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  1. #1
    Join Date
    Feb 2018
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    23

    What's the theory on how ski dimensions scale with skier size?

    I've been thinking about this a bit for the last month and thought I'd put it out there in case anyone had either off-the-cuff or more-thoroughly-thought-out ideas on the subject.

    Say you start with a skier who's a given height and weight (for example, 6', 200#). And say they're very happily skiing on a certain pair of skis (say 110mm underfoot and 190cm length).

    Now imagine I scale that person down by 10% (height-wise) to make a new, smaller skier: height of 5'5" and weight of 145# (since weight scales approximately like height^3). I was trying to think about what ski dimensions they should be on to most closely approximate the experience of our original skier. Does the answer depend on whether you're trying to get equivalent performance in powder or hardpack? I know there are concerns about ski stiffness as well (which may or may not scale like the thickness of the ski), but let's start simpler and just talk about what the length and width should be for our smaller skier.

    I can't exactly justify it based on first principles, but I had a gut feel that the ski length should scale up and down with the skier's height. Certainly that keeps things in proportion in terms of what fraction of the ski's length the skier can move their center of gravity over. Can anyone justify that more rigorously? Or does anyone disagree (why)?

    But let's run with that: so our smaller skier is on 171cm skis. If we think "equal performance" in powder is about "equal pressure under the ski" then we need 30% less ski area for 30% less weight. So that means the width would need to be about 80% as wide as the original, putting our smaller skier on 88mm wide skis.

    For hardpack, if we're trying to keep angles the same as our skier tries to edge the ski, the geometry argues that the ski width should scale down linearly with skier height. That would argue (I think?) for only a 10% narrower ski than the baseline (99mm wide).

    Is there "theory" on this stuff? Or at least widely accepted intuition? It seems like (almost) every ski out there keeps the same width underfoot for all the sizes in length. I always thought that was very counterintuitive. What do you think? What dimensions "should" our smaller skier be on?

  2. #2
    Join Date
    Dec 2007
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    PugSki Jong
    www.apriliaforum.com

    "If the road You followed brought you to this,of what use was the road"?

    "I have no idea what I am talking about but would be happy to share my biased opinions as fact on the matter. "
    Ottime

  3. #3
    Join Date
    Dec 2011
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    4,971
    Epicski called...they want their thread back.
    Quote Originally Posted by XXX-er View Post
    the situation strikes me as WAY too much drama at this point

  4. #4
    Join Date
    May 2011
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    Sonoma & Truckee
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    The smaller skier should definitely buy the red ones.

    / end thread.

  5. #5
    Join Date
    Dec 2007
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    Hell Track
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    All of your math ignores on the ground conditions. A short ski is less stable than a long ski, regardless of what size skier is standing on it. A set of moguls is spaced the same, regardless of what ski you're on. Trees don't space themselves out wider for bigger skiers on bigger skis.

    Plenty of people have the skill and strength to drive most ski lengths (at least most ski lengths that are actually produced). The length they're on is more dictated by the terrain they're skiing.

  6. #6
    Join Date
    Nov 2004
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    YetiMan
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    10,778
    If me and dantheman had equivalent skier-mass-to-surface-area/length, Iíd have to be on skis so long (if they even existed) I couldnít fit them in typical ski spaces like mogul troughs or entry chokes and whatnot.

    Itís one of the things that sucks about being a large man who also loves ďaction sportsĒ. I ride a 55 lb dh bike on not-super-rad trails because I had a horrendous wreck when normal mtb stuff folded up under me on a normal landing. I surf a 7í6 standup paddle board because itís the only thing I can find that has volume and also downrails and rocker. My pow skis are 140 underfoot. All of those things are classicly kooky. It sucks being big....and one thing about being big is that we werenít born big so we know what it was like not being big.....whereas small people donít necessarily know what itís like to be big.

    I think Iíd give almost anything to be average size. Fit in normal seats...buy a wetsuit on sale....not have to turn every bicycle into a fucking engineering project.

  7. #7
    Join Date
    Oct 2003
    Location
    Banff
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    20,273
    or you can buy the ski that YOU like, and not worry about other people (bigger, smaller, taller, shorter) are using?


  8. #8
    Join Date
    Jan 2006
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    Alpental
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    5,404
    A very wise man once told me, short skis suck. Even the red ones.
    Move upside and let the man go through...

  9. #9
    Join Date
    Aug 2016
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    No longer Alexandria, VA
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    My eyes glazed over reading this.

  10. #10
    Join Date
    Sep 2001
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    Before
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    20,125
    Quote Originally Posted by LiveEastSkiWest View Post

    I can't exactly justify it based on first principles, but I had a gut feel that the ski length should scale up and down with the skier's height. Certainly that keeps things in proportion in terms of what fraction of the ski's length the skier can move their center of gravity over. Can anyone justify that more rigorously? Or does anyone disagree (why)?
    Your gut feeling is common and by and large wrong.

    Read Geoffrey Wests Book SCALE.

    One common misconception spelled out is that most things don't scale linearly, they are either sublinear or super linear.

    And besides, mofro is right.
    Merde De Glace On the Freak When Ski
    >>>200 cm Black Bamboo Sidewalled DPS Lotus 120 : Best Skis Ever <<<

  11. #11
    Join Date
    Mar 2012
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    The Bull City
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    I prefer the ski that looks coolest in the lift line over what's actually best for the terrain and conditions I'm skiing on any given day.
    Here's the formula for coolest looking ski:
    Go that way really REALLY fast. If something gets in your way, TURN!

  12. #12
    Join Date
    Nov 2012
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    flatland
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    ^^^ i think you're on to something

    Quote Originally Posted by ill-advised strategy View Post
    ...I think I’d give almost anything to be average size...
    Your wish will come true. It's just a painfully slow (d)evolution... trust me - and it's worse than the growing pains you remember. 20# of mass & 2.5" of height went missing. Never to be found again.

    *

    Ludicrous thread... there are people (in this thread) that use a ski way longer than you would think appropriate and do it with aplomb.

    dis tu "All of your math ignores on the ground conditions"
    "knowledgeable in escapades of the flesh"

  13. #13
    Join Date
    Sep 2018
    Posts
    906
    Quote Originally Posted by Gepeto View Post
    ^^^ i think you're on to something

    Your wish will come true. It's just a painfully slow (d)evolution... trust me - and it's worse than the growing pains you remember. 20# of mass & 2.5" of height went missing. Never to be found again.

    *

    Ludicrous thread... there are people (in this thread) that use a ski way longer than you would think appropriate and do it with aplomb.

    dis tu "All of your math ignores on the ground conditions"
    Excellent use of the word aplomb.

  14. #14
    Join Date
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    Do you like Gladiator movies?

  15. #15
    Join Date
    Mar 2008
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    northern BC
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    a ski can not tell how tall you are

    a ski can only tell how fat you are

    its not those stretchy ski pants that make you look fat

    its your fork that makes you look fat
    Lee Lau - xxx-er is the laziest Asian canuck I know

  16. #16
    Join Date
    Oct 2003
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    Quote Originally Posted by reckless toboggan View Post
    Epicski called...they want their thread back.
    It's summer
    mtbr called, they want their 27.5 vs 29er thread back
    Quote Originally Posted by blurred
    skiing is hiking all day so that you can ski on shitty gear for 5 minutes.

  17. #17
    Join Date
    Dec 2007
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    Quote Originally Posted by XXX-er View Post
    a ski can not tell how tall you are

    a ski can only tell how fat you are

    its not those stretchy ski pants that make you look fat

    its your fork that makes you look fat
    to be fair, the stretchy ski pants certainly aren't helping the situation.

  18. #18
    Join Date
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    Quote Originally Posted by toast2266 View Post
    to be fair, the stretchy ski pants certainly aren't helping the situation.
    does arcteryx do support stretch pants yet?

  19. #19
    Join Date
    Aug 2014
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    Imaginationland
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    Long skis are dangerous. I sold all of mine after a high speed crash. I am very interested in the formula to ensure I am on the proper length ski for maximum safety. Riding long skis to show how cool you are is not for me. Please keep me updated for my safety. Thank you.


    I am 5'10 165lbs.

  20. #20
    Join Date
    Apr 2005
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    A LSD Steakhouse somewhere in the Wasatch
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    10,759
    #redraxftw
    "When the child was a child it waited patiently for the first snow and it still does"- Van "The Man" Morrison
    "I find I have already had my reward, in the doing of the thing" - Buzz Holmstrom
    "THIS IS WHAT WE DO"-AML -
    ski on in eternal peace

  21. #21
    Join Date
    Aug 2016
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    No longer Alexandria, VA
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    Quote Originally Posted by NW_SKIER View Post
    Long skis are dangerous. I sold all of mine after a high speed crash. I am very interested in the formula to ensure I am on the proper length ski for maximum safety. Riding long skis to show how cool you are is not for me. Please keep me updated for my safety. Thank you.


    I am 5'10 165lbs.
    Angulation, damnit! It's all about angulation!

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  22. #22
    Join Date
    Dec 2003
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    Seattle
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    Quote Originally Posted by SumJongGuy View Post
    Isn't that the one for perfect off load ramp angle to chair speed?
    Quote Originally Posted by Downbound Train View Post
    And there will come a day when our ancestors look back...........

  23. #23
    Join Date
    Mar 2006
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    Missoula, MT
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    19,974
    There's a theory?
    I don't see...any theory...at all.
    [Captain Willard voice]
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  24. #24
    Join Date
    Mar 2008
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    northern BC
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    Quote Originally Posted by toast2266 View Post
    to be fair, the stretchy ski pants certainly aren't helping the situation.
    It doesn't matter how things look ... the ski will know
    Lee Lau - xxx-er is the laziest Asian canuck I know

  25. #25
    Join Date
    Feb 2010
    Posts
    28,862
    ez
    .

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