Cold skis

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MN Hoser
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Cold skis

Postby MN Hoser » Sat Feb 28, 2015 12:39 pm

What is it that makes skis fast in cold snow? I'm referring to below 10F. Is it long pressure points and low camber?

Jay

osloskier
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Re: Cold skis

Postby osloskier » Tue Mar 03, 2015 2:20 pm

Lots of contact area is good, but I don't think the camber has to be low. My coldest skis are old Rossi X-ium skate skis which have zero splay but a fairly high camber. The tips are quite stiff and tend to dig into the snow, so they are fast only when it's both hard and cold. I tried to use them in wet, soft snow once. Never again. :shock: That experience prompted me to start looking for a warmer pair, and I ended up with the diametric opposite, a pair that does not glide well in dry snow. If you're interested I can take some pics of both pairs so you can compare.

Quote from an article at skiaktiv.no, they are interviewing Madshus' "global category manager for skis" Bjørn-Ivar Austrem about ski selection (http://www.skiaktiv.no/artikkel/3071/ve ... g-ski.html):

Splay: Splay determines the pressure zones of the skis. Skis for warm snow conditions have a marked splay to improve the glide. This yields shorter pressure zones and helps reduce the water film between the base and the snow, which creates suction. Skis for cold conditions, on the other hand, have long pressure zones to produce optimal glide. In cold conditions, a large contact area is an advantage to create a water film that reduces the friction.

– From the splay technology and defined pressure points we get more variables that allow us to tune the characteristics of the skis and how they will behave, says Austrem.

I believe the second mention of "water film" in the quotation is wrong. According to various scientific papers I've read, you never want a water film. The ideal seems to be a tiny, round water droplet surrounding each snow/ski contact point.

The structure is also important, it should be fine and well worn. I have never owned a fine structure sufficiently worn to test that, but I believe I achieve the same effect with Kuzmin's high speed brush, which helps noticeably for cold conditions. I also believe the Norwegian and Swedish teams use steel scrapers to shave off the peaks of the stone ground structure before waxing. They use scrapers from Primateria and a Norwegian guy I've forgotten the name of. There is a paper by Primateria about their results from glide tests which is interesting. I can try to find references if you'd like to read them.

MN Hoser
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Re: Cold skis

Postby MN Hoser » Tue Mar 03, 2015 8:24 pm

I'm interested in the Primateria paper. Thanks for the info on skis. As for camber, I'm referring to the camber mainly at full body wt.

I'm thinking about ordering a new set for cold hard pack.

Jay

Chris
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Re: Cold skis

Postby Chris » Tue Mar 03, 2015 8:47 pm

I think loaded camber height is a bit of a red herring in this situation. Once the center portion of the ski is off the snow when you are standing on it, it doesn't matter much if it is 1mm off the snow or 10mm. The length of the contact zones and pressure profile in them is what matters.

MN Hoser
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Re: Cold skis

Postby MN Hoser » Wed Mar 04, 2015 8:56 pm

Snow is not a flat surface, so I think it does matter if the loaded camber is 1mm or 10mm since a lower camber will carry more weight. There are also the angles. From Zach:

115. The 115 mold has also been around for years. The major difference between the 115 and the 610 is that the 115 has a high point further forward on the ski. This means that, at rest, the angle of attack of the forebody of the ski is steeper. As the ski is loaded and the materials are forced to conform to a flat surface, the steeper angle of attack means more material deformation, and more tension carried in the materials. This tension creates a tight and snappy response, and really secure edge pressure in motion. The 115 is a great ski for hard transformed snow – violet conditions. But in conditions with high static friction, or where the snow crystals can absorb energy from the skis, the added tension feeds energy into the snowpack and steals running speed from the equation.

So I'm thinking about taking 115 mold ski and making it into a fast cold hard track ski. I'm a little nervous that Zach gives it a thumbs down for that application.

Jay

osloskier
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Re: Cold skis

Postby osloskier » Thu Mar 05, 2015 11:13 am

I was looking for the Primateria report yesterday and couldn't find it. Then it occurred to me that it might be written in Swedish. Bingo, there it was.

I'll see if I can find the time to translate the most interesting stuff. But even untranslated, the electron microscope photos and the glide test graph is great stuff.

http://www.primateriasport.se/PDF/Glidt ... 020401.pdf

Summary:

The tests in Boden and Kronby produced many interesting results which allow some interesting conclusions to be drawn, that should be useful to improve ski glide in general, but particularly in cold weather and prepared fresh snow. One interesting observation is that it is possible with both paraffine and fluorinated wax, even if it takes a fairly long time, to relatively easily produce smooth glide surfaces, which is a requirement for good glide in cold conditions. By instead making the glide surfaces truly smooth using Primateria's products, unwaxed skis almost reach the glide of skis prepared with fluor products. That this can be done very quickly with Primateria tools is a big plus. Finally the tests show that there is a great potential to achieve absolute world class glide by combining Primateria products with modern high quality glide waxes.

Translation of Table 1:

Code: Select all

Ski pair   Prep                                              Comment
A          Stone grind S6-1                                  Unwaxed, stone ground base is standard for most skis today (my comment: I
                                                             assume they mean as delivered from the factory)

B          Swix LF4, brushed with Swix T01183B nylon brush   Normal wax prep

C          Toko HF blue wax + Swix FC7 powder, brushed       Standard "pro" waxing
           with Swix T01183B
         
D          Scraped with P-cut, brushed with R-brush (fine    Unwaxed, prepared with Primateria products to remove surface defects
           steel Primateria rotobrush)
         
E          Like D, but prepared with structure tool PH30     Unwaxed, prepared like D but with manual structure
           from Speedy Ski on rear glide surface
         
E2         Like E, but also waxed like C                     Like E, but also with high flouor wax/powder


In Table 2, there is only one new row, A and C are unchanged from Table 1. For row D, they have prepared the ski like E above, but rotobrushed with nylon in addition to polish it further. Without any wax at all, this produces a glide which almost reaches a full standard race prep with powder.

Figure 4 is an untreated stone ground base.

Figure 5 is a stone ground base waxed by a pro.

Figure 6 is an unwaxed stone ground base treated with the P-cut scraper, fine steel rotobrush and nylon hand brush.

Figure 7 has been scraped with a tool from "a competing company". I bet that's Kuzmin. They note the surface contains more defects than Figure 6. I note that they didn't brush it at all, so the comparison is unfair.

The tests in Table 1 were conducted in temps between -12 and -17 centigrade. In the second test (table 2) temps varied between -7 and -12. Rh was 85 and the snow was prepped fresh snow in both cases. Average run speed was 25 km/h.

The tests seem carefully set up, Atomic picked skis that were as identical as possible for them, they tested that the skis themselves performed the same, the order of runs was rotated so all skis were tested in each slot in the sequence, etc.
Last edited by osloskier on Thu Mar 05, 2015 12:05 pm, edited 3 times in total.

MN Hoser
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Re: Cold skis

Postby MN Hoser » Thu Mar 05, 2015 11:58 am

Interesting, thank! I'll have to translate the captions for the micrographs later. Micrographs along with glide tests would be really valuable.

Jay

osloskier
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Re: Cold skis

Postby osloskier » Thu Mar 05, 2015 12:27 pm

Updated with translation of tables and captions.

MN Hoser
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Re: Cold skis

Postby MN Hoser » Thu Mar 05, 2015 8:41 pm

Thanks. Overall, those skis look pretty smooth, so I'm thinking they hardly have any visible structure. So the idea is just or fast ski in cold snow.

Jay

osloskier
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Re: Cold skis

Postby osloskier » Fri Mar 06, 2015 1:58 am

I think it looks like they have scraped away about half the structure depth. You can still see the longitudinal grooves.


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