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# speed control in pure carving - Page 5

Uh Fellas,
More psi equals more friction, even with wax this physical law holds true. So I would say we cannot forget that fact. A working skis is being pressured and in turn is pressing harder into the surface of the snow. When I seek glide I use the least amount of edge and pressure because it produces less friction.

I agree with Rick that "The falline is the mother of speed." I would also add that we spend more time out of the fall line than we do in the fall line. Unless of course you are just making adjustments to keep you in the fall line. Which in my book is not turning.
The original question defined the turn type as pure carves, which eliminates pivot entry as an option. Which I was gently trying to remind you TDK.
Ricks last post says very well how to seek or lose speed using carved turns. The only question that remains is why choose pure carve if you want more speed control than we can accomplish using this tactic?
Quote:
 Originally Posted by justanotherskipro Uh Fellas, More psi equals more friction, even with wax this physical law holds true. So I would say we cannot forget that fact. A working skis is being pressured and in turn is pressing harder into the surface of the snow. When I seek glide I use the least amount of edge and pressure because it produces less friction.
Did you know that its slower to fly through the air than it is to maintain snow contact in DH!

So when you want to slow down you engage your edges and you start arching!

We often talk about rr-tracks. If a train comes to a curve does it slow down because of increased friction?
Quote:
 Originally Posted by JASP The only question that remains is why choose pure carve if you want more speed control than we can accomplish using this tactic?
Ya know... that's a pretty good question.

But maybe not the last question. Quite often I hear myself telling students to make 'shorter turns' in order to control their speed better... though I wonder how many of us have really thought about *why* this actually works.

Obviously, we'll spend "less time in the fall-line" when making a single 10' radius turn than when making a single 20' radius turn. But what if we consider a 120' long slope and compare the total time in the fall line for each series? Assuming perfectly round turns for the moment:

For our

10' radius turns we'll end up covering 20' down the slope for each turn and making 6 total turns. Doing the math we get a total ski-track length/distance of 188.5'.

For our 20' radius turns we'll end up covering 40' down the slope for each turn and making 3 total turns. Doing the math we again get a total ski-track length/distance of 188.5'. ... suggesting that we are spending exactly the *same* total amount of time in the fall-line for both turn radii.

Even if we opt for elliptical turns (perhaps semi-circular turns with a 45-degree crossover) so long as we use the same 'turn shape' for both turn radii we always end up with exactly the same amount of *total* time in the fall line over the given total distance.

So, the real question is: What is it about a 10' radius turn that *actually* produces a slower overall speed down a slope than a 20' radius turn?

Is speed an automatic attribute of ski/snow interaction based on radii? Is the length of each time-segment in the fall line (per turn) more important than the total time*? Are we unconsciously doing biomechanically different things (that matter to speed) as radii increases? Are there movement pattern elements that are optimizable to gain or shed speed despite turn radii?

I think these are relevant questions for both instructors and race coaches since an instructor generally teaches speed-shedding techniques and the race coach generally teaches speed-accumulation techniques.

.ma
I don't think the 10' radius turns spend less time in the fall line than the 20' radius turn; I think they spend more time out of the fall line.
If we break things down into 'inches of travel at each slope angle' I think we'll find exactly the same number of total inches accumulate at each precise slope-angle by the end of the 120'.

This suggests each skier would spend exactly the same number of inches in (and out) of the fall line.

---
Hmmm... re-reading what I wrote conversationally above I wish I had gone with my original nerdy-wording for that post - using inches of travel rather than time in the fall line because our 'time in the fall-line' is actually related to our 'current speed' - a variable in any case due to acceleration.

So: When thinking about this be sure to consider the idea of 'traveled-inches' in the fall-line vs. 'time in the fall-line' as different ideas. The difference is kinda important in figuring out speed generation vs. turn radii.

.ma
Originally Posted by JASP
The only question that remains is why choose pure carve if you want more speed control than we can accomplish using this tactic?

This is a silly question. Its the same as -why do you have an electric guitar amplifier if you dont play in a band? Or, -why do you have motorbike when you live in land with winter half of the year? We want to carve because its faast, fun and exiting but our problem is that we pick up speed very easily and that becomes dangerous if we dont know how to slow down. Same as cranking that Marshall stack late at night in the studentapartmentcomplex.
Michael,
Now you've done it. Why did you have to get all mathematical? I was have a great time intuitively.

Let's see. two 10' radius curves, same as a full circle 2*r*Pi = 2*10*pi=20*pi

one 20' radius curve, 1/2 a circle = 1/2 *(2*20*pi)=20*pi
Same total distance.
Same total descent.
Why is the smaller turn slower?
Only thing I can think of assuming equally efficient carving, is that it takes more g-force to make the smaller turn and hence more force against the bases and hence more friction along the base and more energy spent in snow compaction.
michaelA, you're right speed is based on the amount of time spent accelerating. So if I accellerate for a shorter time I will be travelling slower. All I need to do is turn far enough out of the fall line to slow to a speed such that when I turn back into the fall line I will not accelerate past the speed I wish to be moving.
Nice thought Michael & JRN,
The duration of the acceleration is probably the key. Twenty accelerations of one second verses ten accelerations of two second durations. Assuming we accelerate at a constant rate, then the exit speed would be higher for the longer duration.
Ghost,
I think the G forces would have to be less if we are moving slower, but when we add in the muscle power it takes to bow the ski more, this explains the increased pressure per square inch and thus the extra friction.
TDK,
Yes an airborne skier is slower in the air but who said anything about leaving the ground? Gliding is not flying. We are talking about braking while carving. To me carving is a seeking speed maneuver so discussing braking seems a bit out of place or at least at crossed purpose with the chosen maneuver. My solution is to seek a different tactical solution if I am trying to ski slower (add braking).
Ghost...

Kind of a nuisance, isn't it - knowing part of the answer must be 'friction' in some sense but not knowing exactly how to pin it down .

G-Force is dependant on speed combined with turn radius so it certainly plays a role - but since our shorter turn is (in theory) at a slower rate we'd have less G-force creating pressure and therefore less friction in the shorter turn.

Thinking about it further we might notice that our highest pressure is coming out of the fall-line where we also have our highest edge-angles (relative to the slope surface). This is also typically the location of our highest speed. But assuming we're on very firm snow or ice, the added pressure might not make much difference at all...! (since the snow/ice will deform so little and kinetic friction will increase so very slightly despite the pressure increase.)

JRN,
That's one way of looking at it! Shrink (or grow) your turn radius until you find the desired speed, then stay with it.

Still, the main thread question is essentially 'where does speed control come from in a carved turn?' I think the answer can be found by figuring out *exactly* how our speed accumulates from one turn to the next. Does it really matter? I think it does to any instructor promoting speed control and to any coach promoting a speed increase.

Our exact turn-shape makes a big difference and when teaching speed control ... "knowledge is power". On steeper slopes most students implement exactly the *opposite* turn shape they need to control speed due to an instinctive defensive rush to get the turn started and thru the fall-line. The only way to overcome this is to know what can be done instead.

JASP,
Just checked before posting and see you've caught up and passed me by. The *Duration* of our acceleration is key.

More later, gotta run...

.ma
The reason shorter radius turns produce slower speed is that when we are carving there are no braking properties to mention. Therefore if you spend longer time in the fall line (bigger radius) you will gain more speed that you cannot loose later on. Common sence really.
Michael,
The way to understand the friction is to look at a trial answer and close in on a solution. Since we are traveling the same distance and descending the same vertical, start by assuming (erroneously) the same speed. At the same speed, the acceleration and force vary directly as 1/R. So if we somehow were to travel or start at the same speed, we would need more acceleration for the smaller turn, which would slow us down a bit. The slower speed would result in less acceleration, which would speed us up a bit, but not as much. a=V^2/R, so for the same a, V varies as the square root of the radius. 4 times the radius would require twice the speed for the same friction.

That being said, I think the real reason shorter turns slow us down more has more to do with the turn shape. We naturally tend to stay in the same corridor with both turns, and make incomplete ( turns at the long radius and more complete turns with the short radius C.
Quote:
 Originally Posted by Ghost That being said, I think the real reason shorter turns slow us down more has more to do with the turn shape. We naturally tend to stay in the same corridor with both turns, and make incomplete ( turns at the long radius and more complete turns with the short radius C.
Exactly. And since we get double ammount of speed controlling checkups we also keep our speed better under controll. I still think that the real reason though is that when we do larger r turns we stay longer in the fall line and we gain therefore more speed. Speed that we can only cut if we stear our skis across or uphill.
Quote:
 Originally Posted by Ghost Michael, That being said, I think the real reason shorter turns slow us down more has more to do with the turn shape. We naturally tend to stay in the same corridor with both turns, and make incomplete ( turns at the long radius and more complete turns with the short radius C.
Here's a thought...
Can we make short radius carved turns at the same speed as GS carved turns? How fast would those turns happen?
Quote:
 Originally Posted by justanotherskipro Here's a thought... Can we make short radius carved turns at the same speed as GS carved turns? How fast would those turns happen?
Well some people can make short radius carves at the same speed as other people can make GS radius carves, but I"ve found that I can carve at higher speeds with a longer radius. I think a good estimate of the maximum g-force most people can carve a turn is about 3 or 4 gs (i.e. pushing into the turn with about 3 or 4 times the force their weight pushes down with).
Given that acceleration = V^2 / radius, the speed would vary as the squae root of the radius of the turn. ie with a 20 meter turn you can go twice as fast as with a 5 meter turn before things start to fall apart.

Maybe what your getting at is that we don't like going faster on shorter skis and naturally limit our speed more :. I've certainly noticed that I ski faster, but speeds seem slower when I'm on the SGs as opposed to the SCs.
With my SL skis I go way over the speed limit for normal gromers. With GS skis I need an empty or closed slope. At this one resort in Norway they had something they called morning ski from 7 to 9. Only 100 skiers and 10 slopes. If there was no traxs infront you knew that there was nobody in your way.
Quote:
 Originally Posted by tdk6 If there was no traxs infront you knew that there was nobody in your way.
...Yeah, nobody, but not nothing, watch out for that ridge that blew up across the whole dam run beyond the second blind rise:.
Ghost,
Here's a math problem for you and Michael...
Think back to high school physics and Newton. A curved path requires some force to make an object deviate from it's linear trajectory. Apply this to these two turn types being performed at the same velocity. Let's call that lateral acceleration. Again assuming the speed remains constant, the G forces required increase as the radius decreases. Why? Well we are forcing the skis (and the skier) out of their preferred state of linear motion.
Where does that power come from? IMO muscle power is the source. Which explains the rise in pressure that bends the skis into a deeper arc.
Yes, the force is equal to mass times velocity times velocity (again) divided by radius.

Yes the force decambers the ski. The boot loads the mid-ski in one direction, and snow loads the whole ski in the other direction.

No, the force need not come from muscle power; PSI-man turns without any muscles. He's gravity powered.
Quote:
 Originally Posted by Ghost ...Yeah, nobody, but not nothing, watch out for that ridge that blew up across the whole dam run beyond the second blind rise:.
Yeah, you need to know exactly what the slope looks like so you can cannon yourselfe over that ridge knowing precisely where to land and how to bear off.
Ghost,
Position over the skis is a good starting place because it allows us to have a positive effect when we begin to actively manage and direct the skis. How do we actively manage and direct the skis? With body movements and they are what require muscle power. Which explains the rigorous training regimine used by top skiers. Why strength train if the muscles are so unnecessary? When we turn away from the fall line, gravity is not a lateral force so there must be other forces involved to create a lateral acceleration. Why even standing requires muscle power to resist the pull of gravity, so I would submit that Gravity cannot do both jobs simultaneously.
Yes we use muscle power to adjust position, and yes it does take strength to resist lateral forces with a bent knee, hip, or ankle, but PSI man makes turns and does not have ANY muscles.
Ghost,
Interesting technique to apply - pick an arbitrary ‘wrong’ answer; then systematically work thru error-reduction iterations until finding a correct solution. ...Might be a strictly ‘Guy’ thing though. It’s sorta like how Guys drive to unknown destinations while refusing to ask for directions. We might ‘miss’ a whole bunch of times - but each ‘miss’ gets smaller until we can go, “Hey, Look - there it is!”

JASP,
I like the exercise proposed in post 134 - making medium turns at a given ‘ski-speed’ and then trying to make short turns of the same shape and using the same ski-speed across the surface of the snow. This would demonstrate definite differences and also reveal a fly in the ointment.

In particular we'd notice that our ski speed along its surface path would not match our upper-body speed through the air above. With short radius turns our upper-body will travel a much shorter path (relatively speaking) than our skis will travel and more slowly along that path as well.

Tracing the circular ski-path in the snow for short turns we might see a radius of 4’ but our upper-body (perhaps our CM) might trace out an elliptical path with a side-to-side radius of 2’ with a crossover-to-crossover radius of 4’. ( a 2-1 ratio per turn )

This alternate path for the upper-body directly affects Ghost’s G-Force evaluation above since only the bottoms of our skis actually get close to "the speed in a given radius" that his G-Force evaluation looks into. The actual G-Force at the ski as calculated for a given ski-speed and radius is always less than expected since most of our mass is well inside that radius and not traveling as fast, nor on as small a radius (elliptical path, remember?). This impacts our ski-pressure against the snow surface and therefore friction, compression and displacement of snow under our ski.

---
Looking at JASP’s lateral acceleration vs. forward acceleration … this certainly fits in there somewhere but exactly how is a matter that needs further investigation due to the varied pressure(s) and varied amounts of friction as just described.

In a pure sense the increase (or decrease) of directly-sideways acceleration does not impact our current forward speed in any way. In nerd-speak only that portion of the ‘sideways force’ not perfectly perpendicular to the instantaneous tangent <cough> of our current path affects our forward speed. Skew that directly-sideways force just a bit forward and some portion of it slows us down. Skew it back a bit and we speed up slightly.

Centripetal force from the bent ski certainly turns the skier but in a perfectly frictionless world that sideways force would not detract from our speed. Without friction it would be a lossless (and progressive) conversion of our down-the-slope speed into across-the-slope speed. Think about a perfect SuperBall hitting a frictionless wall at a 45-degree angle. It would just bounce off at the same speed… where does the force that redirects the ball away from the wall actually come from?

(WHY do I keep ignoring Friction? Well, I like to simplify things as much as possible and figure out what's happening at that level first. Once I know what happens without friction, I can work out what impact friction has on each component of the turn and develop the solution further ... sort of like Ghost's "Start somewhere wong, then make it progressively 'righter" thing above.)

---
JASP,
Let’s stay away from muscular/biomechanical involvement for a while longer and first try to figure out the purely mechanical foundations of what’s really going on with turning & speed-control.

If we know exactly what’s going on (mechanically) with the slope, snow, skis, gravity, ski-path, (etc) in isolation - then we can pin down exactly what is required of the skier (biomechanically) to reduce or perpetuate speed. The Bio stuff is essential - but it is on top of the fundamental mechanical situation. Some of this can be figured out with Rigid-Body dynamics but I think we’re going to need another look at Non-Rigid (segmented) Bodies to pin it down properly.

But hey… it’s Summer. Not like we got anything better to do right now.

.ma
just a short vacation away and very surprise to see so many reply on this topic. i did my best to go through most of the postings over the last 2 hours. it looks most people, if not all, contribute to this topic is elite skiers. great to get insights from you all. here is my feedback.

tdk - why one should not brake at lower_C?

justanotherskipro - it is fun to ski with pure carving. it is also a very good means to ski through icy slopes, which sometimes just happen to be the only run downhill. if one can carve with good speed control why not use it most of the time for fun?

one thing seems no one directly address but otherwise already mentioned is to cut off skating at high_C. i think cut off skating but still able to bend the skis to a short radius(to slow down) is the hard part.
Quote:
 Originally Posted by carver_hk tdk - why one should not brake at lower_C?
I don't recall if it was in this thread or not, but a braking maneuver in the lower part of the turn is very defensive move incomparison to redirecting the skis at the top of the turn. Read this thread. The only problem is that when you start making those types of adjustments (top or bottom of the turn) you are no longer making a pure carved turn.

Quote:
 Originally Posted by carver_hk justanotherskipro - it is fun to ski with pure carving. it is also a very good means to ski through icy slopes, which sometimes just happen to be the only run downhill. if one can carve with good speed control why not use it most of the time for fun?
Not to speak for JASP, but I think that his point is that when you start making movements that control the speed of your turns (other than adjusting turn shape), you are probably no longer making a pure carved turn. Watch racers in a slalom course. Very few turns are purely carved. If they were they would blow out of the course on every run. Rather they use tactics to control/maintain their speed so that they stay in the course.

Quote:
 Originally Posted by carver_hk one thing seems no one directly address but otherwise already mentioned is to cut off skating at high_C. i think cut off skating but still able to bend the skis to a short radius(to slow down) is the hard part.
See the thread I mentioned above. The reason no one has mentioned it is ebcause you specifically stated that you wanted to apply speed control to a pure carved turn. When you start cutting out parts of the turn with redirects and rotational movements you are no longer skiing a pure carved turn. Sure you are still carving, and you may be going fast, but you are not skiing an arc-to-arc purely carved turn.

Later

GREG
Quote:
 Originally Posted by carver_hk what options do we have? i can only think of: rebound, arc radius, arc shape (how complete the half circle is). what else?
Ski on a flatter slope.
Quote:
 Originally Posted by tdk6 You should never brake your speed during the second half of the turn. ....
just wondering if its a safety consideration?
- i dont have the intention to use redirection or rotational type of manuveurs. perhaps it helps to re-state what comes up to my mind when i want to control my speed. welcome to further comment.
1. skating - without redirection, right after hook up(ie. both skis bite into snow at desired radius), push the skis without further bending the skis but accelerate like rollerblading
2. rebound - throw body forward to tap the rebound force. this force will then accelerate the body forward
3. bigger radius - i dont quite understand why but it seems faster.
4. less complete C - so that more time is spend on fall line in proportion.
to cut down speed
1. skating - use just enough force to bend skis to the desired radius. if really have excessive power due to speed, try to absorb the force by down unweight. the aim is to cut down the skating force element
2. rebound - throw body upward instead of forward to dissipate the rebound energy.
4. more complete C
terrain, snow surface condition or other environmental conditions are not considered as those are not options in some cases.
Thanks Heluva,
Yes, Adding delay moves takes us out of the arena of pure carves. Which is not always a bad thing. In his last post it became a little clearer that he is seeking speed which is different than adding delay moves. Sorry we didn't catch that sooner it would have saved a lot of writing to the contrary.

I question why Carver did not include projecting the Com into the turn with both legs (bilateral activity) to gain speed instead of stepping (cross lateral activity). Only gains inches in each turn but it adds up over the course of twenty turns.
Quote:
 Originally Posted by justanotherskipro Thanks Heluva, Yes, Adding delay moves takes us out of the arena of pure carves. Which is not always a bad thing. In his last post it became a little clearer that he is seeking speed which is different than adding delay moves. Sorry we didn't catch that sooner it would have saved a lot of writing to the contrary.
by speed control i mean the ability to speed up or slow down. the idea is to look at what options is available on the two sides.
Quote:
 Originally Posted by justanotherskipro I question why Carver did not include projecting the Com into the turn with both legs (bilateral activity) to gain speed instead of stepping (cross lateral activity). Only gains inches in each turn but it adds up over the course of twenty turns.
my current practice of changeover is the first way of your statement: projecting the Com into the turn with both legs (bilateral activity)
I dont quite understand what is the second way: stepping (cross lateral activity)
want to tell how it works? thanks in advance.
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