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

[BlueB]

On 25/03/2017 at 1:55 PM, Tanglefoot said:

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.

Standard GS, SL and BX Kesslers have tightest radius towards the nose and loosest towards the tail. Some of the boards made for Canadian team around Olympics had a bit of "hook" towards the tail, like what Coiler calls VSR. I had a custom free caving Kessler 170 that had that geometry too. I can't tell you about stock 168 free carver, as I didn't have it in my hands... 

Edited March 26, 2017 by BlueB

[philw]

• "clothoid" suggests a gradual tightening. You could stick two of those back-to-back, but then you'd likely describe it differently.
• Kessler's US patent text is fairly impenetrable. The diagrams look like the front has the tighter radius in the diagrams. 
• I took a photo of my 156SL, rotated and overlaid the curves... the curve at the front is tighter than that at the rear, and it looks "clothoid": it tightens towards the end. 

Obviously the overall design is a combination of multiple factors, of which side cut is only one aspect. 

The aim of the curve? Well, the start of the turn is very different from the end. Most people probably have a pressure shift front-to-back through a turn; turn shapes are in general not arcs of circles; rider speed may well vary through a turn. Taken together, I think it's not surprising that a simple geometry isn't the optimal solution.
 

[Tanglefoot]

Well, I am glad I remembered to write "If I understand the Kessler web site correctly".

However, I still feel that the illustrations and explanations on the website are trying to tell me that the sidecut tightens up towards both ends. 

Must have a read of the patent one evening - maybe after I have traced, overlaid and compared the sidecuts of all my boards.

[Allee]

I always thought the purpose was to launch you into the trees, when you get on the wrong sidecut at the wrong time ... or maybe that's just me.

[lowrider]

I miss these pissing contests !

[Tanglefoot]

Clothoid, schmothoid. It's been a busy afternoon at the Tanglefoot Technology Centre. Today' hands-on workshop was held in the Geometry Lab, and the theme was "Sidecuts".

Firstly, a 9.5 metre radius was drawn on a piece of cardboard with the aid of a sharp pencil and a long tape measure. The Goltes SL was aligned with the resulting curve, and the match was perfect. The board was then turned 180 degrees, and again the match was perfect. I am not one to jump to conclusions, but this is surely a 9.5 metre single radius board.

The Kessler SL was next. On close inspection, there was some local deviation from the curve in places, of around one millimetre. One of the technicians then traced along the edge of the Kessler and turned it 180 degrees for comparison. Now there was a visible discrepancy of around two millimetres, and the evidence was mounting. There is indeed a change in radius along the length of the board, and it appears to increase from a large radius at the tail to a smaller radius at the nose, just like several of you have stated previously.

I therefore stand corrected, but I will ask you all to ponder the following: The change in sidecut is extremely small along the length of the board. Surely, the camber profile and the flex pattern of the board will be far more important in determining the turning radius once you are riding hard enough to bend the board more than a few millimetres? Anyone?

[BlueB]

Oh, here we go! Right in time for an all summer discussion, the traditional "Radius vs. Flex Pattern" thread :). We had quite a few of those over the years... Never the less, it's an interesting topic and you'll get all sorts of answers, including inevitable topic drifts. 

I've got my  ready. 

Edited March 28, 2017 by BlueB

[Corey]

1mm difference? Wow. It never ceases to amaze me how small things are perceptible to us. 

[bigwavedave]

To further confuse the matter, don't forget to factor the influence of taper. Most modern boards have varying amounts of taper, independent of the type of sidecut (variable or single).

[Tanglefoot]

I've been losing sleep over this. 

I have therefore decided on an analytical approach involving an online arc-segment-radius-calculator. According to the initial calcs, an arc segment of width 1500 mm and height 30 mm will have a radius of 9390 mm. This is a close approximation to the Goltes SL sidecut, and the measurements have just come in from the lab to confirm this.

By altering the arc height 1 mm, the radius changes only 300 mm. So what's going on? Kessler state a variable radius of 7-11 m for the 156 SL on their website.

CLEARLY, the flex pattern has a much greater influence on turn shape than this subtle change in radius along the length of the board. I will be comparing the flex, damping and natural frequencies of the two boards as soon as the bindings are off for the summer.

[Tanglefoot]

And taper.

[Corey]

Cool, that lines up better with what I expected, but I was too lazy to do the math.  ;)  

Flex pattern is a big deal.  I know the Coiler Nirvana comes in three flex patterns that move the thicker part of the core profile fore-aft.  On the Energy models, the core is notably thicker under the rear foot than the front foot even to the bare eye.  I still haven't ridden all three flex variations of the same board, but would like to.  

Also decamber/camber plays a role.  Bruce made an Angry for me with some alternate camber profile.  It just didn't work for me - it felt very soft.  The replacement board feels great, and apparently he didn't change the stiffness.  I don't understand...

[BlueB]

6 hours ago, Tanglefoot said:

By altering the arc height 1 mm, the radius changes only 300 mm. So what's going on? Kessler state a variable radius of 7-11 m for the 156 SL on their website.

CLEARLY, the flex pattern has a much greater influence on turn shape than this subtle change in radius along the length of the board. I will be comparing the flex, damping and natural frequencies of the two boards as soon as the bindings are off for the summer.

You can't just put a variable on top of radial and decide "it's only 1mm difference...". Your best bet is measuring and calculating the various segments of variable one, piece by piece. 

 

I'm really interested how are you going to measure the last 3 variables, you mentioned... Especially the natural frequency... 

[JRAZZ]

If I tell you that the difference in the width of the nose is a millimeter you'd say that it's nothing.

If I tell you that the difference in sidecut radius is 3m you'd say that it's easily detectable, right?

 

It's the same difference:

Nose: 30mm, Waist: 25mm, Effective length:137/2     =>  Radius is 10.43 m

https://www.wolframalpha.com/input/?i=n%3D30,+w%3D25.5,+l%3D137%2F2,+(4l^2%2B(n-w)^2)%2F(4(n-w))

 

Nose: 29mm, Waist: 25mm, Effective length:137/2     =>  Radius is 13.41 m

https://www.wolframalpha.com/input/?i=n%3D29,+w%3D25.5,+l%3D137%2F2,+(4l^2%2B(n-w)^2)%2F(4(n-w))

 

It's not crazy that we can detect this.  We see this all the time where we look at something that looks small but has a big effect.  We're just looking at the wrong thing.  The effect is magnified in a way that's easily detectable.  When going 20mph the 29mm nose (13.41 meter radius) will give you a centripetal acceleration of 5.96 m/s/s (a 175 lb person will weigh ~205).  The 30mm nose (10.43 meter radius) will give you an acceleration of 7.68 m/s/s (same 175 lb person will weigh 222 lb).  Certainly seems detectable to me!

 

Nerd out! (drops pencil)

 

 

p.s. 

Makes you look at construction quality and accuracy in a whole new way, doesn't it?

 

p.s.s.

Yes, I might have gone overboard.  You tempted me!  It's all your fault!   I have a condition.

 

p.s.s.s.

Yes, I know sidecut radius does not directly equate to turn radius, don't make me do flex pattern calculation.  I'm warning you!

Edited March 30, 2017 by erazz
Added parentheses. I need help

[workshop7]

^You labeled your widths incorrectly.  You have them in millimeters (mm) and with the nose width numbers you listed, 29 and 30, you should have used centimeters (cm).  You were right when you infer that the difference of one millimeter in the width of the nose of one snowboard to the next (with all other measurements being equal) is not going to make much of a difference.  However, one centimeter certainly will.

[wulf]

Please take a look at Kesslers website illustration. The tighter radii are just in the very tip and tail region.

Kessler Clothoid Shape

I've used Excel to illustrate the radii on my SL 163 (260/200/240mm @1510mm effective edge)

With the typical taper of 20mm on most carving/racing boards the radius in the nose MUST be tighter than in the tail section.

Probably Sean or Bruce could enlighten us on that ...;-)

Edited March 30, 2017 by wulf

[philw]

On 27/03/2017 at 5:55 PM, lowrider said:

I miss these pissing contests !

With respect, you misunderstand completely the nature of the discussion. It's not a win/ lose scenario, we're trying to understand something which to us is important. You're flat out wrong if you think intelligent discussion has to have winners and losers. Bah.

Taper: that's a good point. It's key in powder boards, but how does it work in powder and on hard pack?

[JRAZZ]

8 hours ago, workshop7 said:

^You labeled your widths incorrectly.  You have them in millimeters (mm) and with the nose width numbers you listed, 29 and 30, you should have used centimeters (cm).  You were right when you infer that the difference of one millimeter in the width of the nose of one snowboard to the next (with all other measurements being equal) is not going to make much of a difference.  However, one centimeter certainly will.

 

 

I feel so sheepish

[bigwavedave]

6 hours ago, philw said:

Taper: that's a good point. It's key in powder boards, but how does it work in powder and on hard pack?

 

7 hours ago, wulf said:

With the typical taper of 20mm on most carving/racing boards the radius in the nose MUST be tighter than in the tail section.

Not necessarily, but most likely. I used to assume that the variable side cuts on raceboards resulted in their taper, but then thought there are plenty of powder boards out there with lots of taper and a near radial sidecut, so they're not necessarily directly linked.

This is what Bruce had to say about the effect of taper while discussing building a new carving board. Rather than trying to paraphase, and get it wrong, here's what he said:

"It does a few things. Increases directional change as the wider nose wants to dart off in the other direction quicker just due to the wider nose having the sidecuts pointing in different directions more. Does the reverse at the end of the turn and does not push you across the hill as this really isn't ideal for racing and does reduce pop a bit as you don't get that kick at the end. The boards do not want to finish the turns as strong with lots of taper. Also when using nose decamber, the edge actually engages later as the tip of the sidecut is off the snow until you roll onto the edge so it helps to have a wider nose as it uses the quicker direction change capability to reduce the delay the decamber creates for initiation."

There are a lot of variables in play building a board that works well─a science and an art.

 

 

[wulf]

 Nice quote: ... "a science and an art building a board that works well" 

Scenario: What if we shake things around? Taking a modern SL shape and reverse the sidecut. Wider at the tail, norrower at the nose. Having the tight radius at the tail.

Would that work ...?

[Corey]

Donek had a prototype like that in Aspen a couple of years ago.  Most people said it was weird, but I recall someone saying they loved it.  I didn't try it.  

[BlueB]

10 hours ago, wulf said:

Please take a look at Kesslers website illustration. The tighter radii are just in the very tip and tail region.

Kessler Clothoid Shape

I've used Excel to illustrate the radii on my SL 163 (260/200/240mm @1510mm effective edge)

With the typical taper of 20mm on most carving/racing boards the radius in the nose MUST be tighter than in the tail section.

I don't think you completely understood that Kessler's illustration... It's more about decamber (rocker) of the nose and tail, he's talking about there and about effective edge gradually increasing as you tip the board higher and higher on the edge (tighten the turn radius due to edge inclination and resulting decamber of the board). At no point he spells out the details of the variable radii along thee edge. 

You can have taper with perfect radial sidecut. Imagine a "normal" radial cut board, with no taper. Now, in your mind, rotate tose 2 arcs a bit outwards at nose, around points at the middle of each arc. It will result in wider nose, narrower tail, aka taper. 

[BlueB]

1 hour ago, wulf said:

Scenario: What if we shake things around? Taking a modern SL shape and reverse the sidecut. Wider at the tail, norrower at the nose. Having the tight radius at the tail. 
Would that work ...?

Depending on the application. But, yes, it would carve and hook the end of the turn nicely. I often carve switch, Scooby just watched the switch carving on my modern SL, board other day.
Also, I rode couple of boards reverse mounted (bindings facing the tail. It worked too. You have to change your inputs a bit too. 
Last but not least, I have few boards with few mm reverse taper (I believe its called flare?). One of them is my favorite hard pack carver. We are not talking here about full reversed modern SL shape, though. 

Also, search up Inca snowboards. Some of their models had massive flare (like 40-50mm!). They also were inventors of camber/rocker hybrid profiles. I think they had camber at the nose tail and between the bindings, while they had rocker right under each binding. When tipped on the edge, the board acted as if you had Magna-traction but applied in different plane. 
It appears that all the people using the mixed profiles and variations of magna had to wait for Inca's patents to expire. I even believe there was a law suite between Inca and Burton... 

Anyways, the flare can work, but it's not the ideal geometry for racing, where you need to be able to release your edges quickly. 

[Mig]

1 hour ago, BlueB said:

I don't think you completely understood that Kessler's illustration... It's more about decamber (rocker) of the nose and tail, he's talking about there and about effective edge gradually increasing as you tip the board higher and higher on the edge (tighten the turn radius due to edge inclination and resulting decamber of the board). At no point he spells out the details of the variable radii along thee edge. 

You can have taper with perfect radial sidecut. Imagine a "normal" radial cut board, with no taper. Now, in your mind, rotate tose 2 arcs a bit outwards at nose, around points at the middle of each arc. It will result in wider nose, narrower tail, aka taper. 

I think it is about both, decamber and tighter radii in the nose and tail. Cambered part has a constant radius, decambered parts have tighter and tighter radii the closer you get to the contact points:

"Kessler Shape Technology (KST) is the dynamic interaction between the baseline and sidecut. The 2005 patented technology uses all the advantages of the rocker line in combination with a sidecut based on a clothoid geometrical formula. It is the sophisticated interaction that is causing the brilliant revolution!

The KST Baseline shows reverse camber. However under pressure, the front and back contact points move towards the middle of the ski or board. The nose and tail rise slightly. The aggressive radii are being negated. This results in turns being easier to initiate, easy edge changing, and a safe, catch-free downhill run with increased stability.

However, it’s when the ski or board is edging that the interaction between the sidecut and the rocker line really comes into play. As the ski or board tilts, the contact surface area with the snow is increased, allowing the rider to consciously select the radius of choice. This is where the full force of the clothoid shape comes into effect, giving the rider totally controlled carving ability and a high level of grip, also on icy conditions or at high speed. World-class performance and easy handling."

And yes, you can have taper with single radius sidecuts. The Fullbag Blunt Diamond and Lifer both have respectively 30mm and 15mm of taper and a single radius sidecut, as an example.

Edited March 30, 2017 by Mig

[bigwavedave]

3 hours ago, wulf said:

 Nice quote: ... "a science and an art building a board that works well" 

Scenario: What if we shake things around? Taking a modern SL shape and reverse the sidecut. Wider at the tail, norrower at the nose. Having the tight radius at the tail.

Would that work ...?

Like Cory said, reverse scr (larger radius in nose & tighter radius tail) has been done, but not common. Sean said it was an accident that sort of worked.

What I was pointing out was that the type of scr doesn't necessarily dictate the amount of taper. In other words, you could have a variable scr in a board without taper.