Have you skied same ski in different lengths and does it "scale?"

Thread on 8K's in reviews ended up arguing over whether heavier skiers could provide good judgements on skis for lighter skiers, and vice versa. Thought it deserved its own thread, so credit to Ski-Ra, Skier219, Tromano for the idea.

Here's my hunch: Some skis "scale," meaning that a shorter version will produce the same feeling for an equivalently lighter skier, (or put in a more technical way, the various flex patterns are linear relative to the length). And no, some don't. Which I assume means that they are non-linear; hard to predict how a different length will feel. What would be more useful IMO is to try to agree on which models scale and which don't. If there were a consensus on some, maybe Tromano could read more reviews. 

No data on the scaling from me.

However, it should be noted that cores (wood, foam, whatever) are the components that ski manufacturers have complete dimensional control over via their in-house milled production.  It would be easy to adjust the dimension to scale down for longer/shorter skis.

This cannot be said for the sheet metal layers, as those are probably only available in steps of thicknesses as they come in rolls from the foundry.

Finally, skis really shouldn't scale that well, as most skis scale only for length, not width.  All things being equal, this would suggest that shorter skis have a higher torsional rigidity relative to longitudinal rigidity.  It would take some creative tweaking of many other components to re-approximate the characterisitics of the longer ski.

No easy answer here.

I have owned the Dynastar Contact 11 in both the 172 & 178cm size. Both worked for me at 220 lbs plus. The 172 has a wider range of turn shapes, the 178cm is more stable in choppy or knee deep snow. No surprise here.

I own the 172cm Dynastar Contact 4x4 and demoed the 178cm size. Same conclusion as above.

My opinion on gear usually aligns with Dawgcatching and other reviews here, even though I have 65 lbs on Scott. This is true even when I post the fist review on a model (no cynics, please).

Michael

I don't think a single person can say if the various lengths scale.  Really, you'd need the same person in different sizes to evaluate it correctly.

Generally when I test different lengths of a ski, I am looking for the one that is "just right" for me, and that's where I evaluate the characteristics in detail.  All I can say about the other lengths is that they were too short or too long, not how their characteristics scale off those of the correct length. 

Quote:

Originally Posted by skier219 

 

I don't think a single person can say if the various lengths scale....

I completely agree and have some thoughts that have been simmering in my contorted brain about this matter, but...before I waste everyone's time with these these half-baked theories and off-base conclusions:
 

Does anyone know if formal ski tests (i.e., those by our favorite? ski mags) tests each ski in a variety of lengths?

Yes, SkiPress.  If a ski is unisex and both men and women testers test it, they usually specify different lengths, dimensions, opinions, and of course rankings.

For example, the Dynastar Legend 8000 was ranked #3 by the men for "Freeride, Midfat (MSA)" in 172 cm, but was ranked #7 by the women in the same category in 165cm.

The men's opinion:

"The Legend 8000's cool new look belies a retro ski at heart, a throwback to the days of one-ski quivers.  The 8000 is like a multi-tool Leatherman, able to accomplish a variety of tasks with reliability and efficiency.  Whatever snow, whatever terrain - job well done.  You don't want a ski that wows, you just want a ski that works.  There's nothing like an old-fashioned multitasker."

The women's opinion:

"Dynastar's Legend 8000 was really loved by some of our female testers, who appreciated its unyielding stability and super flotation.  The ski requires strength - it's designed for both men and women. And it can be stodgy at initiation.  But once into the turn, keep your head in your helmet. Said one tester: 'This is a Wild West-stylin' ski for cowgirls lookin' for a ride!'"

Quote:

Originally Posted by DtEW 

 

Yes, SkiPress.  If a ski is unisex and both men and women testers test it, they usually specify different lengths, dimensions, opinions, and of course rankings....

That sure is noble of SkiPress, though I'd hardly call testing one length by the men and one length by the women (both of which will vary greatly in ht./wt.) a scientific way of determing if a ski "scales".  Atleast they seem to be trying harder than the other mags (which seem to only ski a single length).  Anyway, I'm still trying to articulate my thoughts about this issue and will weigh in with a rant shortly....

Quote:

Originally Posted by ski-ra 

 

 

That sure is noble of SkiPress, though I'd hardly call testing one length by the men and one length by the women (both of which will vary greatly in ht./wt.) a scientific way of determing if a ski "scales".  Atleast they seem to be trying harder than the other mags (which seem to only ski a single length).  Anyway, I'm still trying to articulate my thoughts about this issue and will weigh in with a rant shortly....

I'll save my many criticisms of how ski mag tests are organized for a separate thread, but I just wanted to give credit here to Ski Press for at least documenting what length(s) get(s) tested. I noticed that this year's Ski or Skiing (can't remember which - maybe both) did not even mention what the test length was. Reading the Ski Press quotes above from DtEW - from three or four years ago, I believe - also reminded me of how awful the writing used to be in their reviews. I noticed gratefully this year that they've toned down the adolescent angle a lot.

Sometimes Ski or Skiing will quote a particular tester, whose bio you can then look up on another page to see whether he or she approximates your size. This can be useful up to a point.

Quote:

Originally Posted by skier219 

I don't think a single person can say if the various lengths scale.  Really, you'd need the same person in different sizes to evaluate it correctly.

Well, exactly true. We could start with a smaller female on the shortest length, and then stack weights into her clothing as she tried longer lengths, until she was up to say 250. Trekchick, you out there?  

No seriously, 219, if you're really talking about assuming each length is designed to have a similar weight to SA ratio, thus similar "flex," probably true. But not exactly the point of my initial question. More typically the uber-problem around here is, "what length should I get?" Thus one skier, confronting two or more lengths. And unlikely he/she will be able to demo those consecutive lengths.

IMO, then, a model with of decreasing weight/SA ratio is relevant; can this one skier assume linear or nonlinear change over multiple lengths? I mean, we use similar models in medicine and economics and chemistry all the time. And we happily devour reviews where one skier tries skis of roughly the same length but different designs, constructions, and sidecuts. (Or am I missing key underlying point about "just right," which is an interesting issue on its own?)

DtEW, also value SPW (and Ski Canada, which releases info about each tester + their fav skis in the test). But the problem with the "male" and "female" sizes for SPW is that you have massive inter-observer error. Just using one person on various lengths standardizes on skiing style, biomechanics, personal biases etc. And damn, those Canadians choose long skis. The women's test lengths are about right for me. 

So ski-ra, half baked theories are what Epic's all about. And the damn season's about finished back here. Go for it. 

So will somebody go find TC before the snow's gone? 

Quote:

Originally Posted by beyond 

 

...We could start with a smaller female on the shortest length, and then stack weights into her clothing as she tried longer lengths, until she was up to say 250. Trekchick, you out there?  ....

Your comment above actually is a good place for me to start with my thoughts.  I believe strongly that:

1. Scaling the flex of the various lengths offered for a given ski is not as simple as it would seem.  In fact it is quite complicated and something that the ski manufactuters don't understand how to do well at all.
2. Because of this ski mag reviews need to do a much better job of determining how a ski feels in it's various lengths (by the various sizes of skiers).  Unfortunately, at best they test only one or two lengths using their full range of testers.  This is useless except for the average size buyer (i.e., a 180# male for the uni-sex model) skiing the size tested.

Why?

So what should be done about this?  In a perfect world a ski would be tested in all of it's lengths offered with each length being tested by the target size skier(s).  Duh!  (Finding the "target" size for each length would involve some experimentation, like what skier219 said above.)  I believe the results would show that few, if any, ski's scale well.  OK, I know that this type of testing probably ain't gonna ever happen, but I can dream that it could.  I can also dream that the tests would provide me better information for selecting a ski and/or send a stronger message to the manufacturers that they're doing a crappy job with this one aspect of ski design (otherwise they've done some amazing things...).  

One (brown-nosey?) clarification - the above helps explain why I value the reviews by the industry Epicskiers that regularly post here. They tend to show more sensitivity to the length vs. skier weight/size issue than the ski mag’s do. I assume that, besides reporting on their own experiences with a ski, they are also basing their statements on input from the various demo’ers and buyers of their skis. That kind of knowledge comes close to what I'm dreaming of and why we understandbly belittle the ski mag reviews here!

As usual, if only I had more time I could have said the above in less words, and on second thought using Trekchick as the tester would work better anyway (atleast for us littler people)....

 I don't think the ski makers need to get into super-detailed finite element analysis to figure it out -- they should be able to use simpler models to get in the ballpark.  That said, though many ski designers do use computational methods to model skis, a large part of ski development is still based on trial and error.  Build, ski, tweak, ski, etc... until it's right.

This is a good reference I recently downloaded:

Computing the mechanical properties of alpine skis
Sports Engineering
Volume 2, Issue 2, Date: May 1999, Pages: 65-84
A. A. Nordt, G. S. Springer, L. P. Kollár

Here's the introduction:

I think this sort of confirms some of what ski-ra is saying.

If someone at a ski shop had the various lengths of a ski model available, it would be very easy to rig up an experiment to test how ski flex scales from length to length.  Take each of the ski lengths, and support them at the tip and tail contact points with a knife edge (or even a fixed round bar).  Then load the skis with weights at the mid-point between the supports, and record the deflection of that mid-point.  Repeat with a variety of weights until a decent set of data is collected, from unweighted through reasonable de-camber.  From that, we can look at the data from all lengths, normalize it, and see how the flex scales (or not).  This would actually make for a great little science project.

Quote:

Originally Posted by skier219 

 I don't think the ski makers need to get into super-detailed finite element analysis to figure it out -- they should be able to use simpler models to get in the ballpark.  That said, though many ski designers do use computational methods to model skis, a large part of ski development is still based on trial and error.  Build, ski, tweak, ski, etc... until it's right.  

 

This is a good reference I recently downloaded:

 

Computing the mechanical properties of alpine skis
Sports Engineering
Volume 2, Issue 2, Date: May 1999, Pages: 65-84
A. A. Nordt, G. S. Springer, L. P. Kollár

 Quote:
 

 Introduction

  

Skis are currently designed in two steps. First, prototypes are built and the ski's mechanical characteristics (including the bending and torsional stiffnesses, ex, vibration behaviour and pressure distribution) are measured in the laboratory (DeRocco et al. 1993, 1996). Second, the skis (which `passed' the laboratory test requirements) are given to expert skiers to try out under actual skiing conditions.

  

The aforementioned procedure has serious shortcomings as it requires the performance of expensive and time consuming tests. Because of this, only a limited number of design concepts can be tried. Consequently the final product may be far from optimal.

  

The shortcomings of the current trial and error design practice could be overcome by the use of models which simulate (i) those mechanical characteristics of skis which presently are determined by laboratory tests on prototypes and (ii) the performances of the skis during actual runs. Obviously, such models minimize the need for extensive laboratory and on-snow testing, and would result in skis which conform to design specifications.

I think this sort of confirms some of what ski-ra is saying.

 

If someone at a ski shop had the various lengths of a ski model available, it would be very easy to rig up an experiment to test how ski flex scales from length to length.  Take each of the ski lengths, and support them at the tip and tail contact points with a knife edge (or even a fixed round bar).  Then load the skis with weights at the mid-point between the supports, and record the deflection of that mid-point.  Repeat with a variety of weights until a decent set of data is collected, from unweighted through reasonable de-camber.  From that, we can look at the data from all lengths, normalize it, and see how the flex scales (or not).  This would actually make for a great little science project.

 

Hm I like it.  Yeah I based my thoughts on a hunch and it's interesting to see that manufacturers are indeed still operating somewhat in the dark ages.  Yeah they don't need to do finite element analysis, but they should be developing simulation models to reduce the trial and error process and to take the guess-work out of scaling the ski's flex for the different lengths.  As for our science project, don't we need to also test torsional rigidity? 

A further thought about all this while shaving this morning...if manufacturers were better at scaling a ski perhaps they might sell more models in lengths that people might want to buy.  For example, maybe there would be a greater market for a 161cm Head im82, a 165 Dyna MR, the 162 AB or Crimson, etc., skis which I almost never see in the store (nor on the feet of skiers) probably for good reason - they're too stiff/heavy for the target skier intended (a small or very small expert).  They might also be able to sell the ski to larger int/advanced skiers that want something shorter because they are still challenged in getting a ski to "come around" quickly - heck wouldn't they make more money selling this ski than some cheaper model?.  Or is it the goal of ski manufacturers to make a much greater variety of models based on the notion that this sells more skis?  Hmm....

Way back when (70's?), Ski and or Skiing magazines used to do that, not only for overall flex but tip and tail flex usung a support part way down the ski and measuring the deflection.  I wish they would do much more of that.
 

Quote:

Originally Posted by ski-ra 

 

 As for our science project, don't we need to also test torsional rigidity? 
 

Sure, why not!  But it would be harder to setup a torque fixture/rig and measure angular displacements accurately.  I think the simple beam deflection test will probably give us the bulk of what we want to know.

As I am a small skier, I only buy skis that scale well, and the one's I own are built very differently for each size or size group.

Going through the rack in the shop, you can easily see that in some models, the thickness under the boot is different at each length, substantially so.You can't see the differences in materials and construction, but you can research that in the manufacturer's data (many salesperson's are in-accurate on this.) If you mount your own skis, you get a look and feel for the construction when you drill.

The B-Squad builds the 164 with foam core and one lower metal layer, med stiff flex, med thickness sandwich; the 174 and 184 =wood core, w 2 metal layers, stiff flex, thick sandwich; the 189, 194=wood core, 2 layers metal, super stiff flex, very thick sandwich. Three different skis deliver the same performance concept for skiers of different size and strength.

The Legend Pro is made in different thicknesses for each length, at least was in 07 and earlier, and the stiffness is very carefully tuned in the 176 for a 135lb approx skier.

The different thickness of each length indicates to me that the ski is turned to different sized skiers and the models I have mentioned are skis I ski all the time and are perfectly suited to me, whereas I am certain that if the 165's were built like the longer skis (Rossi did this one year) they would be total beasts.

Volkl Mantra (and the model predecessors Explosiv) do not vary in thickness, My shorter length skis were relatively much stiffer than the skis my taller friends ski.

Re stiffness: IMO, you should be able to stand on the snow and lift tips or tails off the snow by pressing forward or back in your boots. If you can't activate the flex standing on the flat snow, you will not be able to get the ski to be flexing dynamically on the hill in your turns.

Quote:

Originally Posted by davluri 

As I am a small skier, I only buy skis that scale well, and the one's I own are built very differently for each size or size group.

 

Going through the rack in the shop, you can easily see that in some models, the thickness under the boot is different at each length, substantially so.You can't see the differences in materials and construction, but you can research that in the manufacturer's data (many salesperson's are in-accurate on this.) If you mount your own skis, you get a look and feel for the construction when you drill.

 

The B-Squad builds the 164 with foam core and one lower metal layer, med stiff flex, med thickness sandwich; the 174 and 184 =wood core, w 2 metal layers, stiff flex, thick sandwich; the 189, 194=wood core, 2 layers metal, super stiff flex, very thick sandwich. Three different skis deliver the same performance concept for skiers of different size and strength.

 

The Legend Pro is made in different thicknesses for each length, at least was in 07 and earlier, and the stiffness is very carefully tuned in the 176 for a 135lb approx skier.

 

The different thickness of each length indicates to me that the ski is turned to different sized skiers and the models I have mentioned are skis I ski all the time and are perfectly suited to me, whereas I am certain that if the 165's were built like the longer skis (Rossi did this one year) they would be total beasts.

 

Volkl Mantra (and the model predecessors Explosiv) do not vary in thickness, My shorter length skis were relatively much stiffer than the skis my taller friends ski.

 

Re stiffness: IMO, you should be able to stand on the snow and lift tips or tails off the snow by pressing forward or back in your boots. If you can't activate the flex standing on the flat snow, you will not be able to get the ski to be flexing dynamically on the hill in your turns.

 

Yousa - as a lightweight I gotta remember this advice (and consider going ski shopping with you!)  Nevertheless, more proof that manufacturers do a spotty and sometimes poor job of scaling skis!
 

Thanks!

Quote:

Originally Posted by skier219 

 

Sure, why not!  But it would be harder to setup a torque fixture/rig and measure angular displacements accurately.  I think the simple beam deflection test will probably give us the bulk of what we want to know.

 

Not being the devil's advocate here, just curious....  But isn't the balance between longitudinal and torsional flex important (ala what SJ presented in his "the polarizing factor" thread)?  And does knowing how that stiffness varies along the length of the ski change anything about a ski's behaviour (i.e., do two skis with the same tip deflection ski the same if one is uniformly that stiffness while the other has a soft tip but an even stiffer midsection)? 

Either way, then what?  How do I take this information and determine what ski might be best for me (I might be an engineer, but knowing that a ski's flex is in N-m's or ft-lbs. tells me nothing...at least today)?  Do I need to step into some type of skier profile chamber and exit with a computerized profile sheet or do I learn this from experience?
 

Hmm...a skier profile chamber - if like it (if only I were an inventor/entrepreneur)....

 Great thread, you guys.

Quote:

Originally Posted by davluri 

 

Re stiffness: IMO, you should be able to stand on the snow and lift tips or tails off the snow by pressing forward or back in your boots. If you can't activate the flex standing on the flat snow, you will not be able to get the ski to be flexing dynamically on the hill in your turns.

 

This is a cool idea. I've actually tried this (for a different reason) and was surprised at how much of a mental hurdle it was to apply enough force  - especially forward - to get the tips or tails up. Every fiber was screaming "No! Something is going to give and you are going to end up with those metal tip protectors embedded in your eye sockets!" Maybe this just proves that I am an old-fashioned keep-the-skis-on-the-snow-if-at-all-possible kind of guy.

On a different (related) note. I rode up on the chair one day last year with a self-described mechanical engineer. I can't vouch for his credentials, but he told a fascinating story about having been part of a university class or some kind of consulting group where they visited the manufacturing facility for a famous snowboard company. They heard all about the five different models and the five different constructions that went into giving the models their several performance characteristics. They took an instance of each of the five boards back to the engineering lab. They discovered that the "middle" three boards in the line (i.e., not the beginner board, and not the high-end board) had objectively nearly identical flex patterns in multiple directions. I.e., the constructions (and topsheets) really were different, but from the end user's perspective it was probably a "distinction without a difference." The class reported these findings back to the snowboard company, whose reaction was along the lines of "Really? Wow. I'm so glad you told us that. We really ought to be doing more of that kind of analysis. Probably would save us a lot of money."

Now I understand this is hearsay and that there are all kinds of ways in which you can dubiously pick apart my re-telling of the guy's story. But the bottom line is that this person walked away from the experience absolutely surprised and yet absolutely convinced that these folks had what from a mechanical engineering point of view was a shockingly primitive level of knowledge about their own products.

 Well, I'd like to think you could test the skis you like and the ones you dislike, and hopefully identify quantitative differences between them.  Then you'd be calibrating your qualitative preferences to some hard numbers.  From there, see how potential new skis measure up.

But just for the scaling hypothesis, I think longitudinal beam type loads are enough to start.

I remember that some skis for example the 168 Volkl 5* / 6* got rave reviews from everyone (reguardless of size of the skier) in the 168cm size and I never heard much good about any other length.

I know that some skis like the Titan 9, scott P4 have used sizings where different sizes of ski have different widths.This seems to be a really good idea to me and I wonder why more skis don't scale in width.

There really isn't much cause why a light person skiing on a 170cm ski should have the same width as a heavier person on a 190, if the skis are supposed to have the same performance. I think part of the problem with this is that in the last few years people are soo focused on width and seem to base alot of what they are looking for on the width of the ski... 

This sort of problem comes up a lot in bikes as well. Basicly size S and XS bikes often seem to be relaatively stiff and over built compared to the larger sizes.

Quote:

Originally Posted by skier219 

 Well, I'd like to think you could test the skis you like and the ones you dislike, and hopefully identify quantitative differences between them.  Then you'd be calibrating your qualitative preferences to some hard numbers.  From there, see how potential new skis measure up.

 

But just for the scaling hypothesis, I think longitudinal beam type loads are enough to start.

Fair enough - I'm your typical engineer whose gotta overthink everything....  Now if only that beam load data were available (which brings me back to why ski mag tests could be doing a much better job with this issue).  Until then I'm gonna dream of a day when the ski manufacturers use modern design tools to better scale their skis (and so that I don't have to consider buying skis with pink flowers on 'em).

Back to the OP's question - what have people found concerning flex when trying the same ski in various lengths (or even demo'ing with a group of different skier sizes trying the same ski in various lengths)?

 

Quote:

Originally Posted by ski-ra 

 

I'm gonna dream of a day when the ski manufacturers use modern design tools to better scale their skis (and so that I don't have to consider buying skis with pink flowers on 'em).

The fact that those pink flower skis are out there is proof that the mfrs DO understand that the typical ski model designed around a 5' 10" 180lb guy doesn't necessarily serve all good skiers well. The problem is only that you (and I) happen to have been left out of their focus group on topsheet design.

I actually suspect - based on absolutely no hard data whatsoever - that all the marketing hype about mounting position and weight distribution differences between men and women skiers is mostly that. I suspect that 90% of the difference - apart from the graphics - is precisely about designing a ski model centered on a 5' 4" 120lb skier instead of around the guy mentioned above. The advertising folks don't want to emphasize that because women don't always respond positively and with open wallets when they're repeatedly told how they're special because they're small and weak. Thus the "weight distribution" angle, which is more politically neutral. My guess, anyway.

Quote:

Originally Posted by qcanoe 

 

 

The fact that those pink flower skis are out there is proof that the mfrs DO understand that the typical ski model designed around a 5' 10" 180lb guy doesn't necessarily serve all good skiers well. The problem is only that you (and I) happen to have been left out of their focus group on topsheet design.

 

I actually suspect - based on absolutely no hard data whatsoever - that all the marketing hype about mounting position and weight distribution differences between men and women skiers is mostly that. I suspect that 90% of the difference - apart from the graphics - is precisely about designing a ski model centered on a 5' 4" 120lb skier instead of around the guy mentioned above. The advertising folks don't want to emphasize that because women don't always respond positively and with open wallets when they're repeatedly told how they're special because they're small and weak. Thus the "weight distribution" angle, which is more politically neutral. My guess, anyway.

Well said.  I have two divergent thoughts about women's skis (no offense meant towards the smarter sex):

• If ski's were better scaled by length then there wouldn't be a need for women's skis (i.e., a unisex 160cm model would be soft enough for a 120lb person).  Heck they could even put two boot center marks on the ski (it's not like this ski boot center marking thing isn't getting surreal as it is).
• Offering an almost identical ski but with feminine graphics sells more skis.  Besides a 160cm unisex ski is meant for a 130lb+ and/or stronger skier than that for the women's 160cm ski.  That's why many 165cm+ ski's are too stiff for me.

Hmm...not sure which is the real story