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Can someone clear up the relationship between ski length, ski flex, and skier weight?

post #1 of 26
Thread Starter 

 

Hi all - This developed in Dawgcatching's typically excellent gear review of 80-100 mm skis, after two back and forths, thought it really belonged over here. The reason I want to pursue it is that although the title question seems du'oh, the more Dawgcatching and I got into this, the more we began to question why skis come in different lengths. He brings in the idea that it's the distance from the tip to the skier that counts, (apparently to control tip deviation and steering), not anything about longer skis being stiffer or better for bigger guys. Resistance to bending, I find contrary to popular belief, may not change regardless of ski length since it's determined by cross sectional area. OTOH, I'm having issues trying to comprehend why manufacturers, magazines, charts in stores, and so on all appear to consider lengths as accommodating different sized skiers, if size has nothing to do with it. I'm suspicious of how we define "flex." So read on, and for the love of (deity of your choice) will an engineer or physicist here please settle this? "It all depends" answers will be judged as cop-outs, incidentally. We already know it all depends...wink.gif

Me first:
Originally Posted by beyond View Post

Appreciate the work here. Question: You tend to review lengths in the middle of the range, which makes sense for a variety of reasons. But I wonder to what extent your take is influenced by that length. For instance, you reviewed the 180 length of the Atlas, and as far as I can tell, that's also the length that SJ mentions with a different take on it; obviously you guys have very different weights. So do you think that your reaction to the 173 would similar to his on the 180? Or would the Nordicas you skied in 178 be less "stout," better in bumps, in 170? 

 

I ask because there's a larger issue under this: If a ski is too stiff, or too soft, is it more reasonable to go to a different brand at the same length, or stay with the brand but change lengths? 


This is Dawgcatching now:

 

Good question. With the Atlas, the 180cm is the right length for me. It has early rise tip and tail, and it has a shorter running surface than many of the skis I reviewed. ...

 

On the Nordicas, I used to ski 170cm in all but their Enforcer (177cm).  I stepped up to the next length, as I have improved a lot the past 2 years and am skiing faster now. Also, my everyday skis were on the longer side (Kastle MX78's, Elan 1010's) and I wanted to compare apples to apples.  If I had more demo time, I could easily review the same skis in shorter lengths, and come up with much different feels for each (like what happened with the Mantra).  For bumps, no question the 170cm would be superior. But, I would want more ski elsewhere. 

 

Going down a size on a stiffer ski will make it feel more like a stiffer power carver, which is exactly what we would have on the Nordicas in 170cm, Elan 82Xti in 168cm, Blizzard 8.1 and 8.7 in the 172 and 174cm lengths...

Me again:


Thought this was worth more of a debate. Here's my problem, let's take the the Nordica's we're both talking about. They have three lengths: 170 is the middle, and 178 is the top. That means that by their own design parameters, the 178 is aimed at the heaviest 1/3 of the skier population. Now the average male your age in the U.S. is 182 lbs. You are below the 25th percentile, actually, for weight, and below the 40th for height. So no matter how hard you ski, or how much better you have become recently (and there's solid testimony here you're an expert skier with thighs of steel) , you're now skiing on a ski that has a flex engineered for guys 50 lbs heavier, who presumedly are not cruising the blue runs. Sierra Jim is also an expert skier, and a former Level III. You guys are generally on the same ski lengths. (Say the Atlas 180.) 

 

So by what criteria do you assume that running lengths typically corresponding to 177-178 is "your length?" Seriously, not trying to say you don't have a right to ski on any length you want, or even that it isn't your "correct" length, but rather trying to understand how this idea of "my length" is arrived upon. Because in a practical sense, it colors everyone's reviews, everywhere. It's been said here that the impact of difference in lengths is greater than the impact of difference between brands, and most tended to nod their, ah, keyboards. I also note that we all ski on shorter skis as they get narrower, reverse.  Yet many of us, not just you, are convinced they have an optimal length ski, no matter. Frankly, I find the "eyebrow/forehead" criteria kinda unsupportable in any systematic way.

 

So I'd argue that there is no "my length," that there's a "my flex." It's based on weight, typical speed, and style (power vs. finesse). If the flex is wrong, the length is wrong. And if a ski is too stiff, say the Atlas 180, then the next length down will be softer flexing. That doesn't make it a fat carver, just a softer flexing version of the same ski. Unless you want to define all skis that are below 175 as carvers...

 

 snowfight.gif

Dawcatching's response:

Thanks for the note.  Yes, I agree with you based on flex, yet the downside is that, when skiing fast in cruddy conditions, I need the running length that a certain length ski gives me.  I really liked that Mantra in 170cm (too much ski in 177cm) but 170cm can toss me around in cruddy snow, which is why I wouldn't buy a ski of that length. Likewise, the AC50 is great in 170cm, but that is more of a carver, and for frontside use, 170cm is plenty of ski.  The real key to finding the "perfect" ski is getting the running length required for your conditions (shorter if you live somewhere that doesn't have new snow, has small hills, has tight spaces), or longer based on how fast one skis and how skilled they are (I skied a few runs last year with Eric Deslauries and he is a little shorter than me, weighs a bit more, and was on 191cm Sollie Shoguns for an all-around soft snow, crud, and bump day-being a world class skier has it's benefits).  Once you have that dialed, the next step is getting a favorable flex for speed and skiing style, as well as height and weight.  I don't think anyone can say exactly what that is for every ski they are interested in, without trying a bunch of skis.  

 

With regards to overall length and flex: most skis don't change layup in different lengths, so their flex (deflection under force) won't change. What does change is that a ski with a really stiff tip still has that stiff tip, but it is closer to the skier, and easier to get to the front of the tip and pressure, as well as tip it.  I would argue that I am not flexing a short ski any more than on a longer ski, but I am engaging the tip on a stiffer short ski in a different way than, say on a longer ski, with softer tip, where I can do that "pedal move" where I relax, pull back, pressure the tip, then push the feet forward to engage.  On a really stiff ski, no matter the length, I have trouble doing that, and end up skiing more sidecut and less dynamically.  

 

To answer your general question, I arrived on what is the "correct" length by trial and error.  I found the skis that work well for me in a given length and those that don't, more or less.  I wish I could come up with some magic formula, but am afraid I don't have one. With that said, there are skis that work in more than 1 length (such as the Blizzi 8.1 in 172cm (frontside carver) and 179cm (really stable all-mountain ski). I have typically found a running length (approximate, of course) that works well in softer snow to keep me up and keep from fighting tip dive. 

 
Then my response: 

 

OTOH, think we we define flex differently. OK, let's say construction won't change, although it seems a bit murky whether makers try to create the same handling for target skiers appropriate to each length by changing stiffness, sidecut, or whether they let length itself take care of that. Anyway, resistance to bending - called the second moment of inertia as I recall - will be determined purely by cross sectional area, shape (I-beams versus rectangular say). It has nothing to do with length, far as I can tell. So you're right. But the force that will overcome that resistance is partly determined by skier weight (M x a), yes? OK, hold that thought.

 

Second, polar moment of inertia, vaguely recall you have to tweak it to use for non-circular cross sections, will be resistance to torsion along long axis (think twisting a towel between two hands). So in theory length matters for torsion.

 

I'm also thinking that the actual force being applied against resistance is relative to sq cm of running surface, which will change as the ski gets longer or shorter, and that everyone in the known universe seems to think that heavier guys will flex a ski of given length more than lighter guys, especially the folks making the skis, but maybe they're calling something else flex. Not sure. 

 

The real issue for me is about ski makers. I just don't get the disjunct between the examples you're giving and the lengths that ski companies offer. Let's take the Blizzard 8.1 in 179. You like it as an all-mountain, no issues with tip dive. The 172 is better for carving. Well, the longest length the 8.1 comes in is 179. And everyone in the known universe agrees that the 8.1 is a stiff ski. Forgiving in some ways,yes, but light and stiff. Now the (hopefully) bright engineers at Blizzard designed four lengths of 8.1, apparently to accommodate skiers of different sizes, or more accurately of different levels of force production (M x a above) that will deform the cross section of the mid ski.

 

So what you're saying, really, is that that the longest is appropriate for someone in the 25th percentile for weight who skis fast and doesn't want tip dive. OK, by extension, that means that the 158 is for children under 50 lbs, the 165 is for midgets and women with eating disorders, the 172 is for light males or normal sized females who stick to carving groomers more slowly, and the 179 is for light males who want an all mountain ski. Apparently the engineers at this point went home for dinner and forgot the next am to make lengths suitable for average sized skiers who ski moderate to fast speeds. Let alone heavy guys. Really dumb of them, huh? 

 

Do you see my problem? (Well, this one out of many biggrin.gif ) For all the discussion of tips and running length, the logical extrapolation of your argument is that almost no ski company makes skis suitable for normal sized males who want to ski denser snow. I just am having a hard time buying it... must be missing something obvious (as usual). th_dunno-1[1].gif

 
post #2 of 26

What makes you think that a 179 is too small for a guy at the 75th percentile?

 

I made the same point in the height vs. length thread, that conditions of use, skier line choices, style, and and skill level have more to do with it than biometrics.

 

 

Think about conditions like tight trees, with lots of small branches sticking out, a ski shorter than lenght X might fit through the trunks easier and give the skier more leverage over snags, and be alot easier to ski regardless of the skiers, his biometrics, etc... 

 

In some types of firm lumpy crud, variable conditions, or wind eroded snow, a longer ski will let you bridge across the variableinty or across multiple lups better and provide a more stable platform, again reguardless of the skiers biometrics. In narrow bump lines, you oftne can't fit a big ski or a long ski through, etc...

 

post #3 of 26

Some of the skis I ride are different thickness and/or construction for every length. that makes sense to me, can't see doing it any other way.

 

length is such a strong factor, that I thought of a quiver concept that involved in one slot the same ski in two lengths, each serving the days conditions and the skiers attitude and perceived strength.

 

in general, strong skiers use longer skis in all categories, 'cause they like going fast.

 

beyond: for me, flex is the most critical characteristic. I know this because when a ski goes soft in flex, it's useless, no matter what else is still in tact. flex also comprises pop, snap, rebound, major performance factors, as well as dampening. good skis have greater stiffness built into the flex of each longer model, so your formulas for length to flex can incorportate that for some skis.

I have tested skis that were stiff in flex, but that stiffness did not have a personality, beyond an obstinate lack of bending, no feel, no touch, no smoothness. 


Edited by davluri - 12/8/10 at 6:51pm
post #4 of 26
Thread Starter 
Quote:
Originally Posted by davluri View Post
for me, flex is the most critical characteristic. I know this because when a ski goes soft in flex, it's useless, no matter what else is still in tact. 


icon14.gif

 

What I'm left ignorant about, through, is whether different lengths are intended for different sized skiers. Seems so intuitive, but getting hard to explain why in physical terms. Are longer skis stiffer? And if not, are the length guidelines only about how fast you ski (which of course gets us back to flex from another direction)? This is still giving me a headache...

post #5 of 26

skis (should) be made stiffer as they are made longer. I would say that for intermediate and advanced skiers, who put only moderate energy into a ski at any time. For expert skiers, it's about force into the ski, which is partially a function of weight and height and partially a function of strength and technique which amplify power. Most strong skiers ride a ski just over their head for all mountain. Speed requires a stiff ski or the ski will flap and chatter when pushed on rough conditions.

 

I ride a 176 Legend Pro, which in the broad scheme of things is an average ski length. But for me it is 22cm over my head, therefore skis fairly long. As it is an expert model, it is made fairly stiff in all lengths. I don't know what that does for your headache. All I really know is that since my surgery I'd like all my skis 10cm shorter for another couple months, as my core was completely taken apart and put back together.

post #6 of 26

They should, but does this actually happen for all models? Dawgcatching said the layup didn't change for most models, so that would imply that longer skis should be easier to flex, as a longer portion of the ski would be above the snow before the ski is decambered, wouldn't it?

post #7 of 26
Thread Starter 

Eyeah, longer skis should flex more in the sense of a greater absolute vertical displacement off the midpoint, even if the arc around that midpoint may be the same for any length. Eg, a longer ski will flop more...unless it's stiffer to compensate. Is flex measured as force required to bend midpoint, or is flex measured as displacement at tip/tail off horizontal? 

post #8 of 26

Quote:

Originally Posted by beyond View Post

 

So what you're saying, really, is that that the longest is appropriate for someone in the 25th percentile for weight who skis fast and doesn't want tip dive. OK, by extension, that means that the 158 is for children under 50 lbs, the 165 is for midgets and women with eating disorders, the 172 is for light males or normal sized females who stick to carving groomers more slowly, and the 179 is for light males who want an all mountain ski. Apparently the engineers at this point went home for dinner and forgot the next am to make lengths suitable for average sized skiers who ski moderate to fast speeds. Let alone heavy guys.


This is a thought I have had, but I probably would not have been able to articulate it this well.  Personally, as smaller guy (5' 7", 135lbs) who is a reasonably strong and technically competent skier, I find that the following rule GENERALLY works well for me, which almost validates the manufacturers' sizing patterns. If a ski comes in four sizes (e.g., some Blizzards), I generally like the 2nd size from the shortest. If it comes in five sizes (e.g., some Dynastars), I like either the 2nd from the shortest or the middle one, depending on the same kinds of considerations that Dawgcatching outlines. On a pure body weight basis, my percentile place (among men, but not necessarily among all skiers ... and most skis are still "unisex") might be closer to the bottom than these length choices would suggest. But if you figure in height and ability, I think it seems about right across all skiers, men and women. This leaves me, too, wondering about the lengths that Dawgcatching prefers. But then again, most of the time I don't have the privilege / challenge of dealing with the big spaces and 3D snow that he does. I think many of the Western skiers on this board, if they skied with me on my home turf here in northern New England, would feel like they were skiing in some kind of Hobbit land ... not because the vertical is small, but because often there is precious little "elbow room" in the landscape (or should I say, "skiscape"). For example, it is very common for me to be skiing a bump run that is only two or three ski-lengths wide, with essentially one column of moguls down the middle and half a mogul on each side. No doubt this has a big effect on ski length choice.

post #9 of 26

for the eastern skier, greater stiffness equals greater edge hold as does the length of the edge. another performance characteristic of length.

 

post #10 of 26

Another data point. 25 years ago EVERYONE was on something 20-35cm longer than today. Was everyone on the wrong length before? Is everyone on the wrong length now?

post #11 of 26

Everyone is and was probably on the correct length. Longer straight skis may be better for skidding or traditional technique. As construction and shape have changed, shorter is better for carving short turns without having to use ridiculous amounts of sidecut. Imagine the shape of a 205 cm ski with a radius of 12 m.

 

If you think about it, the shape of skis for carving long turns at high speed have not changed that much (i.e. SG). The big difference is in SL type skis where even pros were at one time unable to carve turns with.

post #12 of 26

You're missing the other essential element in your subject line: skier height.

post #13 of 26

I noticed something about testing flex. when you are standing on flat packed snow in your skis, you can pressure the skis tip and tail and notice if you are affecting the pressure of the tip and tail on the snow. My theory on this is that if you can't flex the ski in this manner, (without extreme weight shift beyond some muscle pressuring the ski) then you are likely not going to affect it much while skiing, and then you will be along for the ride.

 

example: if I were to test the Legend Pro 184cm this way, I would not be able to get the tail off the snow with my normal skiing input. The 176cm I can affect.

 

granted the forces on the hill are greater and will contribute to getting the ski to bend, but still, I think the static flex test means something.

post #14 of 26
Quote:
Originally Posted by chris719 View Post

They should, but does this actually happen for all models? Dawgcatching said the layup didn't change for most models, so that would imply that longer skis should be easier to flex, as a longer portion of the ski would be above the snow before the ski is decambered, wouldn't it?


another reason a small company with a limited budget is likely to short the consumer. the skis I ride from the big companies are engineered for each length and made for the projected size and strength of the skier.
 

 



Quote:
Originally Posted by tromano View Post

Another data point. 25 years ago EVERYONE was on something 20-35cm longer than today. Was everyone on the wrong length before? Is everyone on the wrong length now?



Terrain affects the length of ski because wide open faces and bowls are skied at higher speeds = higher forces = longer skis will work.

so ski length is tied somewhat to the mountain you most ski.  

post #15 of 26
Quote:
Originally Posted by davluri View Post
another reason a small company with a limited budget is likely to short the consumer. the skis I ride from the big companies are engineered for each length and made for the projected size and strength of the skier.

 

I honestly don't know where you're getting this from.  This is surely not the norm - at least not in my experience.  Longer almost never equals stiffer.  Go to your local ski shop and go down the rack of skis hand flexing each model that is available in each of the available lengths.  I've done this hundreds of times over the years.  It's more often that the shorter skis of the same model are the ones that are stiffer in flex.

post #16 of 26


 

I can relate to Dawcatching's response.  I know this sounds odd, but there may be a bigger difference in skier "feel" and performance for a particular ski based solely upon ski length, than for the difference between similar type and length skis from different manufacturers.  In other words, a HEAD and Volkl carver in a 170cm will seem more similar (less different) than the  difference between skiing the HEAD in a 170 and 180cm, or the Volkl in a 170 and 180.

post #17 of 26


dynastar legend pro and rossignol b-squad. each length an entirely different ski. at least in the model a couple years ago when I bought those models. not saying a small company couldn't do it.
 

Quote:
Originally Posted by Noodler View Post

Quote:
Originally Posted by davluri View Post
another reason a small company with a limited budget is likely to short the consumer. the skis I ride from the big companies are engineered for each length and made for the projected size and strength of the skier.

 

I honestly don't know where you're getting this from.  This is surely not the norm - at least not in my experience.  Longer almost never equals stiffer.  Go to your local ski shop and go down the rack of skis hand flexing each model that is available in each of the available lengths.  I've done this hundreds of times over the years.  It's more often that the shorter skis of the same model are the ones that are stiffer in flex.

post #18 of 26

height is a factor on length just like a fulcrum. 


We just talked about this in another thread.

 

Weight has a factor to deal with the flex of the ski, as well as length.

A really long ski that is tooo flexy will just disfigure itself with a heavier person. The heavier person can flex a higher flex ski easier than a lighter person.


Now that that is out of the way.

 

The torque that a taller body puts on a ski is different than a shorter person.

Which also has to do with how they flex and how you control them. 

 

I'm a beginning skier and I notice differences in ski lengths the first year I was out. Stability wise, vs their flex. 

 

By saying a ski is "my length" is basically saying "I am comfortable on this ski in most occasions."

 

I've got 180's, and I love them, mostly for the fact its like riding in a Mercede's and the fact they are super stable.
But when I skied 166's, I had to try soooo much harder than I do in these 180's.

Are 180's my length? Nah, But I like them.

 

Length and flex is based upon conditions, height and weight, and personal preference.

if you want to ski a 230 all day cause you like it, than ski a 230. 

 

I hope that wasn't confusing. It all makes sense in my head. haha.

They posted it in a more mathematical way in the other thread.

 

But.

The thing to remember, different lengths vs flexes are going to act different.

 

The same flex in 2 different length ski's is going to be different even though its the same flex due to leverage. 

Unless the manufacture is adjusting how stiff the ski's are based upon leverage numbers of the longer ski vs flex rating.

 

Just think of standing on a 4 foot 2x4 between 2 sawbucks, and standing on a 10 foot 2x4 between 2 saw bucks.

The 10 footer flexes more, but they have the same flex rating. 

post #19 of 26
Thread Starter 

OK, so to sum up, no one really knows if ski length is related to skier weight. Or more accurately, "it depends..." wink.gif

post #20 of 26
Quote:
Originally Posted by beyond View Post

OK, so to sum up, no one really knows if ski length is related to skier weight. Or more accurately, "it depends..." wink.gif

 

Again, what makes you think there is any relationship between a skiers weight and length of the ski? What sort of relationship are you looking for? A causal relationship, a statistical correlation, some sort of function describing optimum length given weight?

 

I know what works for me. And it is a whole range of sizes from 165 to 195 and probably alot more besides that. I do not think that sizing of skis really is analogous to sizing a bike or sizing a ski boot where the primary factor to think about is the persons biometrics. Skis are not sized for fit to a persons body in any real way that I can tell. You do not go in for a fitting. You demo for size and pick the size you like best. You pick a size of ski, lengths width, etc... to fit the line you will be skiing and your own personal style. That is -- what you want the ski to be able to do.

 

There is no such thing as not being able to bend a ski. Hookes law tells us that, even the longest / stiffest ski will bend under a light skier. Whether or not it bends sufficiently to ski the line the skier wants to ski is another question.


Edited by tromano - 12/11/10 at 10:08pm
post #21 of 26
Quote:
Originally Posted by beyond View Post

OK, so to sum up, no one really knows if ski length is related to skier weight. Or more accurately, "it depends..." wink.gif



its depends on skier style, skier skill, where they are skiing, skis camber profile, skis flex profile and how much force they can exert on the ski. 

 

all these reason add up to some laughable 'what ski should I get" threads

 

post #22 of 26

Skier weight is a factor in choosing the best ski length.  A heavier skier will exert more force on the ski: more downforce will need to be supported without sinking in powder, and more turning force will be required to accelerate the skeir around a turn.  On snow the ski can dig into, a longer length will support more force before loosing grip.  On ice, a longer length might not have sufficient pressure to dig in, but even on ice a heavier skier will be able to make a longer length dig in than a lighter skier (pressure being force divided by area.

 

Skiing speed is a factor in choosing the best ski length.  A faster skier needs more force to turn him.  The force required to accelerate a skier around a turn of a given radius varies direclyt as the skier's mass (directly related to his weight) , varies inversely with the turn radius and varies directly with the square of the skier's velocity squared(F=mv^2/R).  However, speed will only increase length so much; although the skier may need more force to turn going faster, the skier still needs to engage the edge and the only force available for that purpose is his weight (unless he is able to find places to do banked turns, e.g. tree wells devil.gif; mind your eyeseek.gif). 

 

A secondary factor where speed comes into play is making skiing rough terrain easier at speed due to fore-aft balance considerations and for soaking up bumps.  You would prefer a longer ski for skiing rougt terrain at speed, where as it wouldn't matter as much skiing slowly.

 

Flex of ski versus length of ski is a little more compicated.  Skis resist bending so that weight applied at the centre is transmitted to the tips and tails, so that we can  apply and make use of forces at the tips and tails.  The stiffer the ski, the more force gets transmitted at any given bend put into the ski.  If you want to bring enough force to spread over a bigger area, the ski should be stiffer near the boot.  That doesn't mean it will be, some are some aren't.    The good ones are.  Stiffness is also a little more complicated because a longer ski with the same construction will be easier to bend due to the lever length effect, so you might not notice it is stiffer.  Think of bending a short length of 2x6 versus a long one.   If you cut the long board into short lengths, you will see they have the same stiffness.

 

Ski Length is a factor in stability.  In the old days it was pretty simple.  Longer was more stable and length was absolutely needed for stability.  Now, not so much, and not in all skis. Well maybe I didn't try the unstable skis in the old days, but that's how it seemed.   A soft ski that is made longer will be even more unstable than a short soft ski, because the added length just gives you more unstable weight out there flopping around, e.g. Rossi Bandit.  However you have to be pushing it past it's envelope, within the envelope the longer ski will seem more stable.  A stable ski that has built in vibration absorbing that can handle the extra mass of the added length will be more stable due to the extra mass requiring greater forces to vibrate it, e.g. SX11.

 

Stability above refers to the ski being controllable on a hard surface with small bumps at high speeds, and where that speed is when the ski just won't cut it.   Stability in terms of wanting to make a turn when you don't want it to is related to sidecut, stability in terms of skier being comfortabe with fore-aft balance is not what I'm  refering to as stability.

post #23 of 26
Thread Starter 
Quote:
Originally Posted by tromano View Post

Again, what makes you think there is any relationship between a skiers weight and length of the ski? What sort of relationship are you looking for? A causal relationship, a statistical correlation, some sort of function describing optimum length given weight?

I'm looking for something so obvious (or idiotic) that no one here seems to be able to say yes or no. I'll break it down into premises and conclusions: 1) Skis come in several lengths. 2) Ski makers, retailers, consumers, and Epic recommenders all operate as if these lengths have a correspondence to a skier's size (let's say weight and height), such that bigger skiers are steered to longer skis. 3) However, as far as I can tell from the actual engineering (following Dawgcatching's argument, recall), the ski's cross sectional area, not its length, is what determines its resistance to bending force. 4) Therefore (conclusion), ski makers, retailers, consumers, and Epic recommenders are wrong in acting as if heavier, bigger skiers exert more force on their skis and thus need a longer ski. 

 

So, controlling for all those other variables everyone very reasonably brings up, speed, snow, style, color of your parka, whatever: ARE LONGER SKIS DESIGNED  FOR BIGGER SKIERS? 

 

edit: Ghost actually came closest to answering my question by bringing up length as about support against downforce, lever length, but left it up in the air whether a longer ski was actually less stiff or just easier to bend, and more to the point whether the people who make skis intend longer skis for bigger people. Or if you like, greater downforce. 

post #24 of 26


 

Quote:
Originally Posted by beyond View Post ...but left it up in the air whether a longer ski was actually less stiff or just easier to bend, ...


I seem to remember the Dynastar product guy that SierraJim interviewed (on video) a while back talking about changing the stiffness for different lengths of a ski model to account for the leverage factor. Perhaps he didn't really say this and I just inferred it, but my impression was that they purposefully make longer skis stiffer and shorter skis softer so that each length feels like it has the same stiffness as other lengths of the same model (or perhaps it would be better to say that it takes roughly the same amount of pressure to bend after leverage is considered).

post #25 of 26

According to Seth Morrison, K2 made last the generation of Obsetheds with a different core profile for different lengths with skier size as a factor.

 

 

"On another note the waist width stays the same on all lengths of the ObSethed, were as other companies get narrower as they get smaller. The core profile is all that changes from the sizes. 189 and 179 are totally different in that respect, think size of the skier and making the ski forgiving for that individual."

 

Full info here:

 

http://www.backcountry.com/store/review/200020710/All-Mountain-Performance.html

 

post #26 of 26


 

Quote:
Originally Posted by beyond View Post

Quote:
Originally Posted by tromano View Post

Again, what makes you think there is any relationship between a skiers weight and length of the ski? What sort of relationship are you looking for? A causal relationship, a statistical correlation, some sort of function describing optimum length given weight?

I'm looking for something so obvious (or idiotic) that no one here seems to be able to say yes or no. I'll break it down into premises and conclusions: 1) Skis come in several lengths. 2) Ski makers, retailers, consumers, and Epic recommenders all operate as if these lengths have a correspondence to a skier's size (let's say weight and height), such that bigger skiers are steered to longer skis. 3) However, as far as I can tell from the actual engineering (following Dawgcatching's argument, recall), the ski's cross sectional area, not its length, is what determines its resistance to bending force. 4) Therefore (conclusion), ski makers, retailers, consumers, and Epic recommenders are wrong in acting as if heavier, bigger skiers exert more force on their skis and thus need a longer ski. 

 

So, controlling for all those other variables everyone very reasonably brings up, speed, snow, style, color of your parka, whatever: ARE LONGER SKIS DESIGNED  FOR BIGGER SKIERS? 

 

edit: Ghost actually came closest to answering my question by bringing up length as about support against downforce, lever length, but left it up in the air whether a longer ski was actually less stiff or just easier to bend, and more to the point whether the people who make skis intend longer skis for bigger people. Or if you like, greater downforce. 


It would seem that the only person who could answer your question definitively is someone who has designed skis professionally.

 

A longer spring of the same rate can store more energy than a shorter spring. Longer skis can absorb and store more energy even if "stiffness" at a point is the same. Also given failure modes for soft snow, e.g. snow collapsing under the ski -- a longer ski provides more surface area and provides less pressure at the tip which prevents tip dive under power.

 

All things being equal -- same line, same speed, a bigger skier does exert more force on the ski. That should be fairly obvious. However in reality all things seldom are equal and just because you are 250lbs does not mean you are going to out ski a medium flexing 170cm ski.

 

Ultimately, I think that more powerful skiers do better on bigger skis than less powerful skiers would prefer. Controling for all the variables you said.

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EpicSki › The Barking Bear Forums › On the Snow (Skiing Forums) › Ski Gear Discussion › Can someone clear up the relationship between ski length, ski flex, and skier weight?