 Poster: A snowHead
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I've been doing a bit of fag-packet calculations and basic modelling on the forces involved with using fat skis on piste. It seems that as a ski gets significantly fatter than say the natural width of your foot, the lateral or side forces on your knee go up significantly. This isn't an issue in powder or soft-snow where the pressure is evenly across the base of the ski so the forces act up the leg, but when on piste with the edge biting into the hardpack.
Without wanting to rewrite everything here, this is the article : http://www.powpowpow.org/could-fat-skis-cause-knee-problems-in-the-longer-term/
I welcome discussion, comments and critique. I know I'm no expert but I think it's an interesting topic for discussion.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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I'd say you need to factor in how your ski style changes with fats on. From my own experience when I'm using my fatter skis (108mm) on piste I tend to ski more relaxed, I'm not attempting consistent carved turns , the turn radius is naturally larger than my shorter , thinner (SL--ish 65mm) skis. Also I guess the flex and user friendliness of skis comes into play. Most fatter skis will be softer than more piste orientated skis, that's got to have an impact one way or the other. I'd say there's too many variables to make a concrete conclusion. If I take out my SL skis for a day I think my knees ache more than a day on my fat skis but then if I have fats on I'm probably off piste rather than on hard piste.
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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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I'm not considering purely carved turns. Any turn where the ski is on the edge, whether it's carved or skidding/slipping, the ski will be wanting to lie flat and so as long as you're off the flat, you'll be exerting those forces on your knee.
As you say, you'll probably take your piste skis out if you're going to be skiing more on-piste, but my thoughts are more aimed at the skis that are being marketed as 'all mountain' and 50/50 piste/off-piste which are now exceeding 100mm in width underfoot. In those cases, I can envisage people skiing on-piste far more with what I consider 'fat' skis.
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feef, interesting little read, I think maybe the length of ski has something to do with it, sometimes fatter skis are longer than normal piste skis?
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Those who ski fat skis on the piste are still relatively few compared to the number of piste skiers.
Those who do would likely be younger and fitter so perhaps more able to cope with these forces in the short term.
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But hey I am tup creek "younger fitter" nope 
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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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feef, no question that they put additional strain on your knees IME but whether you notice might depend on whether you've already got a weak knee. I have a partially torn ACL/meniscus/worn patella and can only do about 2 hours on my fat skis (110mm) on or off piste before it aches too much and I have to pack up. I can ski all day on my 79mm skis without a problem. Before I had the injury I don't recall any differences in feeling/reaction between ski widths and my good knee is still unaffected.
PS Your diagram at the top of the page doesn't display properly (won't scroll) in IE11.
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livetoski, I don't see how it would, as the castor effect is being produced primarily be the part of the ski underfoot and it would be a right old bit of noodly rubbish if you could get part to flex laterally.
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| Raceplate wrote: |
PS Your diagram at the top of the page doesn't display properly (won't scroll) in IE11. |
The diagram at the top is just a crop image of the full size one in the article, it's not supposed to scroll 
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| livetoski wrote: |
feef, interesting little read, I think maybe the length of ski has something to do with it, sometimes fatter skis are longer than normal piste skis?
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Not if you consider it only from the view of lateral forces. Certainly a longer ski will affect torsional forces as the ski acts as a level in the same plane as the snow. The lateral forces is as the ski tries to lie flat and that would be the same force whether the ski was 30cm long or 30m long (not taking into account the effects of the weight of the ski itself)
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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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under a new name,
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as the castor effect is being produced primarily be the part of the ski underfoot
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Yep agreed, I was thinking more of the general stresses being placed on the knee by the length of ski as well as the width, I am no expert on the dynamics, but find that as Waynos said above short, stiff SL skis make my knees hurt more than my long softer fat skis, but I am sure that is down to skiing style of fat skis.
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| livetoski wrote: |
under a new name,
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as the castor effect is being produced primarily be the part of the ski underfoot
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Yep agreed, I was thinking more of the general stresses being placed on the knee by the length of ski as well as the width, I am no expert on the dynamics, but find that as Waynos said above short, stiff SL skis make my knees hurt more than my long softer fat skis, but I am sure that is down to skiing style of fat skis. |
This is a perfect example of what I'm saying tho. Referring to knee pain due to ski type doesn't mean it's due to this particular force in isolation or some other factors. There are so many ways we can tweak our knee in skiing that the effects of an increased lateral force due to ski width could be ignored or overlooked in favour of the more common issues.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| feef wrote: |
| Raceplate wrote: |
PS Your diagram at the top of the page doesn't display properly (won't scroll) in IE11. |
The diagram at the top is just a crop image of the full size one in the article, it's not supposed to scroll |
So why put a scroll bar at the side? Why not put "click for full size image" instead?
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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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odd.. no scrollbar here. Can you screenshot it and mail me it? I'll PM you an email address
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feef, Interesting. I haven't used snowblades for some years, but I did notice, when I had the odd few hours on them, that they made my knees ache significantly more than ordinary piste skis. They are, of course, a lot wider. Maybe the effect is similar? Of course most people on snowblades are young and fit (and arguably daft) not OAPs.
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You know it makes sense.
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| feef wrote: |
| odd.. no scrollbar here. Can you screenshot it and mail me it? I'll PM you an email address |
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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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That's very odd. I think IE11 is putting that in, but for no good reason as the full image is being displayed, there isn't anything else TO scroll on that one 
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Poster: A snowHead
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feef, start a new thread. Could fat skis cause display problems in Windows? 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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feef,
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| as the full image is being displayed |
I don't know much about these things but maybe it's not the full image? It does actually scroll a few pixels but that's all.
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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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| Raceplate wrote: |
feef,
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| as the full image is being displayed |
I don't know much about these things but maybe it's not the full image? It does actually scroll a few pixels but that's all. |
I'll try with a different image, that could also solve any confusion with readers thinking there's more to see in the 'featured' image than there actually is.
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livetoski, I don't think ski length is involved. I can find some muscles more tired on my SLs but that's because I'h hooning around doing lots of tight carved turns so having to cope with higher forces.
On my widest skis which are only 98mm I can feel some knee pain, that I have been putting down to exactly what feef is discussing.
And I get neither from my longest GS skis at 191cms. Even when hooning around doing great big carved arcs.
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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 had a comment from a Biomechanist who concurs with what I've suggested, so it's nice to know I'm on the right track
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I haven't noticed any difference in my leg muscles or knee joints after skiing on fats on piste, and I believe I'm super tuned to my body's signals (I would have said very tuned but if we're talking about fats then let's use the appropriate vocab).
In 3D snow it was an entirely different story, it was definitely easier and my legs and knees did not tire as quickly as before when I skied on my skinnies (which are more mid-fat than skinny, at 90mm).
That's not to say I carved on piste though — I still haven't got the hang of this carving fandango...
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after a very big day in powder I recall being very surprised to see my knees quite "puffy" and swollen - definitely a result of a big, non stop day out. I was on about 100mm underfoot , but in very soft fresh powder. Subsequently I have found it so inch less effort on super fats ( 135mm ) on those kind of days it makes me think that what you are saying must have some sense and therefore make ski selection more important in the long term.
So I think you have justified my unruly quiver!
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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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mishmash, What I'm saying isn't relevant to those cases. What I'm saying is using a fat ski on the piste, rather than in the powder, could result in some greater-than-normal lateral forces on the knee. But yes, it can justify a quiver as you want narrower skis for the piste and keep the fatties for the pow.
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feef,
Interesting hypothesis.
My thoughts are:
They'll be no change of angle at the ankle because of boot.
In theory they will be slightly increased load on the medial collateral ligament if on an edge on a hard piste, the difference between a 90 and 100mm underfoot will be minimal as it will be a 5 mm displacement of contact point.
ACL
Four main ways of rupturing
Hyper extension : cannot see any effect of wide ski
Boot induced ( fall directly back wards) : can't see an effect
Phantom foot ( fall backwards whilst falling into the slope with uphill hand back) : can't see any effect, if anything piste ski more waisted therefore potentially worse as this injury relies on the back of the ski aggressively carving.
Slip catch: downhill ski washes out and rapidly re-grips: described in racers not one for fat skiis, I suspect..
Powder is a risk factor for ACL so may be an association with fat skiis but more the powder than the ski.
MCL.
In theory possibly more load but this would only be relevant if the skier had absolutely perfect body position otherwise the out of position hip , pelvis would be far more likely to alter load at the knee( think skiing in a knock knees position due to poor hip and pelvic alignment)
I suspect that the number of variables of snow, vis, boots, technique fitness etc are so large that that any effect would be very marginal.
Hopefully that justifies my narrowest ski in last 5 yrs as a Mantra
Jonathan Bell
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| Jonathan Bell wrote: |
feef,
Interesting hypothesis.
My thoughts are:
They'll be no change of angle at the ankle because of boot.
In theory they will be slightly increased load on the medial collateral ligament if on an edge on a hard piste, the difference between a 90 and 100mm underfoot will be minimal as it will be a 5 mm displacement of contact point.
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between 90 and 100 I agree, but, for example, my all mountain skis are 85 underfoot and the Volkl Gotama is 107, that's a much bigger difference. What sort of forces are we talking about, and what sort of factor of increase would we see if, at an extreme case, you increased the width of the ski from 76 (Rossi Purist elite) to 106 (Rossi Soul 7). If you're used to skiing on 76 and then change to a 106, would the increase be sufficient to be noticed simply because your body isn't used to the increased lateral forces?
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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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Aren't there other factors in the skis construction which influence this also? I got a pair of Line Prophet 98's last season and was very surprised just how easy they are to get on edge and ski on piste. Not tiring on the knees/legs at all. OK I know they're not "that" wide.
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I think there's a little discussion relevant to this in "How to make a ski hold" in Chapter 8 of "Ultimate Skiing" (I happened to be reading that section this morning)
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You know it makes sense.
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| Claude B wrote: |
| Aren't there other factors in the skis construction which influence this also? I got a pair of Line Prophet 98's last season and was very surprised just how easy they are to get on edge and ski on piste. Not tiring on the knees/legs at all. OK I know they're not "that" wide. |
With a waist of only 98 they probably aren't any wider than your natural foot and/or ski boot so I wouldn't expect there to be a significant issue there as it's within what's 'normal' for your body. I'm only considering cases where the ski is wider than the foot/boot such that you're levering yourself up off the ground, not just leaning on an edge
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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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| Princess? wrote: |
mishmash, puffy knees  Are you what we would politely term 'a mature vintage'. |
I m a mature cheddar not an extra mature cheddar!! This was after 8,000m of powder vertical. It s not an effect I had observed before but you are right , maybe its because I'm getting old... But thats quite a few Grands Montets in your language, on a 98mm ski from what I recall. Pre-op..... Still prepared to take on all comers tho'!
"But yes, it can justify a quiver as you want narrower skis for the piste and keep the fatties for the pow.." - Thats what I m talking about - I wasn't fat enough! (ski wise..)
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Poster: A snowHead
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I tend to feel my knees creaking following a couple of weeks hooning around on my DPS Wailers which are 112mm underfoot. I think I'm willing to put up with a bit of discomfort following a trip away, knowing that it will have cleared up after a couple of weeks at home. I'll agree that it's probably down to the increased amount of torque required to get them on edge. However, once on edge they carve very well, even on quite firm pistes; modern fat skis have way more torsional stiffness when compared to ~100mm width skis from a few years ago. Those things would just wash out and judder in the same circumstances - they just didn't want to be up on edge. Also, can't help thinking that fat skis on piste expose any deficiencies in lateral alignment very quickly. I can only use myself as an example as I have a bit of a varus in my right foot (a bit knock kneed on my right side) and this usually results in my right IT band being sore after a trip. I wear orthotics to correct this but maybe the right side one needs tweaking a bit. I'm quite lanky also, so don't have to use as much force as a shorter legged person to generate the same amount of torque on the binding. So, all other things being equal, maybe those shorter in the leg suffer more than I do. And finally, I think I use a bit too much knee angulation and not enough hip angulation when carving large radius turn and this can't be helping. An interesting study but is there any existing literature out there? Would also need to consider the stack height of the binding too.
Last edited by Poster: A snowHead on Thu 14-11-13 1:43; 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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feef, I too have 98mm skis on a 98mm lasted boot - perfect all rounder IMHO. You can feel the difference though when swapping to much fatter skis, same as you can when putting a pair of narrow SL's on.
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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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| feef wrote: |
| With a waist of only 98 they probably aren't any wider than your natural foot and/or ski boot so I wouldn't expect there to be a significant issue there as it's within what's 'normal' for your body. I'm only considering cases where the ski is wider than the foot/boot such that you're levering yourself up off the ground, not just leaning on an edge |
Not sure whether the width of the foot or the width of the contact from ski boot to binding is what you would be looking at. In a 26.0 boot a width of ~100mm is pretty common, however I've just looked at the sole of my boot and the width of the sole piece that connects to the binding is only ~70mm so there is a significant difference there.
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| charlie.wilkinson wrote: |
| feef wrote: |
| With a waist of only 98 they probably aren't any wider than your natural foot and/or ski boot so I wouldn't expect there to be a significant issue there as it's within what's 'normal' for your body. I'm only considering cases where the ski is wider than the foot/boot such that you're levering yourself up off the ground, not just leaning on an edge |
Not sure whether the width of the foot or the width of the contact from ski boot to binding is what you would be looking at. In a 26.0 boot a width of ~100mm is pretty common, however I've just looked at the sole of my boot and the width of the sole piece that connects to the binding is only ~70mm so there is a significant difference there. |
As the ski, binding and boot effectively become one fixed and rigid object, the width of the boot sole isn't relevant.
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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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Jonathan Bell, terrif, just wanted I wanted to hear. This thread had been making me nervous, as I've just replaced a 75mm all-mountain ski, with a slightly longer (158 instead of 152, but rockered) 85mm one and was wondering whether prolonged use on piste would affect my slightly dodgy knees. I feel reassured that the minor difference won't have any adverse effect, but will be of assistance - as felt the case when I tested them - in variable conditions, as well as off-piste. Thank you, as always, for posting your thoughts.
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I had posted here last year on a different thread but a similar topic, over the past two years speaking to mountain rescue crews in Canada and a number of European resorts, they have all said anecdotally they believe there is a relationship between an increase in accidents and injuries and the extend use of fat skis (100M or greater under foot). Intrestingly enough they were talking about accident on PISTE!!!!! Not in the back country where these skis see most of their use.
The factors and reason are below. I don’t think anything under 90 could really be considered a fat ski!
- Lack of control on Icy piste – Increased collisions
- More slow backward falls due to lack of control and balance on the ski
- Inexperienced skiers using fatter skis to keep up with marketing/ fashion trends
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Fattes13,
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I don’t think anything under 90 could really be considered a fat ski!
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Even if you're a lightweight midget? I suppose mine aren't fat, exactly, but they're not a skinny piste ski, for sure.
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feef,
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As the ski, binding and boot effectively become one fixed and rigid object, the width of the boot sole isn't relevant.
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So if the binding is made wider to accommodate fatter skis would this help?
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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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| livetoski wrote: |
feef,
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As the ski, binding and boot effectively become one fixed and rigid object, the width of the boot sole isn't relevant.
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So if the binding is made wider to accommodate fatter skis would this help? |
no.The distance from the edge of the ski to the centerline running down through your leg from your knee is the relevant measurement. What and how you're attached is irrelevant when the whole lot becomes one system
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Fattes13, interesting. I could believe that.
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FAQ
