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I'm painting a very large target on my fat ass

 Poster: A snowHead
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. . . but here goes


As part of a larger project I've been delving into the argument about 'parallel tracks' and I can say it's been fun . . . yeah, right Wink But by assiduous use of the Mark-1 eyeball, a lifted finger to the wind, some ill-prepared experimentation and just a soupçonne of common sense, I've prepared a postulation on the farce that this subject became. I'll keep it as simple as possible and try to use allegories that are relevant and repeatable to the lay reader's terms of reference.

As one of the most vociferous advocates of straightforward Euclidian geometry to explain the apparent conundrum of two skis scribing congruent paths into the corduroy it came as not a little disconcerting to realise that veeeight's fatuous experiments contained a hint to the explanation in that it illustrated if you apply perpendicular force to a single ski it will bend . . . which, as far as I can ascertain, is where they stopped, and we now continue.

If we go back to basic human physiology . . . our 'Inner Monkey' (read the thread) if you like, we know that the mechanical system that is our foot and leg has an elastic latitude in the connective tissues and ligaments allowing us to spread our legs wide while still keeping our feet flat to the floor (overpronated), further this system is capable of absorbing and returning energy independently of muscle motive power . . .

With the foot overpronated and force inserted through the big toe/ball of the foot the energy transfer will naturally be laterally to the inside of the contact point . . . 'star' jumps are the basic demonstration of this. This system has a lot of lateral flexibility in the foot itself, the ankle and the knee, compounded by the oblique insertion of the Femur head into the Pelvis . . . which is why 'Star Jumps' where both legs are equally stressed, are easier than 'Cross Jumping' where both feet cross under like the “skier's Edge” machine and essentially most of the work to absorb and return energy is undertaken by the 'outside' foot and leg.

As CEM will tell you, when you laterally load the outside of your foot, the bones form a 'stack' and lock together creating a more rigid structure than as when above, you load the inner side of the foot. You can experience this yourself by standing and crossing one leg in front of the other and trying to get both feet flat to the floor.

What the hell's this got to do with carving a turn?
Essentially the downhill or outside ski is resisting both a gravitational/downward force and a centripetal/outward force through a flexible structure while the uphill ski is resisting similar but reduced forces through a more rigid structure. This, along with our body morphology goes a way to explain the differing insertion angles we see between the skis of 'balls to the wall' racers where the downhill ski is doing all the work and the uphill ski is barely dancing its tips around the turn.

To keep the downhill edge engaged requires pressure to be levered against the inner side of the boot by the adductor muscles of the thigh and groin to compensate for the innate lateral (outward) flexibility of the leg under that stress, The stiffer the boots and stronger the muscles the better the ski will stay at the desired edge angle. Soft boots, flappy thighs and fat skis will make this harder and may force the skier to 'A' frame in order to achieve the desired ski angle to the snow surface.

On the other foot, the uphill ski is having a much more relaxed time of it, not only is it less pressured but also the inner tip lead required to maintain ski separation induces a natural and more acute insertion angle to the ski. In this configuration the mechanical structure of your leg is more laterally rigid than your downhill leg, easily maintaining it's edging angle and is far less influenced by adductor/abductor strength, boot stiffness and ski width. In fact it's more likely that differing ski angles at mid carve will be exaggerated by soft and/or ill fitting boots, fat skis and poor fitness. When we perform less aggressively the differing angles become less apparent but are no less important.

All the above is subject to the speed of the skier and the desired radius of the turn though NOT the radius of the skis . . . that will become relevant shortly.

Using basic geometry it is and was possible to explain the apparent ability of two skis to leave “parallel” tracks but this required the skier to have greater than child bearing hip width and/or the inner ski to bend in a tighter arc than the outer whilst bearing less pressure . . . of course both of these are impossible * and (forgive me if I don't bother re-reading his drivel and paraphrase in the alternative) I think goes some way to explain Vee8's “rejection” of geometry as an answer. But it was the image of his Heath Robinson contraption to bend a ski that hid the secret . . . we slide on a deformable surface that exhibits progressive and non-elastic resistance . . . It's snow itself that contains the answer.

There are many threads on slushNuts that question how and why a ski's sidecut radius has any relevancy to their real-world experience. It doesn't help that there seem to be boogerall consensus to the explanations in that they all appear to focus on just one and usually geometric aspect of ski manufacturer's statement that a ski has 'x' radius. Well . . . as it plays an important part in this post, we're going exploring.

In it's simplest explanation a ski's radius 'x' is just the size of the 'bite' out of each side of the ski at rest. extrapolating that bite will complete a circle with radius 'x' ... BUT ... That's not the whole story and that radius is not fixed. A ski is a machine that functions in three dimensions.

experiment: Take a piece of stiff card, A4 is adequate, and draw a simple curve from one side to the other, cut it out and you've two pieces of card. Keep the one that's thinner in the middle, like your skis. Now lay that piece flat on the table with the bite facing you. Grab the sides of the card and raise the back of it towards you while trying to keep the curved bite touching the table surface. You can only do this by bending the card bringing the two sides closer together . . . effectively shortening the radius, it's a logarithmic progression rather than a linear one so that the more you bend the card the shortening of the radius accelerates (there is an optimal point where this changes but we'll never bend a ski far enough to reach that)

There are two points of interest in this:
One is that it demonstrates how a ski with sidecut radius 'x' can cleanly cut a carved turn with a radius much smaller than 'x'

Second, is that for a small bend in a ski there is a great difference to the measured radius on the ground and if we take two skis, mid carve, in 'parallel' tracks it will take very little difference in bend for them to have the same point of origin for their radii.

There's the rub . . . How do we bend the inner ski more than the outer when we're putting less pressure into it?

The answer? It's because we are putting more pressure into the outer or lower ski that it bends less than the uphill ski.

experiment: We'll do this with our skis flat and just imagine that they are inclined to the snow surface (it doesn't matter as the results are the same as will become clearer later)

Build yourself four 6 inch stacks of books or magazines and place them on the floor so that your skis can sit on them in parallel and about a foot apart. Make sure that the books are under the widest parts of the skis and that both skis are supported at the same places. you should now be able to press down on the centre of skis to bend them and you'll see that it takes equal pressure to bend the skis equally . . . no surprises there.

Now . . . take a nice fat cushion or pillow and place it under one of the skis, this becomes your outside or lower ski (why? I'll explain shortly) now press on the centre of the skis and try to bend them by an equal amount. The resistance of the cushion requires you to weight that ski more to achieve the same bend.

This is exactly what is happening on the hill. As we tip our skis onto their edges to initiate a carve we move the insertion of our mass into the points where our edges first meet the snow, our tips and tails. The skis begin to bend and cut into the snow. As the turn progresses we start to compensate for the centripetal force by angulating the edges more and putting greater pressure into the outer ski.
The outer ski is now cutting deeper into the snow but the inner ski is just sitting at a greater angle on its tip and tail edge easily bending till there's just enough edge engaged to support the reduced force in that leg.

Coming to the mid point in the carved turn and the outer ski has achieved equilibrium by cutting and compressing a channel in the snow creating a flat in cross section platform for the ski to run on. The skiers mass and all the other forces are supported under the whole length of the ski and the ski is bent in a stable condition. The ski can only change its bend shape if the skier alters the insertion angle or reduces pressure. The snow itself has an influence on where this stable condition occurs and how bent the ski will be in it. ie the harder the surface the greater the angle of insertion, the more a ski can be bent before reaching stability (however fleeting) and the stronger the forces can be applied and resisted,

Meanwhile, back on the uphill ski it's at the same or greater angle to the downhill ski but it doesn't have the same pressure forcing it into the snow surface so it can easily bend until its running length is supporting itself and is happily sharing the same point of origin as the lower ski's turn radius. If you look at so called parallel RR tracks the outer one is always deeper with a wider support platform than the inner or uphill track. At slow speeds and gentle carving the difference will be minimal but still there and measurable.

There are lots of side issues like the size of the sidecut, the linear and torsional strength of the skis, the skills of the skier, but they all fall into the same basic premiss above.
The biggest variable is the type of snow itself, its density and the conditions it requires to deform and compact into a surface capable of supporting the skiers mass and velocity. This is why when a fast carving skier hits a soft patch the ski will bend more, sharply altering both the ski and the turn radius and send him 'highsiding' into the catch-fencing.

In the end it's just a combination of geometry, physiology and physics. And that's it . . . simples . . . wink
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 Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
Can you condense that lot into 3 lines - or less?
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 Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
...and is there an English version?
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achilles & Frosty the Snowman, the smell of sh¡t always attracts flies rolling eyes
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 Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Masque, based on the above there should be swarms around shortly wink

Seriously though, half way through I lost the will to life. 5 minutes of my life that I wont get back.
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I see it's going to be a long, long, long Summer rolling eyes
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Masque, I've said this before: stop using a dozen words where one will do. Assuming your goal is actually to communicate something.
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 After all it is free Go on u know u want to!
After all it is free Go on u know u want to!
Lizzard, nope, so ya, boo, sucks Toofy Grin

Wags, ya better believe it Twisted Evil
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Masque, does verbal onanism make you blind?
(The word is 'soupçon' by the way.)
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Masque, Are back here or still over there? If the latter your OP indicates you should return here soon. Laughing
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Hurtle, I can barely spell in Enlish and now you're correcting my kermit rolling eyes and no, it gifts one 'fingers of steel' and a touch of arthitis wink
Though it might be 'suspected' that I have some common sense rather than suppose that I have a 'hint' of any. Christ, you try and pun in French and all you get is a kicking wink
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Masque, no offence. At least, not much. wink
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 So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
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Masque, if you can't even spell the language, punning it it could be said to be ambitious.
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 You know it makes sense.
You know it makes sense.
Lizzard, (edited 'cos) Je soupçonne que j'ai été un dick


Last edited by You know it makes sense. on Sat 9-05-09 16:24; edited 1 time in total
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 Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
Got very bored after the first 3 lines.....so stopped reading. What a load of shite! rolling eyes
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GreyCat, Laughing there is a pony in there somewhere
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 Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
But do the skis run parallel? Puzzled
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 Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
Masque, T'es Nul
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SMALLZOOKEEPER, peut-être.
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 Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
freestyleandy, independent of any steering input, yes they do, All the above assumes perfectly smooth and consistent snow conditions. Real life requires a bit more input from you to compensate for the ever changing nature of the hill.
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Masque, can you repeat it all but this time see if an helmet makes you a more reckless carver or not.
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Quote:

Je soupçonne que j'ai été un dick

Mais pas maintenant?
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 After all it is free Go on u know u want to!
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pam w, a little less so Blush
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Another thread in BZK sums up my feelings on this one very well.. "Why?".
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Masque, Don't forget that it's meant to be fun. Perhaps you intellectual and scientific energies would be better directed at ...er... something else?
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red 27, fun? what's that got to do with BZK Little Angel
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And love to help out and answer questions and of course, read each other's snow reports.
Masque, U bin drinkin' again?
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So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
Masque, I didn't get past the first sentence, but I'm sure it qualifies as Snowheads Gold if only for the sheer effort you must've put in. Next time the amber liquid calls it might be an idea to hide the keyboard first!!!
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 You know it makes sense.
You know it makes sense.
Megamum, this does not qualify for snowHeads Gold! At least not yet..


Last edited by You know it makes sense. on Sat 9-05-09 21:06; edited 1 time in total
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 Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
OK, if we are being serious for a moment - I think it relates to how skis must be tilted to draw parallel tracks in an arc in the snow. For some reason (god knows why) I suddenly recalled reading or watching something about railway wheel pairs not being able to go round curved track if they were actually set at right angles to the railtrack. IIRC there was something to do with the wheels needing to sit on a cone shaped edge in order to get round the bend. I've just been off and tried to find related info on google about the railway problem and came up with this http://en.wikipedia.org/wiki/Superelevation

I also recall seeing the recent TV adds about the new Dyson's that have a ball to steer them with rather than wheels - this must also enable them to turn on a 'cone' shaped edge. I bet all this relates to how skis need to work to also get round a curve and yet still remain parallel in terms of the track that they leave behind.


Last edited by Otherwise you'll just go on seeing the one name: on Sun 10-05-09 19:12; edited 1 time in total
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God help us Megamum's, being serious..... wink
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arv, I did (probably because I was horribly fascinated by the unbelievable passion he has for the topic) and I think I managed to understand what he was saying. It will be about as much use as a chocolate teapot in helping me with my skiing though. Laughing
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 Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
Please, Please, Please let this thread die. If it goes on for 28 pages I'll be heading to Bournemouth for a Dr Death seminar Skullie
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Iski,, maybe it is too late for me, fancy summing it up it a few lines Puzzled Madeye-Smiley
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arv, Not possible for me I'm afraid, it's like when you can read and make sense of something in another language but can't actually use it to make yourself understood. Anyway, I'm sure your own 'inner feedback' as discussed in the BZK thread - 'skills' versus 'form' based teaching - will be of much more use to you. Very Happy
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Megamum wrote:
I've just been off and tried to find related info on google about the railway problem and came up with this http://en.wikipedia.org/wiki/Superelevation.


Megamum, the link doesn't work 'cos of the full stop at the end, but this does http://en.wikipedia.org/wiki/Superelevation . Smile
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More here on rail wheel sets. I used to think going round a curve was primarily achieved by the coning of the wheels - in part that seems true - but it is a complex subject.
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 After all it is free Go on u know u want to!
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Masque, Read this and seems logical.... is there some kind of scientific paper you can publish it in then? Toofy Grin
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Masque, Toofy Grin

I really hate to ask but:

Are you saying that the inner ski bends more (so describing a tighter radius than the outer one) because it's subject to less pressure than the outer ski ?
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II wrote:
Masque, Read this and seems logical.... is there some kind of scientific paper you can publish it in then? Toofy Grin


It would do well in the Lancet as an example of OCD Toofy Grin Toofy Grin
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