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# Parallel tracks?

I origanally posted this in the Ask a Pro forum, but the only one to offer their view was Rick. Thanks Rick. I thought I would open the topic to everyone, & maybe get some more insight.

Okay a quick, but maybe not so simple question for the Pros. It is a given that balance is directed to the outside ski in order to maintain alignment, bend the outside ski & utilize sidecut & decambering characteristics.

So my question is: If the outside ski bends more than the inside ski in a turn, how is it that the tracks in the snow appear parallel?

Maybe someone with a little physics background can explain this in laymans terms that a simple minded guy like myself can understand. I know the answer is staring me in the face, but I just can't put my finger on it.

JF

Today I made a few turns & got a couple of pics. I made these tuns with maximum pressure to the outside ski. As usual you can click on the pics to make them larger. You know they say a picture is worth a thousand words & all:

Left footed turn

Transition

Transition (different angle)

JF
If the skis are tipped to the same angle and the snow is hard the bend should be about the same despite the greater force being RESISTED by the outside ski, so long as the inside ski has enough force to press it into the dialed up tipping-angle-dependent turn size.
I too have been wondering about the same for quite sometime. Thanks for bringing it up.
http://www.youcanski.com/en/coaching/inside_ski.htm
The desirable ski track is like this:

It doesn't look like the tracks are parallel all the time but obviously many people would say they are parallel. There is a huge pressure difference between the two skis most of the time. While bending the skis takes pressure. So there is practically a time difference in bending each skis?
Well, the tracks are "parallel," in the sense that they remain the same distance apart always (theoretically). But of course, they are not straight lines, so the inside track follows a tighter radius arc than the outside track.

What's interesting about this is that, while the tracks are "parallel," the tips of the skis that carve them must diverge slightly! (And so must the tails.)

Best regards,
Bob
To answer your question directly, the bending of the ski doesn't necessarily have anything to do with the actual track shape. Rather, the trajectory of the bent ski does. If the slightly less bent inner ski is running a track that is *concentric* with the slightly more bent outer ski, then you get the result shown. So what if the outer ski needs to be flexed deeper to do that. At any given point along that turn, the ski is tangential to the actual trajectory. It is scribing the track shown.

The other thing to keep in mind in this case is that the distance between the ski tracks is significantly smaller than the radius of the turn. That has some implications when you look into the math, namely, that we can approximate the two tracks as being more or less equal in certain types of analysis. In the real world, that tells us that the tracks are very much the same.
Quote:
 Originally Posted by Bob Barnes But of course, they are not straight lines, so the inside track follows a tighter radius arc than the outside track.
That assumes both skis arc about the same center point. Do they?

What if the inside ski's center point was one track width over?
I don't know, but it would seem that if the pressure was only enough to slightly decamber the ski and maximize the use of the ski's sidecut, parallel tracks are relatively easy to achieve...but when we begin to really bend the outside ski consequently tightening it's arc, the inside ski would begin to smear it's track a bit more relative to the pressure differential between the two skis?

no?
The inside ski does not have a smaller/tighter radius than the outside ski.

(they are not concentric arcs)
Quote:
 Originally Posted by cgeib That assumes both skis arc about the same center point. Do they? What if the inside ski's center point was one track width over?
You can take two coins and get the answer to that question. If you stack two of the same coin and offset their centers you will see that the arc converge.

The inside ski runs a tighter arc.
What seems to be forgotten here is the muscular tension of the inside leg which holds the inside ski in position, relative to the outside ski.

If you are applying so much pressure to the inside ski, as to create the appropriate arc relative to the outside ski, then you have more on the inside ski than the outside. Even if the inside ski is tipped to a greater angle than the outside, for it to truly "carve" that tighter arc, it would require significant pressure. And I'm not sure that is what is intended.

In turns other than RR track turns, the tension of the inside leg must be a factor.
I thought it was because the inside leg was shorter then the outside leg. It seems pretty simple to me.

Sorry, I don't normally visit this forum but I was bored.
Quote:
 Originally Posted by 4ster So my question is: If the outside ski bends more than the inside ski in a turn, how is it that the tracks in the snow appear parallel?
Quote:
 Originally Posted by Bob Barnes so the inside track follows a tighter radius arc than the outside track.
That is how I would see it also.

Quote:
 Originally Posted by Pierre You can take two coins and get the answer to that question. If you stack two of the same coin and offset their centers you will see that the arc converge. The inside ski runs a tighter arc.
Good way to demonstrate it.

Quote:
 Originally Posted by vail snopro If you are applying so much pressure to the inside ski, as to create the appropriate arc relative to the outside ski, then you have more on the inside ski than the outside. Even if the inside ski is tipped to a greater angle than the outside, for it to truly "carve" that tighter arc, it would require significant pressure. And I'm not sure that is what is intended.
Yep. (Aren't you supposed to be skiing?)

Its also interesting that we are not following an exactly circular path. Round yes, circular no. The two ski paths are following completely different non-circular, but round paths where the radius is changing as the pressure builds or reduces during the progress of the turn, causing increasing/decreasing ski bend.

Nonetheless, fundamentally, for the path of the inside ski to not converge with the path of the outside ski(when pressure is being applied more or less equally to both skis as appears to be the case here), then the inside ski fundamentally has to acheive tighter radius than the outside ski in order to avoid the convergence depicted with the overlapping coins.

In my opinion, parallel ski tracks are an interesting theoretical discussion but is not useful because I don't believe that we should be skiing with parallel ski tracks. In fact I think the tracks should be wider at the fall-line and narrower at transition, and as I said before its not circular. I also don't believe in 50/50 ski weighting , particularly at the apex of the turn. All of that points to the discussion of parallel ski tracks to be entertaining, but irrelevant to good ski technique.
first this assuming RR track turns like the one pictured. if we go beyond it opens up a whole new can of worms.

let talk about decambeing a ski. in the bigger pictures its a really small force that is required to decamber a ski so small in fact that moderate speed RR track turns barely put a ski into reverse camber in alot of cases.

curious 4ster on scale of 1-10 how 'dynamic' were those turns, that produce the tracks pictured. My guess is about 6. I could be wrong but just follow me. I am still curious in your opinion how dynamic they are.

lets say for a railroad track turns on dynamic scale of 1-10, a 1 is very flat slope with min edging but still RR turning, a 4 or 5 is the average park and ride turn we see everyday from the public being made on blue groomers, a 7-8 is instructor skiing kinda of fast. a 8-9 is racer freeskiing, and lastly a 10 is a great SL racer in SL gates. I am assuming alot but those are rough real world averages of what how 'dynamic" peoples RR turns are on the hill.

let say all the ways up to say 5 that both ski are being pressure nearly equally and edge nearly equally, there doesnt have to be divergence in the tip in this level. the skis simply decamber the right amount with out much thought on whats happening with (passive) rotary movements.

Let take it up a notch and we will find one of the biggest flaws or myths about how our skis railroad track turn. during extremely tight carves(think SL or near raduis) the inside ski simply can not follow the same path as the outside ski. there are many ways to get around this, the most common you see in high end skiers is slightly diverging tips. the outside ski will have alot more pressure on it than the inside ski, this mean not only is the outside ski bent more its also taking a larger arc. That arc get larger proportionally to inside ski arc, as the turn raduis gets smaller. so again is a slightly diverging tip. this shows up in videos over and over again.

also notice in the second video the changing stance width, it never stays the same. its not a technique flaw at all is just what has to happen to allow both skis to arc cleanly in those very tight arcs.

'If the outside ski bends more than the inside ski in a turn, how is it that the tracks in the snow appear parallel'

they appear parallel in the turns you showed because you werent that dynamic. In a dynamic railroad track turn like the ones I showed in the video parallel tracks are not left but instead its 2 nearly concentric circles that get closer together during the transition.

So IMO parallel tracks need not a be a goal or a by product of a good RR turn unless you are trying to pass a PSIA exam. think outside the box and I think you will agree with me that they should not be parallel in the highest end of turns.

haha borntoski beat me to it.
But your post is much better than mine Bushwacker.
So IMO parallel tracks need not a be a goal or a by product of a good RR turn unless you are trying to pass a PSIA exam. think outside the box and I think you will agree with me that they should not be parallel in the highest end of turns.

I have been thinking this for years while listening to my PSIA friends tell me different, because they are triing to pass level III.

My RR skiing looks like bushwacker say's. It's very comfortable and very natural. I have also been told I look very efficent in my skiing.

I find RR tracks very easy to do and always have.
Quote:
 Originally Posted by Max Capacity So IMO parallel tracks need not a be a goal or a by product of a good RR turn unless you are trying to pass a PSIA exam. think outside the box and I think you will agree with me that they should not be parallel in the highest end of turns. I have been thinking this for years while listening to my PSIA friends tell me different, because they are triing to pass level III. My RR skiing looks like bushwacker say's. It's very comfortable and very natural. I have also been told I look very efficent in my skiing. I find RR tracks very easy to do and always have.

PSIA should be more open to other ideas , instead of this is the way its is and the way its always going to be mindset right now.

your not skiing wrong you just not skiing how they would want you to if you were taking a PSIA exam.

Railroad track IMO has 2 sets of definition.

1.a exam task at PSIA L2 and L3
2.every other carved turns out there done at higher dynamic level than at the exam. IE high end freeskiing.
Some great input so far, thanks everyone.

Quote:
 Originally Posted by vail snopro What seems to be forgotten here is the muscular tension of the inside leg which holds the inside ski in position, relative to the outside ski.
I have to give some credit to Rick here. He mentioned inside leg muscular tension in his response when I first posed the question in Ask a Pro.
Quote:
 Originally Posted by borntoski683 In my opinion, parallel ski tracks are an interesting theoretical discussion but is not useful because I don't believe that we should be skiing with parallel ski tracks. In fact I think the tracks should be wider at the fall-line and narrower at transition, and as I said before its not circular. I also don't believe in 50/50 ski weighting , particularly at the apex of the turn. All of that points to the discussion of parallel ski tracks to be entertaining, but irrelevant to good ski technique.
I tend to feel the same way BTS. The question actually came about while I was skiing with a friend. We were talking about pressure to the outside ski & the fact that it bends more than the inside ski. She asked "why are the tracks parallel then?" I didn't have a good answer, but I would try to get one.

I thought it was a good theoretical question.

JF
Quote:
 Originally Posted by BushwackerinPA curious 4ster on scale of 1-10 how 'dynamic' were those turns, that produce the tracks pictured. My guess is about 6. I could be wrong but just follow me. I am still curious in your opinion how dynamic they are.
In my world they were a 9. On your scale I would say 7. This was on a moderate blue slope on about a 1/2 inch of groomer churned sugar over old solid, very firm machine made snow. Speed was about 25 to 30 mph. Skis are very sharp race stock Volkl Racetiger SL's. The turns were not my definition of RR turns. They were dynamic flexed entry turns with outside leg extension to the apex. My focus was to have maximum pressure to the outside ski, equal edge angles & minimum inside ski lead through a combination of inside foot pullback & outside leg extension. I only intentionally left the inside ski on the snow, so there would be a track in the snow.

I think if I had saved a few more of the photos I took, we would see that there was some change in the width of the tracks around the apex of the turns, as has been mentioned.

My definition of RR turns is much more passive focused on lateral movements & more even weighting, with very little fexion or extension. Basically the arc develops slowly as edge angles progressively increase.

BTW, the Japanese guy seems to get thrown to his inside ski frequently.

I posted the transition pictures because I thought they were cool .

Great discussion. I'll have some good ammo for my friend.

Thanks,

JF

PS: BWPA, that was one of the most understandable posts of yours I have read .
The japanese guys isn't being "thrown" to his inside ski. Some have speculated that he is doing it intentionally.

If not intentional, then it has more to do with him "falling" on the inside ski from not enough attention on getting to the outside.
Quote:
 Originally Posted by borntoski683 The japanese guys isn't being "thrown" to his inside ski. Some have speculated that he is doing it intentionally. If not intentional, then it has more to do with him "falling" on the inside ski from not enough attention on getting to the outside.

Yes, I now remember this vid from an earlier thread. On one of them I thought he was doing a White Pass kinda turn intentionally. Whatever it is, he rips .
JF

This is an interesting discussion, and I think that the various answers and opinions reflect a range of underlying assumptions. I'm not sure it's really of much practical importance, although it is one of those things where a misunderstanding could lead to erroneous conclusions that result in technical errors for those who try to "make it happen."

Is a turn "round" (part of a true circle) or simply curvy and "rounded"? Could be either, right? A good skier can ski a line of pretty much any shape, with the right blend of skills. But in reality, I think that very few of our "round" turns are actually, technically, round.

Whatever the shape of the arc, do the arcs of both skis share the same focus ("center")? Sure, sometimes. Surely not, at other times. Should they? I'm not sure why they should.

Are the tracks of the front wheels of a car "parallel"? Parallel curves are defined to be the same distance apart at all points. But that depends on how you measure it, doesn't it? Obviously, the car wheels' mounting points on the chassis don't change, and the car's width does not change, so the length of a line between their pivot points remains constant. (Some sophisticated suspension and steering systems, tire flex analyses, and such may possibly alter this simple relationship slightly. I don't know, but for simplicity, let's consider that the wheels steer on simple pivot points, each about a fixed axis, at each end of a fixed-length axle.)

So the wheels remain the same distance apart at all times. But what about the tracks? It depends upon which points on each track you're measuring from, doesn't it? Let's imagine an abandoned highway heading due north, where we "slalom" left and right across the freshly-painted (so we leave tracks!) centerline, weaving a tight sine-wave-shaped path. Do the tracks remain the same distance apart? It depends on whether we measure them along a line perpendicular to one track or the other, or along an east-west line (perpendicular to the center line). I know--this analogy cries out for an illustration, but anyone with a good imagination should be able to picture what I'm describing.

Perhaps a simpler way to look at it arises from looking once again at the exercise known as "pivot slips." Here are a couple familiar animations that I have posted before (copyrighted):

(Please excuse the Neil Diamond reference. It's a long story...based on the torture that some people find this maneuver to entail!)

Skier's feet (stance width) remain the same distance apart throughout, but skis appear to move closer and farther apart.

In these animations, the feet (the skis' pivot points) remain the same distance apart from left to right. Yet the skis appear to move closer and farther apart--just like the wheels and tracks of the slaloming car. (In theoretically "perfect" pivot slips, the skis would actually move on top of each other when they rotate 90 degrees across the fall line. In reality, the skier's pelvis must pivot at least a little to allow the skis room, as shown in the overhead animation.) If these skiers were to engage their edges appropriately to make the skis travel the direction they're pointed, these pivot slips would become turns--but the relationships of the feet and skis could remain the same. Measured from left-to-right (perpendicular to the fall line), the tracks would remain constantly the same distance apart. Measured in a line perpendicular to the skis, the track width would vary--narrowest in the transition, and widest at the apex (the fall line, in this case).

Does it really matter? For most skiers, these picayune dissections of technicalities probably don't matter at all. I doubt that understanding it is necessary for anyone, just to make great turns. But misunderstanding concepts like this often create a very wrong image of what "should" happen in a skier's mind, and that image can translate to quite wrong movements! I've seen instructors attempt pivot slips with the mistaken mental image that their skis should remain separated the same distance throughout. That mistaken notion causes them to rotate their pelvis and upper body, rather than their legs in their hip sockets. In an exam, that's a fail! And when translated into actual skiing, it's a critical handicap.

Best regards,
Bob Barnes

### "Parallel curves" are "equidistant," but....

All right, I couldn't resist. Here's an illustration of the concept I tried to describe above:

In each case, the tracks of the left and right skis are identical in shape--like the edges of the coins in Pierre's analogy (post #9 above). In the left illustration, the red lines show that the tracks are equidistant throughout the turns, when measured from left to right (like the skier's feet in the pivot slip animations). But the blue lines in the right illustration show that the very same tracks vary in width when measured across the skier's direction of travel (or when measured from a point on one track to the nearest point of the other track)--again, like the ski separation in the pivot slips.

Clearly, these tracks were made by skiers whose legs rotated in their hip sockets, resulting in some degree of "counter." If the skier were to remain "square" throughout--if his/her pelvis were to constantly face the direction of travel, the same direction as the skis--the tracks would look different. The inside track would form a tighter arc, and the blue lines in the illustration would remain the same length throughout.

(I'm also ignoring other factors that can affect stance width, such as the lengthening and shortening of each leg when inclined into a turn.)

Best regards,
Bob
Bob, you should add inclination to the mix of factors

### Conclusion?

I suggest that, in the reality of most technically accurate turns, the tracks will fall somewhere between those I drew above (with a lot of "counter," and the pelvis facing constantly directly down the fall line), and the alternative in which the pelvis remains "square," facing the same direction as the skis.

Best regards,
Bob
Quote:
 Bob, you should add inclination to the mix of factors
Thanks, BTS. As I noted, I have intentionally ignored other factors like inclination and the "long-leg--short-leg" thing that typically accompanies it. Those are variables that we can--and do--control independently, which of course will also influence the separation of the tracks.

Note that inclination alone does not necessarily affect stance width. If the pelvis remains parallel to the slope angle as the skier inclines, the legs actually form two sides of a parallelogram and remain the same lengths. While this relationship rarely happens in real skiing situations, it's intriguing that many skiers and instructors actually do emphasize it as a focus ("lift the inside hip," "keep your pelvis and shoulders 'level' with the hill," etc.)--and often (confusingly) in the same breath as "long-leg--short-leg.

All of these variables certainly show that the tracks do not need to remain the same width (and thus "parallel"). Whether they ever actually do, or should, remain equidistant is another question. And it still depends on how you measure that distance!

Best regards,
Bob
great explanation - thank you Bob
BB,

Wow, I return home from another strangely good day of wet snow skiing to this !

Thanks so much for taking the time with such a clear explanation/visualization. I luv it .

Remember, it is a theoritical question as to why the tracks appear to be parallel. I think this whole thread has cleared alot of things up for me.

Thanks,

JF
For what it's worth, here's another illustration--this time of tracks made by a skier whose hips (pelvis) remained square to the skis throughout the turns:

In this example, the tracks of the inside and outside ski are different shapes. Like concentric circles, the inside ski travels in a tighter arc--which would require either more edge angle (and enough pressure to bend it into the tighter arc), or more active guiding, or both.

This time the tracks remain the same distance apart when measured across the direction of travel (blue lines), but vary when measured across the hill (red lines). They generally reveal a skier with minimal independent leg rotation and, consequently, minimal hip counter.

As I've suggested, "real" carved tracks made by good skiers tend to fall somewhere between the tracks in my two illustrations, as the legs rotate in the hip sockets, but the skier's pelvis and upper body follow them through the turn (like the chassis of a car following the front wheels). Real turns involve some counter, but not usually the complete "upper body facing down the fall line" counter of pivot slips and of the first illustration (post #23).

Again, other variables including inclination, angulation, and simple personal preference will also affect stance and track width.

Best regards,
Bob
Quote:
 Originally Posted by Max Capacity I thought it was because the inside leg was shorter then the outside leg. It seems pretty simple to me. Sorry, I don't normally visit this forum but I was bored.
I think Max is right, one leg is shorter then the other and on the next turn the shorter leg becomes the longer leg.
Great explanation MAX!!!
umm ya I was bored also
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