Biomechanics of Dynafit toe release?

First off: I love the weight, stride and convenience of Dynafit bindings, and I have trusted/will continue to trust them on hairball descents.

HOWEVER...since blowing out my knee, I've had a couple musings on the release characteristics of Dynafit toe pieces.

My own injury (for which I take full responsibility), occurred when one ski hit some mank/glop at high speed, and I kept going while my lower leg stayed put. The ski never released -- and EVEN IF THEY HAD, I think the injury would have happened before the binding had a chance. So...I do not think my injury was in any way caused by Dynafits.

That said...I do have my Dynafits cranked to 10 (but not locked for this mellow descent).

I was wondering if any of my suspicions are accurate:
(1) Dynafit release at the upper end of the spectrum (i.e., DIN maxed out) is less reliable than the middle of the spectrum...and less reliable than another binding at that same level -- even another AT binding like the Fritschi;
(2) Do Dynafits not release in an inherently knee-friendly way/direction? That is, even when a proper release happens, does the force on the leg required to get the Dynafits to release at the toe mean that one is more likely to do some damage than a Fritschi, Naxo or alpine binding. I suspect this is true. This is more about the direction of release than an "absolute" force on the knee question.

I prefer to keep my skis on/rarely go down...so I accept the responsibility for what happened (and having my skis not release has saved me more often than times I've been injured due to no release)...but this incident got me wondering about future releases with Dynafits. I am most certainly NOT blaming the Dynafits for the injury as I think it happened just *before* going down, but it made me think about the mechanics of Dynafit release.

I am generally more conservative in the backcountry (although this injury did happen in the BC near my backyard, it was really a bit of "$hit happens"), so it is *very* rare for me to ever have a release from Dynafits. In fact, thinking back over at least 3 years of skiing on Dynafits, I can think of only one other eject I've had from them, so I'm definitely unexperienced in their release...hence the above questions.

Thoughts?

No replies yet? Strange.

When I first got Dynafits in about '98 I threw them on a Vermont Tester in the shop. I think I set them at a very moderate 6 or 7 and went through the tests. My recollection is that they released within the standard range for alpine bindings.

Of course that doesn't really answer your question and I think you have some very good points especially the one about poor release performance at maxed out DIN. I usually go to about 9.5 on AT bindings thinking that might help.

My only usefull point is that Dynafits (without the toe locked) might actually release better in the Phantom Foot type ACL tear. That's how I did my knee and there really aren't any binding designs that address it. In a phantom foot tear the boot wants to swing forward pivoting at the knee like one is kicking a ball. Upward release toes don't really address this but a dynfit toe (again not locked) might allow the boot to swing forward even though the DIN settings in the heel wouldn't come into play at all.

Just a thought. Although the lower, softer cuff of AT boots might make Phantom Foot ACL tears less common anyway...

What does this have to do with biology?:confused:

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Originally Posted by sar13

No replies yet? Strange.

When I first got Dynafits in about '98 I threw them on a Vermont Tester in the shop. I think I set them at a very moderate 6 or 7 and went through the tests. My recollection is that they released within the standard range for alpine bindings.

Of course that doesn't really answer your question and I think you have some very good points especially the one about poor release performance at maxed out DIN. I usually go to about 9.5 on AT bindings thinking that might help.

My only usefull point is that Dynafits (without the toe locked) might actually release better in the Phantom Foot type ACL tear. That's how I did my knee and there really aren't any binding designs that address it. In a phantom foot tear the boot wants to swing forward pivoting at the knee like one is kicking a ball. Upward release toes don't really address this but a dynfit toe (again not locked) might allow the boot to swing forward even though the DIN settings in the heel wouldn't come into play at all.

Just a thought. Although the lower, softer cuff of AT boots might make Phantom Foot ACL tears less common anyway...

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Thanks...yes, I thought there would have been more (=any) replies, too.

Interesting points about the phantom foot; makes perfect sense.

In my case, the uphill ski (and lower leg) stopped moving/slowed extremely fast, and the rest of my body (downhill ski & even the thigh of my uphill leg) kept moving. This cause a rotation around a fixed piont (my knee). The injury may have occurred before *any* binding had a chance to release, but the ideal release required would have been one where my heel was fixed and my toe released laterally. It doesn't *seem* like the Dynafits do that release very well (and, again, this injury probably would have happened even if they did).

I feel comfortable with their heel release, it's just the toes that I'm skeptical of.

I think you're right: maxing out any binding may cause strange behavior.

Hm.

There is no vertical/upward release with a Dynafit toe, and the toes won`t release without any lateral deflection or rotational twisting motion begun at the heel axis. Don`t ski them in tour mode unless you absolutely don`t want a release.

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Originally Posted by col_surfer

and the toes won`t release without any lateral deflection or rotational twisting motion begun at the heel axis....

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I think this is the issue at hand. If the heel stays in place, the toe can't rotate = torquing the knee.

Thanks!

Tour mode does not equal "no release"...it just seems to increase the DIN by a couple notches. The skis *will* come off (say, in an avy), but probably not before knee/leg injury.

I have a tough time believing the toes "won't" release in ski mode. They are held in by a spring. Apply enough force and the spring will allow the boot to come out. I'd like to see a test of the straight upward release at the toe using a VT tester sometime in ski and tour mode.

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Originally Posted by sar13

I have a tough time believing the toes "won't" release in ski mode. They are held in by a spring. Apply enough force and the spring will allow the boot to come out. I'd like to see a test of the straight upward release at the toe using a VT tester sometime in ski and tour mode.

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I'd be curious about that test, too. I read somewhere that it is effectively a DIN 12 or so.

In an avy, you'd get tossed around so much they definitely *would* come off. As you say, it's just a question of how much force is enough.

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Originally Posted by sar13

I have a tough time believing the toes "won't" release in ski mode. They are held in by a spring. Apply enough force and the spring will allow the boot to come out. I'd like to see a test of the straight upward release at the toe using a VT tester sometime in ski and tour mode.

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No one said they won`t release in ski mode, they do. In tour mode, they are locked and you will UNLIKELY release, unless the force is pretty severe. I broke a ski through the core, between the front and back screws of the toe mount, hitting some deep snowmobile ruts, and the bindings didn`t flinch. I also got caught in a slow-moving, wind slab avy which let me go after 100 yards, but also did not release in tour mode and I fought like hell to get my skis free. Both instances involved substantial forces.

The release at the toe in ski mode is due to a lateral or twisting motion, there is no true vertical release. I am familiar with the phantom foot concept and don`t think the release mechanism in a Dynafit will help avoid that. In a fall, when the hip aligns below the tibial plateau, the tail of the ski becomes a forceful lever which shears the ACL. If a skier is prone to skiing in the backseat, the Dynafit binding probably isn`t for them until they either refine their technique or learn to fall properly without creating a bad scenario for their knee. Not sure about the VT tester, but after several hundred days on Dynafits, I`m familiar with how and when they release.

I think that was a typo by sar13 (..."tough time believing the toes 'won't' release in ski mode")...I think he mean "tour" mode.

But your first hand evidence is pretty hard to refute.

I would tend to think there is some force that could get them to release, though it might be leg-breaking. You're saying that the skis or screws will give before that force is reached, though.

Interesting & scary stuff.

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Originally Posted by col_surfer

There is no vertical/upward release with a Dynafit toe, and the toes won`t release without any lateral deflection or rotational twisting motion begun at the heel axis. Don`t ski them in tour mode unless you absolutely don`t want a release.

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I thought surfer was referring to ski mode with his forst sentence here. But I could be wrong. I just didn't retype his whole sentence since UAN had already quoted it.

And I am certainly not refuting his personal experience with Dynafit release. I have far fewer days on them and was never caught in a slide while using them. But, since the Dynafit is the only binding I know of that doesn't have something in front of your toe that is screw to the ski, I think it is more likely to release with the type of force I described than any other binding, given that it may take too much force to be worth anything from an injury prevention standpoint.

Bump for any maggots with time on their hands and a ski shop release tester.

I have been googling this for a bit, and come up empty - thought Lou Dawson would have had some info.

I have been skiing in lockout (usually 3-4 clicks) because when I first got dynafits I had some pre-releases.
Sounds like I just wasn't seated all the way and had some ice or snow in the pins or under the toe spring since there are apparantly other clydesdales out there skiing hard with no toe lockout.
But, lockout didn't bother me since DIN 10 or 12 doesn't freak me out either.

But, turns out that the "DIN 12 in lockout touring mode" is perhaps an internet rumor?
Would love to know that value really is.

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Interesting feedback here from a wildsnow comment
http://www.wildsnow.com/?p=917#comment-8038

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One small problem, more of a binding thing, is instant toe binding release when making smooth carved turns on hardpack piste. The toe release problem on piste is probably exacerbated by the stiffness of the Zzero4C that just transmits energy that much more efficiently to the toe. I compensate the problem by locking the toe in order to stay in on hard piste or hard granular snow. I seem to come out easily enough, anyway, with full toe lock.

This Dynafit toe release on harder snow is a problem that I discovered on my 1st generation Tri Step, and even to a lesser degree on the 2nd Generation of that binding. The current toe that released is a Comfort. I am big enough, heavy built, and I have carried around 220 lbs plus since 18 years of age as a logger, pro patroller, ski tourer, etc., so there is some strength required to move that bulk. Anyway, after a dangerous release of the Tri Step while in a fast controlled carved turn on refrozen smooth granular in the backcountry, I went to the shop to troubleshoot the problem. I learned along with the guy at the shop that I could actually stand in the bindings, skis on the carpet, and cause the old and the new then 2nd generation binding toe to release simply by pushing down with the ball of my foot.

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I'll be glad to test mine as soon as I can but that won't be for another couple of months as all the tuning equipment is put away in lieu of bike season.

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Originally Posted by Core Shot

I have been googling this for a bit, and come up empty - thought Lou Dawson would have had some info.

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Lou says:
http://www.wildsnow.com/articles/dyn...nt_2001_2.html
"Last time I checked the Dynafit binding on a DIN setting checker, the sideways release was pretty close to the number, but the vertical release was higher than the number indicated."

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Originally Posted by Core Shot

Interesting feedback here from a wildsnow comment
http://www.wildsnow.com/?p=917#comment-8038

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"Interesting" is certainly a generous description of that.
He's posted that info elsewhere, but doesn't have much to substantiate it.
And it's certainly not a normal experience: something had to be wrong with the setup.
(For instance, last month we didn't plan on any lift-served skiing, but after getting smoked out of a second day on Adams, we want back to Hood, and after some touring, we gaped around on Palmer riding the lifts. Two of us had race backgrounds, and were using our Dynafit setups on salted race lanes to make true GS turns, i.e., what tele skiers would typically call superg turns. No prerelease, either from lightweight me, or my much bigger brother. Certainly any binding -- downhill or touring -- can prerelease under the "right" conditions, but a properly set up Dynafit will not prelease like he describes.)

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Originally Posted by Core Shot

Bump for any maggots with time on their hands and a ski shop release tester.

I have been googling this for a bit, and come up empty - thought Lou Dawson would have had some info.

I have been skiing in lockout (usually 3-4 clicks) because when I first got dynafits I had some pre-releases.
Sounds like I just wasn't seated all the way and had some ice or snow in the pins or under the toe spring since there are apparantly other clydesdales out there skiing hard with no toe lockout.
But, lockout didn't bother me since DIN 10 or 12 doesn't freak me out either.

But, turns out that the "DIN 12 in lockout touring mode" is perhaps an internet rumor?
Would love to know that value really is.

===========
Interesting feedback here from a wildsnow comment
http://www.wildsnow.com/?p=917#comment-8038

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my only comment \ observation is the following;

when you do the van halen, you must do it with your toe locked
your heel, while being able to release laterally at DIN10, your toe stays locked in.

Also, lock your toe into the binding. Hit the heel of your boot with a rubber mallet. Id be surprised if you can get it to pop out within a reasonable amount of impact force.

*what im saying, i dont think a locked toe is equivalent to any sort of din and if it was, is probably something ridiculously high. the mechanics of release will also be such that it will take a huge amount of force and then catastrophically let go I think. so almost no elasticity.



and from playing around with them
id say the vert & lat release id also agree that the vert is off by 1 or 2 high

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Originally Posted by Core Shot

But, turns out that the "DIN 12 in lockout touring mode" is perhaps an internet rumor?
Would love to know that value really is.

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My buddy said they ran them through a number of times and they always came out a 10 in lockout mode.

I've never had the problems that Lou mentioned. I've used mine in resorts a number of times and the biggest problem I've had is the bracket on the back of the boots loosening up. I worry more about breaking a pin when jumping around in bounds. That and my boots are way to soft for all day lift served.

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Originally Posted by wendigo

My buddy said they ran them through a number of times and they always came out a 10 in lockout mode.

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Which toe lever position? And with the heel engaged or disengaged?
(With the toe lever in position #3, and the heel disenaged, twisting out felt roughly comparable to twisting out of my alpine downhill bindings, set at 7. That leads me to believe that with the toe lever in position #3 or higher, and the heel engaged, effective lateral release must be way higher than 10.)

ill also just quickly add that the more i use my dynafits, the easier certain clicks get
the plastic is wearing, and as such, would be dangerous to assume that a click 3 on jonathans dynafit is the same as a click 3 on mine.
just something to keep in mind.

Locked position. I'm guessing heal engaged.

But I don't really care what the din is, I ski mine locked and they work the way I need them to

I'm a bigger kid and I ski with the toe locked. The toe and heels of Dynafits don't release like an alpine binding. In most falls, the heel should be doing the releasing. If the toe stays locked, it's acting like a non-releasing tele binding. I spend 1/3 of my time on non-releasing tele bindings anyway and have never had a problem. That's just my justification for tour mode while skiing. Plus, I think you get half a gnar point per ski in tour mode while skiing. It's minus half a gnar point for every boot left in tour mode though so watch out for that.

Regarding dynafits and locked toes, I suggest taking a close look at what happens when you put the toe in locked/tour mode. Now I ought to go home and double-check :) but, locked mode basically puts a wedge/block underneath the tab/lever you push on to release yourself from the binding. Its not just tightening a spring or whatever, its putting a physical obstacle in the way of the moving part, so in order for the boot to come out of the toe there is going to be some serious distortion or breakage involved. I wouldn't ski in toe-locked mode without taking a close look for yourself.
And I'm very doubtful of those 10 or 12 DIN claims :)

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Originally Posted by corn dog

Regarding dynafits and locked toes, I suggest taking a close look at what happens when you put the toe in locked/tour mode. Now I ought to go home and double-check :) but, locked mode basically puts a wedge/block underneath the tab/lever you push on to release yourself from the binding. Its not just tightening a spring or whatever, its putting a physical obstacle in the way of the moving part, so in order for the boot to come out of the toe there is going to be some serious distortion or breakage involved. I wouldn't ski in toe-locked mode without taking a close look for yourself.
And I'm very doubtful of those 10 or 12 DIN claims :)

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no need to double check cd
you are absolutely right that there is a "wheel chock" of sorts that is blocking up the toe lever from the base plate with the "speed bump"

the wheel chock, or block, is specifically designed to not come undone from a torque or force applied by the toe pinchers when its locked into tour mode....otherwise, why would it be called locked? And really, Ive put some pretty stout loads on dynafits by sidehilling some bulletproof wind slabs that make me think it would take A LOT of force to come out of them when locked.
The exception here is that inf you come out from the heel, have a forward fall, and somehow manage to hit the tour lever with the front of your boot which should pop you out.

Id like to hear from someone who released from the heel with a locked toe and took a fall as to what happend.

Ive released from my dynafits a handful of times (because i was a moron and either forgot to fully clear the toe sockets or had my DIN too low for my new shorters BSL) and each time was with the toe lever where it was "supposed to be" for skiing. It was a super smooth release honestly. Not as good as a marker or a naxo, but still pretty damn good. I didnt feel any residual\latent forces or torques on anything after my heel popped out other than a very slight time delay between feeling my heel go out and hearing the metal slack of my toe sockets popping out.

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Originally Posted by pechelman

Id like to hear from someone who released from the heel with a locked toe and took a fall as to what happend.

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Originally Posted by pechelman

It was a super smooth release honestly.

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I've released twice: once vertical when my tip went under a horizontal log (hidden by some sweet pow) and once lateral when I hooked a tip on some sort of shrubbery (the alpine vegetation kind, not the Monty Python kind).
Both times it was so smooth that I didn't realize at first I had released.

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Originally Posted by Jonathan S.

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mmmmhmmm
and thats only 12din?
yea right

i had seen that before, and forgot about it, but it seems to throw significant doubt that anyone would release from a locked toe peice if that guy was hanging from one that was locked.

at least im assuming it was locked...
(it had to be, because in ski mode, boots can pop out easy)

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Originally Posted by pechelman

at least im assuming it was locked...

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Yes, the toe lever had to be in tour mode.
I'd be curious to know which position though.
I've been able to test twisting out in the third position. (Haven't tried fourth or fifth.) That's reassuring to me in case I'm skinning up through potential avalanche terrain, since I conclude from that the third position will allow a release if entrained in an avalanche. (Skinning up in late spring and early summer snow though, I always use the fourth or fifth position.)

^ ill say that from the 2 sets that i own, the toes lock into different positions
they require different force and effort too
nothing on them makes me think their locking force would be standardized by the clicks

that may just be my experience though, but its also why im treating this locking\toe release issue with such skepticism and stubborness

I agree that variations can occur on account of wear/newness and also mounting (i.e., distance and angle between the binding and the separate base plate).
However, the number of "clicks" refers to the number of teeth/cogs at the end of the toe lever that are engaged with the bump on the baseplate (i.e., # of clicks minus 2 equals extent of engagement), so I think that is a very important factor.

yea
i understand that

and im just saying i dont think thats a good standard *except* on an individual case by case basis

one set of my bindings acts similarly at 4 where my other is at 2
thats what im getting at