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Fireside Contra Chat with Bruce


Jack M

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At the beginning of the carving era, ski manufacturers were supposed to have borrowed carving snowboard designs to begin experimenting with carving skis.

Starting to wonder whether the transfer of knowledge will happen in the same direction again, or whether this concept of analysing and experimenting with edge load distribution has already been developed in racing skis and/or filtered down to the carving skis available to the public.

Google searching on "ski design flex torsional resistance sidecut" turned up lots of commercial sites but also these

https://www.researchgate.net/publication/268279279_Effects_of_ski_stiffness_on_ski_performance

https://mafiadoc.com/sidecut-radius-and-kinetic-energy-equipment-semantic-scholar_59d90bfc1723dd30eee25df9.html

And this discussion
https://blisterreview.com/gear-reviews/ski-nerdery-running-length-edge-hold
threw up this contribution
"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."

This Head ski video talks about the same interaction between flex and torsional resistance.

_________________________________________________________________

PS: Pleased to see Sean Martin's videos on the physics of a snowboard turn have made Wikipedia as an external link on the "Ski geometry" page.
https://en.wikipedia.org/wiki/Ski_geometry

 

Edited by SunSurfer
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Thanks for that post.  Here's what I think is the important take-away:

9 hours ago, SunSurfer said:

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.

It helps to understand why a one board quiver killer is unlikely.  The post doesn't say it, but I think we all know the ideal "pressure distribution signature" changes based on snow conditions.  Snow is not a solid, flat plane.  It's a 3-dimensional problem, in motion.  The amount of snow compaction, at different depths affects the trench being carved.  How deep the trench is behind different parts of the base and how much it resists compaction affect how much load it can bear.

I ride every day I can, and from one snowfall to the next the hill undergoes daily or even hourly changes.  Right after a dump, I'll be riding soft boots, hanging out in the bumps and trees looking for pow to surf.  That might last a day or two.  Without new snow, a series of packed powder days begin.  First day is still pretty soft, trenching a few inches.  Plenty of hold everywhere unless the whole trench blows out from being too loose.  Queue long SCR Nirvana.  Get on the nose a little to tighten turns, but be careful not to blow out against the loose snow; it's not an EC day.  Next days are more packed and less powder.  I like to call it "chalk" at it's peak.  Trenching about an inch.  Still lots of boards work; there's so much grip available.  But things are speeding up now, queue a smaller SCR so you're not taking up the whole run, but still having a blast getting low as you can every turn, wearing holes in your cloths.  But now the sun comes out and things get soft by the end of the day, or there's a little rain event that evening.  Your packed powder is replaced by granular refreeze.  Bring out the Contras and Thirsts.

The pressure distribution tolerance of the snow is changing all week.  Climate change is bringing more wet snows and refreeze cycles earlier in each season.  Having gear that still hangs onto a carve while all the other skiers and boarders are slip skidding away is fun.  I hear more cheers from the lift on those days than hero days.

12 hours ago, Carvin' Marvin said:

Different strokes for different folks and all that.

Ditto.  The Contras and Thirsts aren't going to please everyone.  The pressure distribution seems to work better in icy, variable grip conditions, but if you don't carve in those conditions you may be happier with something tuned to the conditions you ride more often.  If you want a soft, tight nose, they don't have it.  They shift some tip and tail pressure towards the center; they'll feel different.  But seriously, I rode almost 60% alpine last season, and over half of that was on two boards, a Contra 12 and a Contra 10.5.  I gave all my older boards their shot, but there weren't many days that I could charge harder on the old than the new.  Those days were all soft-ish conditions.  Yes, be careful, you can overflex Contras (and Thirsts) in soft snow.  Those are the conditions Nirvanas were tuned for carving.

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Johns post says it all I believe...where and what you ride is number one for deciding what Stick to use...thinking there is one that works for all is a concept I use by using a softer Stick, but knowing the conditions is paramount to not getting hurt, when it is too soft and having trouble when it gets Icy is also part of that...

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I promised yesterday to share some beta on the K168.  Nothing secret, just what can be observed by handling one with feeler gauges and a straight edge.

My analysis says it's a 8-12-10 VSR, where the 12 is reached just before the rear inserts, 1550 mm effective edge.  It starts straighter at the very tip of the effective, but drops below 8 near the saddle between the camber/rocker.  Eight is a fair average over the first 200 mm.  Same at the rear, but the min radius there hits a bit more inboard of tail rocker.  Ten is a fair average for the last 250 mm.  The tip and tail engagement is done by rolling onto the rocker profile, not relying on sidecut induced flex, so tip and tail blending toward straight inside the effective is to be expected.

The remaining 1100 mm is a where one would expect it to be two "clothoid" curves, one from 8 to 12, and one from 12 to 10.  But that's not exactly what I found.  A clothoid curve is one where the curvature (1/R) is changing at a constant rate.  The rate of change of curvature I observe is not constant.  It is changing constantly, but interestingly, that rate at which is is changing is constant.  So it's the rate of change of rate of change that appears to be constant during these transitions.  The graph of curvature expresses itself as a clothoid curve, making the actual sidecut curve a clothoid anti-derivative curve.

I could share all the graphs of this, but I can't upload any more attachments to my account.  You'll have to visualize.  What you should see if imagining a graph of radius over the length of the board is a smooth curve, no abrupt changes to slope.  Like a throwing a ball up from 8 m and letting gravity slow it down to zero at 12 m and start dropping back to 10 m.  The rate of a acceleration actually bumps a bit higher at the rear inserts, but you get the picture.

Core profile is interesting too.  A micrometer shows it's very much table topped between the inserts.  Way more than I was expecting.  More than Bruce is doing on the Contras.  I speculate that this might be a characteristic of the K168 that is not as pronounced on other sizes.  Could be part of what makes it good for free carving.  Someone with more sizes would have to take a micrometer to them and report back.

The K168 and Contra are different.  What the K168 and Contra have in common is that the radius changes every inch, and that the rate of change is changing smoothly throughout.  I can model them both with the same spreadsheet math just by changing up position and coefficients of control points.  So if you want G-codes for milling K168 knock offs in new sizes, I have you covered.  Where they differ in appearance is that the "flying W" of the K168 has its low points out at the tip and tail and the Contra brings them closer to the inserts.

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Hi Johnasmo

Thank you for taking the time to post your thoughts and expertise, what a cool collaboration with Bruce! 

Can you comment at all on stance width and stance location in relation to the 'flying W' of the SCR and it's possible affect on the turn.

Wide vs a narrow stance, wider or narrow W adjusted to a riders preferred stance width ... vs a stance that is shifted maybe a cm forward or a cm backward in relation to the reference 'Flying W' stance?

I have spend quite a bit of time testing my Nirvana, but did not get a chance to experiment much with this with my Contra; covid and too much powder this year!

This is mainly a curiosity I have as I tend to experiment with all my boards in hopes to get to know them better.

Thanks again for sharing your knowledge!  Your posts are just a pleasure to read!

Cheers

Rob

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1 hour ago, johnasmo said:

You’ll have to visualize.  


 

Wait, you’re telling me I “have to visualize a clothoid anti-derivative curve?!?” I have enough people at home whose job is to make me feel stupid, I’m not sure I should have to pay for the privilege here...

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13 hours ago, RCrobar said:

Can you comment at all on stance width and stance location in relation to the 'flying W' of the SCR and it's possible affect on the turn.

Nothing radical with regard to setback and taper.  Each sidecut profile is adjusted for length, radius, and setback.  Taper is calculated to bring the waist to near or just before the setback.  The tightest radi are still in front of and behind the inserts.  The location scaled by board length *and* target radius to keep longer SCR from initiating too slow.

Setback is 40 on 170+ lengths, 35 in the upper 160's, 30 or 25 if getting into BX sizes.  Insert separation is 500 mm for alpine, 560 mm for BX.  There are Contra BX sidecuts too, but none were built last season.  They push out the radius tightness even on lower SCR as compensation for lower generally low angulation.  Stick to normal Contra if the goal is EC carving.

Anyway, I'd start centered and see how it goes.  If you normally shift your stance fore or aft because you like to drive more with your front or rear foot, try starting centered and being more neutral at first just to see.  The tightest radi are still in front of your front toes and behind your rear heel, so fore/aft pressuring still has an effect, but focus your attention (direct the flex) closer to your feet than before.  I'm centered on center inserts in front, and using center inserts but shifted binding disk back one hole for a 20 inch stance.  On my older Coilers I tended to shift forward.  I don't know if my change is a reaction to the board or I'm evolving a more neutral stance over time on all boards.  I was adjusting cant/lift last season across all boards and I ended up more centered on all of them.

What I posted earlier about shifting pressure may be misleading:

On 5/17/2020 at 12:17 PM, johnasmo said:

They shift some tip and tail pressure towards the center; they'll feel different. 

It's not so much about shifting pressure from tip/tail to center, but preventing it from being shifted too much away from center towards  tip/tail as you increase edge angle.  When the board can't cut very far into an icy surface, a center stiff board risks unweighting the center as you go higher on edge; the stiffness of the board prevents the center from being flexed out to bear much load, concentrating downforce at the ends of the tip/tail.  In those conditions, a tight-long-tight sidecut shifts too much load bearing pressure from the center to the ends.  Contra flex/sidecut are trying to keep the low angle and high angle pressure distribution more consistent.  Not necessarily centered, but more consistent over edge angle, which may "feel" more centered compared to other VSR boards.

What you should (I hope) feel with the Contra is that instead of attacking the hill with the tip of the board, you are attacking it with the area in front of your boot and riding out the turn with good center traction.  The feedback from the board should lead to a more centered and neutral stance than other boards. 

Design intent and design reality don't always match.  I feel like its working, but hope to get more long-term feedback from other owners on the forum comparing them to their other boards in various conditions.  Sample size is the number of Contras Bruce built last season.  Bruce, Dave R., and myself are only a sample of three.

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  • 6 months later...

174 ordered and waiting on Bruce to fine tune the Contra softboot build. PM if you have over the last season gotten a softboot board from BV. 
Once this bad boy comes in keep an eye out for a Nirvana VCam 174 that will be up for sale that is in pristine condition. 

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Love that name - lots of opportunities for word play:

Look, another Contrarian!

Are all these chats Contra productive? 

Contrary to the popular opinion... 

Bringing boards from Canada is Contraband. 

Edited by BlueB
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4 minutes ago, BlueB said:

Contrary to the popular opinion... 

I am writing my contrarian ideas as we speak...

 

I am a huge huge fan of my 166 A/T Contra. This board is truly a quiver killer. It can do pow and groomers, I even did bumps and enjoyed myself (I'm not right in the head). It's forgiving and capable...

 

but...

 

As much as it's awesome, it lacks a certain level of excitement that I get from my NFCB. It's quiet, capable and PREDICTABLE. The NFCB can, at certain times, grab and TURN. To me it just feels that in good conditions it's just slightly more capable. Like a sports car that fells ever so slightly dangerous.

If I don't know what the conditions are going to be like or if I want to cover all my bases I'll grab the Contra. If I know it's going to be good I sometimes gravitate to the NFCB.

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Just tried the Contra today. I liked it so much i bought it off of @yamifumi You can see the vids of my riding here. 

Specs on this board are:

Contra - 172cm - 20cm waist - 48cm stance - 12.5m SCR - Built for 200lbs rider to be stiffer than usual, i weigh 170ish - Hammer head nose w/ flat sharp tail - P-tex with Black top + white logo

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On 5/14/2020 at 1:45 PM, Jack M said:

160A36DA-5E64-4CCF-8CE9-CF442526B8F2.jpeg
I asked @Bruce Varsava at Coiler to simply tell me more about these new "Contra" shapes.  Well if you've met Bruce you know you're gonna get everything you ask for and then some!  One thing led to another and now I have taken delivery of two demo units to test in December.  A 174, 20.5cm, avg 12.5m, and a 166, 20cm, avg 10.5m.  I'll compare to my custom Kessler 175/20.5/10-14, and my stock Kessler 168/20/8-12.  Those Contra sidecut numbers need explanation.  Here was the gist of the email thread with Bruce, posting with his permission:

"
The Contra was designed from scratch as a board to handle a wide range of snow that we get from climate issues. It actually uses a lot of designs from previous freecarve models but puts them together in a unique package.
Softer mid and tail allow for excellent ice grip and control on steeps. Bit stiffer nose punches through crud nicely. Sidecuts are different - not nearly as nose-grabby, and with less bouncing. Turns are altered more through angulation than fore/aft movement although a bit of that still helps. Kinda like but not quite an elliptical sidecut.

Been working on them for about a year with help from the Montucky bros. Testing has confirmed that they work extremely well. I was out on a few occasions in rather shitty stuff and didn't realize how bad it was until I got on a Nirvana which is not too bad of a board but these surpass them quite easily especially in less than ideal snow. I was definitely bouncing around more on the Nirvana. .
The Contra uses a mid tight sidecut similar to an elliptical but we have extra goodies thrown in here and there. @johnasmo is the real genius behind these sidecuts and has a system in place which allows for super consistent design and therefore consistent feel throughout the entire line. 

The Contra really gives the feeling that all parts are working in complete unison. First ride on one I immediately noticed it had a clean raceboard feel in a board that turns tight and biggest bonus is it works well in a stupid wide range of snow. I have had a few instances where I started a day on a Contra then went back to a traditional board and could not believe how shitty the conditions were. Get this feedback from a lot of riders. They just eat up the crappy snow we get all the time now. Grip is stupid high also as they seem to just hang onto almost anything.


I bet you wonder how this all started (-:
Each part of the Contra I have done before although the new sidecuts are a lot more involved. Never did all these things in one board so that was the goal to blend it all together. After seeing that a few other builders were designing boards with a mid tight sidecut and getting good results, I figured it was time to get to work on the freecarve boards. Last 4 seasons I was actually working on softboot and BX stuff which really required me to up the game in regards to my design system as softy boards are actually a bit more complicated to design. Softies are a great success story for me, sold very few raceboards last season and a lot of softboot boards so the design time was well spent. Now that the softy program is up to date, I used the new design system to work on the Contra and it took all of three prototypes to get a really nice board. I had to experiment with different ways to control stiffness along with the type of stiffness and when you get it right, it is exceptionally good. 

Reality is most guys need the easy rider boards which the Contra excels at. Not to say it isn't great for more skilled riders as it is,  especially when it allows you to ride hard in sub ideal conditions.  

Contra sidecuts are a bit more involved so we just use one radius to describe them. However, the actual number to suit your needs has to be a bit tighter than what we are used to referencing from previous boards.
The reason is that they like to stretch a turn better than tightening one so you simply get a tighter sidecut which will happily go faster and be plenty stable. I would say on average you go with .5 to 1m tighter than what you would normally want from any of my previous designs. 
Most popular has been a 12.5m  so I'll go with that for the 174 demo. The 166 is a real sweet board with the 10.5m. One of my favorites!

Some other exciting news as I just secured an autoclave which will allow me to use the hi end pre-preg carbon/glass similar to what a certain European manufacturer who makes a lot of black boards uses (-: 

An autoclave is a heat/pressure vessel which is what they use to press their boards. Unfortunately, the Covid issues have slowed this project down as I have not even been able to pick up the Autoclave yet. 

My only problem is I am old! Elbow just gave out yesterday and I'm starting to sound like a broken record complaining about injures but I'm a few weeks away from 59 yrs old and it is the reality of a lot of hard mileage on my joints. Held up better than hoped for last season just finished which was a surprise as I did about 95 boards since Sept. Plan is to do about 80 boards next season as I am supposed the be off now till Sept.

With the pandemic on the go, no golf so I have been busy making up a few stock Contra's which will be available in fall. 

As of writing this I already have about 60 of the 80 orders for next season but won't be starting those till fall. 

Can I golf now, puuuulllleeeez!
BV
"

Can't wait for a k168 vs Contra in-depth comparison! 

Edited by Tddragon
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On 12/24/2020 at 10:35 AM, Tddragon said:

Can't wait for a k168 vs Contra in-depth comparison!

Geoff shipped them to me via 2-day USPS Priority Mail on the 12th. They went from Massachusetts to Rochester NY and are still en route to me in Maine. 🙄

Not that there is any snow to ride on, that is. 😭

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Guys, snowboards please not politics. Can we just talk about the Contra?

 

Like how I am completely conflicted with this board. Sometimes it's the greatest thing since this bread-slicing app I just downloaded on my iPhone and sometimes I really just want to cry.

I rode it Friday and while I admit that I sucked more than usual I had moments where it hooked up and was really really fun. I do find it more eager to complete turns than a racing board like the VSR or the REV. Flexier too but the overall impression of my 166 A/T is TURNEY!!! It's not a F2 SL 162 type turney (or MADD type turny for that matter) it's way more mellow than that especially on the nose or tail. But once you get it to bend in the middle it hooks up and turns so quickly! It's really fun!

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Ok the contra news from my bump is based on a monster to a contra comparison. Switching to a new board has a learning curve and one day didn't do it. So order the new board now.  Who doesn't like a new board ? Bruce can't hit the slopes either till the province opens again  in about 27 days. All the snow so far is man made on beginner runs. Crappy snow on crappy slopes for a crappy end to a crappy year and I know the new year is going to be awesome after all i have this year to compare it to. Actually the start was pretty good" snow wise " 6th day rained out. Happy New Year all !

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I'm going to change my opinion based on new data...

This sidecut is awesome! There's something about it that I can't quite put my finger on but the way it hooks up and then releases is addicting! Yes, it's turny in the 166cm and ~10m radius but it's not hooky and definitely stable at speeds. The more I ride it the more I like it!

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40 minutes ago, JRAZZ said:

I'm going to change my opinion based on new data...

This sidecut is awesome! There's something about it that I can't quite put my finger on but the way it hooks up and then releases is addicting! Yes, it's turny in the 166cm and ~10m radius but it's not hooky and definitely stable at speeds. The more I ride it the more I like it!

Now you need the 185 Monstah version for some big Colerader size turns. Mine has an 11m scr, which works great in soft snow and powder, but I think an 11.5m scr would work a little better on groomers.

Since you're likin' that sidecut, maybe somebody has an 8rw you could try.

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