.

But then again, we have also seen a drunk karaoke ACL, a sewing machine incident ACL, and a donkey basketball ACL in the past few years... ultimately, your choice of binding may not have any bearing on whether or not you get through life with two intact ACLs.

[macon]

Maybe... maybe not. I texted to see how many knees they have repaired, but over a few years, and several surgeries a week, that number won't be small. Until then, I am going to listen to some very smart people, who are subject matter experts on repairing torn ligaments and tendons, who also ski a metric fuck ton, (And 2 of them are damn good skiers), who for themselves, won't ski bindings without that mechanically sliding AFD.

It's a fool who doesn't learn from their own mistakes, and an complete moron that doesn't learn from the mistakes of others...

Is it 100% effective? probably not... If some yahoo skier that cranks the DIN on their bindings to the max because it makes them feel cool during their go-pro youtube edit,, nothing it going to keep that knee connected...

I personally prefer the sliding teflon AFD that is standard on Shifts and certain Pivots, but not for reasons you describe.

My point was that it is extremely shortsighted to claim these sliding AFDs are saving people's ACLs. The phantom foot condition isn't mitigated by a toe release, so the assertion doesn't stand up to a simple free body diagram. It is quite literally misinformation, as it has not been shown to be true and doesn't make sense mechanically. Speaking as someone who has torn their ACL (and both MCLs and meniscuses), I don't think it's responsible to spread misinformation under the guise of it being a professional medical position.

As someone who was torn his own ACL (albeit not on skis), I would love to see the original study redone with the modern Teflon sliding AFDs and with GW/WTR boots included

Agreed

[skimaxpower]

This thread can end now. DGamms crushed it, despite his sworn oath to first do no harm.

As a doctor and a park rat, I am doubly amused by the above comment

As someone who was torn his own ACL (albeit not on skis), I would love to see the original study redone with the modern Teflon sliding AFDs and with GW/WTR boots included.

As someone who works in a ski town hospital that does 300+ ACL repairs per year, I can assure the TGR crowd that we have seen ACL tears from people using fixed AFD, sliding AFD, and tech bindings. No comment on the overall safety of any the systems, as I suspect the total number of skiers using fixed AFD bindings far exceeds the total number of skiers in the other two groups.

But then again, we have also seen a drunk karaoke ACL, a sewing machine incident ACL, and a donkey basketball ACL in the past few years... ultimately, your choice of binding may not have any bearing on whether or not you get through life with two intact ACLs.

[MagnificentUnicorn]

DGamms, do you really do 300+ acl repairs or is it reconstructions?