variable side-cut radii...advantage...purpose?

[1xsculler]

So, what is the purpose, advantage, etc. of variable side-cut radii over a single side-cut radius? 

[Zone]

See the other videos associated also.

Well explained by Prof Donek

 

[Eric Brammer aka PSR]

When you look at any curvature, along a snowboard's edge, it behooves you to have some background in curved geometry. Often, a pure arc segment won't work; we apply pressures between two feet, on a flexible plank, in different tempos. A Parabolic curve doesn't really help, as it's tightest curvatures are out near the ends of an arc segment. (Skiers can use this on flex-controlled skis, but only because All their Pressure is exerted at One [broad] Point at the ski's middle) However, we've got a few 'extra' moves Skiiers don't have, nor ever will have. Hold on a sec, while I explain the 3-outa-4 performance attributes Skis share with Boards...

Both vehicles can be; Pressured into Flex, usually near the middle (though Boards can apply Pressure way, way out along the length of the vehicle; Note Ryan Knapston, or, Tom Burt).

Both vehicles can 'tipped up on edge', no advantage in either case, other than that most Boarder's feet/bindings interfere prematurally. Both Vehicles can be rotated in a variety of planes in regards the being horizontal the the snow surface;

Skis can be rotated individually; Boards can be rotated around one foot, or both feet, or at a point beyond foot placement, so, that's in Boarding's favor, [as is Pressuring].

Lastly, though, a Ski cannot be 'twisted' amid-ships, in control. A snowboard can, and often is by combining the 3 forces upon it of Rotation, Flexion, and Pressuring, but DOING SO AT INDEPENDANTLY CHOSEN POINTS ALONG THE VEHICLE, points chosen by the rider's footwork and body position.

Ok, so what curvature could possibly be best for these extremes? The Quadratic Cuvature. It looks, mathematically, like a clothes-line strung out with a progressive weight group  on it that puts the heaviest weights in the middle, the lightest at the far ends of the line...It's what set Burton apart in '89-91 as the sidecuts offered by Burton re-defined the ease of carving, while letting freestylers still spin, even on cambered boards.

So, with 'variable arc' sidecuts, you may never know just what in the curve got altered from a pure arc-section; But, it'll have 'areas' that offer more, or less, curvature based on expected bending points, and desired outcome. 

I've been on 'Wren' sidecuts since '88, and I've seen some great variations on the theme, the best being, IMHO, the rotated Assymetric sidecuts of the early-mid '90's, and Volkl's 3-D sidecut that put select tighter curves near where you put your foot's pressure, with loosened torsional flex also tossed into the board's build. Nowadays, it's figured out by computer, so, no Slide-rules, but rather a pretty precise design of curvature that anticipates the rider's likely usage as well.

 

Edited March 20, 2017 by Eric Brammer aka PSR

[Bobby Buggs]

My Coiler VSR all mountain does any type of arc my ability level asks for. I find it easier to vary the turn shapes on a VSR board than a single side cut. I rode a single for the first time in years 2 weeks ago and felt locked into similar type arc in every turn, I was not able to control the size as well as I can on my VSRs. That could have been me but Im very happy on my VSR boards. The only negative I notice on my all mountain is running flat and at certain speed it feels like the different radii are fighting , if that makes any sense, sometimes I dont 

[Corey]

Eric, sidecuts have evolved since what you're talking about.  The general theme is a tight nose, large middle, and medium tail radii.  How the various makers get there is their 'secret sauce'.  Coiler talks about welding wire templates, Donek has various math models, Kessler has clothoid, etc.  

All boards can carve varying radii, but the spread of available radii from a single-radius board is much smaller than the current variable sidecuts.  Hopping off my Donek Rev 163 (progressive 7 to 12m sidecut) and onto a Donek Proteus 170 (fixed 11m sidecut) is a rude reminder of this, as the Proteus isn't as eager to start a turn.  I sometimes over-commit for the first turn or two on the Proteus before I remember.  

[Jack M]

21 hours ago, Eric Brammer aka PSR said:

When you look at any curvature, along a snowboard's edge, it behooves you to have some background in curved geometry. Often, a pure arc segment won't work; we apply pressures between two feet, on a flexible plank, in different tempos. A Parabolic curve doesn't really help, as it's tightest curvatures are out near the ends of an arc segment.

Pretty darn sure parabolic sidecuts are tightest in the middle.  A curve that tightens at the ends wouldn't be a parabola, by definition.  The long side of an ellipse would do that.

Pure arc segments (radial sidecuts) have been used with great success across many brands of skis and snowboards.

[Eric Brammer aka PSR]

21 hours ago, Eric Brammer aka PSR said:

a Ski cannot be 'twisted' amid-ships, in control. A snowboard can, and often is by combining the 3 forces upon it of Rotation, Flexion, and Pressuring, but DOING SO AT INDEPENDANTLY CHOSEN POINTS ALONG THE VEHICLE, points chosen by the rider's footwork and body position.

Ok, so what curvature could possibly be best for these extremes? The Quadratic Cuvature. It looks, mathematically, like a clothes-line strung out with a progressive weight group  on it that puts the heaviest weights in the middle, the lightest at the far ends of the line...It's what set Burton apart in '89-91 as the sidecuts offered by Burton re-defined the ease of carving, while letting freestylers still spin, even on cambered boards.

So, with 'variable arc' sidecuts, you may never know just what in the curve got altered from a pure arc-section; But, it'll have 'areas' that offer more, or less, curvature based on expected bending points, and desired outcome. 

 

9 hours ago, corey_dyck said:

Eric, sidecuts have evolved since what you're talking about.  The general theme is a tight nose, large middle, and medium tail radii.  How the various makers get there is their 'secret sauce'.

Corey, where in this is there a timeline? I'm quite well aware of the progression in sidecut developments. Line Skis still use a variation of a sidecut I gave to Jason (when he still was the Owner of them). A few boards in Donek's lineup have my fingerprints on them, too. Just because I'm turning grey around the edges doesn't mean I'm too old-school to know what's what, or why it's the way it is. 

My point was to describe an evolution of sidecuts pertaining to snowboards. Many readers here don't know how we got to where we're at, or why a board would or would not, have a variable radius sidecut. I will not, however, dissect Mervin's Magna Traction, as it's an abomination of it's own peculiar ilk, and makes my feet very nervous...

[Jack M]

10 hours ago, corey_dyck said:

The general theme is a tight nose, large middle, and medium tail radii.  How the various makers get there is their 'secret sauce'.  Coiler talks about welding wire templates, Donek has various math models, Kessler has clothoid, etc.  

Pretty sure race boards like Kessler KST, F2 Speedster, Donek Rev, Coiler NSR, etc go tight nose, medium middle, long tail.  Or just two radii - shorter radius in the nose, longer in the tail (Coiler Nirvana, Prior FLC).  Pretty sure the clothoid curve used by Kessler is (basically) a constantly increasing radius from nose to tail.

Tight nose, large middle, medium tail would be a freecarve VSR.  It would have some hook at the end of a turn.  Racers usually don't want this.

[Eric Brammer aka PSR]

3 minutes ago, Jack Michaud said:

 

21 hours ago, Eric Brammer aka PSR said:

When you look at any curvature, along a snowboard's edge, it behooves you to have some background in curved geometry. Often, a pure arc segment won't work; we apply pressures between two feet, on a flexible plank, in different tempos. A Parabolic curve doesn't really help, as it's tightest curvatures are out near the ends of an arc segment.

Pretty darn sure parabolic sidecuts are tightest in the middle.  A curve that tightens at the ends wouldn't be a parabola, by definition.  The long side of an ellipse would do that.

That, Jack, depends on which axis you're using to plot the curvature. If looked at in the Z, the arc goes from longer to tighter. Across the Y axis, you get the ever-tightening curvature that reaches an Apex, the 'unfurls' back towards the longer arc sections. 

This is why I differentiated Parabolic from Quadratic, with a definition inclusive.

 

[Jack M]

Parabolic and Quadratic are the same thing.  A parabola is drawn from a quadratic formula.

I distinctly remember reading a Transworld interview with (Paul? Peter?) Wren during the 1990 season where he described Burton's new quadratic sidecuts.  He said picture a rope hanging between two points. That would technically be a catenary curve, but he was just illustrating that a quadratic (parabolic) sidecut is tighter in the middle and longer at the ends.

[Jack M]

@1xsculler, the cliff notes are, VSR sidecuts allow you to adjust your turn radius by pressuring your feet differently.

VSR sidecuts that go from short at the nose to long at the tail also compensate for the fact that g-forces are light at the top/beginning of a carve where we typically have our weight forward, and heavy towards the bottom/end where our weight has usually shifted to the back foot a bit.

Single radius sidecuts can also be "adjusted" for turn shape by angulation - e.g. tilting the board up higher than your lean angle to tighten the turn.

[lordmetroland]

19 minutes ago, Jack Michaud said:

Parabolic and Quadratic are the same thing.  A parabola is drawn from a quadratic formula.

A perfect geometric representation of The Soul of Snowboarding! Crisis averted!!!

[Eric Brammer aka PSR]

Um, not quite?! A Quadratic can exist in a parabola...But, the amplitude can vary to represent lengths of more intense curvature in a quadratic curve. I put a link in for your toying enjoyment...

27 minutes ago, Jack Michaud said:

Parabolic and Quadratic are the same thing.  A parabola is drawn from a quadratic formula.

http://www.mathopenref.com/quadraticexplorer.htm

Open this link, and 'play' with the slide-bars of varied math values within the equation, and you'll see 'the wire loop' twist in ways you may not have thought of.

BTW, I grabbed your 'parabola' graphic, but couldn't 'tip it on it's ear' and rotate the image 90*, and articulate that more than one section (the Apex, near the cross intersection, for example) could be placed at any ol' point along a sidecut curvature. But, if you used the segment in the upper left quadrant, it could be 'flipped' to create an ever-tighter-towards-the-tail sidecut, or... So, a matter of perspective can change the whole ball-game!

 

 

[Jack M]

15 minutes ago, Eric Brammer aka PSR said:

Um, not quite?!

Of course a board builder could use whatever section of a parabola they wanted in order to achieve... something.  You could align two parabolas to achieve a sidecut that was tighter at the ends and longer in the middle, but the resulting curve would not be a parabola (and I don't think it would ride very well).  A parabola has exactly one vertex, and your slider tool shows that.  As you play with the sliders, the vertex moves around and the direction and "sharpness" of the parabola changes, but there is still just one vertex.

At any rate, quadratic/parabolic sidecuts used on skis and snowboards are typically tightest somewhere near the middle, and longer at the ends, as were the Burtons of the 90s.

[Eric Brammer aka PSR]

22 minutes ago, Jack Michaud said:

As you play with the sliders, the vertex moves around and the direction and "sharpness" of the parabola changes, but there is still just one vertex.

At any rate, quadratic/parabolic sidecuts used on skis and snowboards are typically tightest somewhere near the middle, and longer at the ends, as were the Burtons of the 90s.

Yes, there's this though; A parabola is symmetrical, and has a fixed vertex point.

"Rotated" arc sections are then slices of a parabola. They then are 'quadratic arcs'. Hence, the 'rotated quadratic sidecut' of PJ/M, LaCroix Eagle, Nitro EFT, and Aggression Stealth fame. Moreover, those sidecuts were not only dissimilar in curvature size, but then set at different apex points in regards to the board's fore-aft centerpoint. Hence, another aspect of being asymmetrical in shape.

So, to be concise, a quadratic arc can have it's apex shifted away from the 'center apex', and need not try to form an ellipse, it then is a 'variable' sidecut arc. 

 

[BlueB]

On 19/03/2017 at 7:44 PM, 1xsculler said:

So, what is the purpose, advantage, etc. of variable side-cut radii over a single side-cut radius? 

Let's just forget the sophisticated mathematical definitions and do a simpleton explanation... Radial rides more predictable. Variable can vary the turn shape more. 

[Eric Brammer aka PSR]

Blue B, Thank You. I was trying to educate, while being simplistic. But, here, it's NEVER that SIMPLE. Hopefully, there's answers within the diatribes.

 

[Corey]

8 hours ago, Jack Michaud said:

Pretty sure race boards like Kessler KST, F2 Speedster, Donek Rev, Coiler NSR, etc go tight nose, medium middle, long tail. 

I can't speak for all, but the Coiler NSR and Donek Rev definitely tighten again towards the tail. Sean called it the 'hook' and has been experimenting with how much is good over the past few seasons. 

[Jack M]

3 hours ago, Eric Brammer aka PSR said:

Blue B, Thank You. I was trying to educate, while being simplistic. But, here, it's NEVER that SIMPLE. Hopefully, there's answers within the diatribes.

 

I only pointed out that you were mistaken when you said "A Parabolic curve doesn't really help, as it's tightest curvatures are out near the ends of an arc segment".  Then we geeked out. 

5 hours ago, BlueB said:

Let's just forget the sophisticated mathematical definitions and do a simpleton explanation... Radial rides more predictable. Variable can vary the turn shape more. 

Yeah I tried to do that above.

1 hour ago, corey_dyck said:

I can't speak for all, but the Coiler NSR and Donek Rev definitely tighten again towards the tail. Sean called it the 'hook' and has been experimenting with how much is good over the past few seasons. 

I don't think my c. 2010 NSR 185 has that hook, but it's certainly easier to ride than my new-to-me KST 180.  The waist and tail widths are the same on both boards, so I think it has more to do with the flex.  I had heard about that hook option on the newer Revs.  Rode a buddy's F2 185... definitely no hook.

[philw]

Sean's video seems to describe pretty much what the issues are and to answer the original post.

I don't much care what models the board manufacturer uses (or how confused riders were by their school maths) as there are multiple factors at work and the important thing is how the board feels to ride, which you're not going to get from a model.

 

 

[Buell]

Free-form-freeriding. I like it. 

Maybe free-form freecarving is more apt here? I keep my Kessler SL on the groom, but I love how easy it is to change direction in a carve at any time. 

Edited March 21, 2017 by Buell

[st_lupo]

On 3/21/2017 at 4:56 PM, Jim Callen said:

Yeah, free-form freecarving is probably more appropriate phrasing. 

F^3 Carving then?  Somebody should then definitely develop the perfect cubic sidecut geometry for the ultimate free-form-free-carving deck.  

[st_lupo]

On 3/21/2017 at 3:14 AM, Jack Michaud said:

Pretty sure race boards like Kessler KST, F2 Speedster, Donek Rev, Coiler NSR, etc go tight nose, medium middle, long tail.  Or just two radii - shorter radius in the nose, longer in the tail (Coiler Nirvana, Prior FLC).  Pretty sure the clothoid curve used by Kessler is (basically) a constantly increasing radius from nose to tail.

If Kessler is following the definition of a clothoid, this should be right.  https://en.wikipedia.org/wiki/File:CornuSprialAnimation.gif  If I get the Kessler I'm biding on I'll take some side-cut curvature measurements and compare with my Nirvana Balance (really sorry about nerd mode tonight, I had to look up clothoid a long time ago, otherwise I kept thinking of hanging laundry whenever I heard about Kessler snowboards).  

Edited March 24, 2017 by st_lupo

[Tanglefoot]

If I understand the Kessler web site correctly, the sidecut radius is largest in the middle and tightens gradually and equally towards the nose and tail. Combined with a decambered nose and tail, this allows the board to ride a gentler, larger radius turn if desired. The rider input (change of board angle) will also have a greater effect on the turn radius than it will on a single sidecut board. According to a chap I spoke to at Virus, their boards have elliptical sidecuts, which is a very similar idea.

I have done some back to back runs with an older, 9.5 m single sidecut Goltes slalom board and the wife's Kessler slalom board this winter, and the difference between the two is shocking. The full camber and single radius of the Goltes means that you absolutely have to keep the speed down and perform turns at the correct radius, otherwise the board starts vibrating and chattering and loses composure. The Kessler is much more versatile, quieter and smoother - it fully forgives you if you overcook it occasionally. Both are metal boards with damping layers, so fairly similar in terms of materials.

Now - I have placed one board on top of the other to see how different the sidecuts actually are, and they are identical to within half a millimetre. So it is possible that Goltes have done something more advanced with the sidecut than they have stated on the board. Kessler have patented that shape, after all. Or it is possible that other aspects of the Kessler technology are more important than the sidecut. The decambering of the ends are clearly important, and the materials seem to be very well tuned for the job.

Disclaimer: The Goltes is old, and the Kessler is new. This is clearly unfair.

Edited March 25, 2017 by Tanglefoot

[alpinegirl]

The decambering is a tremendous factor. There are no accidents there. I love the geometry.