 Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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comprex, yeah baby, i'm 6'1" and i need some long skis... anyone making a 205cm 130/115/125 or thereabouts... What do I know? Short skis are for whimps... (or maybe just short people... sorry, shorties...)
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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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The only factor i can think of height wise is that a tall person has a higher centre of gravity. I would have thought weight and power were more crucial factors.
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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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Is it more a question of fore/aft balance. So, as FTS says, a tall person has a higher centre of gravity so it is helpful to have a bit more ski in front and behind them if they get pitched forward of back? or something... 
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I think you're right Arno - fore/aft balance (and pressure). Because of that it's less important than it was in the days of skinny skis when you needed to apply lots of forward pressure to initiate a carve. I think quite a few ski makers only guide on weight not height these days.
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comprex, but surely it's a question of stiffness and ski characteristics in addition to height. My slalom skis are 155 which is shorter than me, but for off piste I'm quite happy around 165 - 170 which is taller than me. On detuned slalom skis I'm happy at 165 ..... On park skis I'm even happy on 176 - I used to ski 200 .... don't know a serious answer to your question though. 
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How short are you anyway?
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You'll get to see more forums and be part of the best ski club on the net.
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At 6'8" (2m04) I don't feel happy on anything less than 175s. The absolute best skis I ever rode were 185s - Dynastar Legend 8000 (drool). They did everything for me. True, with only a couple of weeks under my belt, I don't have a lot to compare with, but speed/moguls/traverse - lovely! 
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comprex, As we carry the most part of our weight(males) around the upper body, the length is important, so yes a ski too short will know if it's too short.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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size is always important in men - ask your women
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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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So why are grass skis so short ?
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CEM, I know there are, ah, more talented s about. I was, you'll perceive, more concerned about the size of my arrow.
Arno, that is troubling because it seems to imply that taller men are somehow in a chronic state of imbalance that needs to be, hmm, corrected or compensated?
easiski, it is the Centre of Mass skier model that gets me in trouble. Can I really extend my skis away from my centre of mass, and use core muscles to pressure the tips or am I merely aligning a set of large massy lumps (connected by weak springs) so that it is my chin and shoulders pressuring the tips to turn in and my behind pressing the tails to exit a turn? F'so I better quit muscle training and start some serious yoga or something.
SMALLZOOKEEPER, what does that say about necessary boot stiffness to ski length?
SnowHot, short. Thick tho. 
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You know it makes sense.
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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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comprex, i suppose that is where my logic takes you. if a tall person hits some slush and it pitched forward by 5 degrees, their COM will move further than a short person pitched forward by the same amount. thus a longer ski will be helpful?
laterally, a tall skier can make their own adjustment by widening their stance
i ain't a scientist so i don't know enough about momentum to know whether it is as simple as this in practice
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Poster: A snowHead
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SnowHot, far naughtier than immediately apparent,
for I am not being original at all with this thread, rather pulling things together from the One for the Boyz thread, the Help your Bootfitter help you thread, the Boot Balance thread, and Bob Barnes' backpedaling through bumps animation.
All of this, in turn, prompted by watching 6-foot Pierre weave through a shark's teeth icemogul field on absurdly short and soft skis, skiing alpine turns in teleboots, knowing he's got a stiff back.
Thus:
Arno, therefore a taller person needs a stiffer boot so as not to be pitched forward as far? And therefore is far more sensitive to balance issues from the outset?
The counterpoint to this is that, for any given upset to the ski travel path, the shorter skier is likely to reach their limit of ankle motion far sooner, whether it is limited by boot flex or by calf muscle tension or something else? The shorter we are, the more stretching called for?
Thus far I don't really -know- anything save that, if I am willing to regard skier height as a viable factor in ski length choice, I can't honestly ignore any of these other factors (Ankle ROM, core strength, boot balance, ski flex, boot flex, all buckles buckled?, last yoga session, et stinking cetera).
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| comprex wrote: |
[
Arno, therefore a taller person needs a stiffer boot so as not to be pitched forward as far? And therefore is far more sensitive to balance issues from the outset?
The counterpoint to this is that, for any given upset to the ski travel path, the shorter skier is likely to reach their limit of ankle motion far sooner, whether it is limited by boot flex or by calf muscle tension or something else? |
i am risking getting out of my depth on momentum, leverage etc but having a stiff boot will reduce the distance a tall person is pitched forward but there will still be the same force moving forward which will be transmitted to the front of the ski by the stiffer boot
i'm not sure it's a particularly controversial thing to say that a person with a higher centre of gravity will have to work a bit harder to maintain their balance than someone with a lower centre of gravity is it?
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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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| Arno wrote: |
i'm not sure it's a particularly controversial thing to say that a person with a higher centre of gravity will have to work a bit harder to maintain their balance than someone with a lower centre of gravity is it? |
No, that's fine, if we stop there. I, however, am tempted to ask:
- should they be continuously working?
- what part of the body is working?
- what is it working against? (gravity, other muscles, boot flex, ski flex?)
The latter two questions being tied to the boot stiffness since extent of motion is tied to my concept of work.
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| comprex wrote: |
- what part of the body is working?
- what is it working against? (gravity, other muscles, boot flex, ski flex?)
The latter two questions being tied to the boot stiffness since extent of motion is tied to my concept of work. |
These are quite interesting questions. I was the subject of some research being undertaken by a PHD physiotherapist on ACL rehab where she rigged my up with a number of sensors and looked at which bits of my body I used to adjust balance. The basis answer seemed to be that all of the body was involved with balance, but I used my ankle and foot muscles a lot, particularly when the corrections were quite small
No idea what this has to do with ski length though!
Anyway, a lot of what is "right" in terms of ski length is personal preference, pure and simple (although for racers they are dictated by FIS rules etc.). I'd say the right ski length is what you feel comfortable with unless someone qualified in these things can see that they are obviously holding you back
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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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| Arno wrote: |
but I used my ankle and foot muscles a lot, particularly when the corrections were quite small
No idea what this has to do with ski length though! |
I think it has to do with length AND width as both you and parlor are correct to notice. Wider skis for taller skiers.
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comprex, Tibial length, weight, speed, temperature, 10 degrees of movement, zetta angle, flexability, blah, blah, blah. 
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SMALLZOOKEEPER, its really all about the boots and the right attitude isn't it?
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Not convinced about wider skis for taller skiers - maybe wider skis for heavier skiers off-piste for extra floatation. Otherwise I would have thought ski width is more related to the type of skiing you're into.
Longer skis for taller skiers makes some sense. I'm quite tall at 6'1" and on skis shorter than 170 cm I feel like I'm about to go over the bars all the time (relatively big mass and high COM). 175-180 cm seems to work fine for me. A combination of weight, height and usage should determine ski length.
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You'll get to see more forums and be part of the best ski club on the net.
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uktrailmonster, notice the relatively big mass & the high COM is true laterally as well; the factors that obviously change are the stiffness of the boot and the bending resistance/modulus of the ski.
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True, but surely increased ski width is primarily for increased floatation in deep snow rather than height/weight of skier. Ski manufacturers don't generally increase the width of their longer skis - well maybe 1-2 mm at most between the shortest and longest lengths of the same model. Width is primarily governed by their intended usage i.e narrower for on-piste, wider for off-piste. This makes sense since a narrow ski is faster edge-edge and a wider ski floats better in powder. Obviously a heavy skier will need a wider ski to achieve the same powder floatation. But on piste, I don't think a heavy skier needs a significantly wider ski than a lighter skier. But they do almost certainly need a longer ski.
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snowHeads are a friendly bunch.
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As a former physicist, my initial thought is to do with moment of force, which some of you are expressing as 'a higher centre of gravity'. A force applied at a distance to a fulcrum creates what is known as a moment. Imagine a balanced beam. Place a 1kg mass 100cm from the middle on one side and it is no longer balanced, to balance it you can place a 1kg mass 100cm from the other side, or a 2kg mass 50cm away.
I'm not certain how this applies in this case, but it makes sense to me that a taller person creates a greater moment of force than a shorter person of equal weight.
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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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uktrailmonster, i agree with you. you don't need wide skis to assist your balance laterally - you can just widen your stance
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| flicksta wrote: |
As a former physicist, my initial thought is to do with moment of force, which some of you are expressing as 'a higher centre of gravity'. A force applied at a distance to a fulcrum creates what is known as a moment. Imagine a balanced beam. Place a 1kg mass 100cm from the middle on one side and it is no longer balanced, to balance it you can place a 1kg mass 100cm from the other side, or a 2kg mass 50cm away.
I'm not certain how this applies in this case, but it makes sense to me that a taller person creates a greater moment of force than a shorter person of equal weight. |
Agreed. As an engineer myself, I just assumed everyone knew that 
Yes, a high centre of gravity combined with a greater mass, simply results in a larger moment applied at the boot/binding interface. The ski has to react and balance that moment against the ground and a longer ski can achieve this with a smaller reaction force - since it acts further away from the binding/boot. It's all about balance of moments if you're into that sort of thing!
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You know it makes sense.
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errr - I don't do science!
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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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uktrailmonster, flicksta, 2 points:
1) It is easy to say 'a force applied at a distance to a fulcrum'. What is applying that force and what is it reacting against, by Newton's third law?
2)
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| But on piste, I don't think a heavy skier needs a significantly wider ski than a lighter skier. |
Agreed. I was playing devils' advocate above.
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| But they do almost certainly need a longer ski. |
Not even remotely proven yet. Why? If any given skier can balance laterally in 75mm of space with a rigid boot and laterally stiff ski , why does this same skier need 175cm ski to balance front to back?
Arno, check the Skiing myth #whatsis :50/50 weight split thread.
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Poster: A snowHead
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Simply test the ski desired in the manufacturers recommended length for your height and weight, then test the ski in the next size up.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| comprex wrote: |
1) It is easy to say 'a force applied at a distance to a fulcrum'. What is applying that force and what is it reacting against, by Newton's third law? |
The force is a result of acceleration (F = ma). The force F acts through the centre of gravity of the skier. It's reacted by a distributed load through the base/edge of the skis, which can be resolved into an equivalent point load. It's the effective position of this load (and hence its leverage) that changes with ski length.
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But they do almost certainly need a longer ski.
Not even remotely proven yet. Why? If any given skier can balance laterally in 75mm of space with a rigid boot and laterally stiff ski , why does this same skier need 175cm ski to balance front to back? |
Tried snowblades yet then?
Ok, laterally you can generate massive forces from the ski edges and you're free to simply widen your stance to increase lateral stability. Longitudinally, there's not much you can do other than change your fore/aft balance on the skis. When on foot, you can put one foot forward to stabilise yourself, but that's not really an option on skis (unless you're telemarking). Not to mention that a longer ski has more edge available to provide cornering force for a heavier skier.
Take it to its extreme and try skiing on 75 x 75 cm square skis. The skis will be way too short to provide enough of a stabilising moment to prevent you going back bottom over tit in the first few seconds and there won't be enough edge length to sustain a high G carved turn.
What isn't proven yet, is just how short can you go and still maintain enough stability. A shorter ski will have to be stiffer to support higher loading. They're getting shorter all the time, but I reckon we're close to reaching the limit.
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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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You need to Login to know who's really who.
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Which acceleration? Combined lateral and longitudinal (unless you ski at constant speed without turning)
The centre of gravity might be over the middle of the ski, but the force due to acceleration doesn't act straight down through your boots. It acts in a combined lateral and longitudinal direction applying a moment which is greater the heavier you are and the higher your CofG.
I guess your point is that a perfectly balanced skier could get away with using a much shorter ski? I guess that's true, hence the very existence of snow blades. But longer skis are still inherently more stable.
The reactive moment at the boot sole may be identical for short/longer skis (providing you don't actually fall over), but the shorter ski has to work harder to achieve it i.e larger force acting at a shorter distance.
Hey if you can speed skate down a double black I'll be seriously impressed!!
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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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"How does a ski know how tall you are?"
The simple answer is that it doesn't, but it can make a good guess based on the forces you exert on it. A tall, heavy skier will exert the biggest forces due to both their mass and it's height above the ski. Or am I missing something?
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comprex, who said anything about 50:50? 
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| uktrailmonster wrote: |
It acts in a combined lateral and longitudinal direction applying a moment which is greater ... and the higher your CofG.
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Therein lies our disagreement. I say the moment is the same. (Same skis, identically pressured and edged). The response to that moment may be slower or faster depending on height, static position of CoM, and, most importantly
how far the CoM was displaced, using muscular force, from being aligned with the resultant force (gravity and turn acceleration) being straight up through the boots, in order to achieve pressuring and edging of the skis.
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I guess your point is that a perfectly balanced skier could get away with using a much shorter ski? |
Yep. Except for 'perfectly' read 'better' along a continuum of trainable proprioception.
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Seems to me that higher CoM means that I can exert a higher force through my boot cuffs to the ski than can a shorter guy. That said, though, if I am a skilled skier, I should be able to moderate that force, so ski the same length of ski that a shorter person of the same body mass would, since the primary item of interest is the decamber I can put on the ski (which is based on my mass) and my balancing over the decambered ski (which may be a bit more difficult for me than for someone with a CoM closer to the skis).
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You'll get to see more forums and be part of the best ski club on the net.
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ssh, my frame of reference deliberately starts at the ski, and assumes identical skier CoM, one skier being merely taller than the other.
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| comprex wrote: |
Therein lies our disagreement. I say the moment is the same. (Same skis, identically pressured and edged).
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How can the applied moment be the same when the forces are acting through a higher CoM? That's impossible, it's a force acting at a distance. If the distance is greater, the moment is larger. It's like saying a car with a high CoM will produce the same roll moment as a car of the same mass, but with a much lower CoM.
I agree the reaction moment applied from the ski at the base of the boot must be identical, regardless of their length, to achieve equilibrium. But as I mentioned earlier a shorter ski will have to produce a higher reaction force to create this moment, therefore it will be loaded more heavily. That's ok if the ski and snow surface can both support that load.
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