Ski comparison graphs.

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Originally Posted by endre

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

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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.

I wonder what the flex pattern of Edg would be?

Another surprise:

Karmas are stiffer than Mantras.

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Originally Posted by focus

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.

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Shhhhhhh, not another word, my love;

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

:smile:


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. :D 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. :D

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. :wink:

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

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.

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

http://www.dpsskis.com/site/static/i...t_lotus138.gif

I like it

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Originally Posted by Tony

Another surprise:

Karmas are stiffer than Mantras.

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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.

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Originally Posted by Tony

Another surprise:

Karmas are stiffer than Mantras.

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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?

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Originally Posted by comish

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.

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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?

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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?

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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)

Endre,

Sorry to get you into this.

Now you are cursed.

Be prepared to answer a trillion questions from now on.

Welcome to TGR!

I guess the "Resident Flex Guru" job is taken now. ;)

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Originally Posted by 72Twenty

I wonder what the flex pattern of Edg would be?

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Much like a Branston pickle, I imagine.

edg

Endre

Slightly off-topic when it comes to the flex of the skis, but do you weigh the skis you test, or have you considered doing this?

I know that some of the flex tests are debunking some myths about certain skis being stiff/noodles etc, and I personally think that weighing the skis might similarly be useful for a lot of people when it comes to weight.

For example, Salomons have reputation for being light because of spaceframe technology, foam core etc, but when I weighed some flat unmounted skis I actually found that, for example, a Karma in 177 weighed less than a Foil in 174. I think a lot of people would appreciate this information as well.

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Slightly off-topic when it comes to the flex of the skis, but do you weigh the skis you test, or have you considered doing this?

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Shure skibomb, we measure weight on all the skis. The weight is an important factor. We also calculate the total base area in cm², and from that we calculate gr/cm².

Light skis can be under 1gr/cm² (the lightest, fatest Goode's about 0,7. Heavy skis are up to 1,4 gr/cm², powder skis never go higher than about 1,2).This is an informative number which says something about the weight compared to size, and therefore something about the construction, the density of the core -and in combination with knowledge of stiffness and information about how the ski was built, it can give us clues to strength and durability issues. These are often too uncertain conclusions to be printed though.

We only use this value as an evaluation factor when we write the test, and only print the real wheight and the total base area.

Are these weights available to us somewhere? It would be interesting to compare some of that data.

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For example, Salomons have reputation for being light because of spaceframe technology, foam core etc, but when I weighed some flat unmounted skis I actually found that, for example, a Karma in 177 weighed less than a Foil in 174. I think a lot of people would appreciate this information as well.

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Here are the gr/cm² values for some Salomon skis:
(capski average:1,039 sandwich average: 1,095)

XW sandstorm: 1,078
Gun: 1,14
Foil: 1,103
SPK: 1,111
Equipe GS race:1,152
Siam no10: 1,029

salomon average: 1,095 (all are cap skis)

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Are these weights available to us somewhere? It would be interesting to compare some of that data.

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Total wheights are published in Fri Flyt every autumn, there is no plan so far to publish these numbers, but maby in the future?.

two comments:

- it would be very useful to see ski weights in your on-line tables

- the stiffness graph .pdf is potentially very useful, thanks, and agrees with my in-hand testing for several skis on the graph. by the way, when i hand-flex a ski i usually find a solid table nearby so i can rest the ski at different locations. this gives me a better idea of the flex profile.

however, i suggest you document the ski length used for each model of ski. that has a big effect. as you know, some companies have a 190 that is softer than the 180 version (and weighs about the same), whereas other models or companies might have the 190 much stiffer than the 180 overall.

i looked all over the .pdf and couldn't find the ski lengths listed. ???

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Originally Posted by frorider

two comments:

- it would be very useful to see ski weights in your on-line tables

- the stiffness graph .pdf is potentially very useful, thanks, and agrees with my in-hand testing for several skis on the graph. by the way, when i hand-flex a ski i usually find a solid table nearby so i can rest the ski at different locations. this gives me a better idea of the flex profile.

however, i suggest you document the ski length used for each model of ski. that has a big effect. as you know, some companies have a 190 that is softer than the 180 version (and weighs about the same), whereas other models or companies might have the 190 much stiffer than the 180 overall.

i looked all over the .pdf and couldn't find the ski lengths listed. ???

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For most of the skis I looked at the length is listed on the graph, right after the label for each line. A lot of them included actual length in parentheses if different from claimed.

It IS a killer .pdf for comparing different skis. If more general info was included with the layers re: weight, actual dimensions, etc..... a lot of work, I'm sure....

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Originally Posted by focus

For most of the skis I looked at the length is listed on the graph, right after the label for each line. A lot of them included actual length in parentheses if different from claimed.

It IS a killer .pdf for comparing different skis. If more general info was included with the layers re: weight, actual dimensions, etc..... a lot of work, I'm sure....

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thanks. my screen is small so those length numbers were almost invisible on the graph, but i can see 'em sortof. i couldn't figure out why the length wasn't listed on the left-hand layer table.

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Originally Posted by focus

If more general info was included with the layers re: weight, actual dimensions, etc..... a lot of work, I'm sure....

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Maby next year, focus. This winter I've got todos waay over my head. :(

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Originally Posted by endre

Total wheights are published in Fri Flyt every autumn, there is no plan so far to publish these numbers, but maby in the future?.

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What issue was this and is it available for sale online? I speak Swedish, so might be able to make sense of it all ;)

It was over three issues (from october til december), the ones depictured in the beginning of this thread. You can buy old ones online here:
http://www.eksponert.no/epages/Ekspo...ries/6000/6100

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Originally Posted by pechelman

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.

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In the real world, it makes every sense to separete these two. Not only is camber a geometrical entity that in a powder ski come into play even when the ski is pretty much unloaded, camber also acts more like preload than stiffness. So, camber doesn not change stiffness, only the relative pressure differnt parts of the ski will make on the snow. This is actually what you are saying yourself, so I don't know why you at the same time argue that one (Endre in this case) should measure these two things at the same time?

For me its perfectly clear that we can understand much more about a ski by knowing stiffness and camber profile separately than to device some kind of measurement that tries to get both of them into one set of numbers. I fact, if we would go that "combi" route, we would have to take sidecut into account to (at least for anything but real powder skiing) since as Endre points out earlier, the sidecut will infuence how the ski bends in a turn.

To Endre: it would be extremely useful to put in some "classics" in the graph like differnt incarnations of the Völkl Explosiv and (at the other end) the Sanouk. Possible?

I love the work you've put into this and think this is very, very interesting. I would actually bet that really good skis will end up showing some interesting correlations between sidecut curve and stiffness if you'd look into it. It would be interesting to know if there are ski manufacturers that have such a theoretical understanding of how these things work together. Such an understadning would of course NEVER replace good old prototyping-testing, but I bet it would still make skis better in the long run.

yea its preload. This preload changes a skis percieved stiffness. No doubt.

HOWEVER, you also missed my point. When you increase the camber, you change the orientation of each layer of the ski at equilibrium. THEREFORE, you also change the skis stiffness (seperate issue from preload).

You are placing the layers in a plane that is not perpendicular to the applied force. Shear is the dominating force in the layers when flexed, however, you are now sending a greater portion through each layer and in-plane to the layer. It may seem small, but tell me, is wood\fiberglass stiffer in bending or in tension\compression? That difference is NOT small.

If this doesnt make sense to you, think of it as "interlaminar preload" or just that much more each material is required to shear before a certain amount of deflection occurs.

As far as sidecut, that is a valid argument, however Im not that interested in what contribution my sidecut, or lack thereof, contributes to my ~100mm skis on a hardpack groomer. The only time Im seriously flexing the sidecut of my skis are when Im on steep terrain, and then the terrain itself has more influence on how much you're able to flex a ski.

and its a simple matter of addition
you dont want to know cambers influence, just fucking subtract it.

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To Endre: it would be extremely useful to put in some "classics" in the graph like differnt incarnations of the Völkl Explosiv and (at the other end) the Sanouk. Possible?

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Shure! I just have to find some to test. I'll see what I can find, probably won't be this month though.

(thanks for the support by the way, I am tired of arguing with that guy)

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Originally Posted by pechelman

HOWEVER, you also missed my point. When you increase the camber, you change the orientation of each layer of the ski at equilibrium. THEREFORE, you also change the skis stiffness (seperate issue from preload).

You are placing the layers in a plane that is not perpendicular to the applied force. Shear is the dominating force in the layers when flexed, however, you are now sending a greater portion through each layer and in-plane to the layer. It may seem small, but tell me, is wood\fiberglass stiffer in bending or in tension\compression? That difference is NOT small.

If this doesnt make sense to you, think of it as "interlaminar preload" or just that much more each material is required to shear before a certain amount of deflection occurs.

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But in the ski, all layers support each other, other wise fibers on top would immediately "crunch" when flexing the ski. Also, camber is so small, I seriously doubt the effect you describe has any effect on actuall stiffness.

Don't get me wrong, I understand camber is a super important concept. But it is in itself so complicated and it will do different things to the ride for differnt riders on different skis in different conditions. Two examples: On hard snow, camber will influence the ride more if you're a "casual" rider. Many race stock skis I've had came almost completely flat becasue you put them so much on edge anyway so the sidecut does the job of "preloading" tips and tail and no camber makes transition between turns smoother. In soft snow, camber will infuence the ride more the stiffer the ski is.

That is the reason I like it to be separate.

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Originally Posted by endre

Shure! I just have to find some to test. I'll see what I can find, probably won't be this month though.

(thanks for the support by the way, I am tired of arguing with that guy)

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Great. No hurry, it was just an idea for the future. Are you in Oslo?

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Originally Posted by HitMe

Great. No hurry, it was just an idea for the future. Are you in Oslo?

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Yes I live in Oslo right now. Won't be forever though, going to find some little pow paradise far away from this city one day.

There used to be a little graph thing on here that you would select different ski models and they would all be compared on a similar graph, that way you could just select what you want to see. Where did that go?

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Originally Posted by 123ski

There used to be a little graph thing on here that you would select different ski models and they would all be compared on a similar graph, that way you could just select what you want to see. Where did that go?

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What cha mean "used to be" and "where did that go"?

It's still here, guess you better read this thread again.

I have updated the PDF with next year's skis, plus a new stndard for describing flex profiles in a row of 5 digits, the "Ski Flex Index" (SFI)

http://www.friflyt.no/files/SFI_2008.pdf

Anyone know if there is a 09 version of the Ski Flex Index graph?

I am not shure if there will be one, I have tested next years skis, but as it looks now it is too much work to trace all the curves. The SFI numbers will probably be published though, they describe ski flex better than the curves. (and take a LOT less energy to produce)

All the data (flex, weight, surface areas, rocker sizes, true lengths etc.) will also be printed in Fri Flyt's ski test issues this fall, about 150 skis tested

Great job Endre; any luck parleying this into professional work?

There were many heated discussions on skibuilders; everyone who thought their ski should "rank" differently had lots to say...

I think it's pretty freakin' awesome.

http://www.friflyt.no/files/SFI_2008.pdf

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Originally Posted by Imz

Great job Endre; any luck parleying this into professional work?

http://www.friflyt.no/files/SFI_2008.pdf

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Wait and see, I think it will be noticed. (at least here);)

e

When will SFI 2009 hit the so called internet?

This fall is all I can say, I have got some other things going on, may be late october?

Any new flex data available?