Ski comparison graphs.

[routter]

I'm guessing, in his analysis, Endre has transposed the X an Y axes, where X should represent the ski length and Y the stiffness?

[endre]

That's right routter, sorry about that.


There is a big PDF comming up, with curves of more than 100 2007 skis, all in different layers so people can turn them on/off as they like. The file is printeable but not editable.

It will be out on some website (probabliy www.friflyt.no) soon. I'll let this forum know.

[endre]

I have made a PDF with flexcurves of 85 of this year's (2006/07) skis. I have more, but it is a huge job to put all in, so I just took the most interesting ones (not carving skis etc).

I have put all the curves in different layers, so you can visualize the different skis by visualizing these layers. (Thanks for the tip Skibomb)

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

I certainly hope this is of good use! If the responce is good (has been so far) we will continue with similar curves next year.

Endre Hals
Fri Flyt

[focus]

Well this is a fine how-do-you-do. The plot thickens...

Okay, there's no way I'm gonna assert I was right if the chart really does say "stiffness" in Norwegian. That was apparently a misstatement by the OP., who I thought we had to trust since the info was all going to be in epic Norse verse. BUT, good on Pechelman for checking out that other thread and discovering that, lo and behold, it's in English. Problem solved.

I totally agree w/ Pech that this Endre dude, who made the tests, was indeed testing for stiffness. He describes, to some extent, his real methodology on the other forum. He was NOT hanging weights as the OP said. He was NOT putting the skis on tip and tail stanchions and measuring for flex (or total displacement) as the OP implied. This is where it all went off the rails, due maybe to language issues or just bad assumptions; who knows?

Anyway, he built an apparatus--which was not mentioned before--that allowed him to bend the ski in little increments--by which he was able to compare the stiffness measured in one area to the stiffness measured in the next. Basically he put his device on just a section of the ski at a time, clamped it down and applied a 500-newton point load to the ski 10cm from the clamp. Then he measured the displacement out at that clamp-plus-10cm location. Then he unclamped everything, moved the ski 10cm, and did it all over again.

As Pechelman says, there are problems with this bit-by-bit method, mostly because it seems to ignore certain aspects of how a ski behaves--overcoming the preload of the camber is one big one; removing the bindings and pretending the ski is free to flex unencumbered is another one. There are a number of other issues that make this test less than a full picture of relevant issues in ski stiffness: A ski is never a true cantilever for instance, and it never flexes while fixed to any location. Nevertheless, these graphs would seem useful (if the f'n thangs were even calibrated ) to compare the pre-mounted, non-real-world, basic stiffness of one area of one ski to one area of another.

Unfortunately, we can't do that yet. But this guy's li'l test is a good start, on the bigger, and more helpful total project of representing ski flex behavior.

Again, I feel bad about the earlier rant. It was true, for what we knew and were being told at that point, buuut alas, those things didn't turn out to be the fact, so ultimately it's my bad... Thanks to Tony, Comish, and Pech for continuing the critical thinking.

FUUUUUUCKKK YOOOOUUUUUU!!!!

There were multiple threads about the subject, and I didn't post until I'd read them and the associated links. The OP, at the time of my post, was NOT the only information we had about the subject. Anyhow, I hadn't seen your reply to my post until just now.

But thanks -- for being a dick, being shown wrong, and then STILL not admitting fault.

You're a peach.

[pechelman]

Endre, Many thanks for posting over here and posting that incredible pdf.
I think it would be interesting, albiet a lot of work, to test a few of the strange skis, such as the BD, by placing strain gauges\taking measurements every 10cm and then flexing the ski as a whole from the mount location as if you were skiing it with a boot. I doubt youd want to go through so much trouble after what youve already done, but I think it might shed some important life on the true macromechanical properties of the ski, rather than just small segments of it.
Either way, thanks again! I look forward to any future updates on your testing!

And I agree with Tony. This is most definitely sticky material. Maybe endre could get with marshal and add that link to his Reccomend list? Right now this thread seems to be all over the place with the pertinent information towards the bottom rather than the top. Tony, thanks to you as well for calling this thread to endre's attention!

[XtrPickels]

Looks awesome. Thanks for getting this up

[Singel]

Fucking kick ass. For anyone else wondering why they are looking at a blank graph: read the text under the title.

[skibomb]

I have made a PDF with flexcurves of 85 of this year's (2006/07) skis. I have more, but it is a huge job to put all in, so I just took the most interesting ones (not carving skis etc).

I have put all the curves in different layers, so you can visualize the different skis by visualizing these layers. (Thanks for the tip Skibomb)

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

I certainly hope this is of good use! If the responce is good (has been so far) we will continue with similar curves next year.

Endre Hals
Fri Flyt

Thanks for following up with the PDF Endre. This will be very helpful to a lot of people!

[endre]

...I think it would be interesting, albiet a lot of work, to test a few of the strange skis, such as the BD, by placing strain gauges\taking measurements every 10cm and then flexing the ski as a whole from the mount location as if you were skiing it with a boot. I doubt youd want to go through so much trouble after what youve already done, but I think it might shed some important life on the true macromechanical properties of the ski, rather than just small segments of it...

The way you suggest is very easy to do, and it has been done before, but the method has some important problems, I'll try to explain some of them:

If you f.ex take a picture of the ski from the side when it is loaded at tree pionts (both tips and the binding area) and then trace the ski's flexed arc, you will get a curve which is a result of a lot of variables:
-the ski's camber (positive or negative)
-the length of the ski
-the moment (length*force)

this would maby provide some Idea of how stiff a ski is, but it is way to unprecise for any real comparison of f.ex a special part of a ski. When you bend a ski into the snow, the ski gets bent differently according to the different snow conditions. When you ski powder the forces are dustributed all over the base, not only at the tips! When you ski ice the tips are loaded until total deflection, which will be determined by the shape of the sidecut.

My point is that ski flex is made up of too many factors to be visualized or tested in an easily understandable way. To communicate flex in a realistic and compareable way, we should all learn the same "language". When everyone gets used to seeing flex as a curve in a diagram, we can start communicating and discussing flex like we've allways been talking about shape, radius and camber.

But I seriously understand your point pechelman, it is much more intuitive to read flex like on the picture below, it just isn't very compareable!:

[pechelman]

Its got nothing to do with being intuitive.
Its got everything to do with producing and devising a test that will most accurately relate whats going on with the whole ski, and not just an isolated 10cm section.

The whole idea behind putting straing gauges and measuring displacement is so that you have a means to quantify whats really going on everywhere. Obviously you know this.

Ski length can be normalized by relating everything as a percent, similar to how strain to failures are specific for engineering materials.

Camber is an important part to how a ski works, so I think your method, while having its merits, is honestly not very useful to the practical person. Excessive camber, in either direction, can place the loads more inplane with the ski and therefore drastically change how it flexes to the skier. As as skier, I couldnt give ONE shit what the fourth 10cm of my ski feels like.
Additionally, this camber will drastically change how much a ski can flex.
Imagine if the legend pro had another few inches of camber. As it is, the metal sheets keep displacements to a minimum.

Also, Im going to be critical here, but I do not appreciate how your curves are smoothed. Did you actually measure the ski in the many places to produce such a smooth curve? What is your certainty that those interpolated values are actually correct? As an engineer, Id prefer to see a point to point graphical represenation. Really Id rather just have the excel data myself and do what I want, but I dont care *that* much.

anyway, i understand where you're coming from of course, its just that we have slightly different methodoligies and philosophies as engineers. In the end, if I had to choose, Id rather have the curves with as many variables as I can incorporate.

My background as a racecar engineer comes into play here, as one of the numbers I most valued in design and suspension alaysis was my racecar's installed rigidity...ie the stiffness of the entire racecar when torsionally and logitudinally loaded from the wheels. It was A LOT of work to get that number through physical and analytical testing, but it was really invaluable.

maybe i missed it somewhere, but whats f.ex?

[endre]

Its got nothing to do with being intuitive.

Intuitivity has everything to do with it! If you can't understand what you see, what's the point?

Also, Im going to be critical here, but I do not appreciate how your curves are smoothed. Did you actually measure the ski in the many places to produce such a smooth curve? What is your certainty that those interpolated values are actually correct? As an engineer, Id prefer to see a point to point graphical represenation. Really Id rather just have the excel data myself and do what I want, but I dont care *that* much.

We measure 15-20 points on each ski, that makes very smooth curves. The tracing we do afterwards is purely cosmetical, and has got no practical meaning

Camber is an important part to how a ski works, so I think your method, while having its merits, is honestly not very useful to the practical person. Excessive camber, in either direction, can place the loads more inplane with the ski and therefore drastically change how it flexes to the skier. As as skier, I couldnt give ONE shit what the fourth 10cm of my ski feels like.

Ofcourse camber is important! I never said it isn't! But it is a different chapter, and you have to separate camber from stiffness, because they do different things to the ski! If you like, I can give you the camber, torsional stiffness, wheight, all geometry and values calculated from it (radius, area etc), dampening frequencies, core thicknesses and so on. You can not, however, put all those numbers together and expect that number to tell you which ski is best. They all say someting, but only separately.

anyway, i understand where you're coming from of course, its just that we have slightly different methodoligies and philosophies as engineers.

So what am I, and where do I come from, pechelman?

maybe i missed it somewhere, but whats f.ex

Sorry for using some norwegian phases, (f.ex. means for instance)

[shirk]

That pdf file kicks ass.

It's nice to see some data that can be used as comparison tool of ski flexes.

[MrZach]

Wow, nice job.

[Tony]

Endre,

Thank you so much for sharing all these excellent work with all of the maggot community. This last pdf you posted is pretty much the works and very practical for mags doing their own one-to-one flex comps.

ATTENTION MARSHALOLSON: THIS PDF SHOULD BE STICKY MATERIAL.

Most probably included in the Recommended Ski List sticky.

We'll need to see to it.

[Tony]

The PDF is now part of the infamous TGR's Tech Talk Recommended Ski List sticky.

Again Endre, hell of a job.

I'd even play myself with it charting the skis I could find in the 0-10 "Relative Skis" flex ranking.

Happy to say they are on the right place in their rank.

DON'T FORGET THE SKIS IN THE PDF ARE ALL 06/07 MODELS. For eg, the 06/07 Gotama is almost as stiff as the Mantra in the PDF while in the "Relative Skis" flex ranking is lower cause it was the Gotama's first version (less stiff).

Two things caught my eye though:

1) The Big Daddy must have been a much stiffer ski in its earliest encarnation, cause for eg. in the PDF is way less stiffer than the ANT but OTOH it is 1 point stiffer in the ranking.

2) The Squad in the PDF has stiffer tail and shovel than the LP but softer mid section. Good to know cause I thought it was a stiffer ski all through.

[pechelman]

But it is a different chapter, and you have to separate camber from stiffness, because they do different things to the ski!

In the real world, it is impossible to seperate camber from stiffness, BECAUSE, camber has an effect on stiffness. The do different things, but it is impossible to ignore the fact that camber has a contribution to stiffness.

The more positive camber, the more the forces from the tip\tail and at the boot will be directed in-plane to the ski, rather than through the ski.

Whats stiffer, flexing a 2x4 thats completely perpendicular to the applied force, or flexing a 2x4 thats 45 degrees from the applied force? I shouldnt have to answer that.

a little real world example for ya;
Why is a bi-directional composite laminate generally stiffer in bending than the equivalent unidirectional composite? Because that SLIGHT undulation in the over-under of each tow in each layer produces a stiffening effect similar to corrugated cardboard. In engineering speak, it places the longitudinal axis more in parallel\in-planewith the applied (bending) forces.

The same is true for camber. It is impossible to seperate these effects in the real world. It contributes significantly to a skis overall stiffness.

FURTHERMORE, especially in skis with metal sheets, the issue of camber is even more pronounced now because in order for the ski to flex, it must induce a significant amount of sheer streeses in the plates and at their interfaces.

I also dont see what your problem is with getting the stiffnesses for each component of the ski, camber, bindings, through the thickness properties, etc, and just adding them. Its a simple issue of springs in parallel. Just freaking add them in the appropriate location as you would resistances in series.

sorry if im being so annoying, guess Im just frustrated you missed my point.

great work on the pdf.

[72Twenty]

I wonder what the flex pattern of Edg would be?

[Tony]

Another surprise:

Karmas are stiffer than Mantras.

[ShawnB]

FUUUUUUCKKK YOOOOUUUUUU!!!!

There were multiple threads about the subject, and I didn't post until I'd read them and the associated links. The OP, at the time of my post, was NOT the only information we had about the subject. Anyhow, I hadn't seen your reply to my post until just now.

But thanks -- for being a dick, being shown wrong, and then STILL not admitting fault.

You're a peach.

Shhhhhhh, not another word, my love;

You had me at "fuuuuuuckkk yoooouuuuuu!!!!"




No, you were definitely right, and I was definitely wrong. How's that?

Look, you were correcting someone, saying "if you read the thread, etc., etc." I'm serious, I thought you meant this thread; the thread you were writing in/we were reading right at the moment. As in, that person hadn't bothered to read the information directly above. Which happens, um, a lot. And it seemed you were taking them to task for that, for not reading what was posted above.

If that is what you had meant, and if the (mis)information in this thread was what was being referenced, then my "corrections" & exasperated attitude make more sense. My POV would be pretty reasonable in that context. But it turns out that was not the case; that you were referring to something else, and that something else was a link to a site with facts in English that told a different story (not clear that this was a thread but whatever). So long story long, I mistook your meaning, and thus ended up with an assessment that was wrong. Sure, internally it made sense. But it was still wrong. Oh hey, did I mention it was wrong? As in, you were right all along, and I didn't realize it at the time.

Now focus, wontcha take me back, baby? I been bad, and sho' nuff done you wrong, but I can be better. I can be everything you need, just give me that chance, shoog; jus' that one chance....

Oh, by the way I am a dick, so deal.

Soap opera over (?) Back to graphs and charts and modulus of elasticity yet?

[jibco]

That pdf is badass!! Thanks.
observations:
It would be great to have an Explosive for reference.
The Goat over lays a PE pretty close
The Fischers are super wack looking (maybe not with bindings?)
Tony, the volkls felt like that to me in the store.

[LaramieSkiBum]

it would seem your working with DP or alteast they have the same thinking:



I like it

[LaramieSkiBum]

Another surprise:

Karmas are stiffer than Mantras.

mine are super beefy and thick. I've tried to destory them, and only have chipped the top sheet. A few core shots, but damn they are thick. Pick a pair up some time, IIRC they have a tip to tail metal strip along the outside edges, but not a full width strip.

Matras OTH seem much thinner and flexy, better suited for powder.

[comish]

Another surprise:

Karmas are stiffer than Mantras.

I agree with this after skiing both. I liked the Karma's more. I would actually consider buying a pair of Karma's while I wouldn't buy a pair of Mantra's. See my reviews if curious on more impressions.

That PDF Rocks! Thanks for doing that. It makes it very clear.

How much variation do we think size makes? Props for including which size was tested. For example, the 177 Mantra is pretty dang soft based on the skis I was comparing (Stormrider, LP) but those were all mid 18x lengths. I'm assuming the 177 mantra being for smaller people is built softer. So, if one really wants to compare, you need to find skis in the same relative length to compare apples to apples. A valid assumption?

[LaramieSkiBum]

I agree with this after skiing both. I liked the Karma's more. I would actually consider buying a pair of Karma's while I wouldn't buy a pair of Mantra's. See my reviews if curious on more impressions.

fyi my karmas have some pretty significant camber too, I have no clue what mantras have, but my perception is that it's not much?

[endre]

How much variation do we think size makes? Props for including which size was tested. For example, the 177 Mantra is pretty dang soft based on the skis I was comparing (Stormrider, LP) but those were all mid 18x lengths. I'm assuming the 177 mantra being for smaller people is built softer. So, if one really wants to compare, you need to find skis in the same relative length to compare apples to apples. A valid assumption?

That's right comish, good point! A longer ski needs to be equally stiffer to get the same amount of power to the tips. ,We don't have time to measure all lengths, and don't make a conversion table, because the ski factories seem to have different ways of increasing stiffness. Some make the different lengths completely different skis. 4frnt EHP 190 and 193 are extreme examles of this. that is why we put both in here. EHP 193 is more like a conseptual ski, unlike any back ski I have ever seen before. 190 is stiff, but still pretty normal.

But in general, you can try to visually scale the curve all directions til the right length, and you will get somewhere near the right increase in stiffness.

(the length of every curve is the ski without the tips)