 Poster: A snowHead
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Ok bear with me on this!
So skis have a given radius, I assume that means if I put the ski on edge and do nothing else it will perform (roughly) the specified radius turn.
However if I apply more pressure, would that ski then be able to turn a shorter radius and vice versa, less pressure a longer radius?
Or put it another way, if I moved off my Scott Missions with their 17.5/16.5m radius to something with a radius about 21m, what difference would I notice?
Cheers,
Greg
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Aren't the missions dual radius?
With a larger radius ski, short turns are likely to be more work but the skis are likely to be less squirrely offpiste.
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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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| DB wrote: |
Aren't the missions dual radius?
With a larger radius ski, short turns are likely to be more work but the skis are likely to be less squirrely offpiste. |
yup hence the 16.5/17.5m figures, so not alot in it really!!
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not sure you'll notice a massive difference going from 17.5 to 21m; if you suddenly tried something with (say) a 40m turn radius, you would find that you need to put a lot more "input" into each turn, which is possibly a bit of a pain on piste if you like carving all the time, but actually gives you more control in soft snow
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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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| kitenski wrote: |
Ok bear with me on this!
So skis have a given radius, I assume that means if I put the ski on edge and do nothing else it will perform (roughly) the specified radius turn. |
Don't think so, the radius refers to the size of a circle of which the edge forms a part (whilst flat)
| Quote: |
| However if I apply more pressure, would that ski then be able to turn a shorter radius and vice versa, less pressure a longer radius? |
Yes, as it should "dig in" more underfoot. Angle to snow should have a bigger bearing though.
| Quote: |
Or put it another way, if I moved off my Scott Missions with their 17.5/16.5m radius to something with a radius about 21m, what difference would I notice?
Cheers,
Greg |
Probably
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Skis bend and form an effectively shorter radius as you apply more pressure. So ski stiffness is at least as important as static geometrical radius in determining the feel. So if you go to a 21m radius ski that is also seriously stiff, you will notice a huge difference compared to your Missions.
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Once skied the same ski in three different sizes 166, 176, and 186 each with a corrsesponding increasing radius. I'm ca 172 cm tall. The 166 was easiest for short turns but was more difficult to control in the offpiste being the most nervous of the 3 sizes. in comparison to the 166 the 186 felt like I'd gone from driving a mini to drive an articulated truck. The turns esp short turns were a real effort and within a couple of hours my legs were knackered.* The 176 gave the best compromise and felt more like an agile saloon. Not too much work on piste and plenty enough float / stability in the soft stuff.
*I suspect the construction of the 186 ski was also a lot stiffer and I'd echo the comments above about ski stiffness.
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If I'm carving a turn and apply more pressure (or let too much pressure build up) the ski 'chatters' because it can't grip the snow for the radius of turn I'm trying to force it to do. Getting a bigger edge angle seems to be the way to tighten the turn without having the ski lose grip.
I might be wrong but I think the turn radius marked on the ski is the maximum radius turn it can do when you only use edge angle to steer your turns.
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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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| rob@rar wrote: |
I might be wrong but I think the turn radius marked on the ski is the maximum radius turn it can do when you only use edge angle to steer your turns. |
I thought it was simply the plan view geometric sidecut radius with the ski completely unloaded. Even when steering with edge angle only by rolling the ski, you are still also applying pressure from your weight and lateral G. It's impossible to completely separate the two mechanisms, although you can obviously change the emphasis between pressure and edge angle.
* Your definition probably amounts to the same thing. But the real life maximum turn radius of any ski will vary with skier mass due to the bending.
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| uktrailmonster wrote: |
| It's impossible to completely separate the two mechanisms, although you can obviously change the emphasis between pressure and edge angle. |
Yes, I agree. I think what I'm trying to describe is excessive pressure, trying to force the ski around a tighter curve than the edge angle alone would take the ski. With excessive pressure (which as you say might simply be the result of weight and lateral G loading) the grip on the ski breaks, negating the benefit of bending the ski into a tighter radius.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| rob@rar wrote: |
| uktrailmonster wrote: |
| It's impossible to completely separate the two mechanisms, although you can obviously change the emphasis between pressure and edge angle. |
Yes, I agree. I think what I'm trying to describe is excessive pressure, trying to force the ski around a tighter curve than the edge angle alone would take the ski. With excessive pressure (which as you say might simply be the result of weight and lateral G loading) the grip on the ski breaks, negating the benefit of bending the ski into a tighter radius. |
All true, but the breaking point you describe will vary with different snow surfaces, so you would never be able to define a single radius number from it. So I think the radius number quoted is just the geometric sidecut radius, not the real life max radius it would carve on edge (which will be determined by skier mass and snow surface)
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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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and all this only applies when you are skiing on hard snow. If the ski is buried in soft snow, you are using its flex rather than its edges to turn
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| Arno wrote: |
| and all this only applies when you are skiing on hard snow. If the ski is buried in soft snow, you are using its flex rather than its edges to turn |
Yes, absolutely.
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You know it makes sense.
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| uktrailmonster wrote: |
| All true, but the breaking point you describe will vary with different snow surfaces, so you would never be able to define a single radius number from it. So I think the radius number quoted is just the geometric sidecut radius, not the real life max radius it would carve on edge (which will be determined by skier mass and snow surface) |
So would it be more accurate to describe ski radius as the maximum theoretical radius that the ski could carve?
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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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rob@rar,
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I think the turn radius marked on the ski is the maximum radius turn it can do when you only use edge angle to steer your turns.
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If you only use edge angle to turn (ie no pressure) the ski cannot bend then won't have an arc to turn on. To describe turn radius in this way would be a difficult thing to measure as it would depend on the ski stiffness how much pressure is applied and the skis side cut. Indeed a ski put on edge with no pressure would probably want to travel the opposite direction if it has any camber (waist is higher than the tip and tail when lying on its base).
The radius is a description of the sidecut of the ski. Imagine that the arc of the sidecut of the ski is part of a circle. If you completed that circle its radius is that of that ski. More side cut = smaller circle = shorter radius = easier to make shorter turns.
When put on edge only the tip and tail of the ski touch the snow but all of the skiers weight is pressing in the centre so the ski bends into an arc until its waist also contacts the snow. The ski tracks along this arc resulting in a turn.
A ski with more side cut (smaller radius) can in theory be bent into a tighter arc (the arc on which it will turn) when put on edge so should be easier to make short turns on. How easily this can be done will also be affected by ski stiffness, skier weight, how fast your travelling and how much you edge the ski.
There are other factors that affect how a ski feels: stiffness Stiffer skis may take more force to bend but will probably grip better but might not feel as nice on powder, different tip shapes can affect how easily the edges engage. Some skis ski shorter than others of the same length depending on the length of their contact surface. Scott use this well to make skis ski short on piste but allow the full length to come into play in softer snow. In combination with the dual radius which is supposed to allow skis to turn tighter arcs on firm snow but be less hooky on softer snow makes skis that can deal with a variety of conditions. The idea being that the longer radius comes into play first (ie when the ski is being used less agressively) and the shorter radius becomes effective when the ski is pushed harder. IME this works well for all mountain skis.
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Poster: A snowHead
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| rob@rar wrote: |
| So would it be more accurate to describe ski radius as the maximum theoretical radius that the ski could carve? |
I don't think you could even carve that big, there has to be some element of angulation involved to carve.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| Quote: |
So would it be more accurate to describe ski radius as the maximum theoretical radius that the ski could carve?
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It would be a nice figure but as there are so many variables would ultimately be little more use (IMO) than describing radius as a measure of the arc of the side cut which is at least a figure that can be measured and stated as is rather than one which can be determined and stated providing that x,y and z all have certan values which would in reality vary from skier to skier slope to slope day to day etc etc.
I might be more interested in what is the smallest arc it could carve 
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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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RPF, Yes, you expanded on what I was trying to say. It's only practical for ski manufacturers to quote a simple geometric sidecut radius. A 17 m radius sidecut does not translate to a 17 m maximum pure carved turn radius. As RPF says, there are loads of other variables involved.
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You need to Login to know who's really who.
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kitenski, You're solution here is to buy both the Shamans and the Nomads off kiwi1, with the super cheap prices he is doing at the moment you get both for the price of one really, this helps you in two ways:
You get off piste skis with both a shorter and longer turn radius.
You really annoy your mates with the Nomads as they will have paid more (and have no Shamons to boot). 
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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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Oh dear - another 24 pages maybe?
Sidecut radius: as explained by RPF and uktrailmonster, refers to the geometry of the ski, and as explained by rob@rar, would be the maximum radius the ski would carve, if you could engage the edges with no sideways slippage at an infinitessimal edge angle.
Carved turn radius: when the ski is put on edge and pressured sufficiently for the edge to be in contact with the snow along its whole length (which should be adequately done my simple body weight for ordinary retail skis), the ski will turn with a radius approximately given by sidecut/cos(angle between ski base and snow surface). On hard snow extra pressure will not change the radius of turn, just result in more sideways force for the ski/snow interface to have to withstand, and eventually cause the ski to break away.
Stiffer skis: transmit more of the force applied by the lump on the ski (you) from the binding position towards the tip and tail (it requires a higher bending moment to acheve a given deformation, i.e. higher force required for given strain at the extremities), so evening out the pressure applied to the snow along the ski edge. Result in a higher performance as it minimises the excess pressure applied to the snow under the binding for a given total force exerted on the rider, and so minimises the chance of the ski breaking sideways. As you get into race ski stiffness, simple body weight will start to become insufficient to bend the ski sufficiently for tight turns at slow speeds. A stiffer ski will also grab more at tip and tail as the camber resists more, so will be harder to twist in dinky skiddy turns.
Soft snow: ski is bent by the force applied at its centre (by you) being distributed along its length and pushing against the snow, so pushing it out the way. The more snow you move underfoot vs at the extremities the more the ski bends. So a softer ski will be easier to turn in soft snow by applying pressure. A stiffer ski will require more force (weight and centrifugal) to get a given bend, so will be more suitable for heavier and faster skiers.
I ski mostly slalom skis (radius around 11m) and off-piste sks (radius 25m). When I first got these off-piste skis (slightly longer radisu and stiffer than my previous Legend 8000s) I tried skiing it the same way as the slalom skis, and fell over to the inside of the very first turn. A longer radius ski requires more angulation for a given edge angle as you have less radial acceleration to hold you up, and if they are a bit stiffer you have to concentrate a bit harder at weighting the outside ski - otherwise it tends not to decamber and just runs straight.
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| GrahamN wrote: |
| On hard snow extra pressure will not change the radius of turn, just result in more sideways force for the ski/snow interface to have to withstand, and eventually cause the ski to break away. |
Thanks, that's what I was trying to explain earlier but with less clarity than you. I had a "light bulb" moment when by taught GS by Phil Smith a few seasons ago when he kept telling me less pressure and more angle to make a fast, tight turn. That was counter-intuitive for me as I'd always tried to apply more pressure to make a tighter turn.
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GrahamN, So true....
I always used to be more one footed through a turn... and was never able to be convinced on an even split anyway... so never got that concerned about it.
Two things I have noticed with new TT skis that may be a tad short... and this applies even more with a plate in the binding...the centre of the ski becmes noticaby stiffer and you can get this shoot off where you expect a bite... and when you aren't concentraing....
This and the TT tail means that on-piste you really need to last few cms to be working out of a turn otherwise a spin can occur. the trick is getting to know your skis and adjust.
The benefits are all off-piste IMV..as you can go for that faster GS turn as the shorter turned up tail still engages in deep snow....
This is also why you no longer need soft skis Off-piste...IMO. A stiffer ski will have returns on-piste..whilst the snow build-up can bend it easier than you'd imagine. You have to find this out the hard-way and be open to adjust. Therefore, you need to have a few different methods of turning to get this quickly. All this isn't really an issue in light fluffy snow, but will come to the fore in heavier stuff..
My method now is point them and react.....
So, to summarise... faster GS turns need a stiffer tip... little s's for a softer ski, or let the snow flex the stiffer ski and go with the rhythm to bounce the s''s
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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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42m = sidecut perfection. Sack up.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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parlor, when did you last do a turn? 
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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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I'm still too jetlagged to do any of this sciency stuff, but I feel that longer radius and stiffer is more fun in general as you get more feedback and energy. Short radius turns might be easier on SL skis but they're a lot more challenging/fun on 37m radii skis (Not actually sure what 196 Lhasa radius is). The impression I get is that stiffer/longer rad means more steering is required, or getting edge a lot earlier in the turn.
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| rob@rar wrote: |
| GrahamN wrote: |
| On hard snow extra pressure will not change the radius of turn, just result in more sideways force for the ski/snow interface to have to withstand, and eventually cause the ski to break away. |
Thanks, that's what I was trying to explain earlier but with less clarity than you. I had a "light bulb" moment when by taught GS by Phil Smith a few seasons ago when he kept telling me less pressure and more angle to make a fast, tight turn. That was counter-intuitive for me as I'd always tried to apply more pressure to make a tighter turn. |
 Except that surely the more angled the ski, the more pressure required to get the edge to be in contact with the snow along its whole length? I'm working on getting as much inclination as I can as early in the turn as I can manage (making progress but not there yet) and this needs extension and pressure early in the turn.
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You know it makes sense.
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| Quote: |
| On hard snow extra pressure will not change the radius of turn |
I don't follow this logic (and that's coming from 4 years of mechanical engineering experience).
I completely understand how greater edge angle will reduce the arc of the ski-snow interface and therefore the 'turn radius'. But surely an increase in pressure on the ski (forward lean into the boot) causes it to flex to a greater extent, also causing the arc to reduce? 
| Quote: |
| Except that surely the more angled the ski, the more pressure required to get the edge to be in contact with the snow along its whole length? |
This is true, but as others have already stated, it may only require the weight of the skier to put the whole edge in contact with the snow...
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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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embramalc, the torsionally stiffer a ski, for any angle at which the ski edge is placed, the narrower the range of degree/extent of flex at which the whole edge would be in contact with the snow.
Not sure but not convinced that weight alone would be enough to flex the ski sufficiently to put the whole edge in contact with the snow when the ski is very edged. I think that additional forces generated in the turn passively or by active direction might be required, hence the whole extension/pressure/redirecting CoM in flowline thing
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Poster: A snowHead
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| embramalc wrote: |
I completely understand how greater edge angle will reduce the arc of the ski-snow interface and therefore the 'turn radius'. But surely an increase in pressure on the ski (forward lean into the boot) causes it to flex to a greater extent, also causing the arc to reduce? |
Sorry, maybe a bit OT here - but does driving the tounge of your boot add more pressure? After a full season of "stay centred, be centred, just flex when you need to to control pressure" with CSIA style training, leaning into the front of the boot is counter-intuitive to what I've learned. "Get forward" is a dogma I've heard repeated a lot, but I can never tell if people think their CoM should actually be in front of their BoS or it's from instructors trying to get their back seat skiers forwards...
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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"What effect" not "What affect".
Sorry, but it has been driving me mad in too many places recently.
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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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| embramalc wrote: |
| Quote: |
| On hard snow extra pressure will not change the radius of turn |
I don't follow this logic (and that's coming from 4 years of mechanical engineering experience).
I completely understand how greater edge angle will reduce the arc of the ski-snow interface and therefore the 'turn radius'. But surely an increase in pressure on the ski (forward lean into the boot) causes it to flex to a greater extent, also causing the arc to reduce?
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If you imagine an infinitely hard surface, once the skis are in contact along their full length and the edges are engaged, you can't physically deflect them any further with pressure. Hard snow may not be infinitely stiff, but it's a close approximation. Soft snow on the other hand is compressible, so you can easily deflect the ski into it with increasing pressure.
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You need to Login to know who's really who.
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| DaveC wrote: |
| embramalc wrote: |
I completely understand how greater edge angle will reduce the arc of the ski-snow interface and therefore the 'turn radius'. But surely an increase in pressure on the ski (forward lean into the boot) causes it to flex to a greater extent, also causing the arc to reduce? |
Sorry, maybe a bit OT here - but does driving the tounge of your boot add more pressure? |
No, it just moves the centre of pressure forward. Increased pressure is achieved more by changing weight distribution across the skis (i.e more weight on the outside ski) and extending the outside leg in the turn (i.e. pushing down through the sole of your outside boot).
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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, thanks, nicely put. That's what I feel in my own skiing. Is there ever a situation that you want to be driving your shin into tounge?
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DaveC,
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| Is there ever a situation that you want to be driving your shin into tounge? |
For me, yes. If I'm being particularly aggressive on harder surface I find it works well in initiation phase..
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| DaveC wrote: |
| uktrailmonster, thanks, nicely put. That's what I feel in my own skiing. Is there ever a situation that you want to be driving your shin into tounge? |
That's a good question. I was taught (a long time ago) to drive my shins forward into the boot to get my weight forward and help the ski tips to bite on turn initiation, but I'm not sure it's such a good idea with modern recreational skiing. I now go for a less aggressive centred approach with just a little light pressure on the front of the cuff. It seems to work well with modern skis, which initiate turns easily anyway, and takes less physical effort.
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My skins used to get sore... no longer see the need to do that, anymore...plus I'll wear the socks full lenght as well
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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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with old skool straight skis you needed to pressure the front of the boots to engage the tips of the ski. With carving skis you want to achieve higher angles and have the force transmitted through the centre of your boot onto the engaged edge allowing it to turn itself. Over pressuring the shins will cause the tails of the ski to wash out.
instead of actively pressing both your shins into the tongue of the boot and trying to get forward, think SHIN PRESS on the inner ski and SHIN TOUCH for the outer ski, this will pull in your inner foot and keep you stacked on your outer leg.
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Interesting point. I generally reckon if you don't have bald patches in your shin hair then you're not trying hard enough (for chaps, obviously. Or maybe German women. ). But it's funny how different skiing attitude translates into different shin pressure.
Case in point - a long weekend in Feb and they were bald and sore, nearly to the point of scabbing. However, after a week's skiing in April with the family, (longer to enjoy, more chilled) the hair barely wore away.
It's good to play with how much tongue pressure you're applying, as well as where your COG is relative to the ski, carve angle etc etc so you can switch modes when the snow or your mood dictates.
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FAQ
