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Perception vs. Reality: CM Path and Movement

post #1 of 19
Thread Starter 
Perception vs. Reality: CM Path and Movement

In this thread I promised that I would soon be posting some CM analysis and how it relates to ski track; meaning if you make certain assumptions about ski tracks and body position, how can those factors effect what your CM will likely do? Just so you do not have to keep referring back to the old thread I am going to post several of the more important images from the other thread (note that some have been modified to reflect proper terminology). It also might be a good idea to review this post that summed up what we were discussing that the previous thread.

http://i79.photobucket.com/albums/j1...ckAnalcopy.gif
http://i79.photobucket.com/albums/j1...Blowupcopy.gif
http://i79.photobucket.com/albums/j1...SepAnacopy.gif




In this new diagram (above) there are three turn style possibilities presented. The assumptions regarding upper body position is also discussed in each area as well as presented in a separate diagram and several accompanying pictures linked from Harb, LeMaster, and a few of my own pictures. The three assumptions are that the skier is using sufficient counter and variable track width, the skier is using little to no counter and constant track width (following the skis), or the skier is using constant track width and counter. All situations are assuming mid to high edge angles (makes a big difference).

Here is a small (poor) graphic of the three situations:




Variable Track Width with Counter (Left):

This scenario allows the CM to travel across the skis very quickly and moves instantly inside of the turn where it remains in balance with the outside ski until the turn completes. The points I wanted to note here were that the CM can move very far inside of the turn, and it spends little to no time “stuck” between the legs (think the opposite of bow-legged skiing) and actually requires no manipulation tin order to move from one turn to the next. I have included some images from the apex of a turn of this type and you can very easily see the huge vertical separation, horizontal separation, large amounts of counter, high edge angles, and the CM very far inside the turn. Combined with the virtue that were discussed in the other thread of this type separation management it creates a turn platform that can be used in slow speed, low edge angle turns, all the way up to the highest levels of racing where extreme angles such as the image below are commonplace.

Benny Raich:

Credit: [http://www.ronlemaster.com/images/20...l-2-SR-wm.html]

Harald Harb:


Some Other Guy:
http://i79.photobucket.com/albums/j1...0001-small.jpg


Constant Track Width with Little Counter (Middle):

This is what is commonly referred to as a stacked or banked turn. It involves skeletal alignment and following the skis while making the turn. I think that the images that I have provided show what this type of turn can cause in a turn but to be clear I will try to hit some of the bigger points. At low edge angles this type of turn works fine, but as the edge angle increases the skier requires a wider and wider transition stance. If you keep a narrow stance and try to use high edge angles you will quickly find yourself on the inside ski at the point in the turn where the angles are the highest (apex). More serious of a problem is the issue of the upper body not countering the turning forces which also causes the skiers weight to fall inside of the turn onto the inside ski. This can lead to all sorts of problems like inside tip lead, back seat skiing, or hip-checking. Often racers can get away with this kind of skiing in SG and DH because the speeds and forces are so great, but it is not the most effective model for typical recreational skiing. Also, if you notice (assuming high edge angles) the CM also spends a VERY long time between the skis/legs and requires a deliberate diagonal move into the next turn (possibly an up and over move?).

Cochran:

Credit: [http://www.ronlemaster.com/images/la...2004-sl-1.html]

Some PSIA Folks (open parallel turns, taken from video from this site and the V1 site):

D-Teamer:

Say hello to the inside ski:



Constant Track Width with Counter (Right):

This one was more difficult to find a blatant picture of because at the apex of the turn sometimes it can be difficult to tell the difference between this and the diverging tracks example. The major difference comes in the width of the legs in transition. At high edge angles the skis need to be so wide that your CM ends up stuck between the skis, which causes the problem of always having your inside ski underneath you during the turn – so you CM rarely departs much from your inside ski. This makes it very easy to put weight on your inside ski and hip-check (as well as a whole bunch of other issues) and does not promote very dynamic skiing. At the beginning of last ski season I was a victim of this type of skiing and pushed for the entire season to get myself away from it.

Example From Video From Epic:





So what was the point of all of this?:

In case you didn’t pick up on it; I personally have a preference in the type of turn I default to. The reason I started these threads was to show that areas of focus that we might be looking at when we are developing our skiing are not always the correct ones. When I look at skiing (any skiing – racers, PSIA, PMTS, [insert 4 letter system]) you can often see that one thing might be being focused on that is tearing the person’s skiing apart. One example of this is the separation of the skis on the snow (the resultant from my diagram). In actuality the skier should be mindful of vertical separation and aim to keep their horizontal separation close to the same throughout the turn. Often you see skiers who have learned to ski via PMTS skiing with constant [narrow] horizontal separation but completely forget about and ignore vertical separation (what happens?). Often you see racers (myself included at one time) over-exaggerating the width of their stance horizontally because the edge angles that they are getting require a wide stance if they are going to keep mostly even tracks (what happens?). Open parallel turns can cause a skier to focus on following their skis and not using separation, which at when the speed, turning forces, and edge angles are turned up from the nice steady pace that they are skied at (what happens?).

If your answer to “what happens” in each situation above was related to balance you’re probably on the same (or at least similar) page with me. The focus of the skier’s skiing should be centered on balance… period. No questions asked – balance and how to obtain it should be the focus. I have more on this later, but I would like the discussion to develop from here before I bring any more information into the discussion. I would also like to discuss why things like artificial separation, artificial edge angles, forced track width, and lack of counter can cause a loss of balance when skiing.

Later

GREG
post #2 of 19
Don't forget, gravity acts straight down to the center of the earth. Some of those "constant track" photos show an "A" frame with the inside ski directly below the CM. If the CM doesn't get inside of the inside ski, the inside ski can't carve. Tracks that I've seen usually show a pretty clean carves. Suggesting that the CM is inside.
When I'm looking at my tracks I look for a simultanious edge change, that is the tracks go from uphill edges to downhill edges at the same time. (Harald has a static drill for this) Sometimes I see the uphill ski appear to change after the downhill one. Right now I'm attributing this to tip lead.
As for balance, Ron LeMaster has a demo of a wide stance vs a narrow one and the balance issues each involves. Suffice it to say that you tip faster in a wide stance but have more control in a narrow one. It's easier to get your inside ski to a higher edge angle if you're narrow. That is, get your CM across both skis. Another thing that I stress with my kids is that, like a figure skater doing a spin, the turn develops faster and easier if everything is as close to the axis of rotation as possible.(narrow stance/little horizontal distance)
Another thought
There is a difference between the Center of Mass and the Center of Gravity.(they're usually close to the same) The CM is the point about which a body will rotate. I'm thinking that in a banked turn vs an angulated one the CM is about the same but the CG is farther inside on the banked one. (not sure but it seems like it might be to me)
As I think about that, the CM of a boomerang is inside the V so maybe the GG stays about the same but the CM is not as far inside with angulation(like the boomerang)
post #3 of 19
FWIW, using the definitions that have been standard in physics for the last 150 years, the only thing that causes a difference in location between CM and CG is the fact that the earth is not flat and the gravitational field of the earth is diverging on the length scale of thousands of km. The difference in location between CM and CG for anything under a few meters tall will be completely negligible (ie, sub micron).

Tom / PM
post #4 of 19
Thread Starter 
Just to clear up something that happened in last years waist steering thread - as Tom/PhysicsMan said, they are interchangable for our purposes. I think what you might have been alluding to SLATZ is that the CM/CoG is moving toward the earth because of the un-balanced nature of a banked turn.

Quote:
Originally Posted by SLATZ
Sometimes I see the uphill ski appear to change after the downhill one. Right now I'm attributing this to tip lead.
Can you elaborate on this more?

Later

GREG
post #5 of 19
Quote:
Originally Posted by HeluvaSkier
Often you see skiers who have learned to ski via PMTS skiing with constant [narrow] horizontal separation but completely forget about and ignore vertical separation (what happens?).
This is not my experience. In fact the inside leg retraction is one of the things that gives away a skier's PMTS training. Anyone that has taken PMTS camps/lessons has likely had vertical separation pounded into their heads as its a major focus in getting bigger angles. Perhaps a beginner might ski without much vertical separation but at that level they aren't ready for the bigger angles so sucking the inside leg up isn't required.
post #6 of 19
FWIW:

The CM (or CG, as Phyicsman notes) has to be horizontally displaced from the base of support because you're turning.

In a static situation, if you draw a right triangle with
- the base of support at one corner (a bit tricky to do, yes, in that you have two feet)
- the CM at another corner
- the third corner where a vertical line down from the CM meets a horizontal line across from the base of support
then the ratio of length-of-vertical-line : length-of-horizontal-line is equal to the ratio of acceleration-of-gravity : lateral-acceleration-of-body.
In a round turn, the lateral acceleration is equal to the square of the velocity divided by the radius of the turn. The acceleration of gravity is a constant.

Of course, this is in a static situation. Skiing isn't static, in that your inclination is constantly changing, along with everything else. At a particular moment, you may be tipped more than the static "balancing point," which just means you'll keep tipping over (increasing inclination) until something else changes (if it doesn't, you'll fall over). All the variables are changing as turn radius changes in the course of the turn, legs lengthen or shorten, etc.

You can describe a static situation quite simply with a little bit of trigonometry and tiny bit of algebra. If you want scientifically to describe or model real skiing, you'll have to use multi-variable calculus (and you'll quickly lose just about everyone except for Physicsman).
post #7 of 19
Thanks for clearing that up Tom. It's something I'd heard about but, as you can see, could only speculate.
As for the tracks, I'm constantly checking and trying to figure out what was happening when I made them. Usually if I'm thinking about engaging the uphill little toe to end/start the turn they come out pretty even. If I think about tipping the downhill ski I get the uphill edge change later. Also if the turn uses higher edge angles it seems the uphill ski track is about a foot longer before it changes.
My goal, of course, is to have the skis change from uphill edge to downhill edge at the same time so that the RR tracks are always matching. It can be done.
post #8 of 19
The title “Perception vs. Reality” is on the mark when trying to decipher how the CM path comes about vs. our individual ski paths.

Attempting to describe these paths, we often align our personally perceived ideas with what we currently know or believe about mechanical theory. When the two seem to align well, we believe we’ve got the right answers.

Unfortunately as sjjohnston mentions above what *actually* happens in the CM/Skis relationship is the result of many interrelated inputs - most of which we probably aren’t even aware of let alone take into consideration.

I do like Heluva’s section on “The Point of All This” though. I think a professional ski instructor *should* fully comprehend what they’re teaching and not just parrot an organization’s dogma (even if that dogma happens to be accurate).

Any organization we represent in the field has the obligation to provide us the (documented) *fundamental reasoning* behind its prescribed teaching. I don’t think any of the current organizations do this to a sufficient degree. Not suggesting that all instructors need an engineering degree. Just that our organizations need to create more material with comprehensive reasoning to back up their school of thought.

I mean, what else are we paying those Demo Team members over a million dollars a year for?

.ma

PS: Just finishing up a post that may be …excruciating… for some. Git yer virtual rocks ready.
post #9 of 19
I realize that this is completely off-topic, but when I look at the non-race examples here: "Some Other guy", PSIA, D-Teamer, Epic--I know which one I'd die to ski like! (Say nothing about being able to fit into that suit)
post #10 of 19
Heluva,

This thread has been rather quiet and I think it’s because the paths you’ve drawn above are dependant on too many undeclared variables and assumptions for us to meaningfully respond. Some of those paths are good generalizations that introduce basic ideas but I’m not so sure they provide substantial support for your arguments on Diverging/Converging vs. Constant-Width skis.

One of the difficulties is their lack of Scale. We can only guess at the proposed turn radii drawn and at the speeds you've imagined. Speed of Travel and Turn Radius taken together are critical for figuring out the necessary path of the CM. So is the Pressure Distribution ratio laterally across the skis.

Another issue is we’ve no way to know if the drawings are intended to be orthographic to Horizontal or to the Slope Surface. Either way, we also need the slope angle identified. This is important because it affects the way each path is drawn quite a bit. The chosen perspective will skew the actual snow-surface distance drawn between each ski and changes the synchronization in Ski vs. CM paths (they end up needing to be drawn a bit ‘out of phase’).
An Orthographic drawing is where the lines of projection (from each object) are drawn perpendicular to the *drawing surface* regardless of its height above or below that surface The actual path of our CM is complicated by the fact that the true path of a carved ski is generally some sort of Parabola. This has an impact because it extends the period of time our skis are traveling (essentially) ‘straight’ during transition. In larger radius turns this forces the CM line into a more concentric path with the skis both into and out of transition.


And then… there is the continuous change in our turn speed to consider. Without going into the nitty-gritty, changing rates of acceleration throughout each turn potentially deliver ever-changing speeds of travel for the turning skier (though our technique can affect speed consistency if we desire).

Consider the typical Carved turn: As our speed increases with a particular turn radius we must incline our CM further to maintain balance (we realign our mass ‘over’ the increased centripetal force). But as we incline our CM further (especially via angulation) we end up tipping our skis more - which in turn, reduces our turn radius still more - which forces yet a further correction to our CM location.


And consider this: If we reduce our turn-radius at a given speed we'll actually accelerate a bit. Also, as we tilt our CM more to the inside we are moving it closer to the center of our turn rotation which also accelerates the skier. (See the thread on "Acceleration Turns" starting about here ).

Each of these smallish things added together contribute far more to CM position than most people think. It’s a highly recursive thing very much like compound interest on a loan - hard to calculate but easy to feel the payments we have to make.

---
Skifex brought up the issue of Ski Design and CM path in the previous 'Perceptions...' thread. Ski design affects the paths as drawn because a ski’s sidecut (and flex pattern) determine how much the ski will turn for a given edge-angle.

Since our ever-changing speed forces us to tip our CM more (or less) we also end up tipping our skis more (or less). This is where Ski Characteristics (along with technique and physique) come into play. Exactly how our ski responds to an edge-angle change determines how much our turn radius will shrink (or grow) for the CM inclination adjustment we've just made. And as this is a recursive process, a little goes a long way. This is why some skis just don’t seem to want to let you fall to the inside; yet others let you fall on your face if you’re not careful. It’s also why shaped skis now rule the world.

(If you’re all wincing painfully yet… just imagine if I’d tried to put formula and numbers to all this. )

The ever changing centripetal force throughout a turn determines the path our CM must follow to remain in balance. Yet we ourselves are messing up the otherwise static speed/radius relationship by tipping our skis more (and less).

Finally, I think the biggest hindrance to drawing an accurate path is the two-footed nature of skiing. To have any hope of describing a probable path for the CM we need to know the exact lateral pressure distribution at every point in the turn. So long as we have two skis on the snow, any change in our pressure distribution ratio will cause the CM path to change in relation to the current path of at least one ski and probably both.


---
I think what Heluva has drawn above is more of a Controlled Outcome for a Given Intent than a universally expected outcome for each technique.

Highly preferential inputs are needed to produce the First and Third pair of paths he's drawn but no input of any kind can produce the outcome shown in the Second pair of paths since that particular set of CM / Ski paths physically impossible.

I realize the image drawn is one we commonly see in books but it’s *not valid* because it implies a straight-line path for the CM while the skis are turning on the surface. Newton would have a problem with this because pressure is needed to bend the skis into a Carve (or to generate turning-friction in a skidded turn) and any pressure we apply to our skis is *

Equally and Oppositely* applied to us (our CM) thereby accelerating our CM away from our skis and preventing the laterally straight path as drawn. Heluva, in your discussion of Counter and its involvement in all this I wasn’t sure if you were suggesting that our invoked degree of Counter affects the path of our CM, or that Counter just helps us manage the relationship between CM path and ski path. I’m guessing the latter but please let us know if it was otherwise intended. The reason I ask is that your paragraph titled “Constant Track Width with Little Counter” has some good ideas but is difficult to understand for the messy wording and unexplained ideas presented. More elaboration there would be helpful.

This really is a complex topic. Maybe it would be better to begin with individual foundational ideas and build up from there rather than starting with proposed outcomes and trying to determine how it might have been done?

---

Slatz,

I’ve never been convinced on that whole ‘simultaneous tipping’ thing. Every time I see a major-domo demo the idea I observe a couple turns that match the described idea, then they go back to skiing normally - with independent rates of tipping as needed for what they’re doing in the moment.

As discussed in Heluva’s other thread there can be an ideal use for Sequential Tipping: An Intentional Ski Divergence out of Transition that will launch our skis on paths complimentary to our expected degree of inclination later on. Initiating a turn with that Phantom thing does exactly this. Tipping the LTE of the old Outside-Ski starts the process quite effectively because there's a small inherent delay between the tipping of the old Outside-Ski and the tipping of the other ski.

PSIA’s past adamance about simultaneous-edge-change should probably be toned down and converted to an exploration of each technique and how it works.

Both Simultaneous-Tipping and Intentionally-Sequential-Tipping are reasonable things to teach a student if we also teach a well-stated, useful purpose behind the technique. Analyzing a student’s tracks to see if they employed the proper mechanism to accomplish a requested drill with a specified technique also makes sense. We just need to make sure our students know the probable outcomes for each technique.

BTW: I’m not sure we actually need to get our CM inside the Inside-Ski in order for that ski to be able to carve. It’s certainly easier if we do, but not strictly necessary. So long as we supply sufficient pressure to the tipped Inside-Ski it will carve properly. On a mild slope we often demo this in the RR Tracks we make while doing Cowboy turns.

.ma
post #11 of 19
Quote: "PSIA’s past adamance about simultaneous-edge-change should probably be toned down and converted to an exploration of each technique and how it works."

Spot on!

The WHAT is usless without some process of HOW and reasonalble WHY.

Most skiers are sequential: Go first to new big toe edge, then release old supporting edge. Safe, secure, habits fostered in wedge based beginner processes.

The popular process of trying to release the supporting big toe edge sooner can mask the habit, but seldom results in true change to the dominant 'order of movement', or sequence of events. The common result is the edge release becoming a 'sooner second', but STILL SECOND and seldom if ever creates a simultaneous-edge-change!

Only by deliberatly learning to lead with a "release first" edge change focus of the old outside support foot/ski, and to allow the new outside ski to follow thru the edge change sequence will you have a movement pattern that can lead to a simultaneous-edge-change by simply shrinking the lead-follow gap in the timing.

A good skier should be able to choose and use any distinct 'order of movement' that meet the needs of the skiing being done. Be that on either end of the spectrum or in the pretty (but not holy grail) simultaneous-edge-change realm in the middle.
post #12 of 19
Quote:
Originally Posted by michaelA
...This thread has been rather quiet and I think it’s because the paths you’ve drawn above are dependant on too many undeclared variables and assumptions for us to meaningfully respond. Some of those paths are good generalizations that introduce basic ideas but I’m not so sure they provide substantial support for your arguments on Diverging/Converging vs. Constant-Width skis.

One of the difficulties is their lack of Scale. We can only guess at the proposed turn radii drawn and at the speeds you've imagined. Speed of Travel and Turn Radius taken together are critical for figuring out the necessary path of the CM. So is the Pressure Distribution ratio laterally across the skis.

Another issue is we’ve no way to know if the drawings are intended to be orthographic to Horizontal or to the Slope Surface. ...
michaelA - Your comments about too many undeclared variables, assumptions and lack of quantification are truly on the mark. This is a difficult area to meaningfully discuss (at least in any depth) without detailed quantitative analysis.

Towards this end, I have developed a quantitative, numerical model of ski tracks that begins to address some of the issues you raised. I developed it in Excel so that it is accessible to a wider audience than if I had developed it in Matlab or some other more specialized programming language. I just sent a copy to Greg, who has promised to put it up on a server so that anyone interested can download and/or run it, much in the same way that my sidecut radius calculator spreadsheet is available on Epic. If anyone is interested in getting an advance copy, send me a private msg containing your email address.

When I receive the URL of where it is posted for Epic users, I'll check it out and then start a new thread describing its capabilities, assumptions, how to use it, etc. Unfortunately, we are leaving on a 1 wk mini-vacation tmmrw night, so I may not be able to check in frequently after it is posted, but I'll try.

To give folks on this thread a heads-up, this first version of the model does not incorporate ANY dynamics at all. It only does the geometry of the ski tracks in the plane of the slope. The inputs are:

1. "Daylight" leg separation at the transition
2. "Daylight" leg separation at the apex
3. Max edging angle
4. Gate offset
5. Downhill spacing between gates (aka, "half wavelength")
6. Sidecut radius

It then outputs:

7. Angle from fall line at transition for the new outer ski
8. Angle from fall line at transition for the new inner ski
9. On-snow track spacing at transition
10. On-snow track spacing at the apex
11. Radius of curvature of track at apex (new inner ski)
12. Radius of curvature of track at apex (new outer ski)
13. Theoretical (ie, many assumptions) edge angle at apex for new inner ski
14. Theoretical (ie, many assumptions) edge angle at apex for new outer ski


In addition to the above scalar outputs, it also produces graphs for quantities like the track spacing, radii of curvature, L&R edge angles, etc. as a function of fraction of the way through each turn.

It clearly shows the smooth (and very large) variation in instantaneous radius of curvature throughout each turn. It also demonstrates how variable "daylight" leg spacing is needed to maintain constant track width, but that this is not exactly the same as demanding parallel shins, etc. etc.

Just to re-iterate, this version does NOTHING with respect to dynamics. In other words, it assumes a sinusoidal path for the average of the L & R ski tracks, and assumes that somehow, the skier can produce that track, but does no calculation or consistency checks w.r.t. calculating downhill and across-the hill accelerations, variation of speed throughout each turn, influence of slope angle, friction, etc.

Sorry for only being able to give a teaser at the moment, but, hopefully, the spreadsheet will be available soon to everyone, but if anyone wants to have a copy to play with before it becomes publicly available, send me your email adr.

Cheers,

Tom / PM

PS - I've just been playing with it myself and it is an absolute hoot to play with the input parameters and see the effects on track width, see that the skier is forced to introduce a bit of A-framing or bow-leg at the apex (depending on the exact situation), etc. In addition, since this model makes no assumption about dynamics, the actions during one section of the course (ie, part of the graph) don't carry over to the next section of the course. Thus, if you don't like my assumption of a fully sinusoidal track, you can imagine chopping out some of the ultra-smooth, long transition of the sinusoid, and introducing the necessary bit of angular redirection at the transition, yet the output for radii of curvature and all the other variables will still be correct as long as the average ski path in the time inverval under consideration (ie, before or after the transition) still remains sinusoidal.
post #13 of 19
Is not the idea to get your CM to go as directly down the hill as possible while putting your skis where ever they need to be to give you the required acceleration to take that path?
post #14 of 19
OK Heluva, ... time to turn on those new Thread Warning Lights for "Very Technical" and "Heavily Moderated".

Awesome PhysicsMan! I'll be sending one of those "requesting PM's" shortly with a sideline note. It'll be nice to poke at this thing incrementally over time so ideas and concepts can digest for a while before biting into the next elephant.


Quote:
Originally Posted by Ghost
Is not the idea to get your CM to go as directly down the hill as possible while putting your skis where ever they need to be to give you the required acceleration to take that path?
In my opinion, No.

To me, Skiing is about sliding for fun and not about getting down the hill as fast as possible (unless you're racing). If sliding is my goal, I would want to manage my CM to support where I'd like my skis to go & how I want them to operate, not the other way around.

The recent thread on 'Directional Movements' got into the nitty-gritty difference in technique that these two very different intentions may require. One is well supported by diving over our skis into every new turn, while the other is augmented by moving with our skis and letting the skis 'pull' us into each direction change.

Each method has a very different feel, each a very different CM/Ski path outcome, yet *both* methods work really well.

.ma
post #15 of 19
Thanks Michael. I guess my above thoughts were too narrow minded.

On further reflection I can see that there are degrees of freedom in free skiing: from the view of racing down the hill, what I had said above; from the view of going where you want when you want, putting your skis where they have to be to provide the needed forces; and most freely, putting your skis on a long leash and giving them more freedom to play.
post #16 of 19
I'm gussing you're heavily into the race thing? Heh, ...then maybe 'Focused' would be a more accurate term than narrow minded. My own problem is being so overly open minded that cold air sometimes flows thru there.

.ma
post #17 of 19
Thread Starter 
Sorry it has taken me so long to get back to this thread. I had a pretty busy weekend and I wasn't able to check back into Epic and really wanted to read over MichaelA's post several times in order to digest it all.

Basically, MichaelA is right about the assumptions - they are numerous. In each turn I was assuming similar speeds (recereational speeds about 15 to 20mph) and similar turn shapes. Now take those three body positions and see how the forces are managed in each. MichaelA, was also correct in what I meant by the use of counter. By no means am I advocating a specific angle of counter combined with a specific angle of angulation - that is all dictated by the turn and the skier should manage it accordingly.

If you notice I did keep re-using the term "high angle carve" which is where some of the observations become most noticable. At low speeds and low angles a skier can get away with most anything they want to regarding their CM and balance - but when you push the turns to the higher end of the spectrum in terms of speed and angulation you will get much different results for each body position. The CM path is essentially a speculation of where the CM would likely be in those situations. Distances and such may or may not be completely accurrate but the path and its relation to the skis would likely be very similar in each situation.

My comments on getting the CM inside of the inside ski were not meant to convey that the inside ski could not carve without the CM being inside of the turn, but rather that when the inside ski is directly under the CM the skier is still using the leg for a significant amount of balance - and likely weighting it without even knowing it - which in a high angle carving situation can cause the skier to ride the sidecut of the outside ski
(similar to park and ride) leaving them in a rather static position over the outside ski. I would argue that this could stem from either using too wide horizontal separation (bow legged skiing) or artificially creating high angles without needing to. Before I was kicked off the PMTS forum : I witnessed a conversation (may have participated actually) where Harald was discussing edge angles and what the consequences of exaggerating them were... while it is fun, if it is adopted into everyday skiing it can be detrimental and a source of balance issues.

BTW, consider these drawings (all of them) a birds eye view of the tracks looking down (perpendicular I guess) to the slope. In order to get these types of tracks at the speeds I am suggesting you would probably need a semi-firm groomed surface and about 20 to 30 degrees of slope depending on how fast and how angulated you want to get. Also - one thing to note this would not really apply to long radius high speed (think DH/SG speeds) as at those speeds skeletal stacking is usually a pretty widely used body position because of the huge centripetal and centrifugal forces that occur.

Later

GREG
post #18 of 19
Quote:
Originally Posted by michaelA
I'm gussing you're heavily into the race thing? Heh, ...then maybe 'Focused' would be a more accurate term than narrow minded. My own problem is being so overly open minded that cold air sometimes flows thru there.

.ma
Not at all Michael. Whenever I see your handle next to the post I am always eager to read it; your posts are always informative. As for myself, I've always been a bit of a speed deamon my parents couldn't afford skiing or lessons for me, so I had to content myself with playing at being a racer. I carefully scrutinized the DH racers and did my best to emulate them for many years. That's where I found the fun and thrill. The last few years I've been getting into other areas of skiing. I just naturally fall into old habbits sometimes. I also played at being a motorcycle racer on public roads. That didn't work out quite as well as the skiing though.
post #19 of 19
Thread Starter 
I usually don't bump threads... but I am bumping this one... in case a few people out there missed it...

I am actually pretty curious what people's reactions to this whole topic are. The other thread was viewed over 2,000 times, and this one has seen far less activity. Because of the parameters I didn't leave a lot of room for debate... and the pictures speak for themselves - but has the topic made anyone 'rethink' track width as it applies to everyday skiing, and how it applies to balance?

As I said before, and probably if you have seen my video from the past season, you can see that I fought 'too wide' of a stance in my slalom turns. Toward the end of the season I toned it down significantly and saw a huge increase in my skiing performance - especially in slalom. So, that is what set me out on this little path of discovery... It was helpful to hear what I needed to do, but more important to me was the why? For years I had been praised for a wide stance, even tracks, and high edge anlges... however, my slalom skiing was still less than par and that was the reason for it. The ultra high angles combined with the wide stance were the root of many of my problems and combined with a lack of rotational counter was creating loads of problems with my own skiing.

Later

GREG
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