Tortional vs longitunal stiffness

[Zeppelinskier]

I was talking to a guy yesterday about skis and he had a pair of k2 madin' aks . The madins are cool skis but like most k2s they are a little floppy in the tips. I showed this guy my moment m1s and told them that's what I "charge" on. He said something how they aren't as tortionally stiff as the madins. Saying something about the triaxle fiberglass weave that k2 does on most of their skis. Granted the madins did feel a little more tortionally stiff but laterally theyvare noodles compared the m1s. Which brings the question what's more imporant to a "charging" ski latterial or tortional stiffness?
Also noted is I know there are guys out there skis on hellbents an obseths that charge harder and huck bigger shit then I can imagein, which kinds adds another element to the equation.

So what are your guy's thoughts on this? Can someone school me on this ski science

[XtrPickels]

FWIW, its TorSion

[NorthernSpotted...]

I don't think it's that simple and probably varies from skier to skier and condition to condition. That said, I think that any skiers "charging" ski will be longitudinally stiffer than the rest of their skis. I also think that it would be torsionally softer than their "hardpack/groomer" ski but stiffer than their "powder" ski. Bottom line is that it should be just right. Also, the better the skier, the bigger the window of acceptable stiffness.

That's my engineering school drop-out opinion anyway.

[Zeppelinskier]

Yeah I was thinking that if these guys who are skiing the less stiff skis have a techique that I have yet to discover. Either that or the flex doesn't bother them. I guess that's a good example but why dies k2 make such a tortionally stiff ski but a realativly soft ski?

Also it's funny how my moment are stiffer than the obseths but lighter...

[NorthernSpotted...]

To make it easier to turn but still hold an edge maybe? That's always been my understanding of torsional vs. longitudinal stiffness anyway. All else being equal, more torsional stiffness increases/decreases edge-hold/forgiveness and more longitudinal stiffness increases/decreases stability/turnability.

Again, I might be making stuff up and there are certainly a lot of people around here who know a lot more about this than I do.

[jondrums]

in my limited experience, a stiffer ski allows more fore-aft forgiveness if you aren't well balanced on your skis or if some unexpected bump shows up. A softer ski will hit a bump and throw you forward, while a stiffer ski will keep you centered a little better. That's why its easier to charge on a big stiff ski, but really good skiers can charge on softer skis. They are just better at staying balanced on their sticks, and anticipate upcoming terrain.

I have never felt a difference between various skis in terms of torsional rigidity. Maybe I haven't skied enough skis, or I'm not good enough to tell, or it doesn't matter. who knows?

[Jarle]

Torsional stiffness = edgehold. Longitudinal stiffness = how much the tips flap/jibbyness/etc.

That being said, sick skiers rip on any sticks even though a certain type of ski fits a particular skier better.

As simple as that

[El Chupacabra]

The K2 Made'n AK/ Kahuna is soft-flexing in every direction.

K2's claim to torsional stiffness as a result of the torsion box design they use has not proven accurate, in my experience with their skis.

[Beyond]

Agree about the outcome (more tip flap, good edge hold) but it's not just K2. A lot of makers have been using the same idea - Elan's waveflex, Nordica's embedded metal in the middle of the Enforcer, Dynastar's milled out shovels for instance - for the same outcome. Kastle just removes some of the tip for lower mass and stiffness. And Stocklis are famous for their tip flap.

IMO this is about how most people (maybe not here) ski. Softer tips are easier to initiate, most people don't have a clue how to start a turn decisively. Softer tails are easier to smear and pivot, most people don't have a clue how to complete a turn and then release.

What I'm less clear about is whether stiff tips mean smoothness and soft tips mean instability. A bit of deflection isn't the same as washing out. (Think about Dynastars again.) I've heard a lot of folks argue just the opposite - that softer shovels absorb more of the vibration. I know that's how Stockli's work. Their tips vibrate like hell. But no one's every accused them of being unstable or rough.

[pfluffenmeister]

Stocklis are famous for their tip flap.

...

I know that's how Stockli's work. Their tips vibrate like hell. But no one's every accused them of being unstable or rough.

Really?!?

Normally I hear that Stockli's are stiff (thus no tip flap).

Granted I've only skied the 184 '06 DP (and, in truth, I did find their tips to a little soft, but I didn't experience any tip flap), and the 194 ~'04 XL (blue w/ red flames), and that thing is stiff as hell.

Anyway, to the OP's question, I think that torsional stiffness enhances edge hold and longitudinal stiffness increases your power to crush!!!

Finding the porridge that is "just right" is, of course, what all happy little pow-mongers hunger for.

[Jarle]

Anyway, to the OP's question, I think that torsional stiffness enhances edge hold and longitudinal stiffness increases your power to crush!!!

Finding the porridge that is "just right" is, of course, what all happy little pow-mongers hunger for.

Actually I find that low-profile tips alá EHP is more important than stiff flex for blasting thru things IMHO, if thats what you meen.

[Steven S. Dallas]

K2's claim to torsional stiffness as a result of the torsion box design they use has not proven accurate, in my experience with their skis.

Disagree entirely. I find that the softer tips on the various Seths and Made'ns ride up over crud and other variable terrain and then the stiff "torsion box" underfoot crushes through. Basically, I think the K2 freeride line is designed to be ridden with a centered stance, not driven with a lot of pressure on the boot cuff, and are great skis in all conditions if they suit your style.

[Zeppelinskier]

All good points.
Maybe I just dont understand how you can have a flappy tip and still have edge hold.

Though the center stance idea makes sense because the tips are flapping but the skier is using the edge under foot? That sounds like a sound reason. But really how is it that you can produce a torsionally stiff ski that not longitudinally stiff?? Thats was baffles me and make me question is K2 torsion box really works.

gawd i needed spell check on my itouch...

[Jarle]

All good points.
Maybe I just dont understand how you can have a flappy tip and still have edge hold.

An edged ski (on carve that is) is a stable ski. Old Hendryx was rindoculasy soft in the longitudal stiffness but were/are supermegaawesome when on carve, due to the torsional stiffness. You could/can charge through anything, anything I tell you, but if you ride them flat in as straightlining or huge turns they do suck on tricky conditions. And thats when the long. flex comes to matter, if you don't stay centered.

[Steven S. Dallas]

Though the center stance idea makes sense because the tips are flapping but the skier is using the edge under foot?

That's how I see it. My first generation Seth Pistols can still rail, even with 250+ days on them; stay centered and the feeling is like running a bobsled track on speed skates. You don't feel the tip engage and the tail release, just the solid edge hold directly underfoot.

[Beyond]

Really?!?

Normally I hear that Stockli's are stiff (thus no tip flap).

Granted I've only skied the 184 '06 DP (and, in truth, I did find their tips to a little soft, but I didn't experience any tip flap), and the 194 ~'04 XL (blue w/ red flames), and that thing is stiff as hell.

Can't speak for all Stocklis, have owned the Laser, Rotor, XL, SS, they have fairly soft front ends compared to their really stiff middles. Took awhile to get used to my XL's tips flapping around on rough ice, while my legs were just feeling smoooothness. SS's are stiffer all over, but the tips are still softer than you'd predict for a ski that burly. It works.

[haydukelives]

I have no idea how you would measure torsion rigidity in the shop while you are fondling their skis, but even the longitudinal stiffness can be misjudged, as this chart taught me

http://www.endrehals.no/Flexcurves%202007.pdf

maybe there is a newer version

[Zeppelinskier]

It more or less just hand flexing but I was just guesing. That chart need to be cleaned up to many skis on there. Though it might be more clear on a larger screen( on my iPod).

Yeah I know carving skis are "flappy" but hold and edge like no other. So maybe on the k2s I'll try and be on edge more and see how it goes. This could be a turning point. Though that brings me to wonder why make a stiff ass ski that's not torsionally ridgided?