What's essential for carving on hard snow?

[razie]

"In our earlier discussions of the carved turn, we assumed for the sake of simplicity that the ski carved uniformly throughout the turn. Field observations of even the most accomplished skiers indicate that this cannot be true. Even the most purely carved turn must involve some skidding." The Physics of Skiing, pg. 37.

They go on to break down the turn into three sections, "the skid stage", "the early carve stage", and "the advanced carve stage". The amount of skidding is greatest at the beginning of a turn which matches the concept of the critical edge angle. Also, I believe the necessary amount of skidding will be more on a hard surface.

The implications of this are kind of astounding. The perfect carve turn is not something that is accomplished merely by the physics of tipping a ski. Tipping the ski to get a perfect arc is an oversimplification of a very complex physical problem. But, this false conclusion has led to the impossible combination of defining expert skiing as creating a perfect arc with no rotary input. Come on, tipping the ski and balancing on the arc is easy. For some reasons those simple and effective movement patterns elude intermediate skiers, but it's not hard to do. What's hard to do is ride the arc on a hard surface and not skid. This is because skidding during the turn is part of the natural physics of how the skis work.

I can only conclude that it's become like the Emperor's new clothes. Whoever recognizes skidding in their own skiing must have low skill similar to whoever sees the Emperor as naked must be incompetent. Therefore, people who have the proprioception to recognize the truth are often silent. On the flip side, I've often seen how people are unable to recognize skidding and/or rotary input in their own skiing or in videos. Creating a perfect track is probably so hard, because there must be movements involved that people are failing to analyze, describe, and teach. Skiers go out trying to tip and ride, letting the ski do all the work refusing to steer since that's "inferior skiing", but instead of the perfect arc, they get what the ski's natural design allows. I can imagine after trial and error, some stumble onto the exact combination of tipping and steering that gives a nice track in some circumstances without even being aware of what they are actually doing.

I understand the need to justify rotary inputs - most skiers use them - and trying to quote a paragraph that seems to imply it (btw what revision of the book you have? that's on page 139, not 37).

The reality is that they never said any kind of rotary input was applied. They only study the skidding, i.e. the output.

Also, on the next page, they explain what they actually mean: that given the snow deformation, some parts of the edge will skid (i.e. have a lateral displacement) based on some factors:

At no point do they imply that someone needs to apply any kind of rotary input. In fact, the 3 phase carve model is a copy&paste from another study, of a 1987 ski racer making a GS turn, which had to skid the specific turn they measured:

Now - if you study a skidded turn and conclude that the ski skids is one thing, but to extrapolate and use this as the basis to conclude that all skiers skid all turns, is... uhh... not mathematically correct. It's a fallacy.

Here is a modern ski racer, making a GS turn in a course, on equipment and using a technique that evolved for some 30 years since that study - I've slowed it down a lot, so you show us that magical rotary input! As far as I can tell, the ski's edge is never displaced off its trajectory during the entire transition and initiation (admitedly, not the cleanest possible, but easy to find and paste here)...


Now - if I was a physicist trying to generalize the model of a ski turn, I would consider a model that allowed for skidding and for all sorts of inputs, like pivoting, edging, pressure and then I would say that they occur more or less in every turn and that would give me a nice mathematical model, fully aware that either of those can be zero at any point of the turn. The problem with that approach is that some then would assume that the zero doesn't have to be zero, forget the DIRT of the BERP and proclaim that all turns must involve pivoting because it was observed in at least one instance and it's part of the model...

That's why I'm not a physicist...

p.s. I do not categorize expert skiing as creating a turn without rotary inputs, although that is certainly a good skill to own and expert skiers do tend to own that particular skill and working to own that skill will improve anyone's skiing - but I try to be mathematically correct in generalizations. I'm not a fan of the word, because it bundles together good inputs with bad inputs and no inputs... and so does "edging" btw...

 

[François Pugh]

View attachment 61886

Tracks don't lie. If you want to know how well you are carving, check your tracks.

 

[Josh Matta]

I understand the need to justify rotary inputs - most skiers use them - and trying to quote a paragraph that seems to imply it (btw what revision of the book you have? that's on page 139, not 37).

The reality is that they never said any kind of rotary input was applied. They only study the skidding, i.e. the output.

Also, on the next page, they explain what they actually mean: that given the snow deformation, some parts of the edge will skid (i.e. have a lateral displacement) based on some factors:

View attachment 61936

At no point do they imply that someone needs to apply any kind of rotary input. In fact, the 3 phase carve model is a copy&paste from another study, of a 1987 ski racer making a GS turn, which had to skid the specific turn they measured:

View attachment 61937

Now - if you study a skidded turn and conclude that the ski skids is one thing, but to extrapolate and use this as the basis to conclude that all skiers skid all turns, is... uhh... not mathematically correct. It's a fallacy.

Here is a modern ski racer, making a GS turn in a course, on equipment and using a technique that evolved for some 30 years since that study - I've slowed it down a lot, so you show us that magical rotary input! As far as I can tell, the ski's edge is never displaced off its trajectory during the entire transition and initiation (admitedly, not the cleanest possible, but easy to find and paste here)...


Now - if I was a physicist trying to generalize the model of a ski turn, I would consider a model that allowed for skidding and for all sorts of inputs, like pivoting, edging, pressure and then I would say that they occur more or less in every turn and that would give me a nice mathematical model, fully aware that either of those can be zero at any point of the turn. The problem with that approach is that some then would assume that the zero doesn't have to be zero, forget the DIRT of the BERP and proclaim that all turns must involve pivoting because it was observed in at least one instance and it's part of the model...

That's why I'm not a physicist...

p.s. I do not categorize expert skiing as creating a turn without rotary inputs, although that is certainly a good skill to own and expert skiers do tend to own that particular skill and working to own that skill will improve anyone's skiing - but I try to be mathematically correct in generalizations. I'm not a fan of the word, because it bundles together good inputs with bad inputs and no inputs...

rotary can be entirely perception....

IMO when the skis are traveling flat you need to actively hold them there or they will try to twist in.... did you turn the ski? no, did you stop them from turning? yes.

 

[mdf]

Here is a modern ski racer, making a GS turn in a course, on equipment and using a technique that evolved for some 30 years since that study - I've slowed it down a lot, so you show us that magical rotary input! As far as I can tell, the ski's edge is never displaced off its trajectory during the entire transition and initiation (admitedly, not the cleanest possible, but easy to find and paste here)...

That was interesting to watch. A big part of what makes the direction of the ski turn right at the end of the clip is swinging the feet forward relative to the knees and the rest of the body. Because the lower leg and its hinge at the knee is at an angle with respect to vertical, that motion traces out a circle or ellipse on the snow surface. So I'm thinking that one key to a clean initiation is matching the geometry of that traced curve to the geometry of the ski.

 

[Viking9]

If I see one more video of a professional skier carving on 150’s I’m going to post a video of a Taiwanese professional Ping Pong player.

 

[razie]

That was interesting to watch. A big part of what makes the direction of the ski turn right at the end of the clip is swinging the feet forward relative to the knees and the rest of the body. Because the lower leg and its hinge at the knee is at an angle with respect to vertical, that motion traces out a circle or ellipse on the snow surface. So I'm thinking that one key to a clean initiation is matching the geometry of that traced curve to the geometry of the ski.

hmm, yeah, that was interesting. I saw it as a fore/aft adjustment, placing the skis where they need to be, as she extended the leg

If I see one more video of a professional skier carving on 150’s I’m going to post a video of a Taiwanese professional Ping Pong player.

Great boots! Both me and my kids use them.

Here's a non-professional 16 year-old carving on them:


Funnily enough - I just got a new 150 WC lifted model for my youngest and I remembered I had this jointer at home and I was grinding away at it two nights ago... I have so many I had to colour-code them with tape (it's the one on the left, the others were sacrificed on the altar of <insert something funny that I can't think of right now>) wife was not impressed with the resulting mess:

...kid's still in one piece... and now carving on them, too...

p.s. this is before figuring out I need to start color-coding them ... about half are 150s and I got 3 more pairs since:

 

[Eleeski]

The wiki page didn't make sense to me. I build concave waterskis. The concave edge helps edge hold, not turning. And the flat spot on the base of figure ice skates has to be huge to allow the balanced straight glides. the flat will be the major factor in ice contact at the shallow carved arcs that are common.

I'm pretty sure a perfect straight edge won't turn just from tipping

Absolutely true! So perhaps something else is going on other than a ski bend. Especially at the start of the turn when there is no load to bend the skis. And the weird contact points generated by the sidecut. And a tipping edge angle that starts very low.

A rotational force applied by the skier seems a lot more logical. That also matches the feeling in rollerblades.

A skidded turn is dominated by this applied rotational force. So to carve, it feels like we must avoid this. The rotational force is still there - it's just minor compared to the other forces we are subject to. Note that it is possible to adjust a carve - twisting against the turn to widen the arc.

Eric

 

[skier]

I understand the need to justify rotary inputs - most skiers use them - and trying to quote a paragraph that seems to imply it (btw what revision of the book you have? that's on page 139, not 37).

The reality is that they never said any kind of rotary input was applied. They only study the skidding, i.e. the output.

Also, on the next page, they explain what they actually mean: that given the snow deformation, some parts of the edge will skid (i.e. have a lateral displacement) based on some factors:

View attachment 61936

At no point do they imply that someone needs to apply any kind of rotary input. In fact, the 3 phase carve model is a copy&paste from another study, of a 1987 ski racer making a GS turn, which had to skid the specific turn they measured:

View attachment 61937

Now - if you study a skidded turn and conclude that the ski skids is one thing, but to extrapolate and use this as the basis to conclude that all skiers skid all turns, is... uhh... not mathematically correct. It's a fallacy.

Here is a modern ski racer, making a GS turn in a course, on equipment and using a technique that evolved for some 30 years since that study - I've slowed it down a lot, so you show us that magical rotary input! As far as I can tell, the ski's edge is never displaced off its trajectory during the entire transition and initiation (admitedly, not the cleanest possible, but easy to find and paste here)...


Now - if I was a physicist trying to generalize the model of a ski turn, I would consider a model that allowed for skidding and for all sorts of inputs, like pivoting, edging, pressure and then I would say that they occur more or less in every turn and that would give me a nice mathematical model, fully aware that either of those can be zero at any point of the turn. The problem with that approach is that some then would assume that the zero doesn't have to be zero, forget the DIRT of the BERP and proclaim that all turns must involve pivoting because it was observed in at least one instance and it's part of the model...

That's why I'm not a physicist...

p.s. I do not categorize expert skiing as creating a turn without rotary inputs, although that is certainly a good skill to own and expert skiers do tend to own that particular skill and working to own that skill will improve anyone's skiing - but I try to be mathematically correct in generalizations. I'm not a fan of the word, because it bundles together good inputs with bad inputs and no inputs... and so does "edging" btw...

You're misunderstanding me. I'm not saying all turns need rotary input. I'm saying all turns relying on the skis' geometry have skidding in the top of the turn. However, by being light in transition and guiding the ski with rotary input the ski can still make a pencil thin track. If there wasn't steering in the top of the turn, then there would be more smearing.

The skis are made to run straight with stability. At 40 mph, if the skis hooked up there'd be lots of broken bones. So, skis are designed to smear into turns. This design has even been augmented lately to increase this smearing transition region by adding rocker. The way the skis can smear easily is by having the edge grip on the snow be very weak for small angles. So at the top of the turn the skis will skid until the edge angles increase and the edge grip increases.

So you can have a turn without skidding, and you can have a turn without rotary, just not at the same time. Basically, many skiers like yourself float through transition carefully guiding the skis while they are weightless until the edge angles have grown, thereby essentially skipping the skidding region.

 

[Chris V.]

If there wasn't steering in the top of the turn, then there would be more smearing.

This debate is becoming awfully confusing from my perspective. It may be another case of people redefining words to suit their personal preferences. "Steering" is a term that seems to have a lot of different nuances of meaning to different people.

Can we agree that because the skis are light in the transition, it's a phase that requires good MUSCULAR CONTROL for the purpose of either redirecting the skis, or PREVENTING them from redirecting?

I'll observe that racers favor skis with full camber because they hook up early.

 

[razie]

@skier So you mean in the sense that @Josh Matta meant it - that's not classic "rotary input" I would say, at the least. It would be a very interesting philosophical discussion if that's an input to the ski - at that point I'm just trying to maintain the "coiled" state of my body, and is also applicable only if the skier did create counter and did not unwind at the end of the turn... it may qualify as an input, but it may also not... I don't think I see it as an input - I would see the unwinding as an input, not the stress to maintain the counter...

The magic of the "high C" (or engagement at the top of the turn) is admittedly complex, extremely interesting and not that easy for me to explain. I don't think there needs to be some steering there (in the classic sense, not the "counter-steering" that Josh mentioned) - I think that just by putting the skis on edge and applying (or allowing) some pressure, will slightly bend the ski slightly and start the carve, which process will feedback onto itself and the carve gets stronger and stronger as the ski digs in more and more and gets more and more bent etc... as the ski digs in, if you want to call that a skid - I guess it may be technically accurate (since it displaces the snow slightly) but it's not material in my view... The process of tipping the ski on edge itself creates sufficient bend to start this reaction - as the tip and tail are wider, so they are torqued slightly into the snow by the simple action of tipping the ski on edge, which is applied at the middle of the ski, the boot area.

I like to avoid this level of detail or discussion, if it doesn't materially impact what I do or what I have to do - if I just focus on a clean edge change, tipping, engagement and carving and if that's roughly the outcome, I will ignore the fact that we could theoretically call the initial compression of the snow skidding etc etc. I like to keep things as simple as possible, but not simpler!

cheers

 

[skier]

.

Razie, I like your skiing, and I admire your videos, so this isn't criticism, just fact. You have lots of rotary at the top of your turn just like many other great skiers, which is easily seen in this video at 0:20. You can see your outside ski in the air, and then it rotates before it's put back on the ground again. When the ski is in the air it will travel a straight line. It's impossible to begin to turn a ski in the air without rotary input from the skier. So, when you see a ski rotating in the air, it's from rotary input by the skier unless there's built up momentum, which is typically not the case, because the rotation happens after transition where there wasn't any previous circular motion in that direction. When the ski is in the air it's a clear give away, but it's just representative of the same technique used when the ski's barely touch the snow, because with that style you're light in transition, and there isn't enough ground reaction force to provide that kind of rotation.

 

[dbostedo]

...You have lots of rotary at the top of your turn just like many other great skiers, which is easily seen in this video at 0:20. You can see your outside ski in the air...

That's a little disingenuous to use as an example, since the new outside ski doesn't appear to be in the air at the start of any of the other turns, and that turn seems to be a stivot thrown in to start braking (i.e. that's not a "normal" turn).

 

[Chris V.]

I think that just by putting the skis on edge and applying (or allowing) some pressure, will slightly bend the ski slightly and start the carve, which process will feedback onto itself and the carve gets stronger and stronger as the ski digs in more and more and gets more and more bent etc.

This! And fore-aft balance at transition has a strong influence on it. We should all stop talking about it, and go out and FEEL it.

 

[skier]

That's a little disingenuous to use as an example, since the new outside ski doesn't appear to be in the air at the start of any of the other turns, and that turn seems to be a stivot thrown in to start braking (i.e. that's not a "normal" turn).

Maybe so, that was just a clear turn close to the camera where it was indisputable. Though, I think that turn is fairly representative of the style. Just the mere fact of being light in transition most likely means lots of rotary at the top of the turn, because there isn't enough ground reaction force for the ski to carve and apply force to the skier to begin rotation. This is especially true of those quick shorter radius turns. I'm sure he's light in most of those transitions, and if you consider the time it takes to fall and look at the speed of rotation of the skis, you'd have to conclude that rotation is happening while light, and therefore, coming from the skier. That's the way people ski. It's great skiing. Just many people inaccurately describe what's happening, i.e. only tipping. There's lots of culture built up around these inaccurate descriptions, so I think it's an uphill battle trying to look at this stuff a different way.

 

[James]

Razie, I like your skiing, and I admire your videos, so this isn't criticism, just fact. You have lots of rotary at the top of your turn just like many other great skiers, which is easily seen in this video at 0:20. You can see your outside ski in the air, and then it rotates before it's put back on the ground again. When the ski is in the air it will travel a straight line. It's impossible to begin to turn a ski in the air without rotary input from the skier. So, when you see a ski rotating in the air, it's from rotary input by the skier unless there's built up momentum, which is typically not the case, because the rotation happens after transition where there wasn't any previous circular motion in that direction. When the ski is in the air it's a clear give away, but it's just representative of the same technique used when the ski's barely touch the snow, because with that style you're light in transition, and there isn't enough ground reaction force to provide that kind of rotation.

You picked the one turn where he moves inside too quickly and has no weight on the outside ski. Likely that was because he's.....stopping.
Maybe pick another?

If one weights their inside ski on little toe edge before transition then when crossover happens the foot is driven into pronation and big toe edge engages for the new turn. It's pretty quick. Is their micro steering/pivoting happening? Perhaps, but practically it's near zero unless it's consciious.
Really not that complicated.

 

[skier]

I understand the need to justify rotary inputs - most skiers use them - and trying to quote a paragraph that seems to imply it (btw what revision of the book you have? that's on page 139, not 37).

The reality is that they never said any kind of rotary input was applied. They only study the skidding, i.e. the output.

Also, on the next page, they explain what they actually mean: that given the snow deformation, some parts of the edge will skid (i.e. have a lateral displacement) based on some factors:

View attachment 61936

At no point do they imply that someone needs to apply any kind of rotary input. In fact, the 3 phase carve model is a copy&paste from another study, of a 1987 ski racer making a GS turn, which had to skid the specific turn they measured:

View attachment 61937

Now - if you study a skidded turn and conclude that the ski skids is one thing, but to extrapolate and use this as the basis to conclude that all skiers skid all turns, is... uhh... not mathematically correct. It's a fallacy.

Here is a modern ski racer, making a GS turn in a course, on equipment and using a technique that evolved for some 30 years since that study - I've slowed it down a lot, so you show us that magical rotary input! As far as I can tell, the ski's edge is never displaced off its trajectory during the entire transition and initiation (admitedly, not the cleanest possible, but easy to find and paste here)...


Now - if I was a physicist trying to generalize the model of a ski turn, I would consider a model that allowed for skidding and for all sorts of inputs, like pivoting, edging, pressure and then I would say that they occur more or less in every turn and that would give me a nice mathematical model, fully aware that either of those can be zero at any point of the turn. The problem with that approach is that some then would assume that the zero doesn't have to be zero, forget the DIRT of the BERP and proclaim that all turns must involve pivoting because it was observed in at least one instance and it's part of the model...

That's why I'm not a physicist...

p.s. I do not categorize expert skiing as creating a turn without rotary inputs, although that is certainly a good skill to own and expert skiers do tend to own that particular skill and working to own that skill will improve anyone's skiing - but I try to be mathematically correct in generalizations. I'm not a fan of the word, because it bundles together good inputs with bad inputs and no inputs... and so does "edging" btw...

I went back and looked at one of my first posts, and I see that the way I wrote it was my mistake. I said you can't turn until you reach the critical edge angle, but that was not what I meant. What I meant was that you won't be edge locked until you reach the critical edge angle. This means that the ski will smear and skid, but it will still continue to turn increasing the edge angles until you reach the critical angle and become more edge locked. My point was that people are floating through transition and steering the skis to skip this skidding phase to give pencil tracks. The irony is that the perfect track is not just from tipping, while people tend to focus on just tipping as perfect carving.

 

[Josh Matta]

I dont think anyone is going to argue that a RR track turn cuases the femur to rotate in the pelvis, I think what most are saying is the rotary is generated by the skis and we just manage it.

 

[dbostedo]

I dont think anyone is going to argue that a RR track turn cuases the femur to rotate in the pelvis, I think what most are saying is the rotary is generated by the skis and we just manage it.

And I think what @skier is saying, is that there's a brief time as you're tipping the skis up after being flat to start a new turn, when the ski will not carve and will skid; This will continue until you get to a high enough edge angle to being a carve. And that if you float or use some rotary, you can get to the carving edge angle and leave clean tracks avoiding the skidding phase. (Presumably it would be a very short lived skid.)

Do I have that correct @skier?

If so, does that imply that you can't make RR track with just gentle tipping of the skis?

 

[skier]

And I think what @skier is saying, is that there's a brief time as you're tipping the skis up after being flat to start a new turn, when the ski will not carve and will skid; This will continue until you get to a high enough edge angle to being a carve. And that if you float or use some rotary, you can get to the carving edge angle and leave clean tracks avoiding the skidding phase. (Presumably it would be a very short lived skid.)

Do I have that correct @skier?

If so, does that imply that you can't make RR track with just gentle tipping of the skis?

Right, that's what I'm saying despite all my bad writing.

 

[HardDaysNight]

Assuming I understand him correctly, I think @skier is making a valid point. In quick slalom turns with a conspicuous float phase there is often quite a bit of redirection at the top of the turn - that is actually the point of the relative weightlessness, to allow the redirection without undue slowing caused by weighted friction.

In pure carved, longer turns (such as GS turns on medium terrain) there is no feeling of float. The sensation is of pressure being drawn from one foot to the other with substantial pressure throughout the transition. This keeps the arc intact throughout. Although I’m not a fan of USST coaching in general, I recall seeing one video in which McNichol (I think it was he) made this point very well.