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Height, Length and DIN

This has been bugging me for a while, I can't work it out in my head. I am pretty good a physics, but I have a feeling I am missing something obvious, so at the risk of looking stupid, I'm posting the question anyway.

The basic formula for DIN is a chart that considers the skiers height, weight, ability, age and boot sole length. All we really care about is the amount of torque potentially applied to the binding before it releases. Sole length applies to the lever and age and ability relate to the potential force the skier will tolerate. Obviously weight is a huge concern as it directly relates to force, but height? The skiers height doesn't really affect the lever in such a dramatic way, as the height is perpendicular to the force vector. I know the center of inertia is further from the fulcrum in a taller skier, but....

Isn't the most important factor the length of the ski? The ski, not the skier, is the lever, the longer the ski the less force is required to release the binding. Right? A longer ski will release with much less force than a shorter ski with the same DIN setting.

I'm just getting back to skiing so forgive the naivety. But do the charts use the height of the skier to presume the length of the ski he is using. In today's' market, any one skier could be using a variety of skis of different lengths all on the same day, with the same DIN setting, but radically different forces at work. Whats the length range in your quiver, I bet it's close to 50cm for some.

Set me straight guys before my head explodes.

Oops, can't edit my dyslexic lenght out of the title, sorry

Bindings are primarily designed to prevent the skier from breaking their tib/fib over the front of their ski boots.

Binding reaction to "twisting" falls is relativley new (say in the last 20-25yrs).

Armed with this...re-evaluate your thoughts, I think you will see why height is important.

Quote:
Isn't the most important factor the length of the ski? The ski, not the skier, is the lever, the longer the ski the less force is required to release the binding. Right? A longer ski will release with much less force than a shorter ski with the same DIN setting.

Well true...sorta, bindings release at a certain setting.  Lets for example say your DIN is 8.  Lets say for illustrative purposes 8 requires 80ft/lbs of torque to release (I dont know what the real number is), the binding wont care if that 80ft/lbs comes from a larger force on a shorter ski, or a smaller force on a longer ski.  80ft/lbs is 80ft/lbs....its irrelevant how it is generated.  We dont want to say have the bindings take 80lbs at the tip no matter what, as that may result in a broken leg...ultimatley your body can handle what it can handle...again how those forces are generated is irrelevant.

Edited by Skidude72 - 9/21/12 at 3:57am

DIN determines the release torque applied to the skiers foot, regardless of the ski length.

Age and weight are poor substitute for strength of skiers leg bones, but they're the best we've got.

Level I, II, III, III+, III++ relate to the skier's acceptance of risk, not skier ability.  Albeit, if you want to ski at high speeds while turning through rutted bumpy frozen tracks, you won't be able to keep your skis on with a low level of risk acceptance, but that's ok, since you probably are accepting of greater risk.

Boot sole length (bsl) factors the applied force at the binding to get the torque applied.

Skier height factors the torque applied at the boot to get the resulting breaking force at the break location on the tib/fib due to the applied torque (applied by the bindings with a given bsl), and, coincidentally, the force applied to the tendons at the knee due to the applied torque (applied to the boot by the bindings and bsl).

before this thread gets too deep i want to stop and try put some reality into the first couple of responses. it is bad juju to be giving incorrect information as to how bindings work and what they can  or can't protect.

Quote:
Originally Posted by Skidude72

Bindings are primarily designed to prevent the skier from breaking their tib/fib over the front of their ski boots. a portion of this statement is true. the binding is designed to protect the bones of the lower leg. the ability for the heel to release upwards generally addresses falls forward that would have the leg bending over the top of the boot. the toe has the ability to address twisting loads that the leg would feel with lateral movement. and the toes are also designed to address a combined load fall of both forward and twisting forces.

Binding reaction to "twisting" falls is relativley new (say in the last 20-25yrs attempts to protect the lower leg in twist which means toe pieces were around from companies like marker, salomon and look-nevada around the late 50's and early 60's. some of the same parameters that go into today's bindings date back to the 60's.

Armed with this...re-evaluate your thoughts, I think you will see why height is important.

Quote:
Originally Posted by Skidude72

Well true...sorta, bindings release at a certain setting.  Lets for example say your DIN is 8.  Lets say for illustrative purposes 8 requires 80ft/lbs of torque to release (I dont know what the real number is), the binding wont care if that 80ft/lbs comes from a larger force on a shorter ski, or a smaller force on a longer ski.  80ft/lbs is 80ft/lbs....its irrelevant how it is generated. this is true in the sense that the binding is a mechanical device that can only sense the forces that are generated through the boot sole. set at your setting it is intended to release when the approximate force is felt by the toe or the heel. We dont want to say have the bindings take 80lbs at the tip no matter what, as that may result in a broken leg...ultimatley your body can handle what it can handle...again how those forces are generated is irrelevant. another partially true statement. your bindings can sense loads that are generated by forward lean at the heel and twist at the toe. so it does matter how the forces are generated for the binding to protect the lower leg.

Quote:
Originally Posted by Ghost

DIN determines the release torque applied to the skiers foot, regardless of the ski length. the binding is engineered to protect the foot and the lower leg below the knee. let's stop talking about ski length in this discussion because the bindings are designed to protect the lower leg not the ski. the ski does not have a clue what binding is on top of it, nor does it care what the DIN setting is.

Age and weight are poor substitute for strength of skiers leg bones, but they're the best we've got. there are studies to prove that the bones of the lower leg become less dense above 50 years of age. that is the reason for an adjustment down in spring tension over the age of 50. your weight is a factor in the retention release formula, not an indication on the strength of your bones. the DIN charts are set up at a base level for "average" height and weight. when finding the initial DIN setting you look at both the height and weight and choose the skier code that you come to first when moving down the chart. the reason for this step is to attempt to make the initial DIN setting relative to the bone size. the concept being that height is a more defined factor of how large someones bones are than weight. 2 men of the same age come into the shop for bindings both are 6 feet tall, but one ways 300 pounds. the theory is that their bones will be somewhat similar in size and strength.

Level I, II, III, III+, III++ relate to the skier's acceptance of risk, not skier ability.  Albeit, if you want to ski at high speeds while turning through rutted bumpy frozen tracks, you won't be able to keep your skis on with a low level of risk acceptance, but that's ok, since you probably are accepting of greater risk.

Boot sole length (bsl) factors the applied force at the binding to get the torque applied. this is the crux statement in terms of understanding the leverage factor on torgue that the leg will feel.

Skier height factors the torque applied at the boot to get the resulting breaking force at the break location on the tib/fib due to the applied torque (applied by the bindings with a given bsl), and, coincidentally, the force applied to the tendons at the knee due to the applied torque (applied to the boot by the bindings and bsl). sorry but i need to flame this statement. this is complete bull\$*%. the skier height is not a factor in this discussion. once again the binding only knows what the boot sole tells it. i have never heard of a boot telling the binding how tall the skier inside of it is.

also you have got to leave the knee out of this discussion cause the knee she don't talk to the boot either that does not mean that modern bindings cannot protect the knee, i am simply saying that current bindings address torque and forward lean that is transferred through the boot sole. this means unfortunately that in certain types of falls the knee can be injured before the binding ever knows that knee is feel pressure. i leave the door open for someone from the knee binding company to explain their product, but for the rest of the brands the rules of physics apply.

for the record, modern bindings have done a great job of reducing the number of lower leg injuries to skiers. the DIN norm has helped the manufacturers accomplish this result. as a skier you should learn what DIN setting works best for you and your style of skiing.

jim

Even though I have worked part time for several seasons as a demo tent/demo shop guy I have never been able to wrap my head around the fact that according to the DIN Chart a skier with a smaller bsl gets a higher setting than a long bsl (both skiers with same weight and height and skier type). I can only assume that a longer bsl spreads out the torque forces more than the shorter bsl, so when the skier makes a mistake and wants a release, there isn't enough torque generated by the longer bsl because it is more spread out and therefore a lower release setting is needed.

It gets kinda weird when the 2 guys are different size and the little, lighter guy gets the higher DIN setting.

Jim, can you straighten out my thinking/explanation on this?

I think the torque of a crash causes a rotating force at the ball of the foot (in a forward fall).  The boot becomes a lever trying to resist that rotation at the heel binding.  The longer the lever, the less force you need to resist that torque.  So the longer boot sole needs a lower DIN to release at the same crash force as a shorter boot would.

Imagine you had a wrench on a bolt and were trying to keep that bolt from rotating as someone tightened a nut on it.  The longer the wrench, the easier it is for you to keep the bolt from rotating.

So you need a lower DIN with a longer wrench (boot) or else it won't release and you'll get injured.

Quote:
Originally Posted by DanoT

Even though I have worked part time for several seasons as a demo tent/demo shop guy I have never been able to wrap my head around the fact that according to the DIN Chart a skier with a smaller bsl gets a higher setting than a long bsl (both skiers with same weight and height and skier type). I can only assume that a longer bsl spreads out the torque forces more than the shorter bsl, so when the skier makes a mistake and wants a release, there isn't enough torque generated by the longer bsl because it is more spread out and therefore a lower release setting is needed.

It gets kinda weird when the 2 guys are different size and the little, lighter guy gets the higher DIN setting.

Jim, can you straighten out my thinking/explanation on this?

Imagine you trying to undo a bolt with a wrench.  If you have a big wrench and push on the end of it, you can apply more torque.

Now imagine the toe piece of your binding is trying to undo your leg.  If it has a long boot sole and pushes on the end of it, it can apply more torque.

Now imagine you have a hold on a wrench as someone is trying to twist the bolt that is going through the nut the wrench is holding.  If you have a long wrench, you can resist a higher twisting torque on the bolt without hurting your hand, but if you have a tiny wrench, it could hurt.

Now imagine your AC ligament is resisting an applied torque on your ski boot, if you have a long tib/fib, you have a better chance.  Mind you if it's a pure twisting force about an axis parallel to your calve, with no forward/backward component, your advantage from your knee being farther up is nil.

Quote:
Originally Posted by Ghost

Now imagine you have a hold on a wrench as someone is trying to twist the bolt that is going through the nut the wrench is holding.  If you have a long wrench, you can resist a higher twisting torque on the bolt without hurting your hand, but if you have a tiny wrench, it could hurt.

Now imagine your AC ligament is resisting an applied torque on your ski boot, if you have a long tib/fib, you have a better chance.  Mind you if it's a pure twisting force about an axis parallel to your calve, with no forward/backward component, your advantage from your knee being farther up is nil.

imagine is all you can do when it comes to the binding having a clue as what kind of stress or pressure any of your ligaments are going through. the binding knows as much about your knee as it does your rotater cuff and your left ear.  chance of what? a chance that monkey's might fly out of your butt? wait, wait, oh uh i feel like i might be falling, quick get that pure twisting force about an axis parallel to my calve so i don't hurt something, whew! that was a close one, i almost didn't get myself into the safe falling position in time. man this is one tough sport!

how are you coming up with this stuff. where is the  statistical data to prove the length of the leg has anything to do with skiing injuries of any type, lower leg, knee, ankle, bone, ligament?????? there is a s*%t ton of data to support injuries to the lower leg, and armed with that data the ski binding companies have built very effective bindings to deal with the forces that come in contact with the bindings through the boot sole. modern ski bindings may be able to protect soft tissue, however they are not and have not been built to sense the soft tissue of the knee or ankle.

leg length being introduced as a factor in binding protection/performance, what are you talking about?

gotta get down to real talk about what bindings can or can't do, instead of regurgitating all the myths.

jim

Edited by starthaus - 9/21/12 at 6:24pm

"sorry but i need to flame this statement. this is complete bull\$*%. the skier height is not a factor in this discussion. once again the binding only knows what the boot sole tells it. i have never heard of a boot telling the binding how tall the skier inside of it is."

Well, at least I got one thing right, at least in concept.

So, in a perfect world the DIN setting should be less that the force required to fracture your tib/fib in a forward fall and tear your ACL in a twisting injury. I presume some one has worked this force out, at least for the "average" adult. Not being able to effectively stress test individual bones, we use height, age and weight as an approximation. The boot sole length becomes a constant and the other variable being the skiers tolerance for injury/risk based on percieved ability.

In the event of a fall, shorter skis should be relatively safer due to less force from a shorter lever.

BW.

Quote:

"sorry but i need to flame this statement. this is complete bull\$*%. the skier height is not a factor in this discussion. once again the binding only knows what the boot sole tells it. i have never heard of a boot telling the binding how tall the skier inside of it is."

Well, at least I got one thing right, at least in concept.

In the event of a fall, shorter skis should be relatively safer due to less force from a shorter lever. this is not a true statement, too many variables to be able to prove this theory. easy to find out however, as there was a clear drop of ski sizing that started to take place in the mid to late 90's. according to your theory we should see a drop in lower leg injury starting about that time. i am fairly confident that did not occur.

BW.

still not biting on the influence of the ski length over force. the binding does not know how long the ski is. it can react to forces (shock) introduced to the ski (shock absorbtion and elastic travel are the other thing that ski bindings do and are related to the DIN setting)

jim

I dont want to get into this so I will just make a few points:

Lever Arms:  Lever arms are important, but they can be abit counter intuitive.

Lets say you hit a rock that imparts a side force on a long ski...long lever, more torque at the binding, binding senses that torque.  It dont know if its a smalll force on a long lever, or big force on a short lever...it just knows what is at the binding, and it either releases or doesnt.  So all things equal short skis will always generate less torque right?  Wrong.  Think about this for a second,,,if a long ski clips the rock at the tip, the short ski will miss it all together (I know this sounds well "duh" but work with me here)....if you are close enough for the short ski to hit it, then the long will hit too...but the long will hit at the same point...ie the same length lever arm.  It dont matter the long ski has another 10-20 or what ever cm beyond the contact point.  Make sense?

Jimbo - Skiers height.  Tall skier = bigger person = bigger bones = stronger bones = can handle higher stress before breaking.  All true.

Also taller skier - by definition longer body  = longer lever arm = equal more force generated at the binding from the same fall then a shorter skier.  Now, work with me here....a shorter skier = shorter lever arm = less force generated at the binding.  As you have correctley pointed out, the binding only knows what is happening at the boot/binding interface.  A shorter skier, (lets say for simplicity of same weight and BSL) as the taller skier, would need to be going alot faster, and have a more dramatic crash to generate teh same force at teh binding.  More force (or put another way, worse crash) required to get the same release?  Bad.  So the binding is set lower on shorter skiers, so they get the same release from teh same fall.  ie if you are going 30km/hr, and the skis hit a rock...the skis should release regardless of how tall or short you are.  That is why shorter skiers have lower DIN then taller.  They generate less force at the binding boot interface then a taller skier....so the DIN is set less so the binding will react the same for the same fall.

Other points on bones - tons of studies proved that people who were obese have higher density (read stronger) bones then those who were not.  Calcium or vitamin D defficineces effect bone strength, as does various diseases such as osteoperosis.  Ghost is right, age and hieght are just approximations.

Final point - we might just be missing words here - but Jim seems to be implying bindings are good at managing twisting falls.  Now to be precise in skiing twisting fall, really means a forward twisting or a backward twisting fall.  Its to my knowledge that bindiings did not protect the legs well from these types of falls.  It was around the early 80s when binding manufacturers started playing with more advanced HEEL and TOE pieces that could release in multiple directions.  Prior to this, heels just went up/down, and toes just went left right.  Even today, to my knowledge, only the better bindings have these features.  Its worth doing the research to learn which ones do (ie ask a reputable ski shop), and if required pay more for it.  Am I wrong Jim?  Or do all bindings have this now...and this actually started in the 50s and 60s?  Which bindings? When did turntables come out? These were likley the first..

Edited by Skidude72 - 9/21/12 at 7:19pm

All the binding knows is what torque it is able to deliver to the boot when set at a given DIN.

The ski and binding deliver that torque to the boot.

You resist that torque on the boot.

Although the binding doesn't know how much you weigh; it only knows at what setting you have set the release. However, if you weigh 300 lbs you likely have stronger bones from carrying around all that weight than if you weigh 80 lbs, so you may use a higher release setting.

If your leg is longer, you have a longer lever arm and can withstand more torque because of that longer lever arm and you may set your binding at a higer release setting if you are 6'6" than if you are 4'8"

What resists applied torque is force at a distance from the axis of rotation.  The equation is pretty simple; it's force x distance = torque.  Push open a door at the door knob.  Push the door open by pushing near the hinge.  Lever arms matter.

Quote:
Originally Posted by Ghost

If your leg is longer, you have a longer lever arm and can withstand more torque because of that longer lever arm and you may set your binding at a higer release setting if you are 6'6" than if you are 4'8"

You sure?

Quote:

... In the event of a fall, shorter skis should be relatively safer due to less force from a shorter lever.

BW.

Doesn't sound quite right.  The skis are not usually the primary lever during a fall, so the ski length is less important than the height of the skier.

The lever delivering the torque around the ball of the foot is the skier's body.  The taller the skier, and the more weight they have up high on their body, the greater the torque.  That's why taller skiers need a higher DIN, to resist the higher torque they generate.  If most of the skier's weight is in their lower body, then the skier height has less of an impact and the DIN can be set lower.

Since the skier's body is made up of breakable bones, ligaments, and movable joints, it is an imperfect lever, and it will break at it's weakest point if too much torque is applied through it.

The force generating the torque is the kinetic energy in the skier's body that is converted into a rotating force when the skis abruptly stop due to being misaligned with the direction of travel.  The lever resisting that torque is the ski boot sole.  The force resisting the torque is the springs in the rear binding.

Since skis flex to fit the snow surface and are usually hooking up with a significant amount of their length during a crash, they can be thought of as a fixed object for the duration of the crash torque event, and their length becomes irrelevant.  So you can think of them as a fixed table or floor the bindings are bolted to when calculating if the torque from the skier's body will exceed the resisting torque of the binding, or if the resisting torque from the binding will exceed the integrity of the skier's bones and ligaments!

The ski length would only matter if somehow during the crash only the tip or tail hooked up with the snow, generating a rotating torque in the plane of the bottom of the boot sole.  This crash scenario is where the toe binding comes into play.  If the tip hooks up, the toe binding should release, and if the ski tail tip hooks up you may get a torn ACL since the heel binding won't release sideways.  Of course any crash is somewhat chaotic in terms of alignment with the skier's body, so there will be both horizontal and vertical components to the torque, and both the heel and toe bindings will come into play.

At high speeds, other scenarios come into play, since the lightweight skis (relative to the skier's much heavier body) can experience sudden jolts of force that are so violent and short in duration that the skier's boots act like fixed objects, and the skis pop off without the skier feeling any significant force applied to their legs.  This is why advanced skiers may need higher DIN settings, to keep the skis on in those types of short impulse events.  But the higher DIN will blow out their knees in a slower speed rotating type of fall.  That's why these types of skiers sometimes tear their ACL's while goofing around on green trails since they had their DIN set for racing speeds and didn't lower it when they went cruising.

Quote:
Originally Posted by Skidude72

I dont want to get into this so I will just make a few points:

Lever Arms:  Lever arms are important, but they can be abit counter intuitive.

Lets say you hit a rock that imparts a side force on a long ski...long lever, more torque at the binding, binding senses that torque.  It dont know if its a smalll force on a long lever, or big force on a short lever...it just knows what is at the binding, and it either releases or doesnt.  So all things equal short skis will always generate less torque right?  Wrong.  Think about this for a second,,,if a long ski clips the rock at the tip, the short ski will miss it all together (I know this sounds well "duh" but work with me here)....if you are close enough for the short ski to hit it, then the long will hit too...but the long will hit at the same point...ie the same length lever arm.  It dont matter the long ski has another 10-20 or what ever cm beyond the contact point.  Make sense? forget about the ski, way too random. not really germain to the discussion.

Jimbo - Skiers height.  Tall skier = bigger person = bigger bones = stronger bones = can handle higher stress before breaking.  All true. that has been proven with cadaver tests

Also taller skier - by definition longer body  = longer lever arm = equal more force generated at the binding from the same fall then a shorter skier.  Now, work with me here....a shorter skier = shorter lever arm = less force generated at the binding.  As you have correctley pointed out, the binding only knows what is happening at the boot/binding interface.  A shorter skier, (lets say for simplicity of same weight and BSL) as the taller skier, would need to be going alot faster, and have a more dramatic crash to generate teh same force at teh binding.  More force (or put another way, worse crash) required to get the same release?  Bad.  So the binding is set lower on shorter skiers, so they get the same release from teh same fall.  ie if you are going 30km/hr, and the skis hit a rock...the skis should release regardless of how tall or short you are.  That is why shorter skiers have lower DIN then taller.  They generate less force at the binding boot interface then a taller skier....so the DIN is set less so the binding will react the same for the same fall. husband and wife come into the shop, weight 30 pounds apart, age about the same, height 6 inches different so let's try this in real world numbers....he is 6 ft tall 179, 40 YO type 2 skier with a 325mm bsl, she is 5'6" tall 149, 42 YO type 2 skier with a 285 bsl. his DIN # is 7, her DIN # is 7. his binding should release at the toe with approx 67 deca newton meters of torque, hers at approx 50 deca newton meters of torque. DIN # is the same but the torque is different based on the bsl.

Other points on bones - tons of studies proved that people who were obese have higher density (read stronger) bones then those who were not.  Calcium or vitamin D defficineces effect bone strength, as does various diseases such as osteoperosis.  Ghost is right, age and hieght are just approximations. i cannot comment on these studies, however i am very skeptical that bones grow like muscles, as in the more you lift the stronger they get. at least not in amounts and percentages that would make a difference to the world of skiers. what the chart helps you do is spot the fat skiers by having you stop on the box on the chart that you come to first when moving down. if a skier is overweight, you will end up stopping on the line that has the skiers height because their weight match will be one or two lines further down the chart. the inverse is true with skinny skiers.

Final point - we might just be missing words here - but Jim seems to be implying bindings are good at managing twisting falls.  Now to be precise in skiing twisting fall, really means a forward twisting or a backward twisting fall.  Its to my knowledge that bindiings did not protect the legs well from these types of falls.  It was around the early 80s when binding manufacturers started playing with more advanced HEEL and TOE pieces that could release in multiple directions.  Prior to this, heels just went up/down, and toes just went left right.  Even today, to my knowledge, only the better bindings have these features.  Its worth doing the research to learn which ones do (ie ask a reputable ski shop), and if required pay more for it.  Am I wrong Jim?  Or do all bindings have this now...and this actually started in the 50s and 60s?  Which bindings? When did turntables come out? These were likley the first.. bindings still only release upward at the heel and lateraly at the toe for the most part. there is some grey area with some brands and or models. just because a supplier says a binding has these grey area release modes does not mean that they can actually defy reality to function in the manner that they advertise. sad to say this but bindings have not really changed since the 80's. are they better than the 80's? absolutely, however much of the improvements are on the materials, and manufacturing tolerance side, and the shock absorption side not necessarily in terms of protection.

Quote:
Originally Posted by Ghost

All the binding knows is what torque it is able to deliver to the boot when set at a given DIN.

The ski and binding deliver that torque to the boot.

You resist that torque on the boot.

Although the binding doesn't know how much you weigh; it only knows at what setting you have set the release. However, if you weigh 300 lbs you likely have stronger bones from carrying around all that weight than if you weigh 80 lbs, so you may use a higher release setting.

If your leg is longer, you have a longer lever arm and can withstand more torque because of that longer lever arm and you may set your binding at a higer release setting if you are 6'6" than if you are 4'8" you cannot withstand more torque because the leg is longer, however you can withstand more torque if the bone is bigger in diameter, which in theory occurs when the frame gets bigger in height.

What resists applied torque is force at a distance from the axis of rotation.  The equation is pretty simple; it's force x distance = torque.  Push open a door at the door knob.  Push the door open by pushing near the hinge.  Lever arms matter.

Quote:
Originally Posted by Skidude72

Quote:
Originally Posted by Ghost

If your leg is longer, you have a longer lever arm and can withstand more torque because of that longer lever arm and you may set your binding at a higer release setting if you are 6'6" than if you are 4'8"

You sure?

Yes, it's simple physics.  The chart also agrees:

"Find the Release Code (letter A through P) which corresponds to the skier's weight, as well as the Release Code which corresponds to the skier's height. If they are not the same, choose the one that is closer to the top of the chart. For example if the skier's weight is 175 lbs. (code L) and the height is 5'7" (code K), choose code K as the correct line of the chart to be reading."

You could be a 1000 lb troll with strong legs, but if you're only 5'7, you still chart out at code K.

That extra height will only go so far, though.  The lever arm for a boot top fracture is the top of your boot, not your knee, and the extra height doesn't change the lever arm in a pure twisting injury.  The stats that went into determining how much each factor weighed upon your leg's ability to "take the torque" accordingly gave height less weight than weight, but height is a factor in your ability to take torque.

Also, as some have noted, height is also instrumental in your ability to deliver torque to the ski (assuming you have the bindings cranked up sufficiently), so taller folk will find it easier to overpower a given DIN.  Torque goes both ways!

Quote:
Originally Posted by starthaus

Originally Posted by Skidude72

I dont want to get into this so I will just make a few points:

Lever Arms:  Lever arms are important, but they can be abit counter intuitive.

Lets say you hit a rock that imparts a side force on a long ski...long lever, more torque at the binding, binding senses that torque.  It dont know if its a smalll force on a long lever, or big force on a short lever...it just knows what is at the binding, and it either releases or doesnt.  So all things equal short skis will always generate less torque right?  Wrong.  Think about this for a second,,,if a long ski clips the rock at the tip, the short ski will miss it all together (I know this sounds well "duh" but work with me here)....if you are close enough for the short ski to hit it, then the long will hit too...but the long will hit at the same point...ie the same length lever arm.  It dont matter the long ski has another 10-20 or what ever cm beyond the contact point.  Make sense? forget about the ski, way too random. not really germain to the discussion. I agree, but the OP asked "why is it germain"...so I explained it.

Jimbo - Skiers height.  Tall skier = bigger person = bigger bones = stronger bones = can handle higher stress before breaking.  All true. that has been proven with cadaver tests

Also taller skier - by definition longer body  = longer lever arm = equal more force generated at the binding from the same fall then a shorter skier.  Now, work with me here....a shorter skier = shorter lever arm = less force generated at the binding.  As you have correctley pointed out, the binding only knows what is happening at the boot/binding interface.  A shorter skier, (lets say for simplicity of same weight and BSL) as the taller skier, would need to be going alot faster, and have a more dramatic crash to generate teh same force at teh binding.  More force (or put another way, worse crash) required to get the same release?  Bad.  So the binding is set lower on shorter skiers, so they get the same release from teh same fall.  ie if you are going 30km/hr, and the skis hit a rock...the skis should release regardless of how tall or short you are.  That is why shorter skiers have lower DIN then taller.  They generate less force at the binding boot interface then a taller skier....so the DIN is set less so the binding will react the same for the same fall. husband and wife come into the shop, weight 30 pounds apart, age about the same, height 6 inches different so let's try this in real world numbers....he is 6 ft tall 179, 40 YO type 2 skier with a 325mm bsl, she is 5'6" tall 149, 42 YO type 2 skier with a 285 bsl. his DIN # is 7, her DIN # is 7. his binding should release at the toe with approx 67 deca newton meters of torque, hers at approx 50 deca newton meters of torque. DIN # is the same but the torque is different based on the bslYes BSL also matters.  But the topic was on skier hieght and why it was considered.  I explained why it matters.  If you use real numbers, with the only difference being skier height, you will notice the shorter skier has a lower DIN.  If it were purely do to bone strenght as you suggest, shorter people would be statistically have more broken legs then taller people.  I find that hard to beleive.

Other points on bones - tons of studies proved that people who were obese have higher density (read stronger) bones then those who were not.  Calcium or vitamin D defficineces effect bone strength, as does various diseases such as osteoperosis.  Ghost is right, age and hieght are just approximations. i cannot comment on these studies, however i am very skeptical that bones grow like muscles, as in the more you lift the stronger they get. at least not in amounts and percentages that would make a difference to the world of skiers. what the chart helps you do is spot the fat skiers by having you stop on the box on the chart that you come to first when moving down. if a skier is overweight, you will end up stopping on the line that has the skiers height because their weight match will be one or two lines further down the chart. the inverse is true with skinny skiers. Dont take my word for it....take googles.  Easy to find lots of articles from reputable sources:  Here is a quick easy one - its on a site for osteporisis but this article talks about bone strenght and factors that effect it in general.

http://www.whatisosteoporosis.net/what-factors-determine-bone-strength/

Just a quick point thou...if bones didnt grow, they couldnt heal once broken.

Final point - we might just be missing words here - but Jim seems to be implying bindings are good at managing twisting falls.  Now to be precise in skiing twisting fall, really means a forward twisting or a backward twisting fall.  Its to my knowledge that bindiings did not protect the legs well from these types of falls.  It was around the early 80s when binding manufacturers started playing with more advanced HEEL and TOE pieces that could release in multiple directions.  Prior to this, heels just went up/down, and toes just went left right.  Even today, to my knowledge, only the better bindings have these features.  Its worth doing the research to learn which ones do (ie ask a reputable ski shop), and if required pay more for it.  Am I wrong Jim?  Or do all bindings have this now...and this actually started in the 50s and 60s?  Which bindings? When did turntables come out? These were likley the first.. bindings still only release upward at the heel and lateraly at the toe for the most part. there is some grey area with some brands and or models. just because a supplier says a binding has these grey area release modes does not mean that they can actually defy reality to function in the manner that they advertise. sad to say this but bindings have not really changed since the 80's. are they better than the 80's? absolutely, however much of the improvements are on the materials, and manufacturing tolerance side, and the shock absorption side not necessarily in terms of protection. Isnt that what I wrote in my first post????????????  Anyway, I agree none of these multi-directional release systems are perfect, but I do see them as better then those that dont have them.  However that is just an opinion based on personal experience (the multi-direction bindings do seem to release with less strain on the legs...ie they function better).  I am not aware of any comprhensive study commparing the effectivness of different bindings, other then meeting a minimum DIN standard.

I'm not trying to be argumentative, but I don't understand why you think the ACL bears no role in relation to the forces applied here. Everything in the chain is connected and subject to force, the skier, including all his body parts, the boots, the bindings, the skis and the ground, or object of impact. There are multiple places were the chain can weaken or break when force is applied to any component. Obviously the role of the binding is to release before damage is done elsewhere. Although the interface is the boot sole, it is acted upon by many components. I'm not sure what you mean by "cares about", but everything is affected by everything else. If the ACL goes first then the binding may not release, so the binding is concerned by the actions of the knee and does react to it.

BW.

Quote:

I'm not trying to be argumentative, but I don't understand why you think the ACL bears no role in relation to the forces applied here. Everything in the chain is connected and subject to force, the skier, including all his body parts, the boots, the bindings, the skis and the ground, or object of impact. There are multiple places were the chain can weaken or break when force is applied to any component. Obviously the role of the binding is to release before damage is done elsewhere. Although the interface is the boot sole, it is acted upon by many components. I'm not sure what you mean by "cares about", but everything is affected by everything else. If the ACL goes first then the binding may not release, so the binding is concerned by the actions of the knee and does react to it.

BW.

You are both right...the knee ligaments matter to the skier....but not the binding.  Bindings were not designed to prevent knee injuries....only broken legs.  The next major advancment in binding design will likley be an improvement in this regard.

Quote:
Originally Posted by Skidude72

You are both right...the knee ligaments matter to the skier....but not the binding.  Bindings were not designed to prevent knee injuries....only broken legs.  The next major advancment in binding design will likley be an improvement in this regard.

Does not the lateral frictionless release of the toe binding not help protect against twisting forces on the knee?

It all helps...but is a long way from being even considered to be effective at reducing knee injuries.

SkiDude 72, you have stated "That is why shorter skiers have lower DIN than taller." (Ghost has more or less said the same or similar). This statement is incorrect. If you actually check the DIN chart you see that two skiers with identical height and weight, the one with the longer bsl gets the lower DIN, or one big guy with big feet can get a lower DIN than smaller guy with smaller bsl. Kinda blows your arguments out of the water as one would think the bigger stronger person gets the higher DIN, but that is not what happens on the DIN chart.

As I stated in a previous post, I have trouble wrapping my head around the stuff above in bold and explanations by Ghost and SkiDude72 seem to argue against the stuff in bold and thus go against the DIN chart numbers.

The only explanation that I can come up with in my non mechanical mind is that the boot pivots at the heel in a release, so the shorter bsl travels or scribes a shorter arc or distance at the toe during a release and the longer bsl has the same pivot point but scribes a longer arc at the toe. Therefore to compensate for the difference, the longer bsl needs to start to release sooner and thus gets a lower DIN. OTOH I probably have my head up my ass and don't really know what I am talking about and it is 3am and I am awake because my dog woke me up in the middle of the night to go out for a pee and poop.

Edited by DanoT - 9/22/12 at 3:26am
Quote:
Originally Posted by DanoT

... Kinda blows your arguments out of the water as one would think the bigger stronger person gets the higher DIN, but that is not what happens on the DIN chart....

Longer foot usually belongs to taller and not necessarily stronger person. Strength of the skier is determined in DIN chart by height and weight. The issue here is: two skiers with the same strength, but different boot sole lengths.

Moment = Force x Perpendicular Distance

In this case:

Moment = bone (skier) strength

Force = DIN value (in a certain way)

Distance = boot sole length

In another words: for the same bone strength DIN value must be lower if boot sole is longer and vice versa. Pure and simple physics.

P.S. Excuse my English

Dano,

Consider it from the boot's point of view.  When you hit a rut in a turn or catch an edge, the binding is trying to twist the boot one way with a lever arm proportional to the boot sole length (bsl), and you are trying to resist that torque with a lever arm that varies with your height.

Short people with long feet will have a lower DIN setting.  Tall people with short feet will have a higher DIN setting.  Boot sole length and height are two different factors.  Long bsl means binding at DIN 9 is able to apply more torque.  Long calve means somewhat (see caveats above) able to resist higher torque, so 175 lb 6 feet tall will have higher DIN than 200 lb 5'9" (at the same bsl age, and risk level).

DIN charts were originally made up decades ago considering forces required to break leg bones given the torque applied to them.  They haven't changed.the numbers in decades as far as I know.  However the same physics apply; lever arms that assist in not breaking bones also aid in not ripping tendons.  These only aid in certain directions and modes of release. I will add thought that bindings have changed a bit with upwards toe release, forward pressure compensation, diagonal release, and I'm sure the release settings in these modes are selectively weighted and a function of the DIN setting.

Quote:

I'm not trying to be argumentative, but I don't understand why you think the ACL bears no role in relation to the forces applied here. Everything in the chain is connected and subject to force, the skier, including all his body parts, the boots, the bindings, the skis and the ground, or object of impact. There are multiple places were the chain can weaken or break when force is applied to any component. Obviously the role of the binding is to release before damage is done elsewhere. Although the interface is the boot sole, it is acted upon by many components. I'm not sure what you mean by "cares about", but everything is affected by everything else. If the ACL goes first then the binding may not release, so the binding is concerned by the actions of the knee and does react to it.

BW.

yes, there is a chain. which is the weakest link in the chain? bone or soft tissue. the binding cannot tell the difference. the part that you are missing is about your body. the binding is a mechanical device that can only function as it functions. they are relatively simple mechanical devices. the human body is way more complex. the part that seems to be alluding you is that the binding in general terms cannot help you with any part of the chain from the top of your head, to below your knee. (the biggest exception to that statement is in shock absorption which helps to keep the binding connected to your person so your body above the knee does not make contact with the earth at a high rate of speed and so you can keep skiing down the mountain) now we could split hairs and find some types of falls that if all the stars align there is a chance that the knee can be spared. but for the most part the bindings work best to protect the bones of the lower leg. again i will make a generalization that we could pick apart the small percentages, but the bottom line is that the bones of the lower leg are stronger than the connecting tissue. that means that if there is high force that the leg can take. but the soft tissue cannot, the soft tissue will be damaged before the bone can transfer that force to the binding. the binding only can sense those forces that are transferred through the boot sole. that is a fact we cannot dispute. in a perfect world where everything is equal, we could do a better job protecting our knees in skiing by never getting our bodies out of position, and if we did get into trouble while skiing make sure that we fall in such a way that the soft tissue of our knee feels no stress.

jim

Edited by starthaus - 9/22/12 at 3:10pm
Quote:
Originally Posted by Ghost

Dano,

DIN charts were originally made up decades ago considering forces required to break leg bones given the torque applied to them.  They haven't changed.the numbers in decades as far as I know.  However the same physics apply; lever arms that assist in not breaking bones also aid in not ripping tendons.  These only aid in certain directions and modes of release. I will add thought that bindings have changed a bit with upwards toe release, forward pressure compensation, diagonal release, and I'm sure the release settings in these modes are selectively weighted and a function of the DIN setting.

the above statement is where all of the binding arguments get very muddy. first of all the research that became the basis of how bindings work was sound many years ago and remains sound today. The stuff you are talking about above is why i keep going on this thread. you have bought in 100% to the marketing hype of the binding manufacturers.

best example would be the turntable heel. years ago when it was introduced, the brands that brought it to market explained because the heel piece rotated below where the tibia twisted, you would have less torque on the lower leg. step in heels fundamentally work the same way. the point of rotation is not the end of the boot sole, but actually if you where to complete the circle that the heel cup begins you would find the center of that circle is just about where the turn table heel sits. so both relieve torque to the lower leg in the same manner. what gives the advantage to the step-in heel is it's ability to slide fore-aft to control the loads forced to the toe piece when the ski is in deep flex. the step-in has room for strong forward pressure springs that help to maintain forward pressure on the bsl while skiing. so online we can have knock down drag out fights about which binding design is better. and after coming away bleeding and bruised i will tell you it just doesn't matter cause you are arguing about stuff that has no difference, and that these bindings function close to identical in forward twisting falls, backwards twisting falls and shock absorption.

there is similar myth busting that could be done to explain how diagonal heels do not change the landscape. as well as the myth of vertical release at the toe. there is solid evidence that links back to those early skier injury studies and to the lab where cadaver bones where bent and twisted that debunk many of the marketing stories of ski binding protection. keep in mind that many of the designs that were introduced from the research really sucked and are no longer on the markets. plate bindings that could release in all directions, plate bindings that were retractable, and a bunch of very poorly conceived products that vanquished to museums. bottom line; skiing is a dangerous sport and you put your soft tissue and some bones at risk every time you do it. just for the record i believe the fun and thrill of the sport way out paces any of the limitations of modern binding design.

jim

I'm starting to realize that at best, the DIN system is a ball park guess based on incomplete information and outdated research. I wonder how accurate the settings are that we put our faith in. All that really matters is that the force required to release the binding is less than the force required to break the bone. There are multiple variables that go into this calculation, but we just use a few basic ones.

This may seem a little random, but whether or not a person is taking steroids (like prednisone for asthma), has a huge impact on bone strength/density. Potentially more than all the other factors combined. I have never seen the question "Do you have any medical or hereditary conditions that may affect your bone strength?" appear in any DIN calculations. Perhaps it's fair to say that this responsibility should fall on the customer and not the technician, but if you are going to train and certify people in the application of safety equipment, it seems reasonable to educate them in all the variables.

When you see information presented on a website, manufacturer's manual or printed chart, there is the tendency to believe that the information is accurate, based in validated research and can be trusted. Can DIN be trusted ? Do we really have enough information about a given individual, to decide if their DIN should be 6.0, 6.5 or 7.0 ?

Not meaning to be critical, just thinking out loud.

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