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

[LiveEastSkiWest]

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?

[Vt-Freeheel]

PugSki Jong

[reckless toboggan]

Epicski called...they want their thread back.

[TahoeJ]

The smaller skier should definitely buy the red ones.

/ end thread.

[toast2266]

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.

[ill-advised strategy]

If me and dantheman had equivalent skier-mass-to-surface-area/length, I’d have to be on skis so long (if they even existed) I couldn’t fit them in typical ski spaces like mogul troughs or entry chokes and whatnot.

It’s one of the things that sucks about being a large man who also loves “action sports”. 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 7’6 standup paddle board because it’s 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 weren’t born big so we know what it was like not being big.....whereas small people don’t necessarily know what it’s like to be big.

I think I’d 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.

[mntlion]

or you can buy the ski that YOU like, and not worry about other people (bigger, smaller, taller, shorter) are using?

[Mofro261]

A very wise man once told me, short skis suck. Even the red ones.

[thefortrees]

My eyes glazed over reading this.

[Buster Highmen]

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.

[SumJongGuy]

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:

[Gepeto]

^^^ i think you're on to something

...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"

[EWG]

^^^ 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.

[mcski]

Do you like Gladiator movies?

[XXX-er]

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

[summit]

Epicski called...they want their thread back.

It's summer
mtbr called, they want their 27.5 vs 29er thread back

[toast2266]

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.

[::: :::]

to be fair, the stretchy ski pants certainly aren't helping the situation.

does arcteryx do support stretch pants yet?

[NW_SKIER]

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.

[skifishbum]

#redraxftw

[thefortrees]

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!

[PNWbrit]

Isn't that the one for perfect off load ramp angle to chair speed?

[stuckathuntermtn]

There's a theory?
I don't see...any theory...at all.
[Captain Willard voice]

[XXX-er]

to be fair, the stretchy ski pants certainly aren't helping the situation.

It doesn't matter how things look ... the ski will know

[margotron]

If me and dantheman had equivalent skier-mass-to-surface-area/length, I’d have to be on skis so long (if they even existed) I couldn’t fit them in typical ski spaces like mogul troughs or entry chokes and whatnot.

It’s one of the things that sucks about being a large man who also loves “action sports”. 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 7’6 standup paddle board because it’s 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 weren’t born big so we know what it was like not being big.....whereas small people don’t necessarily know what it’s like to be big.

I think I’d 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.

what size are you?