Physics behind the DIN chart?

[Deep Days]

It seems counterintuitive (at least to me, who have not taken college physics yet) that a torque force applied to a longer distance exterts less impulse (?) or whatever--that longer boots mean higher DIN.

Why would a shorter boot require less force for retention than a longer boot? Does the longer boot set the "effective" DIN higher because of greater relative forward pressure at the same DIN? Or is there some law that states that rotating force is lost over distance?

What does DIN stand for, anyway?

[marshalolson]

DIN stands for "german industrial norm" in german

bigger boots = lower din @ same weight.
smaller boots = higher din @ same weight.

a bigger boot generates less work b/c it is done over a longer timescale - larger radius rotations spin relatively slower (see: figure skating) and therefore need a lighter spring to release properly.

[Mr.Scruff]

Deutsche Industrie Norm actually, guaranteed to win you any pub quiz

[dk_alaskan]

Longer boots, from what i have been told, need a lower din, shorter boots need a higher din. The explanation i was told is with a longer boot, the force is spread over a much larger area creating more torque. the shorter the boots the exact opposite happens. I could be wrong, so anybody else that has a better explanation, please help set me straight on this topic

[cj001f]

Just get the relevant ISO standard for bindings - it's superceded DIN

[bossass]

I saw this thread and knew Marsh would be on it. Good work man!

[pechelman]

another way to think about it is that a lower binding force (DIN) is needed to retain the skier with a larger boot, since torque is force * distance.

edit: holy crap im late

[SkiED]

^To the guy above me....If torque is force*distance then the larger boot you have the more torque being exerted for the same amount of force. So wouldnt a larger boot need a higher DIN due to the longer boot sole magnifying the torque?

[Sphinx]

Physics is hard!



Max, didn't you ever take high school physics?

[pechelman]

^To the guy above me....If torque is force*distance then the larger boot you have the more torque being exerted for the same amount of force. So wouldnt a larger boot need a higher DIN due to the longer boot sole magnifying the torque?

hopefully this will clarify things even better

I appoligize in advance for being such an enginerd.

so we're dealing with the same skier
Lets assume an arbitrary weight of 200lbs and CG height of 50in.
This translates to 10,000 in-lbs of torque produced by the skier which is resolved at approximately the center of your boot sole.

We're dealing with something called a coupled torque now.
Essentially all this means is there is an downward pointing force at the toe and an upward pointing force at the heel. (assuming a forward fall)
Both are equal as they act at equal distances...approximately (good enough for TGR)


now lets assume two BSL's
350mm = ~13.75in - half that BSL is 6.875in
300mm = ~11.8in - half that BSL is 5.9

again Im taking half since this is a coupled torque.
the force acts at the distance from the coupled torque application point (ie center of the boot) to the ends.

now for the fun part

Torque = Force * Distance

For the 350mm BSL

10,000 in-lbs = Force * 6.875in

Force = 10,000 / 6.875 = 1454lbs


For the 300mm BSL

10,000 in-lbs = Force * 5.9in

Force = 10,000 / 5.9 = 1695lbs


So the larger boot actually produces less force at the toe and heel that the binding needs to resolve and the smaller boot actually produces a higher force at the toe and heel. Another way to think about this phenomena is the concept of Stress, where if you apply the same force over a small area you generate a high stress, whereas if you apply that same force over a larger area you generate a lower stress. Not really the same principle, but it might help.


let me know if this does or doesnt make sense

[PNWbrit]

Warum argumentieren sie mit Deutschen wissenschaftlern?

[summit]

Backwards thinking applies... solving the problem from the wrong end.

Very simply, you are NOT worried about the forces experienced at the toe. You are worried about the forces experienced just in front your heel and those forces being translated up the leg...

you figure out the maximum you want there and then figure out some way to infer when those the forces reach that maximum... so you measure them at the toe!

Think of it as a wrench. You want your hand (the binding toe) to slip off the wrench handle (the boot toe) before you torque off the bolt (your knee/leg).

The longer the wrench (boot), the less force you'd have to apply to the handle (toe) of the wrench (boot) to strip that bolt (your leg/knee).

BUT, you are NOT REALLY applying the force to you at the toe... that is just where the failsafe force-meter is. The force is applie by the intertia/length of your body and/or by the full lever arm of the ski. Once again, the sensor used to infer the torque around your Z axis of your leg simply happens to be located at the toe of your boot along with the release mechanism for the z axis.

[nick > jesus]

It seems counterintuitive (at least to me, who have not taken college physics yet)

Holy crap! max uses improper grammar too!

[Deep Days]

Holy crap! max uses improper grammar too!

Buster, what's the ruling on this? I'm confrused... "me, who has taken," or "me, who have taken"?

Summit, your answer is $$$. I have taken high school physics, but most of the coursework consisted of jungle noises and tossing tennis balls around the room (my teacher was seriously debatably burnt out on acid). I don't think we even touched the concept of torque. I always have difficulty figuring what quantity (i.e. work, force, or power) governs a process...

Thanks for satiating my nerdy curiosity.

[Nobody Famous]

Just get the relevant ISO standard for bindings - it's superceded DIN

Where does one get these, ... preferably for no cost.

[EstoBum]

Where does one get these, ... preferably for no cost.

Good luck, I've been looking for a while without any luck. They're about $60-$70 for the document.

[smmokan]

Buster, what's the ruling on this? I'm confrused... "me, who has taken," or "me, who have taken"?

Its definitely "me, who HAS taken"...

[Nobody Famous]

Good luck, I've been looking for a while without any luck. They're about $60-$70 for the document.

I know ASTM and ANSI and some other orgs sell these, but I was hoping someone here has found a college library (or something similar) that already has these documents. And preferably the info is accessible online.

[EstoBum]

I know they have the ASTM standards in our school library. I looked through the index one day, and they have test procedures for adjusting and testing the binding, but they didn't have the definition of the boot sole/binding interface - which I believe is described only by the ISO standard. Library does not have those.

I'll try to check it out again for release info this evening.

[EstoBum]

Marshalson, Pelchman and Summit are right on this.

I think the confusion stems from not having a definition of what exactly is the DIN specification. We are throwing around the words force and torque - but we don't know how this corresponds to the DIN setting of say 18 (since were Gnar). I would venture a guess that it has to do with the force required to release out of the binding, but I don't have access to the ISO standards.

Looking at a Binding Mounting Chart a 200lb 6' skier falls into a L category. This requires a release at 58 Nm in a twisting boot motion (think of the leg as an axis) and a release at 229 Nm for a forward lean fall. The chart indicates that said skier with a boot sole of 300mm, would require a DIN setting of 6.5. A boot sole of 320mm would require a DIN setting of 6. If we go on the assumption that DIN setting is the release force, then this would make sense as an equal release torque would correspond to a lower force at a longer moment arm or boot sole, i.e. the basic Torque = Force x Distance [look 2003/2004 Tech manual chart]

The ASTM standards for skiing are F 472, F 498, F 504, F 779, F 780, F 939, F 1061-1064. They are pretty mundane, where most of them define standardized methods for measuring and defining ski shapes, and testing procedures for ski deformation, torsional characterestics, and how to test release procedures, and shop procedures. Nothing is of real use, since they are all test procedures, and do not define what the results need to be. I'm guessing ISO standards explain those, as they are cross referenced.

I believe the definition of the geometry of the ski in terms of release torques (according to the ASTM Standard for alpine release) is that the x axis is the width of the ski, the y axis is the length of the ski, and the z axis is normal to the top of the ski. The z axis is assumed to be at 1/3 of the boot sole length, going from heel to toe, and the origin is referenced at 23cm above the bottom of the boot along the z axis.