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Sidecut radius formulae?


quest4powder
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Can anyone explain, in clear english, exactly the difference between different sidecut radius formulae? (Progressive, radial, elliptical, etc.)

While I realize other variables (length, width, longitudinal & torsional flex, etc.) are all involved in determining how a particular board performs, would one type of sidecut be more useful for a specific event (i.e., slalom or GS)?

Is the 'feel' of one noticeable different than another?

Would there be a good resource (in addition to BOL) that would clearly define and explain the difference types of sidecuts?

Thanks for helping to illuminate an otherwise murky subject.

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radial - sidecut shape is part of a large circle.

progressive - a blend of two or more radial curves. (I suspect Volkl's "3D" sidecuts are a 3 radii progressive)

elliptical - sidecut shape is part of a large ellipse. whether it's taken from the side or end of the ellipse, I don't know.

quadratic - a parabola. the shape of the path of a ball thrown between two points if no wind resistence, or the shape of a rope hung between two points, roughly. it is the shape of the curve you get if you graph y = x squared.

There are dozens of ways you could design a sidecut, but they must be matched to an appropriate flex pattern. As other people here have pointed out, the difference between two types of curves is usually 1-2 millimeters or less - you could sharpen your board wrong and have a different sidecut. But it's not just that your edge has a certain curve, the sidecut is also milled into the core, which thankfully you can't change. The shape of anything has an effect on how it flexes, so the flex pattern is equally important.

There is no way to say how each curve "feels" when carved, it's simply up to you to compare boards and see what you like. The goal of every sidecut and flex pattern is to evenly distribute your weight from under your feet out to the ends of the effective edge, while allowing the board to bend into a smooth curve without kinking. The better a board does this, the better the edge hold.

Different companies try several different combinations of sidecut and flex and choose the one that works best for them. It is conceivable that two different sidecuts/flexes will produce the same results, or, the same edge hold strength but with a little different feel to the ride.

One sidecut I don't understand is the two radii progressive, where the front half of the board has one radius and the back half another. I try to use my whole edge while carving, so I'm not sure how this is useful. Seems to me the two ends of the board would be trying to do different things. But I've never tried one.

One interesting thing to ponder is the fact that the shape of the sidecut changes when the board bends. i.e., a radial curve ceases to be radial when you tilt the board up on edge and decamber it. The ultimate sidecut would be one that would stay radial at every edge angle, but that would mean the board would have to actively change its dimensions as you ride.

-Jack

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I think Jack summed up the whole radius question nicely. As for the dual radius sidecut thing, I have ridden boards with this type of sidecut- larger in the front to "ease into the turn" and tighter as you get toward the tail to help shoot you through. I'm with Jack in the whole "I don't get it" department. I found that the tail always wanted to "get ahead of the nose". I mean, how is the board supposed to track in a natural arc if the nose and tail have a different sidecut radius?? Has anyone else had a problem with this? I'd be interested to hear anything.

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Mike- In fact, it was actually a Salomon I was referencing. I had the old 550 series and really wanted to like the board.......but alas, I never could. Makes me a little nervous that so many manufacturers are using a "progressive sidecut" on their boards these day. Don't find nothin' "progressive" about it, nope. -Ted

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progressive - a blend of two or more radial curves. (I suspect Volkl's "3D" sidecuts are a 3 radii progressive)

This is supposition, but here goes:

I had always assumed the '3D' used in Volkl marketing indicated that the sidecuts were modeled in a 3-dimensional space, not a 2-dimensional plane. (I know very little about snowboard manufacturing ... maybe they all do this, mebby nobody does?)

If this is true, then might it be possible the different radii come into effect in stages, as the board is flexed, rather than at different points along the board length? I can see how this would promote a stable and predictable carve, regardless of how the board is flexed, or how far it is inclinated.

Regarding dual sidecuts: I have demo'd skis with some crazy sidecuts as are described above, with larger radii at the tip, and shorter at the tail. They weren't any fun at all, and did not want to release at the end of the carve. To use a driving term, the skis loved to oversteer, and were rather unstable at speed. Not to mention turn initiation was a real PITA too.

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Originally posted by Tommy D

I had always assumed the '3D' used in Volkl marketing indicated that the sidecuts were modeled in a 3-dimensional space, not a 2-dimensional plane.

Quite possible, and probably more, um, probable. I assume this would mean their boards are optimized for one particular edge angle....?

I was thinking perhaps it was a 3-radii progressive because I can see how that might work. If it was matched to a flex pattern that allowed the board to bend more in the middle than at the ends (which I think a lot of boards do anyway), it would make sense to put a longer radius in the middle of the board and shorter radii at the ends.

Thanks all for the impressions of dual-radius sidecuts. Just what I suspected.

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Guest Frappe

My Nitro Torque BX-style board (soon to be the hardboot-powder-board) has a three-radii progressive sidecut.

I don't recall the exact numbers, but it starts larger, then becomes a smaller and smaller sidecut as it nears the tail.

It in no way makes the board harder to carve, but changes the riding style quite a bit. To really get a nice, strong carve at speed that the 164 length and 133ish at most effective edge will allow, it wants more rear-weight than a regular board.

No problem with "oversteer" really, but a bit harder to initiate, and weird to predict how it will turn.

Makes a nice freeride toy though, can't complain.

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Guest Ghostrider

The volkl 3D sidecut or "DDD sidecut" as they like to call it. Is not so much a radius pattern, but a design technique used in manufacturing. The board/ski flex is programmed into a CAD program and then simulated through its range of flex and corresponding angle. The radius (or radii) is then calculated based on the flex to provide maximum tip to tail snow contact through the entire flex range. Basically, its reverse design by setting radius based on the individual flex patterns of the boards to keep smooth edge contact no matter what the speed.

They also do a "Twin Tuned DDD" which is exactly like the DDD except...you guessed it...it keeps tip to tail edge contact even if you are riding switch so the board performs equally no matter which way it is facing, yet still remaining a directional board.

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Guest chillaxin.nl

I own a Nitro CAM with progressive sidecut. Front has a radius of 9.7 and the back has a radius of 7.6. The advantage has been pointed out by Board_ted. You enter the turn more controled and exit the turn with more speed. These kind of radii are also used in slalom races. Personally, i love the Nitro CAM and think this is the best board ever!

Virus also builds boards with 8 radii in one board! If you use the "pendel" technique (enter the turn with your weight more to the tip and exit the turn more with your weight to the tail) you can actually feel the different radii. I had to get used to it, but it definitely gives another dimension to carving. With your weight you can "choose" whether you want to carve tight or big turns without tilting the board more or less....

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Originally posted by chillaxin.nl

I own a Nitro CAM with progressive sidecut. Front has a radius of 9.7 and the back has a radius of 7.6. The advantage has been pointed out by Board_ted. You enter the turn more controled and exit the turn with more speed.

Shorter radii are slower.

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Guest chillaxin.nl

Hi Jack,

I don't agree with you on that...a shorter radius will produce a shorter turn, thus more quickly through the turn, which you need especially with slalom. You will get that kick when you exit the turn. You are talking about the overall speed. Okay, a GS is faster than a SL but the turn of a GS will take longer due to the bigger radius. Don't you agree?

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Originally posted by chillaxin.nl

Hi Jack,

I don't agree with you on that...a shorter radius will produce a shorter turn, thus more quickly through the turn, which you need especially with slalom. You will get that kick when you exit the turn. You are talking about the overall speed. Okay, a GS is faster than a SL but the turn of a GS will take longer due to the bigger radius. Don't you agree?

Not really. A board with a longer radius can make the same size turn as a board with a shorter radius, but it will do it at a higher speed.

The fact that the Nitro has about a meter shorter radius on the tail means that if you ride on the tail at the end of your turn, it will be extra hooky and snap you into a shorter radius turn finish. This might be useful in slalom where the extra energy created could launch you into the next turn. Although at the bottom of the race course I think the guy with the 171 with the 11 meter sidecut will beat the guy with the 171 with the 9/8m progressive sidecut. It just means the board has a lower overall speed threshold.

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Interesting. I've always stuck to Emma Peel of Lib Tech exclusivly for this reason-- 8 sidecut radius. I like it when its responsive. I had MLY 159 for some time, and it had longer side cut radius (9 to 10, I believe) and it was a bit too slow for my taste in responding to carving. Then I switch back to Emma Peel after a year on MLY and went pipe-riding, and quickly forgot how senstitive it was. I've considered talking with Mervin to get a customized Emma Peel in race board structure, and now you're claiming shorter sidecut radius can be slower than longer sidecut radius, Jack? I understand the mathematic applications, but yet its a bit beyond my cro-magnum netherdal brain. Oh yea, that's for 157 to 159. The Madd 158's got 8.8 sidecut radius. Yet, it's technically better than Emma Peel (of coruse, logically since its a freestyle/freeride board as oppose to race board) ? By the way, Im into 157 to 159 mostly for all round riding, and am looking for multi-purpose race board, like Madd 158 -drool-. Of course, I'd like to be good in SL and GS as well. Im hoping Madd 158 will be suitable for GS (tho I dont think I like the notion of it being squirrely when Im hangin' on tight blasting mach 3) as well ?

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Originally posted by Jack Michaud

Not really. A board with a longer radius can make the same size turn as a board with a shorter radius, but it will do it at a higher speed.

I don't see how a board with a larger sidecut radius could make the same size turn as one with a smaller sidecut radius simply by going faster. It would seem that the board would have to have a higher edge angle or the rider would pressure the tip for it to carve as tight a turn as one with a smaller sidecut radius.

And even then, there would be a point where the sidecut simply wouldn't allow the board to bend any further, at maximum edge angle, as the edge would be full in contact with the snow thus preventing any further significant bending of the board (although leveraging the tip might further tighten the turn somewhat).

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Originally posted by LeeW

and now you're claiming shorter sidecut radius can be slower than longer sidecut radius, Jack?

This is nothing new, and it's not a claim, it's a fact of physics. A shorter sidecut radius will be slower <i>while carving a given radius turn</i> than a longer radius sidecut.

Carving is all about balancing forces. As you tilt your board up on edge, the board begins to carve a round turn. This creates centripetal force that you have to balance by leaning. The greater the speed, the greater the force. The greater the force, the more you have to lean. The more you lean, the more edge angle you give the board. The more edge angle, the tighter the board carves. The tighter the board carves, the greater the force. And so on and so on until you reach that magic angle of inclination where everything is balanced. There are well known equations that tell you exactly where this happens for any sidecut radius. I've used them here:

http://bomberonline.com//articles/physics.cfm

It turns out that smaller sidecut radii achieve this balance at slower speeds. If you try to carve an 8m sidecut radius at 30mph, it's just not going to happen. Sure, you can ride your 8m board at 30mph and make long drawn out turns that even leave a thinnish track in the snow, but that's not a true carve of the entire edge.

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Originally posted by quest4powder

I don't see how a board with a larger sidecut radius could make the same size turn as one with a smaller sidecut radius simply by going faster. It would seem that the board would have to have a higher edge angle

Right, the longer radius board has to be going faster and be tilted at a higher edge angle than the shorter radius board. I meant to imply that.

A 10m board could make the same size carves as an 8m board, but it would have to do it at higher speed and higher edge angle.

You know what was really cool, I was riding with Helmut Karvelow at the ECES and we were both demoing the Madd 170. I followed him down one run, and it was amazing - we were both making the same size turns at exactly the same speed. I was in no danger of overtaking him or losing him. It was like syncronized swimming or something! I probably could have ridden in his ruts if I tried.

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I don't agree with you on that...a shorter radius will produce a shorter turn, thus more quickly through the turn, which you need especially with slalom. You will get that kick when you exit the turn.

Unless you left the back half of the board off the snow, dont you get that same "kick" on your way INTO the turn as well?

Seems to me that if the board is on edge and your weight is centered, the front half will be trying to carve a wider arc than the back half. How could that result in anything but drag, as each half gets forced to follow a path different from what it's trying to carve?

Sure you can lean forward or backward, but I have a hard time believing you can shift it enough to keep the front half of the edge from fighting with the back half. Even if 100% of your weight is on your front foot, look at where your front foot is on the board... what's the weight distribution between the front and back halves? A 2:1 ratio would still leave 30% of your weight on the "wrong" edge.

I haven't ridden such a board, so this is all speculation on my part, but I have yet to hear a theory about progressive sidecuts that makes any sense to me. I'm still really curious about it though.

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Im impressed. Im familiar with John Howe's Skiing Mechanics. Of course, Ill admit Im still struggin' with the concept of all those mathematic formulaes. Kudos to you, Jack for the info. I wanna verify if I understand you correctly: as I carve on, say, 8 m sidecut radius of the board-- itll be slower had I carve to 8 m ? I apologize if I appear confused and dumb. I perfectly understand kinetically, but mathematically, Im very interested to understand the concept behind it. The article's a bit too much (akin to John Howe's book, I may add) for me to grasp the concept. More questions at the bottom of your post, Jack.

Originally posted by Jack Michaud

This is nothing new, and it's not a claim, it's a fact of physics. A shorter sidecut radius will be slower <i>while carving a given radius turn</i> than a longer radius sidecut.

Carving is all about balancing forces. As you tilt your board up on edge, the board begins to carve a round turn. This creates centripetal force that you have to balance by leaning. The greater the speed, the greater the force. The greater the force, the more you have to lean. The more you lean, the more edge angle you give the board. The more edge angle, the tighter the board carves. The tighter the board carves, the greater the force. And so on and so on until you reach that magic angle of inclination where everything is balanced. There are well known equations that tell you exactly where this happens for any sidecut radius. I've used them here:

http://bomberonline.com//articles/physics.cfm

It turns out that smaller sidecut radii achieve this balance at slower speeds. If you try to carve an 8m sidecut radius at 30mph, it's just not going to happen. Sure, you can ride your 8m board at 30mph and make long drawn out turns that even leave a thinnish track in the snow, but that's not a true carve of the entire edge.

-SO- if I was going 30 mph, only a small portion of 8m effective edge would be carving (which is the impression Im getting with "thinnish track") ? How is this an exception for those Madd 158 ? I need to dig out those old TW snowboard magazines (early 90s) and re-read those articles about the sidecut radius (which is where I got the idea since then--smaller radii, rapid response).

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Im startin' to get the drift now. As for riding in his trenches, no you wouldn't--nothing like tearing up perfectly groomed courdrary lines. :)

Originally posted by Jack Michaud

Right, the longer radius board has to be going faster and be tilted at a higher edge angle than the shorter radius board. I meant to imply that.

A 10m board could make the same size carves as an 8m board, but it would have to do it at higher speed and higher edge angle.

You know what was really cool, I was riding with Helmut Karvelow at the ECES and we were both demoing the Madd 170. I followed him down one run, and it was amazing - we were both making the same size turns at exactly the same speed. I was in no danger of overtaking him or losing him. It was like syncronized swimming or something! I probably could have ridden in his ruts if I tried.

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Originally posted by Jack Michaud

This is nothing new, and it's not a claim, it's a fact of physics. A shorter sidecut radius will be slower <i>while carving a given radius turn</i> than a longer radius sidecut.

I was also a bit mystified when I first read this statement as the phrasing reverses how I tend to think of it. Another way to say it is a board with a shorter sidecut radius can carve a turn that you'd need more speed and edge angle to duplicate on a board with a larger sidecut radius.

Up to a point.

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