torsdag 9. mars 2017

"Your Skis Maybe a Bit Over Excited"? - XC Ski Flex - Arch Tension and Choosing the Right Ski.

Ah the dangers of Google Translate. If you ask it to take the Norwegian  for what a ski's "spenn" means,  Google will give you 'excitement'..... because 'spenn' has a meaning somewhere around 'tense' and is used for excitment as well as the pre-tension in your ski bend!

However getting the right 'spenn' in the skis you choose is a science. As with all good science there are equations and formulas, where you have to input the data and pre-conditions to get a correct or at least appropriate answer out of it. It is all too easy to get things wrong and end up with a pair of skis which are incorrect for your ability, your usual local coniditons or for that Birkebeiner once in a life time ski-run. 

Trend to Stiffer Skis at Elite Level

For those of you who don't follow the sport, there has been a trend over the last five years or so,  where skiers in the classic, kicking style have moved towards a predominant 'double poling' technique  (Staking in Norwegian) with skiers not doing any diagonal kicking at all, and using a 'service' kick wax to comply with the rules. Mandatory 'diagonal' ie kicking sections have now been introduced but on some runs like the Marcialonga it pays to go fast and pole along.

 Skis for this are accordingly harder in their arches - they have higher pre tensioning in their design, such that the skier is held above the snow and glides on the optimal sections with a good contact area. Also there is a degree of return-spring which helps lift the skier up for the next full body compression which thrusts them forward.

In effect these specialist skis are getting quite like skating skis. You can indeed say that classic (when not fishboning up a hill) is actually parallel skating if you are doing it correctly, with the base of the ski providing the resistance rather than the edge when you power outwards and backwards in skating.

However this type of hard, poling ski is just not going to be anywhere near the ideal ski for a new beginner or even the average club competitor. 

The Wrong Skis Gromit!

This trend to harder sprung skis is too much of a good thing in classic, both for the FIS and perhaps for yours truly! It is a myth that for the average fitness skier or club level competitor, a softer ski gives necessarily bad. (try running this through google translate from some aficionados in Oslo) . 

Take me as a perfect example. I wanted a pair of sports skis, or training skis as they are often called, which are thinner and nearly straight along their legnth, and designed therefore only for prepared runs. I would say that my tour skis were neither all that good for 'tram lines' nor for back country, but after some reflection they have their place and certainly if you are carrying weight or have long down hills, then some in swing on the side and a 2.5 inch or so broad ski is of benefit, especially in new snow. I digress, I had noticed as I wrote yesterday, that pensioners were flying past med despite my good efforts, and they just seemed to have more efficiency out of skinny skis. 

Now as it happens Atomic chose to launch a quite advanced training ski, pretty much pro level, with a 'mohair' insert as their Skintec TM waxless solution. They have been out at least four seasons now, and I saw their distinctive orange markings more and more often over time, especially amongst pensioners who choose to have another round of coffee and cake rather than be bent over a pair of skis in the waxing shed. I was more sure about the tension technology in fact than the waxless because it is a carbon supported system which is compliant until you press in the swing and kick, when they in theory then go through to a new phase when they act like a softer ski. ( Read Yesterday's blog for the skin technology verdict).

The skis work really well in a variety of conditions, but and here is the but, they do not like soft base snow. Here it is hard to get a kick because you seem to just keep digging for traction, while also it is hard to double pole well because the narrow skis on my weight plough down into the substrate. I don't feel the skin is to blame at all. I just really hadn't thought about how the average conditions the last three years or so have been down here, near sea level in South Norway.

Factoring in Variables When You Get *Fitted* for New Skis

There is then a rule of thumb here with conditions. So this should be an input to what level of 'excitement' your skis have ( a particle physcisist may be quite happy with the use of 'excitement' in the direct translation for level of pre-tension, flex or arch stiffness as you like to call it) The first inputs to your skis though are as follows.

1) Weight
2) Style - ability-  goal for season
3) Expected average conditions
4) Height

Usually the common-or-garden shop assistant would have sold you a ski using a height scale ten years ago here, but now luckily they have tensioning machines with feeler gauges at hand in most any decent shop or sports' chain-store. My 208cm skis are the same as those I had measured up for three winters ago, when the kind chap in the ski section showed me that at 110 kg I would just be experiencing some friction on the skin. 

However there in lies the myth- you do not really need to be fully suspended above the snow in the kick section. 

A really good kick waxing job will present very little friction - in fact if you look at the bottom of Pro's ski's while they walk to the start line, you will hardly be able to spot the wax. On a standard ski as well, you don't have to stick to the full legnth kick-zone all the way to wax mark (a good shop should put on by using the aforementioned machine!) and you should also remember that clister is at least an inch back from this at the front of the ski and the heel. In softer conditions and new snow, the whole ski will be in contact with the snow, but in gliding or downhill the most pressure will be where you want it, and a good wax or clister job will not pick up any excess crystals, and in fact should shed them during glide.

So you begin to see that this is not a descending order of factors, it is a set of inputs to the equation which will give an appropriate answer, with some small print.

Weight will give you then a guide for the tension of the ski you need, and height will help a shop assistant a little here if they don't have the skis premarked for kg skier weight as quite a few shops do now. This is because wooden core skis, the majority of amateur training skis, vary from ski to ski. They are luckily for us,  first matched as a pair in the factory, but they usually do not mark the ideal weight because it varies with style you see ! 

Style and ability now comes into play. If you are a keen sports skier, used to 'staking' ie double poling, and you have a powerful kick, plus a knowledge of waxing,  then a stiffer ski is appropriate ie the wax zone is measured as being free by the feeler gauge, or by the old fashioned A4 paper sheet on the floor with both feet on the skis. However, if you live in the North of Norway or ski most often at some altitude, then a softer pair will be better for the softer conditions you will encounter. 

Conditional Rule of Thumb Nr 2

Think of where you are going to be skiing and when you do most skiing:  

Do they prepare good tracks with a heavy machine, which would suit a harder 'spenn' in a ski?

 Do you get a lot of new snowfall or do you tend to ski a lot in older, harder tracks after an inital dump of snow each winter? 

This is then the second rule of thumb- for softer expected conditions, a softer ski will be better ande vice-versa. In hard, abrasive conditions, you want to heave your wax zone off the snow and limit the time the ski engages with the hard snow base, while often using clisters. Also you have the opportunity to double pole more which is proven to be more efficient, hence top elite atheletes are doing it more and more as I mentioned above. 

A softer ski will have less of the recommended wax zone off the snow, but there will be so little pressure exerted there onto soft snow bases that it will not slow the ski down. Over the course of a 10km ski run, you getting frustrated with how hard it is to kick down for grip will be far worse, and any back slipping or reversion to fish-bone style early will not be welcomed. 

Soft skis however have a disadvantage in soft, wet conditions, when the ski can suck more because it is all deeper into the substrate, but a nice thin clister job will help, or gliding the skin with glider spray will stop it becoming water logged and 'sucking' - which was quite extreme one day last week for me as the sun worked its way up a good downhill - it felt like being on a bike and slamming the brakes on as the skin entered a suck from being waterlogged! 

Now I put height at the bottom here, where as traditionally it was at the top. It could be that you rather like a bit of skating, or combi skiing under way just for fun, and are happy to pole along at your own sweet pace. Alternatively you may have poor tramlines or none at all, and need to find both grip and glide on beaten down flat snow. Here a higher amount of stiffness would be what to get, but not so high that you would struggle to get kick-grip.

Height has something to say with stability of the ski and balance such that the leverage of your body is matched by the legnth of the ski, but as said above, it is kind of a rough guide. Some manufacturers like fischer, have a 'short cut' design which is really saying you get a bit better spring from a shorter ski than would be traditional. My racing ski fits I have looked at, are all up at the very longest in the range, from 208 to 212 cm (2.08m- 2.11m) long due to my imodest total weight. 

Vary Your Wax Zone with Conditions

Once you understand the relationship between style, ability, weight and conditions, you can think about what length of wax zone will help get the most out of your skis. 

In softer, cold, new snow conditions you can choose to use a very hard base wax on the legnth of the zone, green or white, while then applying the day wax a good few inches back in, and perhaps stopping a couple of inches in from the heel towards the midsole. Go out and do some test kicks once the ski cools that is. You may get away with the day's wax just under the 'pocket' of the ski where there will usually be crystals when ever you care to look.

 A lighter skier can also use a slightly softer wax, so you could use a purple in the middle of the "pyramid" ie under the boot sole,  if you find the traction a little lacking  - even as cold as minus ten in new snow. The same will be true of a harder ski, which you may compensate for with a 'pyramid peak' of softer wax when conditions are soft.

Fluctuating 'zero' conditions are annoying because you get icing on the ski, or suck if water starts to form under the ski. Some skiers use a combination of a flourinated purple on some of the lenght of the foremost half of the kick zone, as far as the toes of the boot/binding area, and then stop here and use a clister under the sole in the 'pocket' which does not reach as far back as the heel. Thus any crystals which do get picked up will created minimal friction in the glide, and you get a good combination of grip as the temperature rises and falls. 

Hard, icey clister conditions entail that a softer ski has a shorter waxed zone, and once again you can test this out before you commit to the journey with an application which is not as far as the heel, and two to three inches short of the usual wax mark at the front half of the ski. A harder spent ski should be marked with a clister mark , which is usually in my brief glances at good skier's skis, about an inch and a half inboard of the usual mark so to speak. 

Slushy, Easter Conditions  The main thing you want to avoid here is suction onto the snow and water mix, so a shorter kick zone and use of a clister once again not as far back as the heel should be employed. There will be plenty of grip most of the time, unless it freezes back or you enter shadowy or higher areas where conditions are usually hard, 

You have a little challenge here in Easter sun slush,  because ideally you need to glide all the rest of the ski to prevent suction, so you will need to clean off glider to lay clister further out if needs be for more grip. You can compensate for a glider free zone by 'rilling' or just scraping up the areas you have not glided where you may want to extend clister, such that the water finds channels to run from and you avoid suction. Use a rough herring bone pattern to affect this under the heel and longer up the 'reserve' kick zone on the toe end. 

Kick Beats Glide on Longer Runs

Excluding the mostly down hill 'Marcialonga' in Italy, most longer ski runs have significant amounts of diagonal classic kicking. Experienced competitors will tell you that good kick is better than extremely good glide. That is rather to say that even a small percentage of back slipping and frustration will slow you more than a little extra friction. Bad glide though, where the kick wax holds crystals or clumps up even, or as above you experience suck in wet conditions, It is then a combination of 'nailed kicking' and good efficient, "profit" in glide from each kick and on faster, non kicking sections which counts. 

There is then a slight bias to allowing for better kick, so for example on the Birkebeinet which rises several hundred meters in its' arduous 54 km course, you will see some people choosing a little too soft a wax for the uphill and having to scrape and apply harder wax once they encounter a lot of crystals being embedded on their kick wax. Some wise old foxes wax with just one layer of soft wax and let it deterioate up hill, thus reaching colder snow and the harder wax beneath takes over!

This is a very good rule of thumb Nr 3 for ski touring from cabin to cabin, or not wanting to bother waxing much while on holiday or a longer day run. You can always lay a softer wax onto a harder one, and clister will sit on blue wax (if not maybe purple) if the sun melts the nice cold snow in the course of the day, or as you come round the ridge to the sunny side!  This is really where skin-skis (felleski) come into their own, as long as conditions don't verge towards 'blue ice clister'.

Limits of Ski Fun in Poorer Conditions

On that last point, ice-clister days, then I do declare that there is no perfect ski for diagonal kicking style. A reasonable ice clister job for me will last around about 10 km before the skis are bare on my older, softer tour skis. You will see people staking in these conditions a lot on the stiffer, sportier skis and you can presume that their blue clister is going to last longer as a kind of reserve for the sections which are between staking and fishboning. However as you see in big competitions, diagonal can be excluded from most all routes! 

A factor then we experience often here along the coast is thaw back and freeze, which has its worst effect of course on the bases of the 'tramlines' such that a wax job based on temperature is useless, and you have to use and take with you universal clister to make the tour possible with any diagonal kicking. 

Now having said this, if I had bought the Atomic training ski without the skin, then I would get some benefit from 'preserving and reserving' a blue clister job which would ride above the icey substrate, and then the ski would whip down in its' fancy carbon fibre mediated implosion, thus propelling me up the slopes. But that would be another pair of skis, which would be hard to use on the soft, easter conditions we seem to get as early as january these days! 

Two Pairs Are The Answer?

Unless you are very lucky or just ski for a short season, or holiday with stable weather and snow conditions, the actual qaulity of the snow is going to vary greatly over the course of a season. I know some of our local boys just use clister on their favourite pair of training skis,  because there is so often old snow from thaw-freeze events. Easter comes, and the sun shines brightly in the mountains, meaning you may want to either get the tour out of the way early on hard wax, or wait until the nice red wax conditions come in later in the morning. 

If you are just planning for a single long tour, then perhaps hiring skis when you get there is the best solution, and paying the shop to do atleast a good base wax and glider job if needs be for where you are going. The pair should then have a medium to soft 'spenn' such that you cover a range of eventualities if there is the chance for vairation in weather and snow base conditions. 

Planning your tour you want to think about how those base conditions will vary: Runs where they use just a skidoo to lay track will be softer in their bases that a piste machine so think of this too, this being even more true where you are likely to just be following other skiers tracks in the snow. Here you want to think about using a broader tour ski, although you do encounter people on sports skis following well defined back country routes.

Ideally though you want to think about two pairs of skis if you are going to do a lot of training over the course of a long season. One pair with hard flex as recommended for good, firm and hard conditions, and a soft pair for new snow, softer prepared bases, "off piste" ie back country,  and easter conditions. 

How About A Third Pair? 

The typical mid life crisis of 2010 it seems, entailed that the man of the house or lady of the clubhouse would invest in skate-ski kit. For those of you not au fait with XC skiing, there was a great 'Schism' caused by a guy called Koch, who gave up on kicking in the tram lines and propelled himself by a skating style. It was forced out to the sidelines as 'freestyle' only to really beocme a very prominent face of the sport when the ski-shooting biathaletes found it an easier style with a rifle on your back. Now it has eaven taken over the World Championship's longest events, the 30 and 50km for women and men respc. 

As mentioned above, skate skis have a very different look in their pre-bend. They are stiffer and the bend is longer. This means the skier is carried a little more a-loft of the snow, and relies on a fairly pronounced side swipe on the inner edge of the pushing ski, as well as a good deal of use of the entire body and arms to propell, rather gracefully, the whole show forward. 

Now I bought a pair, without investing in the proper boots or longer poles which are 'necessary' and have had some great fun learning. More over they have revolutionised my previously stiff mobility our of the tracks, by vastly improving my balance on skis. When refining my diaganol technique I worked out that in fact it is a parallell skate, with all the weight and thus glide pushed on to the leading ski. 

The real advantage of skate skis is perhaps in being able to go out on days when the bottoms of those tram lines have become concrete-like. I find quite often that the centre 'skate' lane on the forrest roads they prepare here, has a good deal more texture or 'bite' in,  that the concrete of the well worn tramlines, so you can get a very nice skate on the go, and then double pole at high speed in the tramlines. 

I would whole heartedly recommend that someone taking up XC skiing for fitness start off with skate skis (or maybe 'combi' skis if there are still any on the market) or in fact given my own instructive feel from about ten sessions on them, any beginner should be given a go at this 'freestyle' before being confined by the tramlines. 

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