 Poster: A snowHead
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| veeeight wrote: |
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Let's say you are right afterall and both ski tracks are totally identical. Why is that such an important concept to force on us, because I've honestly forgotten!?
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Because the inside ski is NOT tracking a tighter radius than the outside ski. It is laying down an identical track to that of the outside ski.
The inside ski is only conceptually tracking a tighter radius than the outside ski IF you mathmatically relate them to a common (static or moving) centre. But, in reality, both skis couldn't care less about what radii the other one is tracking. The two runners in lanes 5 & 6 show that relative to their respective buddies in the grass area, the piece of string is always 15 metres long.
In skiing this is important, because if you ski thinking that the inside ski has to bend more to track a tighter radius, then your skiing is going to fall apart. It only has to track the same (radius for want of a better word) as the outside ski. |
Bollux, as shown by simple basic geometrical theory. I really don't understand your obsession with the 2 skis having to track the same radius. You'll be telling us next that inside and outside car wheels track the same turn radius when cornering. Out of interest, do you think they do?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| Sideshow_Bob wrote: |
| GrahamN wrote: |
| Sideshow_Bob, thanks for that (fuller explanation of curves similar to what I posted three pages back). Unfortunately we're all quite clearly wasting our time |
It's more to hopefully show the other more open-minded but undecided people still reading (are there any) that there are problems with identical/exactly-overlapping tracks, and that there is actually a tighter arc being skied by the inside ski. |
It was useful for me thanks, although I got the point quite a few pages ago! V8 did originally get me thinking about it carefully, but then I realised he may understand the ski technique but not the maths or physics of what he's talking about. His entire argument for the past few pages has just shown his blind refusal to acknowledge input from other people he clearly doesn't consider credible enough to believe.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| Sideshow_Bob wrote: |
| It's more to hopefully show the other more open-minded but undecided people still reading (are there any) that there are problems with identical/exactly-overlapping tracks, and that there is actually a tighter arc being skied by the inside ski. |
I was convinced about the theory quite a few pages ago. But thanks for taking the time to draw diagrams which illustrate it beyond all doubt. How, now, could anyone possibly disagree?
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| Quote: |
You'll be telling us next that inside and outside car wheels track the same turn radius when cornering. Out of interest, do you think they do?
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Only if you conside that they have a common centre.
Skis don't.
This bozo (plus all the other 25 professional bozos here in this ski town) repeats:
If you ski think that the inside ski has to bend more to track a tighter radius, then your skiing is going to fall apart.
How exactly are you going to bend the inner ski more than the outer ski in a turn, when you have a 90:10 loading, parallel shins, etc.?
The bozos here also are able to reproduce pencil thin parallel lines in the snow, repeatedly, without any inner ski divergence (as demonstrated on sharp stiff skis). Except that it was pointed out to me tonight that parallel only applied to lines, not curves.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Ok - interesting thread - and some nice mathematical demonstrations. Apart from veeeight's characteristic "everyone who disagrees with me is a twit" attitude, which ain't new, the key issue here is one of relativity. Not in the special/general sense, but in points of observation.
veeeight, stands on his skis, makes beautiful parallel turns, parallel to his buddy skiing next to them. His main awareness is of the position of the skis under him and the forces being fed back. He is not a finely calibrated bunch of sensors that can actually measure to within 1-2 degrees tolerance his angulation at each joint. He is not aware of the inherent second-by-second changing fudge in radius change (some of it originating from changes in pelvic orientation) that is going on to keep his tracks separated by the same distance throughout his beautiful railroad turns. All he sees is the result, and he feels the sensation of his legs being a constant distance apart.
The rest of us who have some understanding of maths and geometry, stand and look at the tracks and realise that skiing does not exist in a parallel universe where the rules of physics and geometry do not apply. We can see and demonstrate that stationary or moving, in 2d or 3d, tracks with a constant distance between them are not parallel.
But we should also realise that there is absolutely no point in arguing with someone who fails to realise when they have wandered far from their field of expertise, are using words they hardly understand, and lack the sense to listen to others. So perhaps it is time to stop prodding a stick between the bars of the cage and seeing what happens? 
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| veeeight wrote: |
| The bozos here also are able to reproduce pencil thin parallel lines in the snow, repeatedly, without any inner ski divergence (as demonstrated on sharp stiff skis). |
I don't think anyone would dispute that (though a mathematician/scientist/engineer would prefer "parallel +/- x mm" but never mind that). It would have been easily observable by you to a reasonable degree of accuracy.
- but -
did you establish, for pairs of points created simultaneously on a pair of tracks, the instantaneous centres of curvature and corresponding radii of curvature, to prove or disprove that they are always equal? If so, how?
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stoatsbrother, ...quoth the sage... But one would have to be a bit careful not generally to criticize those who post outside their fields of knowledge - the whole site would collapse if that were banned!
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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Can parallel lines exist on the surface of a sphere?
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| jbob wrote: |
| Can parallel lines exist on the surface of a sphere? |
Yes.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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I'm struggling to resolve the maths in this argument to what I see on the hill with regard to clean RR tracks.
If the inside and outside ski tracks have a common center and the inside track is tighter, then for the inside ski to track a clean line it must either -
have to be tilted more than the outside ski. For most skiers that is not the case.
OR the inside ski has to have more bend / 'pressure'. Again, I'd say that for most skiers that is not the case.
So what's the process enabling the inside ski to track a tighter line and not skid ?
(photo courtesy of http://www.youcanski.com )
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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PJSki, Am i right in thinking that parallel lines on a sphere such as lines of latitude must have differant radii and lines of equal radii such as lines of longitude converge?
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| david@mediacopy wrote: |
So what's the process enabling the inside ski to track a tighter line and not skid ?
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I think this is an interesting question. I think it must be either a steering input (applied torque) or a more forward loading of the tip to engage the shovel. The longer the turn radius, the less these inputs are required. For many of us lesser skiers, this can easily lead to a degree of skidding, especially on tighter turns. I tried to discuss this very point a while ago and several experienced skiers alluded to it. The ski loading is quite complicated in practice and the resultant deflected shape will depend on several factors e.g. the vector load and torque acting through the boot, the amount of snow surface grip and deformation etc. The ski loading is not a simple point load, it's a non-uniformly distributed load acting along the entire contact length. Any change in either the vertical load, fore-aft load distribution, steering torque, edge angle, snow surface grip or surface hardness will affect the deflected shape.
Of course for V8 non of this even exists because he can ski identical inside & outside tracks without the need to conform to simple geometrical constraints.
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You know it makes sense.
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| veeeight wrote: |
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You'll be telling us next that inside and outside car wheels track the same turn radius when cornering. Out of interest, do you think they do?
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Only if you conside that they have a common centre.
Skis don't.
This bozo (plus all the other 25 professional bozos here in this ski town) repeats:
If you ski think that the inside ski has to bend more to track a tighter radius, then your skiing is going to fall apart.
How exactly are you going to bend the inner ski more than the outer ski in a turn, when you have a 90:10 loading, parallel shins, etc.?
The bozos here also are able to reproduce pencil thin parallel lines in the snow, repeatedly, without any inner ski divergence (as demonstrated on sharp stiff skis). Except that it was pointed out to me tonight that parallel only applied to lines, not curves. |
You're going to have to apply a torque loading on the inside ski (or at least a more forward loading on the tip) to hook up the shovel and create the bending that way. The deflection does not come from vertical loading alone. See my answer to the above post.
Pulling out your "expert" card is fine for the ski technique, but you can't use it to describe mathematically how runners follow a track! When it comes to the geometry and physics you are clearly lacking in "expertise". If we're going to puff out our professional chests I can say that I've got a Masters degree in vehicle dynamics and the way you are describing the dynamics of what is happening here are total rubbish. It's not surprising that the pure mathematicians are taking serious issue with your absurd claims.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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david@mediacopy, you are struggling with the same issues as me a few pages ago. but my conclusion was (and still is) i believe it is a combination of steering input, shovel/ski loading which bends the ski into a tighter radius as it can be bent into a non uniform complex shape due to it having varying stiffness along its length.
Head above parapit, I think V8's assertion that we have to have more pressure on the inside ski to deform it into a tighter radius (more than the outer ski) is incorrect. Thinking about it practically, the outside ski of course has more pressure on it but its edge is tracking a certain radius during the turn as most of the force applied is emanating from the middle of the ski, its stiffest section.
The inner ski is being more loaded in the front section (which is the easiest part to deform) through tip lead, steering torque or forward pressure as it bites into the snow. This will allow it (if required) to momentarily transcribe a tighter radius.
Sorry no maths to support this theory but with my skiing hat on i think is correct but am prepared to be shot down...
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Poster: A snowHead
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| Sideshow_Bob wrote: |
Veeeight, are you deliberately trolling now? |
A trolling admission at this point might be a way of conceding that he's wrong (on this little point) without losing much credibility. But I don't think he is trolling. I think he simply doesn't understand the physics and is too blinkered by his "expertise" to take on board the fairly straightforward explanation. A more open minded person might consider that they may just have something left to learn. I like to think I'm open minded too and even entertained his potentially earth shattering mathematical discovery. But on further reflection that Nobel prize is not coming his way
Last edited by Poster: A snowHead on Sat 19-04-08 12:35; edited 1 time in total
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| jbob wrote: |
| PJSki, Am i right in thinking that parallel lines on a sphere such as lines of latitude must have differant radii and lines of equal radii such as lines of longitude converge? |
Correct.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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| jbob wrote: |
| PJSki, Am i right in thinking that parallel lines on a sphere such as lines of latitude must have differant radii and lines of equal radii such as lines of longitude converge? |
Think about slicing through the sphere along the lines. You'll see that for lines of latitude you end up with a flat circle where you make these cuts, with each circle having a different radius unless the lines were cut at equal latitude north and south. Now cut through the sphere along lines of longitude, and you find for each cut you're cutting the sphere into equal hemispheres. Same radii no matter which line of longitude you cut.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| uktrailmonster wrote: |
| Sideshow_Bob wrote: |
Veeeight, are you deliberately trolling now? |
A trolling admission at this point might be a way of conceding that's he wrong (on this little point) without losing much credibility. But I don't think he is trolling. I think he simply doesn't understand the physics and is too blinkered by his "expertise" to take on board the fairly straightforward explanation. A more open minded person might consider that they may just have something left to learn. I like to think I'm open minded too and even entertained his potentially earth shattering mathematical discovery. But on further reflection that Nobel prize is not coming his way |
Having just read through this thread, I think this is a fair summing up.
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You'll need to Register first of course.
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| Quote: |
have similar formal engineering qualifications
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sort of, i think vehicle dynamics is a heck of a lot more relevent to this discussion than my (now largely forgotten) robotics degree...
I am going to wait a while to let everyones brains recover but to me the maths and dynamics discussed are far less interesting and relevent to skiing than body mechanics and physiology. A thread on this with input from the usual maths, science and engineering types PLUS the physicians, boot fitters and physio bods on snowheads would be very interesting...
For instance MB alluded to body mechanics as a big potential reason for scissoring and i agree fully with that. i think a very interesting topic would be to discuss the range of motion of all the skiing joints, the forces the muscles affecting each joint can produce and how physilogy affects skiing dynamics.... another time.... 
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| skimottaret wrote: |
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have similar formal engineering qualifications
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sort of, i think vehicle dynamics is a heck of a lot more relevent to this discussion than my (now largely forgotten) robotics degree...
I am going to wait a while to let everyones brains recover but to me the maths and dynamics discussed are far less interesting and relevent to skiing than body mechanics and physiology. A thread on this with input from the usual maths, science and engineering types PLUS the physicians, boot fitters and physio bods on snowheads would be very interesting...
For instance MB alluded to body mechanics as a big potential reason for scissoring and i agree fully with that. i think a very interesting topic would be to discuss the range of motion of all the skiing joints, the forces the muscles affecting each joint can produce and how physilogy affects skiing dynamics.... another time.... |
Agreed, although anyone with A level maths or physics would see through the problem with V8's aggressively asserted theory.
It would be good to have a thread on the body mechanics and dynamics involved in achieving a non-skidded 2 ski carve. MB mentioned Fischer boots earlier, which are interesting because they counter the "duck foot" tendency most people naturally seem to have.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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For those that truly believe that the inside ski has a tighter radius than the outside ski:
On your right foot click into your normal say GS ski.
On your left foot click into a GS ski of smaller sidecut radius.
Head down the fall line. Turn left. Park and Ride. Leave ultra thin tracks.
In this situation I am prepared to accept that the inner ski is tracking a smaller radius than the outer.
But YOU describe the tracks left by those skis.....? 
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| veeeight wrote: |
For those that truly believe that the inside ski has a tighter radius than the outside ski:
On your right foot click into your normal say GS ski.
On your left foot click into a GS ski of smaller sidecut radius.
Head down the fall line. Turn left. Park and Ride. Leave ultra thin tracks. |
Been there, seen it, done it.
Used to own a pair of Atomic 9.28 Beta Race. Differential sidecut. Built so the inside edge tracks a 28m radius. Outside edge tracks a 27.5m radius (iirc). Skied railroads no problem on them.
Anyway, the point is moot. It doesn't really matter the marked sidecut of a ski. As people have described earlier you can get the ski to track a tighter radius by angulating and pressuring different parts of the ski different amounts to distort the ski.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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veeeight, what something looks like is not at all the same as what it actually is like, particularly if the differences are of the tiny order of magnitude described in detail by GrahamN and also if there are so many extraneous factors competing against a 'pure' result. Shoot me down if you like, I am neither a mathematician nor an engineer - though I have understood a fair proportion of what has been so clearly explained by those that are - nor am I a particularly good skier. I can, however, distinguish - indeed am qualified to do so - between a strong argument and a weak one.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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The point isn't moot. The point is central.
If you park and ride, you are merely riding for the most the sidecut radius of the ski.
People earlier have hypothesised on how to get the inside ski to track a tighter radius, but if you're a decent skier you'll know how difficult this is in practice with a dominant outside ski.
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so the inside edge tracks a 28m radius. Outside edge tracks a 27.5m radius
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Do you really mean that?
Once again:
++++++++++++++++++++++++++++++
For those that truly believe that the inside ski has a tighter radius than the outside ski:
On your right foot click into your normal say GS ski.
On your left foot click into a GS ski of smaller sidecut radius.
Head down the fall line. Turn left. Park and Ride. Leave ultra thin tracks.
In this situation I am prepared to accept that the inner ski is tracking a smaller radius than the outer.
But YOU describe the tracks left by those skis.....?
Last edited by And love to help out and answer questions and of course, read each other's snow reports. on Sat 19-04-08 14:35; edited 2 times in total
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Hurtle, of course I can see your point, however the weakness in all of this is people asserting that you need to bend the inside ski to ski a tighter radius (which is nigh on impossible given sharp stiff identical skis), and/or the need to scissor/diverge your turns at the start when skiing clean carved lines.
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You know it makes sense.
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| veeeight wrote: |
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so the inside edge tracks a 28m radius. Outside edge tracks a 27.5m radius
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Do you really mean that?
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Yes Richard, I really mean that. Are you not familiar with the skis in question? They're asymmetric. What edge is your inside ski on when you're carving? Its outside ege. What edge is your outside ski on? Its inside edge. The were designed so the inside ski can more easily track a tighter radius at the same edge angle.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| veeeight wrote: |
| Hurtle, of course I can see your point, however the weakness in all of this is people asserting that you need to bend the inside ski to ski a tighter radius (which is nigh on impossible given sharp stiff identical skis), and/or the need to scissor/diverge your turns at the start when skiing clean carved lines. |
You still have failed to show how you'd carve a 180. Show me the tracks. Draw them. Remember, there's $100 on it if you can draw identical curves that can be overlapped exactly.
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Poster: A snowHead
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| laundryman wrote: |
I think GrahamN had something relevant to say on this subject a few pages back. You only need a certain amount of force to bend a ski to the extent necessary to get its edge in contact with the snow along its length; further force will not bend it any more if it's meeting a hard surface. So while the inner ski may require more force to bend it to track a tighter curve, that is not to prevent still more force being applied to the outer ski: not to bend it further (because it can't) but to supply the centripetal force (the reaction through the ski) necessary to sustain the skier on the curved trajectory. |
yeah that is a good point as well about additional force on the outer ski not bending it further. This nonsense that high forces neccesarily translate into smaller turn radii has caused a lot of misconceptions with some here.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Sideshow_Bob, perhaps you'd explain then why asymetric skis were dropped, and no one mainstream (apart from G3) are producing these? Like no one in racing etc.?
I give you all the perfect setup where the inner ski does track a tighter radius, and no one likes this?
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| veeeight wrote: |
| Hurtle, of course I can see your point, however the weakness in all of this is people asserting that you need to bend the inside ski to ski a tighter radius (which is nigh on impossible given sharp stiff identical skis), and/or the need to scissor/diverge your turns at the start when skiing clean carved lines. |
But that is my point: your idea of clean carved lines, may not be what actually are clean carved lines. I don't think - though may have missed this in some of the longer posts - that anyone is suggesting that your techniques for efficiently achieving the cleanest carved lines that you personally would like to perceive, are anything but exemplary.
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You need to Login to know who's really who.
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A few reasons.
One, they require two different moulds (symmetric skis only one) and hence are more expensive to make.
Two, the asymetric sidecut is only really effective at certain turn radii. Change the overall turn radius and the effect either diminishes or is exaggerated.
Three, people thought the skis would wear out more quickly. Look at the reviews of the skis where people complain about not being able to swap 'training' and 'racing' edges.
I'm sure there are other good reasons, but I'm not Atomic's product manager so can't say what these are.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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I've found the patent for asymemetric skis. Interestingly, there is not one mention of the inside ski needing to track an tighter radius than the outer ski.
Now, you would have thought that that would be highlighted as a benefit, wouldn't you......
http://www.freepatentsonline.com/4700967.html
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You'll need to Register first of course.
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| Quote: |
is people asserting that you need to bend the inside ski to ski a tighter radius (which is nigh on impossible given sharp stiff identical skis),
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veeeight, do you really believe it is "nigh on impossible" to slightly bend the shovel of the inside ski into a tighter radius if required?
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skimottaret, I think it's hard enough trying to bend the shovel of the inside ski to match the ouside ski already, nevermind trying to make it tighter!
I've seen high speed videos of some boot and foot work done here in Whistler, where the racer was wired up to pressure sensors all over his boots, and whilst he's carving razor sharp lines, parallel shins, it also shows on a seperate screen a dominant outside ski loading with almost nothing on his inside ski and boot cuff, and yet the inside ski is tracking parallel with the outside ski in a razor sharp track.
I'm sure, you've also seen, recreational intermediates, who are no where near the front of their boots, just tipping their skis onto the sides and going for the ride, and producing decent tracks......... I can't even begin to correlate how this is possible when they are not even touching the front of their boots?
As an instructor, would you encourage people to try and bend the inside ski into a tighter arc?
Last edited by Then you can post your own questions or snow reports... on Sat 19-04-08 15:24; edited 1 time in total
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That's a patent for a beginner/indermediate ski with offset bindings and a straight outside edge, not a ski such as the Atomic with a deeper outside edge sidecut. You're fast running out of straws to clutch at.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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Apologies, I misread that patent.
However, the scenario above of having a smaller radius ski on your inside foot still stands - perhaps you'd like to draw out what actually happens on paper at the exit of the turn when you do ski a tighter radius on a inside ski?
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a dominant outside ski loading with almost nothing on his inside ski and boot cuff, and yet the inside ski is tracking parallel with the outside ski in a razor sharp track.
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putting maths to one side doesnt that make you curious as to how this is happening?
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FAQ
