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edging

 Poster: A snowHead
Poster: A snowHead
I've meant to put my closing thoughts on this topic sooner, but hadn't the time to get pictures scanned in etc. - but anyway - I have now!

I do acknowledge that there are more than one school of thought on this, for some, they will prefer to ensure that cuff (and therefore knee angulation) is doing the work, and that the ankle rolling is merely a mental trigger.

Most importantly - we should all agree that the foot must be allowed to work as a foot inside the boot, and not be encased inside a block of concrete.

This "ankle rolling" this is not new. Georges Joubert refers to it in his "Skiing - An Art A Technique" book, and talks about "pressure on the malleolus", and the "muscular effort required by the foor inside the boot" to ensure good hold on ice.

Warren Witherell in "The Athletic Skier" talks about the ankle joint in terms of efficiency - "If you need a few degress of edge, roll your ankle. If more edge is needed, knee angulation is quicker than hip angulation - but it's not as strong. When G forces are high, hip angulation or full body inclination is needed. Quiet upper-body movement allows the best control of the ski through lower body movement. At all times do as little work as possible to achieve a desired result."

In "How the Racers Ski" (Warren Witherell) - In describing what he see's the ski doing in the snow, he describes "Most pressure and edge changes should be instituted primarily by ankle and knee movement".

These books and authors aren't some half baked newfangled fly by night things, these are well respected titles and authors, and now for the third, Ron LeMaster.

The following is shamelessly ripped from Ron's "The Skier's Edge" - so those that already have a copy can sing-a-long at home!

Have you thought about how an ice skate holds? Skates are not nearly as stiff and powerful as ski boots. The ice in any rink is as hard as the worst boiler-plate a skier is ever likely to see, yet a casual skater can describe clean arcs on a rink, while good skiers often struggle to make good turns on snow that is not nearly as hard.

The difference lies in the relative locations of the ankle and weight bearing edge. The blade of an ice skate is directly underneath the entre of the skater's ankle, so when the skate is on edge, the force that the ice exerts on the blade passes directly through the centre of the skaters ankle.





In contrast, the edges of a ski are offset from the centre os the skiers ankle.



In the diagram above, the force S from the snow acts along a line that passes outside the skier's ankle. The distance L from that line to the skier's ankle creates a lever through which S exerts a torque T on the ankle. T seeks to twist the skier's ankle, flattening the ski on the snow, making it slip.

The longer L is, the greater T will be, which is why fat skis are harder to get on and maintain edge.

The key to holding then, is to make the the situation more like a skate - to get the ankle as close as possible to the line along which the force from the snow acts.

The closer the centre of the skier's ankle is to the line S, the smaller the torque on the ankle, the better the hold/grip of the ski on the snow. As well as explaining why a narrower ski under foot holds better, this also explains why skis hold better in soft snow. As the ski is driven further into the snow, the snow's reaction force moves closer to the centre line of the ski, making T smaller.





So: In order to reduce L and T, we can do 3 things:

1. Ski narrower skis (so that it behaves more like a skate) (FIS Limits apply)
2. Use risers, lifters and plates to reduce L (and therefore T) (FIS limits apply)
3. Move, or roll the ankle to the inside of the turn, so that the centre of the ankle is closer to S



The following diagrams shows the effect of rolling the ankle into the turn, plus knee angulation, making the torque T smaller






The following diagram shows the effect of adding lifters/risers/plates to achive moving the centre of the ankle closer to S




As they say, the proof of the pudding etc. Find a nice icy pitch, and actively try and hold an edge on your skis, with and without activating your ankle(s). In short, anything we can do to reduce T the torque on the ankle (which is constantly trying to flatten our ski) will lead to increased edge hold.

Happy Skiing!


Last edited by Poster: A snowHead on Thu 7-06-07 20:44; edited 1 time in total
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 Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
veeeight, while I appreciate your "physics" (sounds more like engineering to me, but then I'm only an ex-physicist) Happy ....

Whether or not I can do anything to my ankle, when I'm happiest in a boot my shin move with the boot. Very little give and take. It works fine for me. I don't think (although I may be unknowingly) I'm actively using my ankle at all. I don't think I can see how to.

And I can edge quite fine thanks.
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Well, the person's real but it's just a made up name, see?
veeeight wrote:

The difference lies in the relative locations of the ankle and weight bearing edge. The blade of an ice skate is directly underneath the entre of the skater's ankle, so when the skate is on edge, the force that the ice exerts on the blade passes directly through the centre of the skaters ankle.






Heh.

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comprex, Have you noticed that a similar debate is raging over the pond at the "other place"? A tale of 3 turns, post #326.

The following are not my words, I haven't contributed in that thread, there are more armchair quarterbacks there than there are here at snowHeads NehNeh

Quote:

Quote:
Quote:
I would be very worried if I was coached into using my ankles to attempt to tip my skis that are locked into a stiff pair of boots, when I have a very powerful pair of thighs that can do the bulk of the work, the bulk of the time. with incredible accuracy.


Grasshoppa, you have much to learn.

Your thighs are incredibly accurate? WRONG. Your hands and feet are. Your legs are powerful, not accurate.

Your feet are "locked" into your boot? Fix that, its not a good thing.

You can evert your ankle inside the boot in fact, and that will result in your ankle pushing against the sidewall of the boot. This shift of balance will create a kinetic chain, chain reaction which results in body parts up your leg and eventually to your hip all moving in that direction..


All this ties in with Euan's EoSB homework, "Hips for power, knees for strengh, ankles for accuracy", which not many seem to have bothered with Laughing
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veeeight wrote:
All this ties in with Euan's EoSB homework, "Hips for power, knees for strengh, ankles for accuracy", which not many seem to have bothered with Laughing


I've thought about it, and thanks to your input in this thread I've got a much better idea of what is being said. But I'm still trying to get my head around it because it seems so alien to all my skiing instincts! I'm hoping to catch up with Euan over the summer so will pick his brains a bit more on this.
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David Murdoch wrote:
I don't think I can see how to.


Imagine a dash butter churn, bottom to cover height H. The plunger is a tight fit in the churn, the cover is tightly fitted to the plunger handle. Now imagine the plunger handle is hinged about H/3 from the plunger itself.

Can you tilt the plunger handle without tilting the churn?
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veeeight, This is my first foray onto this thread and I find your diagrams fascinating. Very Happy

I have a couple of queries though.
Quote:

Have you thought about how an ice skate holds? Skates are not nearly as stiff and powerful as ski boots. The ice in any rink is as hard as the worst boiler-plate a skier is ever likely to see, yet a casual skater can describe clean arcs on a rink, while good skiers often struggle to make good turns on snow that is not nearly as hard.

I used to skate, although spent most of the time on my butt. I would have thought the main reason for a skate gripping on ice, is to do with the loading on the edge. A skate is only say 40cm long and a ski say 170cm long, therefore 4 times more load to make the skate cut into the ice. Puzzled


Quote:

The closer the centre of the skier's ankle is to the line S, the smaller the torque on the ankle, the better the hold/grip of the ski on the snow. As well as explaining why a narrower ski under foot holds better, this also explains why skis hold better in soft snow. As the ski is driven further into the snow, the snow's reaction force moves closer to the centre line of the ski, making T smaller.


I always thought that the main reason a wider ski had less edge grip than a narrow one of similar construction, was more to do with it's torsional rigidity diminishing as width increased, therefore allowing the ski to twist under load, reducing edge angle and pressure. Puzzled
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Spyderman wrote:
veeeight, This is my first foray onto this thread and I find your diagrams fascinating. Very Happy


Have you not read Ron LeMaster's book The Skier's Edge. It's brilliant; essential reading.
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Spyderman, yes, the higher force on a smaller area exerts a larger pressure, so length of blade is a factor, not necessarily *the* factor.

Anytime there is a torque on the ankle (ie: on skis) - that torque will always try to flatten the ski - away from the critical edge angle that is making the ski grip. Racers will always try to decrease this torque by the methods outlined above (narrower skis, higher lifters, rolling ankles) - which is why FIS have placed limits on these.

As to the torsional stiffness, yes you are correct, but this is only 1 factor that is commonly seen in the marketplace, in the sense that in general, wider skis are torsionally less stiff that narrower skis. However if you were to obtain a fat ski with identical torsional flex as a narrow ski, you'd still be fighting T, the torque placed on the ankle, that will constantly be trying to flatten the ski. So, although my iM88's are reasonably torsionally stiff - I still have to work harder in getting then up on edge, and holding them there gripping, than when compared with my iSL RD slaloms on an icy pitch.

Bear in mind that the words and diagrams above are not mine, but those of the *guru* Ron LeMaster. wink (I've edited my post above, and put the book references in bold - essential bookshelf material for any ski geek. But the colour slides are from a presentation Ron gave us a couple of years ago).


Last edited by You'll get to see more forums and be part of the best ski club on the net. on Thu 7-06-07 21:12; edited 2 times in total
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rob@rar, veeeight, Thanks guys, looks like I need to get hold of some bedtime reading.
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Spyderman, if you can wait 2 weeks, I'll lend you my copy.
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Careful now, Foxy. You'll have SZK moaning that we are propogating Disney stuff! Laughing
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veeeight, it Disney matter what he thinks!
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You know it makes sense.
Wear The Fox Hat, Thanks, I'll wait then. Ski test MK to BBQ should be enough time to read it. Unless it's War & Peace.
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Otherwise you'll just go on seeing the one name:
Spyderman, I found it easy to read, but it appealed to my way of thinking. Except some of it was above my head.
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 Poster: A snowHead
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I've had it 3 years now. And I still read it from time to time. And still glean additional information everytime I re-read it.
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veeeight wrote:
I've had it 3 years now. And I still read it from time to time. And still glean additional information everytime I re-read it.

Ditto. I have to confess that it mostly lives on my bedside table and I often read a section or two. I think I understand most of it now, even if I can't put that much into practice Embarassed
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veeeight wrote:
Anytime there is a torque on the ankle (ie: on skis) - that torque will always try to flatten the ski - away from the critical edge angle that is making the ski grip.

That of course is the limiting factor. If there is too much lateral "play" in your boots, you would need incredibly strong ankles to resist that torque. No one has ankles that strong. That is why plastic ski boots were invented in the first place. And that's why downhill course records plummeted in the late 60s / early 70s when ski boots became markedly stiffer.

There are as many ski teaching philosphies as there are ski teachers. I personally prefer to work "from the core outwards"; so get the hips and trunk right and then work towards "fine-tuning" from the knees and ankles. I believe that a racing turn is primarily initiated by moving the feet "under" the core out to the side, and the ankles play little role in turn initiation.

It is clear that many others like to work "from the foot upwards". That is fine too Smile
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veeeight wrote:
Spyderman, yes, the higher force on a smaller area exerts a larger pressure, so length of blade is a factor, not necessarily *the* factor.


I'm afraid you lost me there, V8.

The difference between the length of ski and skate is a factor of at least 4 while the difference in width between a GS ski and a fat powder ski is a factor of less than 2. How can the length NOT be *the* dominant factor?
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Because it isn't.

Get an ice skater, and a skier with extremely short snowblades (in fact so short that they are the same length as an ice blade) on a skating rink, and get them both to speed skate around the rink.
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I'm afraid there's something seriously wrong with your theory then.

Because if the width is *the* factor, it would only account for less thn 50% reduction of force from a skate blade DIRECTLY under the ankle and a ski edge that's 65mm wide.

While I have no doubt about narrower ski hold edge better than wider one and geometry has a lot to do with it. The theory, if correcct, would predict a snow blade of 65mm wide to hold the edge at least half as well as a skate of the same length (assuming they're sharpen to the same degree).
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Well good luck with that then. I'll leave you to time the two athletes around the rink. My guess is that the skater will outperform the skier way more than your 50% margin.

As I've pointed out before, it isn't my theory. It's an established one I subscribe to.


Last edited by Then you can post your own questions or snow reports... on Fri 8-06-07 15:25; edited 1 time in total
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So obviously something else pretty significant is also at play in the picture that the theory had not bother to account for then.

I don't ice skate. So I don't even know what else is different, let alone if those differences matter.
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I have often wondered what would happen if an expert ice skater attempted to skate down a smooth, well-watered, World Cup slalom course on ice skates. I have never heard of it being attempted.
(But I do remember seeing someone somewhere descending a luge track on ice skates - as a stunt for a movie, perhaps...?)
As someone who was a part of ski-racing in the late 80s, when Derbyflex and "lifters" transformed the sport (before it was restricted by FIS), I can say that the leverage from being lifted over the ski has an enormous effect.
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abc wrote:

The difference between the length of ski and skate is a factor of at least 4 while the difference in width between a GS ski and a fat powder ski is a factor of less than 2. How can the length NOT be *the* dominant factor?


the skate blade is rigid.


V8, you and abc are on about two separate but required factors, a) the skier applying the requisite pressure b) the ski responding properly to the requisite pressure.

One needs both a strong span and strong abutments for a proper bridge, pointless to speak of A dominant factor because that is improper conflation of two separate problems.
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I read the bits about the skater vs skier edging where the assumption is that the skater has their ankle relatively ridgidly held in the boot. I have an actual observation if its of any use to the discussion - apologies for interuption if its of no use.

I can skate passably, but years ago saw a second hand pair of leather boots the right size so bought them. These boots were, quite frankly, 'knackered' any support around the ankle was non-existant and the boots were floppy across the ankle line. I've skated in them ever since buying them without any problem and now find stiff hire boots far more difficult to skate in. I wonder if the way I skate in them is different to the people that skate in stiff boots?
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Megamum,

Quote:

assumption is that the skater has their ankle relatively ridgidly held in the boot


I hope you didn't make that assumption up, as I can't find any reference to me making it! wink

But your actual experience demonstrates that you can edge a skate without stiff boots, precisely because the blade is directly below the centre of the ankle.
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