Sooth Ski: Comparing Skis with Measured Data (2100+ skis!!)

[abraham]

For bending and torsional stiffness, it is more complex. We measure everything in between the supports of the machine, which we typically place at the points where the tip/tail start to rapidly curve up (not at the point of early-rise or at the start of the rocker, that would be too short in most case). Right now, the comparator displays the average value between that. Having a little variation about where you put the support is not critical.

I wonder what you'd get by measuring where the ski crosses +0.5/1/1.5/2 cm vertically from the contact points? That might give you some interesting information about how the ski does in various 3d conditions. Not sure what your machine can actually do, just thinking about options.

I appreciate the nerdery, I'll have to think about this before asking more questions.

[Charlie Don't Surf]

Did you happen to have a similar tool for hockey sticks?

Sent from my motorola one zoom using Tapatalk

[kid-kapow]

This is deeper than you might think!

I do get all of the variables that you mention and fully agree that reflecting all is not only impossible, but kinda meaningless as the variance in production and/or temperature on the materials / how they feel in use is just too great - completely leaving snowpack or skier weight / ability level considerations to one side.

So I am very much supportive of an approximation that is good enough, that is - that gives an overall understanding of the ski, where experienced ski enthusiasts like us can infer how said ski will ski based on the parameters you choose, the materials in the ski and the terrain we ski. Hell, as long as the measurements are standardized then it is an incredibly helpful tool in trying to get these insights.

I also get that it is a tool that can be used incorrectly, like when people look at tech bindings and solely focus on weight. Overdoing the focus on a mm there or a gram there could detract from the main benefit of these data as I see it, good enough approximations to understand how a ski will ski. I had one more point I was going to make here, but forgot it - too tired.

As for the MFree - I am very curious how that construction being so ABS influenced responds to colder temperatures compared to a more "standard" construction, or different wood types or titanal. I've been wondering if the smoothness in the hybrid core was down to it being more compliant torsionally, but that doesn't seem to be the case at all compared to say the Atris - which is very, very interesting.

Again, thanks for your awesome replies - it takes a lot of time to write so detailed replies which is most appreciated - and the awesome database! I really, really appreciate the work that you guys put into this!

[Jason4]

Have you tested multiple skis from the same model/year? I'd be interested in knowing which manufacturers are the most consistent in a production run and which are the least consistent. I just got a new pair of skis that have visibly different cambers and are about 100 grams different in weight from one to the other. It'll be interesting to see if I'm sensitive enough to feel a difference in the snow.

[sk8rat6587]

Did you happen to have a similar tool for hockey sticks?

Sent from my motorola one zoom using Tapatalk

Hockey sticks seem pretty standardized and reliable with flex ratings and accurate kickpoint now. If this was 15-20 years ago with the early composites I think it'd be more relevant.

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[alude]

I do get all of the variables that you mention and fully agree that reflecting all is not only impossible, but kinda meaningless as the variance in production and/or temperature on the materials / how they feel in use is just too great - completely leaving snowpack or skier weight / ability level considerations to one side.

Yeah, I didn't mean to say that you didn't think about all that. You clearly did. There is just a lot to talk about, maybe more than I am willing to type here. Would be more fun around beers! :-)

I do think it is possible to consider most of the important variables. There are much more complicated things! One exemple is the directional stability (https://www.mdpi.com/2504-3900/2/6/315). It is a relatively simple concept to understand and you can use a full finite element model of the ski to calculate it. However, you can use a simpler equation to describe what is going on. It is still "complex" with 5 variables, but all the variable are currently available in the comparator (i.e., camber, ski length, bending stiffness, sidecut radius and edge angle). The idea would be to have some "stability" metric that people can compare instead of looking at all these variable independently. Some might push for other definitions of stability, but I think this one has meaning and that there are many different type of "stability".

I am really curious to see how you guys are interpreting the data. Please share your analysis so that we can discuss it and improve.

As for the MFree - I am very curious how that construction being so ABS influenced responds to colder temperatures compared to a more "standard" construction, or different wood types or titanal. I've been wondering if the smoothness in the hybrid core was down to it being more compliant torsionally, but that doesn't seem to be the case at all compared to say the Atris - which is very, very interesting.

Change of camber and stiffness has been studied here: https://www.researchgate.net/publica...ber_properties

Basically, the stiffness of a ski doesn't change much with temperature because the stiffness of fiberglass, carbon fiber and titanal doesn't change much with temperature, and these are the main contributor to a ski stiffness. If a ski has A LOT of ABS you might see different results.

Camber changes because the different materials have different coefficient of dilatation. If the layup is not balanced above and below the wood core, then its camber/rocker will change with temperature. Designers are typically avoiding building ski like that.

Damping also varies with temperature. I do not like damping (and I think it has little effect)! :-)

[alude]

Have you tested multiple skis from the same model/year? I'd be interested in knowing which manufacturers are the most consistent in a production run and which are the least consistent. I just got a new pair of skis that have visibly different cambers and are about 100 grams different in weight from one to the other. It'll be interesting to see if I'm sensitive enough to feel a difference in the snow.

100g between the two skis of a pair and different camber?? I would think this is now fairly rare.

We did limited runs of what you describe (e.g., measuring all the skis from the 5 pairs on a shop wall). We got pretty consistent results. I would say around 10% on bending stiffness. We didn't compare manufacturers.

[alude]

Hockey sticks seem pretty standardized and reliable with flex ratings and accurate kickpoint now. If this was 15-20 years ago with the early composites I think it'd be more relevant.

We don't have a comparator for hockey sticks but we built the same machine for hockey sticks (https://soothski.com/technology-measure-ski-properties/). It is in used for quality control, R&D, benchmarking, etc.

Hockey sticks are challenging to test and many informations are missing, like the flex on the minor axis (not always proportional to the flex of the major axis), the torsional stiffness of the shaft and the blade stiffness. Mass properties (mass and mass distribution) are also super important because you are dealing with impacts.

But yeah, the big question is what is relevant? Hockey players seems less particular about their sticks than skiers about their skis! :-)

[river59]

Abraham raises good points regarding different methods for assessing stiffness over the length of a ski. I looked up the 190 Salomon Qlab (labeled lab in the app) because it has some pretty unique characteristics w/r/t bending stiffness over length and it is a ski that I love. I found that it was measured as one of the stiffest skis in the database, which is understandable.

That ski in particular is incredibly stiff underfoot and through the tail. However, its stiffness decreases substantially as you move forward of the mounting zone. If I selected that ski sight unseen because I was looking for something that was extremely stiff, I would probably be surprised at the actual stiffness over the length of that plank.

[kid-kapow]

https://www.tetongravity.com/forums/...7&d=1627633314

Y There are much more complicated things! One exemple is the directional stability (https://www.mdpi.com/2504-3900/2/6/315). It is a relatively simple concept to understand and you can use a full finite element model of the ski to calculate it. However, you can use a simpler equation to describe what is going on. It is still "complex" with 5 variables, but all the variable are currently available in the comparator (i.e., camber, ski length, bending stiffness, sidecut radius and edge angle). The idea would be to have some "stability" metric that people can compare instead of looking at all these variable independently. Some might push for other definitions of stability, but I think this one has meaning and that there are many different type of "stability".

Yeah, you def get to this point of too much analysis, at least for me. I tap out well before I need to do actual calculations, but I love that you guys and others provide data that have already been proscessed - I can then just integrate it into something that makes sense to me. Or the good enough approximation type analysis i

Basically, the stiffness of a ski doesn't change much with temperature because the stiffness of fiberglass, carbon fiber and titanal doesn't change much with temperature, and these are the main contributor to a ski stiffness. If a ski has A LOT of ABS you might see different results.

Does this qualify as a lot? PU is a significant portion of the construction, a lot more than I thought initially. That was also why I was so keen to see actual data on their torsional stiffness, to gifure out if their smoothness was down to a damp construction that was stiff torsionally, or torsional compliance


thanks again for you very thought out replies and liks to research - much appreciated

[alude]

Abraham raises good points regarding different methods for assessing stiffness over the length of a ski. I looked up the 190 Salomon Qlab (labeled lab in the app) because it has some pretty unique characteristics w/r/t bending stiffness over length and it is a ski that I love. I found that it was measured as one of the stiffest skis in the database, which is understandable.

That ski in particular is incredibly stiff underfoot and through the tail. However, its stiffness decreases substantially as you move forward of the mounting zone. If I selected that ski sight unseen because I was looking for something that was extremely stiff, I would probably be surprised at the actual stiffness over the length of that plank.

You are totally right. The comparator, as of now, is better at making a first rough pass.

Let us know if you want to see the full stiffness profile of a few skis. Just select them in the comparator and post the link here.

One exemple is the Mantra 102 vs the Mindbender 99 Ti. Very similar skis overall, but with two main differences: camber height and tip stiffnesses. Once loaded, the MB will show more rocker due to its higher camber. Combined with its softer tip, it should float slightly better. On the other hand, the increased bending and torsional stiffnesses of the Mantra's tip should give it a slightly higher speed limit, more edge grip and a more precise turn initiation.

We typically ignore the EI bump in stiffness in the center section of a ski (often a binding retention plate). That section often become much stiffer with the addition of the binding/boot.

[alude]

Does this qualify as a lot? PU is a significant portion of the construction, a lot more than I thought initially. That was also why I was so keen to see actual data on their torsional stiffness, to gifure out if their smoothness was down to a damp construction that was stiff torsionally, or torsional compliance

Damn, I missed that. This seems like a lot!! First time I see so much. I wonder how they build that. Is it also titanal behind the sidewalls?

It would be great to have more info about the PU used, but the stiffness and damping properties of plastics generally vary somewhat with temperature... It also seems like a complicated layup. I would be curious to see if, and by how much, its camber is changing with temperature...

[alude]

We just added 95 new skis from 2021-22... Enjoy!

[alude]

I put here a response to this thread (https://www.tetongravity.com/forums/...36#post6434836) in order not to distract from the main topic of the thread while diving deeper into data analysis.

My confusion comes from the fact that most people and reviews talk about about the metal-Bodacious as a pretty serious ski, needing speed, skilled/strong/heavy driver etc. While on your graph several skis that are talked about as more mellow or playful skis - for example Bentchetler 120s and Rustler 10s are 10-15% stiffer to bend. But as you mention; there are other factors than just flex at play here.

If you look at the geometry of the metal-bodacious, you will see that it has less taper than both the 16/17 bodacious and the 11/12 Billygoat. It also has the same rocker starting point as the 16/17 bodacious, but rises up much slower (i.e., more of an early-rise than a rocker). Waxoff describes that has "And yes, that long effective edge will bite on ice with sharp edges, but you have to edge them past the "flat camber/full rocker" 's pivoty tendencies before loading the edges.". At first glance, the Billygoat seems like it has less rocker because its rocker starts further away from the center. However, it rises up super quickly. The part that is up in the air also tapers toward the tip, so it has even less chance to engage. The metal-bodacious keep widening in the rocker section, almost all the way to the end of the ski. In snow that gives a bit, the low rocker of the metal-bodacious will engage and you will feel the full length of the ski.

It is tricky to make sense of all of these variables and figure out which factors are most important in a given set of skis. Subjective feedback is awesome and hopefully we will be able to use it with the numbers to compare skis when that feedback isn't available. We are looking forward improving how we present these numbers so that they are useful.

Regarding your question about review the Friflyt skitest has data on both metal and non-metal Bodacious. The metal is rated at 7-6-5-5-6 tail to tip, and the non-metal at 5-6-6-5-4. But then again, those numbers are neither extremely high/stiff, nor so far off from one another that it can not be explained by manufacturing tolerances I guess.
For reference, they rate the Bentchetler 120 at 4-5-5-5-5, the same as the Rustler 10.

Makes total sense now!

From my understanding, Friflyt rating is based on how a part of the ski ranks in stiffness with respect to a selection of similar skis. The normalization is kind of "black magic". If I remember correctly, it is based on skis of similar length (and maybe width). So a rating of "5" for the 120mm Bentchetler might not mean the same thing as a "5" for the 100mm Rustler 10...

Another difference is that Friflyt numbers are normalized with respect to their location on the ski. So a "7" on the tip is not the same "7" as the one in the center of the ski (i.e., tips are typically 5x softer than the center section). When we calculate our average bending stiffness, we just do an arithmetic mean of the absolute raw values along the full length of the ski. So if a ski absolute stiffness distribution is 1-4-5-4-1, then our average is (1 + 4 + 5 + 4 + 1) / 5 = 3. With normalization, the 1-4-5-4-1 could translate to 94558. It could be anything really. This is a great way to quickly communicate how stiff part of a ski is relative to the other skis in that category. You can't however go back to an average number with that.

The single average stiffness number has drawbacks. For exemple, if you increase the tip stiffness by 2x, the average is only 3.2. That change in the tip gets kind of lost because the other part of the ski are so much stiffer. However, at the same time, the arithmetic average put too much emphasis on the tip/tail when you considered how skis are loaded... Anyways, we need something better!

Below are our raw measurements. It still doesn't explain why the tip/tail of the metal-bodacious (19/20) are 2 points stiffer than the non-metal on the FriFlyt scale... could be many things!

[J. Barron DeJong]

... Anyways, we need something better!

Below are our raw measurements.

Is there a reason those raw measurement graphs can’t be your ‘something better’?

[alude]

Is there a reason those raw measurement graphs can’t be your ‘something better’?

The feedback that we were getting when we built the comparator was that this data representation was too complicated and hard to interpret for most people. It is even easier to over-interpret. But the crowd here seem to want these details and even more (well, some ;-))! I love that and we might go back to the old representation. It will take a little bit of time to change that though... but we are listening.

[sf]

From my understanding, Friflyt rating is based on how a part of the ski ranks in stiffness with respect to a selection of similar skis. The normalization is kind of "black magic". If I remember correctly, it is based on skis of similar length (and maybe width). So a rating of "5" for the 120mm Bentchetler might not mean the same thing as a "5" for the 100mm Rustler 10...

Another difference is that Friflyt numbers are normalized with respect to their location on the ski. So a "7" on the tip is not the same "7" as the one in the center of the ski (i.e., tips are typically 5x softer than the center section). When we calculate our average bending stiffness, we just do an arithmetic mean of the absolute raw values along the full length of the ski. So if a ski absolute stiffness distribution is 1-4-5-4-1, then our average is (1 + 4 + 5 + 4 + 1) / 5 = 3. With normalization, the 1-4-5-4-1 could translate to 94558. It could be anything really. This is a great way to quickly communicate how stiff part of a ski is relative to the other skis in that category. You can't however go back to an average number with that.

The single average stiffness number has drawbacks. For exemple, if you increase the tip stiffness by 2x, the average is only 3.2. That change in the tip gets kind of lost because the other part of the ski are so much stiffer. However, at the same time, the arithmetic average put too much emphasis on the tip/tail when you considered how skis are loaded... Anyways, we need something better!

Below are our raw measurements. It still doesn't explain why the tip/tail of the metal-bodacious (19/20) are 2 points stiffer than the non-metal on the FriFlyt scale... could be many things!

Yes, there is some kind of normalization in the FriFlyt data, but I don't think it's between types of ski / lengths etc, but rather towards the average at any given time. In other words a 5 was maybe stiffer back in the days than it is now, since skis were stiffer on average back then. (or were they?)

Your point about a x in the tail might be different than a x in the tip is interesting, and has pretty big implications for how one interprets the FriFlyt numbers.

But this is only my understanding. There has been a couple of threads on this earlier as well. Doesn't take anything away from your point that yours and the Friflyt numbers can't be compared directly since you use quite different methods.

[J. Barron DeJong]

The feedback that we were getting when we built the comparator was that this data representation was too complicated and hard to interpret for most people. It is even easier to over-interpret. But the crowd here seem to want these details and even more (well, some ;-))! I love that and we might go back to the old representation. It will take a little bit of time to change that though... but we are listening.

I’m a mechanical engineer, so you can certainly factor that in when considering my opinion vs what a wider audience may be looking for.

Maybe a ‘why not both’ approach? Provide graphs for those looking for details and then simplified number for a simpler generalization? That’s kind of similar to what you’re already doing with width and rocker measurements.

For putting simpler numbers to flex, what about doing something like tip/mid/tail where those numbers are the flex at 20%/mountpoint/80% of ski length. Maybe you don’t just use the flex number at that exact point of the ski, but average it over some distance centered about that point.

I think using a 1-10 scale for flex probably makes sense, with 5 being average of all skis. Of course tips and tails are softer, but i’d still call an average flex tip a 5. So a perfectly average ski would get a 5/5/5 designation. A ski stiffer overall and especially stiff tails might be something like a 7/7/8

[alude]

Yes, there is some kind of normalization in the FriFlyt data, but I don't think it's between types of ski / lengths etc, but rather towards the average at any given time. In other words a 5 was maybe stiffer back in the days than it is now, since skis were stiffer on average back then. (or were they?)

Your point about a x in the tail might be different than a x in the tip is interesting, and has pretty big implications for how one interprets the FriFlyt numbers.

I found this about the Ski Flex Index (SFI):
http://www.endrehals.no/

Ski Flex Index
A longer ski needs more stiffness to distribute the same amount of pressure to the tips of the ski. Flex curves from two skis of different length is therefore not directly comparable. To compensate for this, the stiffness has been recalculated. Through a formula based on average flex curves from skis of different sizes, I have made an index for flex/length.
SFI is a row of five numbers, each number corresponds to a part of the ski: Back tip, back ski, mid ski, front ski and front tip. A completely average ski would have the numbers 5 5 5 5 5, while softer skis will have lower numbers, towards 1 1 1 1 1. A very stiff ski can be 9 9 9 9 9, but in theory the numbers can go higher, since absolute stiffness is a practical impossibility. 2 5 5 5 2 is an average ski with very soft tips, 8 5 4 5 8 is a ski with very stiff tips and a pretty soft mid. 7 6 5 4 3 is a ski with a stiff tail, average mid and a soft front.

There are many theories about ski flex and what is the “best” flex pattern. I have made this diagram as a contribution to that discussion, it is a tool to give your arguments a better foundation. Read it, make an opinion and fight for it.

I still don't know what that means exactly, but "5" seems to mean average at that point on the ski for some subset of skis. This is vaguely defined, but maybe it is enough to shop for skis.

This is not an absolute scale (and I think it is a good thing to help people figuring things out quickly). On an absolute scale, every measured skis would be very close to a 1-6-8-6-1 as the tips/tails are 5-10x softer than the center sections.

[alude]

For putting simpler numbers to flex, what about doing something like tip/mid/tail where those numbers are the flex at 20%/mountpoint/80% of ski length. Maybe you don’t just use the flex number at that exact point of the ski, but average it over some distance centered about that point.

Do you think the averaging sections should be divided by a fixed amount (e.g., 20%, 50%, 80%) or that it should be variable (e.g., rocker section, center to front contact point, center to rear contact point, tail rocker)?

[sf]

I found this about the Ski Flex Index (SFI):
http://www.endrehals.no/

Ski Flex Index
A longer ski needs more stiffness to distribute the same amount of pressure to the tips of the ski. Flex curves from two skis of different length is therefore not directly comparable. To compensate for this, the stiffness has been recalculated. Through a formula based on average flex curves from skis of different sizes, I have made an index for flex/length.
SFI is a row of five numbers, each number corresponds to a part of the ski: Back tip, back ski, mid ski, front ski and front tip. A completely average ski would have the numbers 5 5 5 5 5, while softer skis will have lower numbers, towards 1 1 1 1 1. A very stiff ski can be 9 9 9 9 9, but in theory the numbers can go higher, since absolute stiffness is a practical impossibility. 2 5 5 5 2 is an average ski with very soft tips, 8 5 4 5 8 is a ski with very stiff tips and a pretty soft mid. 7 6 5 4 3 is a ski with a stiff tail, average mid and a soft front.

There are many theories about ski flex and what is the “best” flex pattern. I have made this diagram as a contribution to that discussion, it is a tool to give your arguments a better foundation. Read it, make an opinion and fight for it.

I still don't know what that means exactly, but "5" seems to mean average at that point on the ski for some subset of skis. This is vaguely defined, but maybe it is enough to shop for skis.

This is not an absolute scale (and I think it is a good thing to help people figuring things out quickly). On an absolute scale, every measured skis would be very close to a 1-6-8-6-1 as the tips/tails are 5-10x softer than the center sections.

Huh. I stand corrected

[J. Barron DeJong]

Do you think the averaging sections should be divided by a fixed amount (e.g., 20%, 50%, 80%) or that it should be variable (e.g., rocker section, center to front contact point, center to rear contact point, tail rocker)?

My honest answer is: I have no idea which would be better.

That said, if it were me I’d try starting with fixed values along the length, and not consider rocker profile. That seems like the simpler method to implement, and for users to understand the methodology. If you try that and then find that certain types of skis give weird values consistently - like every heavily rocketed ski shows really low flex in the center and really high in tips/tails - where you might loose some nuance between skis within a class, then maybe consider a more complex algorithm.

Thinking more about how those points for flex measurement are determined, I think it makes sense for the center point be located at the recommended mount point, and looking at the two curves you posted above, maybe that measurement is averaged over a fairly large distance (250mm?) since there’s some irregularities in that zone that should probably be averaged out. For tips/tails maybe you do something like 50% of distance from mount point to tip/tail and average it over a smaller area (100mm?). My thinking is that by using percentages from the mount point you eliminate some variability that could be introduced between skis with traditional vs centered mounts. Could also go with 5 measurement points as above if you want to provide some more resolution in the flex profile numbers. Maybe 30% and 60% of distance from mount point to tip/tail.

Last thing would be deciding how to handle different lengths of skis. Do you just group lengths separately and do your flex comparisons within that length group, or do you try to normalize those numbers somehow so you can compare all lengths? Or do you just throw all lengths in the mix and if longer skis are stiffer than shorter, then so be it? I think I lean toward the latter, but again, no idea if that would actually turn out to be best.

[alude]

FYI, we added 480 skis last week. This means that we now have 850 skis from 2021-22 in the comparator. We measured everything we could put our hands on (well, almost). This includes many long and wide skis, so hopefully the Sooth Comparator (https://soothski.com/) will be more useful now to TGR skiers. Still hoping to add more brands/skis this year, specially the smaller brands.

Thanks to Ski Essentials for letting us measure skis in their warehouse. It was a blast and a real treasure cave!

[gavinski91]

We don't have a comparator for hockey sticks but we built the same machine for hockey sticks (https://soothski.com/technology-measure-ski-properties/). It is in used for quality control, R&D, benchmarking, etc.

Hockey sticks are challenging to test and many informations are missing, like the flex on the minor axis (not always proportional to the flex of the major axis), the torsional stiffness of the shaft and the blade stiffness. Mass properties (mass and mass distribution) are also super important because you are dealing with impacts.

But yeah, the big question is what is relevant? Hockey players seems less particular about their sticks than skiers about their skis! :-)

I've always wondered how much of a market could be made of helping hockey players find a stick that works best for their shot. Having gone through a fitting for golf clubs and seeing how much of a difference that can make, I would imagine the same could be said for hockey sticks. There just isn't a Foresight/GCQuad equivalent for hockey that I'm aware of.

[alude]

You can get "custom" equipment with Bauer: https://www.bauer.com/en-US/my-bauer-landing-page.html

I know they have a stick fitting app that you can use, but couldn't find where it is available. Their reps and some specialized stores have it. It tells you which stick is right for you after filming a few slap/wrist shots.