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Ski Nerdery: Running Length & Edge Hold

A question came up recently from a Blister member, John, in the Comments Section of our review of the J Skis Masterblaster, and we thought it was worth highlighting. We also thought that some of you might want to offer your own two cents.

And just a bit more context here (though you can read the whole exchange below the Masterblaster review): John was asking me about edge hold on ice — which is something that a whole lot of skiers care a whole lot about. We were talking about the edge hold on ice of the Liberty Origin 96 (a very good ski) vs. the Nordica Enforcer 93 and the J Skis Masterblaster.

Regarding the Origin 96’s edge hold on ice, I wrote this: “The Origin 96 is a heavily tip and tail rockered ski, with a relatively short running length. That is not the profile that is going to excel on ice, but on anything relatively soft, its edge hold is excellent.”

John’s Reply:

“Regarding edge hold, I know the whole industry is currently using the “running length” argument as a basis for edge hold, but that doesn’t make complete sense to me. I’ve skied super short slalom skis with short effective edges that held like ice skates (ice skates themselves have very short running length) and super soft stainless caped skis that also had bombproof edge hold (Volant 15 years ago – don’t know about them today).

I suspect the key is torsional rigidity and wonder if manufacturers are relaxing torsional rigidity to improve looser, more playful, more forgiving characteristics. So, when the [blister review of the Liberty Origin 96] referred to the Origin 96 as being comparable to the Nordica Enforcer 93 in edge hold, which is rated fairly highly in this area (e.g., your experience with the ski on Stauffenberg), and with J Skis (like so many other manufacturers these days) stating the Masterblaster has race-ski carving performance, it lead me to think the stiffness underfoot of the Origin 96 may indicate acceptable hard snow edge hold. I believe the Enforcer 93 could be sufficient for my needs and look forward to the Deep Dive AB with the Masterblaster.”

My Reply:

Lots of good thoughts and questions in there, John.

And regarding running length — note that in my comments about the Origin 96, I don’t merely mention the ski’s “relatively short running length,” I say that it is “heavily tip and tail rockered” too. And I think that’s pretty key. On a non-rockered slalom ski or ice skate, you’re right — the total running length / effective length is very short. Let’s make up some fake numbers here, and imagine that the running length of a slalom ski is 140 cm. It’s pretty easy to imagine that the running length on the Liberty Origin 96 (say, in a 182 cm or 176 cm Origin 96) is also around 140 cm.

But the big difference is the significant amount of tip and tail rocker on the Origin 96 — whether you are skiing relatively steep, sheer ice on-piste, or chunky, nasty ice off-piste, it is very easy on a heavily tip and / or tail rockered ski to get too far forward or too far back on the ski, so that you are over-pressuring those rockered tips or rockered tails. And if / when you do overpressure those tips or tails, the ski will want to wash out — slide out — from under you, in a way that will be less true of a non-rockered slalom ski or ice skate. The full length of the slalom ski and ice skate are in contact with the ice, and maintain contact with the ice.

But of course, there are other relevant factors here, too:

Weight

The Origin 96 is a relatively light ski — much lighter than the Masterblaster, and still noticeably lighter than the Nordica Enforcer 93. And when trying to gain purchase / grip on ice, weight is your friend. This is one of the reasons why race skis are so damn heavy — you want to keep that ski planted and connected to the firm snow.

Metal / Titanal

The more you care about edge hold, the more weight is your friend. And adding layers of a damping material like titanal will also help the ski stay connected to the snow.

So to me, the weight of a ski (heavier is better) and the materials of a ski (titanal vs non-titanal) will likely be greater factors — alongside how rockered / non-rockered a ski is — than the torsional rigidity of a ski.

If weight + rocker profile + materials are all equal, then yes, I think you’d be right, John — the more torsionally rigid ski may well perform better on ice.  But in the specific case of the three skis we are discussing: the Liberty Origin 96, Nordica Enforcer 93, and J Skis Masterblaster, I think the weight and material differences are bigger factors than the respective differences in torsional rigidity of the skis.

And to be clear … 

I offer this not as the final answer on this, but as food for thought. Look forward to seeing what you, John, and other readers think…

 

23 Comments

  1. Ryan Clapp December 8, 2016 Reply

    In most cases weight is only the “symptom”, or the outward appearance of tortional rigidity. The small difference in weight between the skis would translate to minimal force difference. Due to the fact that the ski makes up a small portion of the mass traveling down the hill/making the turn. However, heavier skis in most cases are more rigid, and therefore deflect less under tortional and bending loads. Therefore it’s the rigidity that matters and it is driven by the material and construction and can’t be viewed independently.

    • mogsie December 9, 2016 Reply

      I would say that you are partly right but…Skis can now be ligth AND tortionally rigid. One ski that was very tortionally rigid were the Steadfast who were also very light (no metal and meant to be backcountry skis). they could really grip an edge but at the same time as I picked up speed, I felt that the skis (because of their light weight) had the tendency to want to bounce around and , therefore, leading to a lost of edge grip…

  2. Kevin December 8, 2016 Reply

    It seems like the other factor not being discussed is the amount of camber that a ski has as well as flex pattern. A ski with a lot of stiff camber will allow you to distribute the force along a greater portion of the edge. The goal in turning is to ‘accelerate’ and that edge of the ski needs to distribute the force across the whole of the ski without letting the edge start to deflect. Some shapes and flex patterns do not adequately ‘bridge’ the force forward to the tips (and tails) of the skis to allow it to be distributed evenly.

  3. Blister Member
    John December 8, 2016 Reply

    Hey, Jonathan. First, I didn’t expect to generate a whole new thread. Thanks for taking the extra time to address this. You bring up some good and interesting points. I’ve also given it some thought since our last exchange and like you, I think that it is important to “keep that ski planted and connected to the firm snow”. I recall that both the slalom race skis and the Volants I mentioned were very damp and had little chatter. The race ski did it with metal, stiffness and energy, while the Volants were pretty soft and lifeless but were very damp. It makes me wonder if vibration is a major killer of edge hold. Maybe the oscillating pattern of engaging and then releasing results in overall poor edge hold. When you refer to the heavily rocketed skis washing out with too much weight on the shovels, I believe you, and that would be a reason to dismiss those types of skis for my specific needs here. But I also wonder why that section of the ski washes out when weighted while shovels on other skis do not? I suspect, as you pointed out elsewhere, that it at least partially pertains to how reduced vibration keeps the ski connected to the snow. You mention that stiffness, weight and metal all contribute to edge hold and, again, I believe you. But I wonder if the way they do this is by reducing vibration as well as better torsional rigidity. Anyway, just some additional thoughts if you or anyone else wants to comment further. Regarding the skis, I’m looking forward to your A/B of the Enforcers, Bonafide and Masterblaster, etc.

    • Author

      Yep, I think you and I are thinking about this in a very similar way. And to be clear — I think it’s often or even always a bad idea to isolate any 1 factor and say, “THIS is why X” – and I think most / all of the folks chiming in here understand that. But with that said, I agree with you that reducing vibration is a very important factor. And I’ll start the A/B-ing tomorrow…

  4. Blister Member
    Michael December 8, 2016 Reply

    No discussion on edge hold is complete without mentioning how a ski was tuned.

    • Author

      True, but for the purpose of this conversation, I think we can bracket and isolate issues of tuning. I.e., assume that for any of the skis we are discussing / imagining, that they are all working with the same tune. So I’m more interested (for now) in the materials, rocker profiles, weight, and flex patterns of the skis.

  5. Blister Member
    Jamie Forster December 8, 2016 Reply

    This discussion reminds me of my favourite ever ski. It was an Elan 4S that I bought in 1989 – in those days, if you wanted a performance ski you got race skis, anything else was a rental.

    They were longer than I’d normally ski (they were 195 and I was 173cm and 70kgs ringing wet) but were racing pro friend’s sponsor ski and he didn’t need them so was selling them cheap.

    I raced club on them (GS-type courses) skied piste, powder, trees, bumps, crud, dropped cliffs, couloirs (including the Sudan Couloir via Hawaii 5 0). The gripped, floated (as much as any in the early 90s) and shredded fast top-to-bottoms down Blackcomb. I absolutely loved those skis. Of course, skis have changed immensely since then and I’ve owned better skis, but none that I remember with the same fondness.

  6. Don December 8, 2016 Reply

    Interesting indeed. I notice there has been no mention of sidecut. I had always considered the difference maker on edge hold to be a flat or rockered tail and the sidecut. My Line Prophet 115’s (186) have better edge hold in real firm conditions than my Moment PB&J’s (188). My belief there is that the with the Lines the tail is locked down due to lack of rocker and they have more sidecut. In reality that also means the Lines have a longer running length. As far as weight and torsional rigidity, I feel the skis are comprable even though the Lines have metal and the Moments don’t. For an everyday hardpack ski I wanted a waist width a bit narrower than the PB&J’s and a shape more like the Lines. Enter my J Skis Masterblasters which I’ll be taking out for the first time this weekend.

    • Author
      Jonathan Ellsworth December 9, 2016 Reply

      I’m rather tempted to downplay sidecut here, Don, while you (and many others) may justifiably not wish to downplay it. I.e., I don’t want to turn this into a discussion of slalom skis vs GS skis. Instead, I’m personally / selfishly interested in (in the same way that I’m interested in bracketing the issue of tuning and assume that the skis we’re imagining are all working with the same tune) thinking about a group of skis that all have a similar sidecut. E.g., in a group of 10 skis, all of which have a tight 14 m radius – but incorporate different weights, materials, tip and tail shapes and rocker profiles – which skis will exhibit better edge hold, and why? Or alternatively, if we take 10 skis all of which have 27 m radius – but incorporate different weights, materials, tip and tail shapes, and rocker profiles, which skis will exhibit better edge hold, and why?

      Having said that … I suspect that it’s fair to say that skis with tighter sidecut radii will often hold better on ice … though I think I won’t say more about that right now, since that could quickly point us down a different rabbit hole.

      And to your other big point, I totally agree: flat tails come in quite handy when edge hold is at a premium.

      • Don December 9, 2016 Reply

        Hi Jonathan! I follow and that totally makes sense regarding sidecut. That was actually my reaction to the tuning comment above. For sake of conversation we’ll just assume that the tunes are equal! Anyhow, great discussion here. Stuff like this is why I love Blister!

      • Jed January 23, 2017 Reply

        Jonathan,
        I completely agree that a discussion of sidecut radius and sidecut profile is distracting when talking about edge grip. Yes, it has an effect, but the effect that sidecut has on edge grip has FAR more to do with HOW you’re turning the ski rather than how the ski responds, in a torsional, flexural, and pressure distribution sense, to impulses and changes in the ski surface.

        But because you opened this door, and you so rarely do, I’d like point out that you’re not strictly correct when you say “I suspect it’s fair to say that skis with tighter sidecut radii will often hold better on ice.” The overall sidecut radius of a ski has no effect on how a ski holds on ice, only how the sidecut changes throughout the skis length does. I think this is best illustrated in extremes. A ski with a longer sidecut radius will bend less than a ski with a tight sidecut radius for a given edge angle. If you’re maching on a slalom ski and put it on edge, it’s all of a sudden going to want to bend in an arc FAR tighter than your body – or even the edge hold – can support. This is going to result in you basically pushing the ski into an arc that it can’t sustain, and it breaking loose, putting you on your ass. Conversely, if you’re going slowly on a DH ski and try to make a quick turn, the ski won’t respond because it can’t bend into a tight enough arc, and you’ll end up on your ass once again. Edge grip in both of these scenarios has a great deal to do with HOW you’re loading the ski, how fast you’re going when you load it, and what radius turn you’re trying to achieve – and that in turn has a great deal to do with HOW tight the sidecut radius is. There’s (obviously) a reason that SL and DH skis have different sidecut radaii – they’re designed to have GREAT edge grip at very different speeds, and for very different turn radaii.

        Cheers,
        -j

  7. Blister Member
    Jed December 9, 2016 Reply

    We’ve got some seriously interesting stuff above, and I thought it worthwhile adding a few cents of my own. I’m a ski design engineer for K2 and LINE – I don’t want to suggest that I’m THE authority on all things related to edge hold, but I have had the opportunity to measure (many) skis in ways that most people can’t, and a large part of my job deals with improving – or at least tailoring – the amount of edge hold a ski has.

    Before getting too deep, I think it’s worth mentioning that edge hold, unlike the flex or rocker/baseline profile of a ski is impossible to measure. It’s a feel. A skier will notice when a ski has better edge hold than another, but those observations are extremely hard to qualify and quantify. You can say one ski has better edge hold than another, but beyond that, meaningful data gets pretty sparse.

    Camber, rocker (I’ll dive a little deeper here later on), flex profile and sidecut profile all have profound impacts on edge hold. All of those variables can be wrapped up into a single measurement – pressure distribution. A ski with great edge hold has a pretty distinct pressure distribution signature, and one that doesn’t change drastically with increased edge angle. Intuitively, one would think that a uniform pressure distribution would mean that a ski has better edge hold – that’s not the case. Skis with good edge hold characteristics have three distinct areas of high pressure – one in the tip, one underfoot, and one in the tail. The effects that rocker, camber, flex profile and sidecut profile have on this pressure distribution is how and why they affect the ski’s edge hold.

    In general, the more balanced the flex profile (the stiffer the tips and tails, and particularly the tip, are in comparison to the midbody of the ski), the better pressure will be distributed to the tips and tails of the ski, and the better the ski will be able to maintain an edge. Adding camber to a ski has a very similar effect to the pressure distribution – you get more pronounced ‘spikes’ in the pressure distribution at the tip and tail.

    The way that sidecut affects edge hold is fairly complicated and nuanced, but basically the sidecut profile determines how the ski bends, and how the pressure distribution changes with increased edge angle. Obviously, a ski with a lower sidecut radius will bend more than a ski with a large sidecut radius. If the transitions from a small sidecut radius to a large sidecut radius are abrupt, the ski will want to bend a great deal in one location, and very little in another, resulting in poor edge hold.

    Torsional rigidity is interesting, mostly because it is assumed that the more torsional stiffness a ski has, the better edge hold it has. There is some truth to that, but increasing a ski’s torsional stiffness beyond a certain point has a pronounced negative effect on the edge hold. The torsional stiffness of the ski keeps the entire ski at the same(ish) edge angle, and therefore forces the ski to bend in the same(ish) arc. The more torsionally rigid a ski is, the better that that same edge angle is maintained throughout the ski. However, where a very torsionally stiff ski can be problematic for edge hold is on surfaces that are not perfectly planar – really, all ski surfaces. If the ski hits a small bump while on edge, that bump needs to be absorbed one of two ways – it either twists the ski, or it bends the ski (it’s really a combination of the two, but you get the idea). Skis with soft torsional stiffnesses will tend to twist more than bend, allowing full edge contact to be maintained (the problem with skis with low torsional stiffnesses is that the edge angle is poorly maintained throughout the running surface of the ski). Skis with high torsional stiffnesses will force the skis to bend, usually pulling part of the edge off the snow with it, and reducing edge contact and therefore edge hold. All this is to say that there is a sweet spot of torsional stiffness that will keep a fairly constant edge angle throughout the ski, but allow enough deflection in certain cases to maintain edge contact.

    The reason most rockered skis have worse edge contact than a fully cambered ski on hard snow is that the rockered sections of the ski are – for all intents and purposes – large cantilevered beams. The vibration characteristics of these beams tend to have low frequencies and high amplitides – tip flap/flop. These vibrations, or flapping, pulls the ski off the snow, reduces edge contact, drastically changes the pressure distribution of the ski, and reduces edge hold. This is why a 165cm slalom ski has excellent edge hold while a 190 heavily rockered ski (but with a similar amount of effective edge as the slalom ski) has very poor edge hold. The overall shape of the rocker profile, as well as the flex pattern in the rockered section can be tailored to reduce these effects, but not eliminate them.

    Cheers,
    -j

    • Blister Member
      Jamie Forster December 9, 2016 Reply

      Awesome contribution. And what a great idea: technical people from manufacturers chiming in with some comments on general topics like this.

    • Blister Member
      Tom December 10, 2016 Reply

      Nice! Thanks for the actual engineering input.

  8. Blister Member
    John December 9, 2016 Reply

    Jed, Thanks for chiming in. That was very informative, particularly the part about how less torsional rigidity can actually increase edge hold in that it keeps more edge in contact with the snow while going over bumps. The part about pressure distribution is also enlightening. I’m curious about that. How do you measure pressure distribution? Is it an instantaneous measurement or over time, sort of like the difference between engine torque and horsepower? Does the tip and tail pressure hot points benefit edge hold in that it keeps the tips and tails from chattering and hence in contact with the snow (i.e, if the ski has high pressure at the tip and tail it must mean there’s a lot of stored energy in there fighting against the snow which implies, to me, that even if they break free there’d be little chatter and little vibration)? Otherwise, I can’t think of why a pressure spike at the tip and tail would be better than a uniform ramp up in that same pressure throughout the ski.

    • Blister Member
      Jed December 9, 2016 Reply

      John,
      Good questions. We measure pressure distribution on a machine of our own design. We don’t do this measurement on snow. It’s a static measurement done in a lab, so there’s no time influence.

      To be clear, you still need pressure all along the edge – edge contact is key to edge grip – but you want the ‘spikes’ at the tip and tail to keep the tips and tails engaged. As you’d expect, those spikes are fairly small compared to the spike underfoot, but significantly higher than the mid-forebody and mid-aftbody.

      The one element I left out of my above post is mass. In general, the more massive a ski is, the damper it is (mass damping), and therefore the better the ski will retain edge contact. Mass is a completely independent property from stiffness or torsional stiffness, but can have an effect on how well a ski grips.

      Thanks,
      -j

  9. Blister Member
    John Freeman December 9, 2016 Reply

    Supernatural info Jed, thanks

  10. Blister Member
    John December 9, 2016 Reply

    Jed,

    Your insight really makes perfect sense now that you’ve enlightened us all. There must be pressure points on the tips of the ski to keep it engaged. Anything farther out from that pressure point is, as you’ve stated, cantilevered, and just flaps up and down not only disengaged from the snow but also acting to disengage the rest of the ski from the snow. So, you’d want those pressure points as far out as possible. Hence why a short slalom ski still has great bite. Which is in line with what Jonathan has been saying all along about heavily rocketed skis and his aversion for taper on skis meant for edge hold.

    I actually have some minor experience in this area if you could call it that. If you’re old enough you may recall the Solomon Pilot system introduced at the end of the 89/99 season. It was a big deal at the time and meant to replace the X-scream, the best selling ski of all time. I invented a precursor to the Pilot around 1995. I actually showed it to Solomon around 96/97….they ended up introducing the Pilot System in 1999. (but that’s another story). IMO, and since it didn’t work I would say in the opinion of the ski community, they introduced a poorly conceived design. They decreased stability for other attributes. A primary objective of my design was better stability. I still have my last prototype for posterity sake. Sentimental value I guess. I actually came up with a better way to accomplish the original objectives and more but never got around to working on it with my career moving in another direction. C’est La Vie.

    Anyway, very glad you chimed in and helped with all of this. All this discussion will help my selection process tremendously. I suspect the same for the other readers. I hope you stayed tuned in.

    John

  11. Blister Member
    tjaard January 19, 2017 Reply

    Of course no practical value for choosing alpine skis, but Eagle River Nordic measures and publicizes pressure distribution for all of the (XC) skis they sell:

    http://www.ernordic.com/skidata.html?cart=1484851421539613

    Click on a ski to see a graph of the pressure distribution and a discussion of it.

  12. Jed January 23, 2017 Reply

    Tjaard –
    I’m glad you brought this to light. Nordic skis are far more sensitive to variations in pressure distribution than alpine skis, especially classic skis where the wax pocket is more aggressively cambered than the rest of the ski. If blister ever decides to start reviewing Nordic Skis, I’ll leave this discussion to my Nordic Ski Engineer fellows, but suffice it to say it’s fascinating. Obviously, very little of this has to do with edge grip, but more with how a ski either responds to kicking in a classic stride, or glides (both classic and skating). Having spent hours discussing these characteristics with Nordic Ski engineers has left me convinced that the Alpine Ski world has a massive amount to learn from the Nordic world when it comes to pressure distributions and gliding… but I digress.

    Last spring I had the opportunity to tour the Madshus factory just outside Lillihamer, Norway. Full disclosure here, Madshus is part of the K2 Sports family, and I’ve been drinking Madshus Koolaid for a number of years. That being said, Madshus measures pressure distribution, camber pockets, and rocker line on EVERY SINGLE SKI that comes out of their factory in Norway – and saves that data in a public database. Dealers can scan an RFID chip in the ski and access that data for each ski – very similar to what Eagle River is doing. They do all of this in a production environment, and the machines they’ve developed to take these measurements (quickly and accurately) are nothing short of breathtaking…

    I’d love to see something similar to this in the Alpine world. Granted, I think a great deal of this data could/would get lost, but the better and broader the dataset, the better ski companies and ski shops can choose the right ski for a customer.

  13. Simen Stori March 12, 2017 Reply

    This: https://youtu.be/fiMCRR8P9MU explains the torsion conundrum very well.

  14. Scott May 5, 2017 Reply

    Great discussion. This hits a sweet spot for me. Like Jed, I am a mechanical engineer, although I don’t design skis for a living. I am a ski race coach and spend a lot of time on very hard snow. Lastly, I am 6’4″, about 240lbs. I should be the product tester for the edge grip measurements (I know they are not done on snow, just kidding), I can make almost any ski loose edge grip with enough speed in a carve. In other words, with my mass, its pretty hard for a ski to hold me in a carve on an icy surface.

    What I can add to the discussion is that I think ski weight is a non-factor since you have a 150lb+ person pressing down on the ski. What the weight is a very good indicator of, is the ski construction (I propose this as the better term) which dictates most of the aspects of the ski that Jed explained as critical to edge grip.

    I like this statement from Jed, “edge contact is key to edge grip” , as this is both static property and a dynamic property. I also feel that side wall construction is very important to edge grip, because if you have local deflection of the sidewall, that will make you loose edge contact.

    I own two pairs of Liberty Origin 96’s, a 187cm and a 182cm. It is a very interesting ski with all its rocker and its very stiff mid-section. With razor sharp edges and some tip and tail detuning, the ski has pretty impressive grip on ice, not race ski level, but better than most skis. I tried sharpening the edges tip to tail and not detuning when I first got the skis. The tip hookup was very erratic due to the rocker and tip flap, just as Jonathan and Jed described. Once I dulled back the edge on the tip and tail, the ski became predictable when rolled on edge. You could tell there was less edge gripping, but what was in contact held pretty well.

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