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Edge to edge quickness

post #1 of 27
Thread Starter 
I'm impressed with the technical knowledge and analysis of this community so I thought I would ask something that's been bothering me for the past year. Last year I was looking for something wider for softer snow. As I did my research, I found frequent reference to edge to edge quickness with a basic philosophy that fat skis are slow going edge to edge. I even had a salesman show me that the ski had to travel further to get from one edge to the other.

As an engineer (yeah, that's probably my entire problem), I don't understand. Since edging is primarily angulation and getting from one edge to the other is a matter of angular movement, not linear, why does a wider ski take longer to go from one edge to another.

I have two theories that make no sense. One is that the fat skis have a greater rotational inertia and resist rotating more. The other is that the torque required to edge a fatter ski is greater since it has a longer arm length. I haven't broken down to the point of doing any calculations, but I just can't believe that either of these effects amounts to a hill of beans.

I was concerned about buying too fat a ski for this issue, but I started laughing the minute I stepped into the demo pair of Pocket Rockets and haven't stopped laughing yet. Am I finally going to stop laughing when this inexplicable quickness issue causes me to hit a tree? Can someone explain this to me?
post #2 of 27
Consider 64mm underfoot. That's about the same as boot sole with. To engage and edge, you move laterally but the boot simply rolls onto it's inner edge.

Consider 82 mm underfoot. To engage an edge, when you move laterally the whole boot rises using the edge as hinge point.

The salesman is right, the leg must travel more. But you must also move farther to generate the necessary lifting force to get you and the boot up off the ground to engage that edge. Your torque theory is correct too, you just forgot to add your body weight.

Hope this helps.
post #3 of 27
Just buy the Pocket Rockets. They are really quick, as you say, and they take little movement. I like your hill of beans theory. I ski trees all the time and have not hit one yet.
post #4 of 27
I think the issue is more one of flex and sidecut rather than width. The main reason fatter skis are slow edge to edge is that they are generally straighter and softer than skinny skis so they don't launch you from turn to turn like slalom skis do. It would be interesting to compare the quickness of something like the B5 with a conventional skinny straight ski, I suspect the B5 would be much quicker because the huge sidecut means you can really load up the ski and let it fling you into the next turn.

FWIW my 79mm waist Legend 8000s are much quicker edge to edge than my 70mm waist 4x4 Powertracs.
post #5 of 27
Preface: "slow" is a relative term.

Generally speaking, wider-waisted skis are designed with less sidecut and roll "slower" because of their width. I also think edge-to-edge quickness is primarily a hard-snow characteristic and not important for skis which normally see soft-snow/pow use.

I think of quickness as both- roll and rebound. Contemporary slalom technique is now more linear than ever- a series of short arcs linked by a more direct line through and over gates, rather than around gates. Strategy now favors skis remaining on snow and being rolled from edge to edge, rather than "skate stepped" or other transitions of the past.

Rebound energy is important, but "roll and bite" is also key. A narrow-waisted ski with enhanced shovel geometry rolls quickly during the transition and rapidly de-cambers into a new arc when the tip and tail lock in. I like a ski with a shovel that bites fast and hard. Radical tail geometry helps keep the arc going, whereas a little less geometry makes it easier to release the arc and transition into the next turn.
post #6 of 27
anytime someone asks for a ski that is quick edge to edge i feel like "thats like asking for a quick pedaling bike, i mean really how fast can you move your feet? thats how fast your skis will be edge to edge..."
yeah yeah i know there is some physics involved but i know lots of guys/girls that can turn a B3/8800/gotama faster than most people on WC slaloms.
post #7 of 27
Edge to edge quickness one gets from a narrow waisted i.e. sub 70mm waist ski will likely benefit the skier who jams turns like a slalom racer; but who free-skis like a slalom racer? I don't and I sure haven't seen anybody else do so in my days on the hill lately.
post #8 of 27
Quote:
Originally Posted by waxman
but i know lots of guys/girls that can turn a B3/8800/gotama faster than most people on WC slaloms.
That's true… but that's like saying Skip Barber can race a Cayenne through an autocross course faster than an average person can pilot a 911. He can, but that doesn't mean the Cayenne is a better vehicle for autocross.

A B3 or any other big-mountain ski is optimized to perform over a much broader range of conditions and serves up some compromises at the extreme ends of the spectrum. I guess we'll just have to disagree about a B3 performing as well as a wc slalom ski on a slalom course or in rapid short-radius turns on hardpack. (Maybe Bodie will switch to B3's from his new SL boards??) But, shouldn't be any disagreement that a slalom ski is less than ideal for rippin' down a steep with lots of fresh stuff.
post #9 of 27
Thread Starter 
Great stuff, thanks. I did try my pocket rockets in the slalom gates last year and I did more of that over the gates thing than through. Must have been doin it right, except for all the skis slapping together stuff.

But really, I think I'm hearing that edge to edge quickness is a feeling thing, not a scientific time measurement thing. The issue of bite does seem to be an issue of total ski design, not waist measurement. I suspect to build a slalom ski with a 90mm waist would end up with shovels that looked like, well, shovels. Then you would have this whole torsional rigidity issue.

If all that is true, then it really is an oversimplification to try to say that edge to edge quickness is a function of waist width. In fact, the real definition of edge to edge is debatable and might be better described as bite to bite quickness.

I am still in the camp with Waxman that it is about how fast you move your feet and I question BigE's assessment of lateral movement since the skis at 'release' are relatively free to move side to side and you don't have to necessarily move your leg to get over them, the ski can actually move under your leg to get to the next edge. The rest of what BigE said does make sense to me from the torque standpoint, but I still don't have the calculations.

Regardless, it seems that the general opinion is that it is only a real issue when you get to one far corner of our multifaceted sport, the slalom corner. For now, I should turn off my brain and keep laughing. Maybe when I'm bored of the fat thing I can get me some short radius hard biting skis.
post #10 of 27
Everyone needs more toys! Go for it.
post #11 of 27
For me, the quickest edge to get to is the one right under the edge of my foot (mid 60's). The further away from this line the slower it is to get it to a critical angle. That's what my experiences have shown me. My quiver goes from 64 to 89. Later, RicB.
post #12 of 27
Quote:
Originally Posted by retiredat40
I am still in the camp with Waxman that it is about how fast you move your feet and I question BigE's assessment of lateral movement since the skis at 'release' are relatively free to move side to side and you don't have to necessarily move your leg to get over them, the ski can actually move under your leg to get to the next edge. The rest of what BigE said does make sense to me from the torque standpoint, but I still don't have the calculations.
Moving your feet is not a measure of edge to edge quickness of the ski. It's a measure of how fast you move your feet. Does'nt say anything about the ski at all. I mean if you were wearing work boots, would moving your feet quickly say anything about the edge to edge quickness of the workboot?

"Edge to edge quickness" actually measures something about the ski. It does not consider any clever gyrations that you have to do at "release" or other point to jump quickly from one edge to the other.

You need to have some restrictions on the skiing style to make a sensible definition:

Consider linking turns on hardpack. You need to get from one edge at turn completion to the other at turn initiation. Suppose you do this just by rolling the ski, NOT by moving the feet. To roll the ski, I mean moving the hips inside the turn far enough that the skis go up on edge.

A narrow ski will engage quickly as you roll from one edge to the other -- you don't need to move very far inside before the ski engages. Think of how fast edge engagement happens when you roll a skate from side to side. -- it's almost immediate, because it's so narrow. That's what edge to edge quickness is about.

A slalom ski with the low 60mm waist is "fast" edge to edge as well, but not even close to a skate.

A very wide fat ski needs to lift you off the snow before its edges are even close to engagement. That takes time and effort. You can even feel the lift happening!

You are correct that the shape will also contribute to this, but the effect of the waist is by far the dominant factor.

The sense of edge to edge quickness is a real thing, it does not vary from skier to skier. All skiers will certainly say that edge to edge quickness of a slalom ski is quicker than a fat ski -- provided they use the accepted definitions. Otherwise, that quickness becomes skier and style dependent and any definition is meaningless.

Hope this helps clear things up.
post #13 of 27
There is another factor that contributes to the feel of a fat ski being "slow" edge-to-edge when used on a firm surface.

As you attempt to put such a ski on edge, not only does it take more energy because your (weighted) feet have to rise upward from a flat ski position (mentioned above), but there is more sideways torque trying to restore the ski to flatness on the snow.

Not only can you feel this extra torque directly (and have to overcome it with muscular action), but if there is angular slop at any of the points of connection between your lower leg and the ski (ie, between leg and boot, sideways deformation of the boot, between boot and binding, between binding and ski), all of these have to be overcome before the fat ski will get to the edge angle you seek.

For example, there can be as much as a few degrees of sideways movement between a bolted-down ski boot and the lower leg of a skier exerting lots of edging torque on such a boot. This is due to deformation of the flesh of the lower leg and, to a smaller extent, deformation of the plastic of the boot. If you need to apply less torque, there will be less deformation at these junctions.

I was surprised to also measure that there can be as much as an additional couple of degrees of sideways movement from the boot lugs to the ski base when under sideways torque due to "give" in the boot-binding interface, flex of the mounting rails or other mounting system, etc.. As with the leg-boot interface, if you need to apply less torque, there will be less angular slop at these junctions as well.

While the sum of all these sources of edging "slop" might only be a degree or two for a narrow ski (ie, which puts less flattening torque on the lower leg and all the intermediate junctions), they might add up to 4 or 5 degrees with a wide ski that puts more flattening torque on these junctions when used on a packed surface. This is not a huge angle, but I think it certainly is enough to give the skier a sense of edging "slowness" - ie, 4 or 5 degrees more motion of the lower leg might be required to get the ski to edge by the same amount.

My feeling is that in leasurely, mostly skidded-turn recreational skiing, this extra required edging motion of the lower legs isn't usually first noticed as undue "slowness", but rather, will first make itself known by a difficulty in achieving critical edge angle (ie, holding) on icy surfaces. I think this is one of the reasons powder skis give many people trouble on ice. You can overcome this by angulating more, but you don't have to work so hard and use such exaggerated movements if you are on a narrower ski.

In higher performance skiing by a more advanced skier, all of the effects mentioned above will be sensed by the skier.

HTH,

Tom / PM
post #14 of 27
Quote:
Originally Posted by PhysicsMan
I was surprised to also measure that there can be as much as an additional couple of degrees of sideways movement from the boot lugs to the ski base when under sideways torque due to "give" in the boot-binding interface, flex of the mounting rails or other mounting system, etc.. As with the leg-boot interface, if you need to apply less torque, there will be less angular slop at these junctions as well.

Tom / PM
Yes, this is an effect that isn't often addressed but you can definitely feel it when it happens. I find it's particularly accentuated with my Salomon Snowblades when I get them up on edge, perhaps partly due to some compression of the rubber pads that the boot sits on.
post #15 of 27
You want edge to edge quickness? I have a pair of Elan Steaths only 41mm in the waste. Unfortatly, they aren't that good in the soft stuff.
post #16 of 27
and then you get into the questions of boot-out, lifters, etc.
post #17 of 27
Quote:
Originally Posted by PhysicsMan
While the sum of all these sources of edging "slop" might only be a degree or two for a narrow ski (ie, which puts less flattening torque on the lower leg and all the intermediate junctions), they might add up to 4 or 5 degrees with a wide ski Tom / PM
When I want to be quick edge to edge I finish the turn with a "pop" of knee angulation. The rebound off the edges of a lively ski can pop you right of the snow......not the best for carving but damn quick to release from the turn.

The edging slop so eloquently described by physicsman dampens this ability to pop the edges in. When I got my first pair of 80mm skis I felt like my boots weren't stiff enough laterally. I hated them on hard packed until I added a plate to about FIS maximum height. That changes the angles so you are more directly over those wide edges.

Newf
post #18 of 27
Quote:
Originally Posted by newfydog
When I want to be quick edge to edge I finish the turn with a "pop" of knee angulation. The rebound off the edges of a lively ski can pop you right of the snow......not the best for carving but damn quick to release from the turn.
I agree, but that's all about *you* not the ski!

Quote:
Originally Posted by newfydog
The edging slop so eloquently described by physicsman dampens this ability to pop the edges in. When I got my first pair of 80mm skis I felt like my boots weren't stiff enough laterally. I hated them on hard packed until I added a plate to about FIS maximum height. That changes the angles so you are more directly over those wide edges.
Yes, in fact, the line from the edge to your CM is closer to the ankle with the plate, so there is less torque on that joint. You really are "more directly over those wide edges".
post #19 of 27
Quote:
Originally Posted by newfydog
When I want to be quick edge to edge I finish the turn with a "pop" of knee angulation. The rebound off the edges of a lively ski can pop you right of the snow......not the best for carving but damn quick to release from the turn.

The edging slop so eloquently described by physicsman dampens this ability to pop the edges in. When I got my first pair of 80mm skis I felt like my boots weren't stiff enough laterally. I hated them on hard packed until I added a plate to about FIS maximum height. That changes the angles so you are more directly over those wide edges.

Newf
The most desired use of the rebounding energy ("pop") of the ski in current slalom technique is to aid in retraction of the extended outside leg and set up for a cross-over or cross-under transition to a new edge by rolling the skis. For efficiency, the goal is not to use the energy to move up and off of the snow.

You're right, using the energy to rebound off of the snow does make it possible to rotate the ski faster and establish a new edge for a direction change, but as BigE stated this isn't a measure of the physical edge-to-edge speed of the ski. I battled my "old school" tendency to check and pop when I first transitioned to a shaped ski. But now that I'm focused strictly on arcing turns, I'm trying to keep all energy flowing forward in the direction of travel.

Spent most of my youth growing up in Colorado. However, a move to New England a few years ago has forced me to learn a whole new way of using my edges. My brother moved west to Seattle and he and I skied together at Whistler last spring. He still has the "western push" that just doesn't work most of the time in New England conditions.
post #20 of 27
Quote:
Originally Posted by medmarkco
But now that I'm focused strictly on arcing turns, I'm trying to keep all energy flowing forward in the direction of travel.

Spent most of my youth growing up in Colorado. However, a move to New England a few years ago has forced me to learn a whole new way of using my edges. My brother moved west to Seattle and he and I skied together at Whistler last spring. He still has the "western push" that just doesn't work most of the time in New England conditions.
Funny, I have changed my skiing the same way, lettingthe skis scoot through to the other edge without popping up and breaking the smooth arcs. I grew up in the east and attribute those habbits to eastern snow, and thought they didn't work out west.
post #21 of 27
Thread Starter 
I am not surprised that someone who goes by Physicsman would come up with detailed analysis of the whole system that adds very understandable points. Thanks for that.

BigE, your post is well stated as well. I agree with your point about rolling the ski, which was really the basis for my question in the first place. Since I was assuming angulation for a fat ski is the same as that of a skinny ski for the same hip movement, it seemed that if I do the same movement from one turn to the next, my angulation change would be the same regardless of the ski. Your point about the skier lifting higher on a fat ski speaks directly to the issue of torque since the arm length is essentially 1/2 the width. I am now starting to think that might be slightly more than that hill of beans I was guessing at. I really haven't played much on hard snow with the fat skis.

My point on the ski being free to slide sideways at release wasn't a reference to technique as much as the feeling I get when making very smooth transitions (or no transition if your following the release thread). The feeling is as if you are connected to pivot points on the snow, rather than actually moving across your ski. From that feeling, I suspect that the new edge starts to engage almost directly in line from where the old one left off, rather than a full ski width shifted over (this might require field work to investigate). In other words, the ski moves slightly sideways as it is passing through flat and into it's new angulation.

Regardless if that previous paragraph made any sense, I now think that the issue comes down to the extra torque on the wider ski playing itself out through the slop of a less than rigid system of binding, boot, cuff, and might as well throw in my sloppy knee joints (they might be worth a few degrees as well). Bigger is just going to take more effort to get quick and steep angulation or for the same effort it is going to take longer if you ever actually overcome the slop.

Thanks to all. My brain is starting to feel better.
post #22 of 27
Quote:
Originally Posted by newfydog
Funny, I have changed my skiing the same way, lettingthe skis scoot through to the other edge without popping up and breaking the smooth arcs. I grew up in the east and attribute those habbits to eastern snow, and thought they didn't work out west.
They work, but they aren't mandatory. I believe Western snow conditions support a broader range of techniques, but generally - and this is a very broad generalization - the lack of necessity seems to focus less attention on arcing and carving.
post #23 of 27
Quote:
Originally Posted by Martin Bell
and then you get into the questions of boot-out, lifters, etc.
there is a trapaziod 20mm lifter on them already, so boot out is not an issue.
post #24 of 27
For you physics types or engineers think of the following. Which would be quicker?... rolling from edge to edge on the blade of an ice skate or rolling from edge to edge to edge on a 4ftX8ft piece of plywood strapped to your foot. Is it the angular velocity of your leg (the same for ice skates or the plywood to get the same edge angle on the snow or the vertical distance the edge has to travel (tan(theta)*width) between turns that dominates? I defer the answer to better minds due to too many post-election micro-brews.
post #25 of 27

Elan Stealth

Phil Pugliese,
they should be exactly 87-45-67, "the second-generation carving hybrid", if I remember well
You will be smart enough to keep them as a very unique piece of equipment, won´t you... Congratulations!
BTW, they were not bad on hardpack but must be a tragedy in softer snow. Wasn´t there one more model, Phantom, with identical measurements?
post #26 of 27
Sorry, 87-45-87, of course
post #27 of 27

whtmt

Retired at 40: Your longer arm length is correct. The ski width controls the length of time it takes to move from the engaged inside edge to re-engage the ski's new inside (old outside) edge.

Visualize a vertical pole attached to the center of the ski in the boot sole area. The pole's height is the same as your lower leg at the knee cap level. Now you're on a slope of 20 degrees and you are traversing perpendicular to the fall-line. You measure the time it takes to disengage the inside (uphill side) edge and re-engage the new inside (Old Outside) edge. Now do the same experiment using a snowboard of any width. Without question it will take significantly longer to engage the old outside edge of the snowboard as opposed to the ski as a factor of the snowboard's width.

Two seasons ago we (in the adaptive ranks), took a snowboard and mounted it under a mono-ski, which is used by disabled skiers who have sustained spinal cord injuries. The ski uses a normal single shaped ski. Skiing the mono ski is virtually identical to the movements an able bodied stand-up skier makes. However, when the snowboard is attached the movement of the center of mass across the ski moving from one edge to the other takes much greater effort and a longer time period to re-engage the new edge. So I believe your theory is correct about the lever arm length.

Chris Devlin Young, a member of the US Disabled Ski Team is the inventor of this snowboard equipment and its development. Chris is also seen on the inside cover of the new and revised PSIA Adaptive Teaching Manual recently unvailed.

whtmt & Mackenzie 911
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