SCR - How To Measure It?

[barryj]

I have a buyer/end user understanding  of SCR  but is there a tool to measure it...say on a finished board?   

How is a board with a specific degree scr created?

What is the math in simplest terms - a board  with a 12 degree scr is 12 degrees out of what.... total angle?

......and how is a VSCR created on the same plane?

Yes!....still on alpine injured reserve and I have way too much time on my hands and desperately need to get out on the hill!  

[ursle]

It's a 12 meter (36') scr, if you laid the ski down and traced the sidewall, that trace would become a 36' circle, but, that was 20 years ago, today, the tail is tapered, thinner than the tip, makes it easier to get out of the carve, and the skis and boards have variable sidecut, the tip is 12 m, the mid is 14 m and the tail is 17m, add some rocker and then try to imagine the shape of the sidewall.

Thanks Kessler

[SnowFerret]

SCR is a radius, not an angle. Theoretically, you could trace the edge of your sidecut onto a piece of paper, complete the circle, and then measure it to determine the radius.  You could also use a set of radius gauges and try matching them to the sidecut, but I don’t think there are gauges available in the size of snowboard radii.

 

Variable SCR would be a whole other story since it isn’t a constant radius. 

Edited March 6, 2020 by SnowFerret
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[lowrider]

Agree with above ! Then you tip the board on edge every thing changes depending on stiffness of board weight of rider, how you balance on the fore aft loading, plate, no plate, footprint of binding on board, how you peddle etc. It's a starting point but not the be all end all. Best evaluation is of a similar manufacturer of similar construction.

[big mario]

First one includes a handy dandy plug in calculator.  If you suspect there are multiple radii, measure each chord and Sagitta individually.

Just used this last week to determine a radius on an eyebrow roof I had to reframe.

The google is awesome

https://www.liutaiomottola.com/formulae/sag.htm

http://mathcentral.uregina.ca/QQ/database/QQ.09.09/h/darryl1.html

https://sciencing.com/calculate-arc-area-6326701.html

 

Edited March 6, 2020 by big mario

[rwmaron]

1 hour ago, ursle said:

It's a 12 meter (36') scr, if you laid the ski down and traced the sidewall, that trace would become a 36' circle, but, that was 20 years ago, today, the tail is tapered, thinner than the tip, makes it easier to get out of the carve, and the skis and boards have variable sidecut, the tip is 12 m, the mid is 14 m and the tail is 17m, add some rocker and then try to imagine the shape of the sidewall.

Thanks Kessler

Would the radius or the diameter be 36’ in this example?

[lowrider]

22 minutes ago, rwmaron said:

Would the radius or the diameter be 36’ in this example?

A side cut radius of 18 would create a circle with a diameter of 36. Degree's would be the length of the arc. Don't bring degree's into the conversation unless your designing a board and you want to introduce multiple  radii then you might want to explain how you blend the 3 into the boards total length. You might define that process as so many degrees of the total circle. Eg; if the side cut is 14 ,16,18 the length of each arc could be described as "X" degree's.

[JRAZZ]

 

 

[Jack M]

3 hours ago, big mario said:

First one includes a handy dandy plug in calculator.  If you suspect there are multiple radii, measure each chord and Sagitta individually.

Just used this last week to determine a radius on an eyebrow roof I had to reframe.

The google is awesome

https://www.liutaiomottola.com/formulae/sag.htm

http://mathcentral.uregina.ca/QQ/database/QQ.09.09/h/darryl1.html

https://sciencing.com/calculate-arc-area-6326701.html

 

Good links.

To summarize, find the sidecut depth - s, and the contact length - c, then sidecut radius r is:

r = (4s² + c²)/8s

This of course is an average along the whole contact length, it does not account for VSR or non-radial shapes, but it gives you an idea of how big or small the board will carve.

Keep in mind the board's published sidecut radius is actually slightly longer than the longest radius it will truly carve.  The higher the edge angle, the tighter the carve radius, as the board bends more.

Additional reading here.

[barryj]

Good Stuff Guys!    I'm a visual person, got any  action diagrams, examples??

 

13 minutes ago, Jack M said:

The higher the edge angle, the tighter the carve

Jack,    I understand a board with a 10 sc radius makes a tighter carve radius than a 14  .......but  If scr is radius,  what "edge angle" are you referring? 

[Jack M]

13 minutes ago, barryj said:

I'm a visual person, got any  action diagrams, examples??

That's the diagram from one of Mario's links.  It goes with the equation I posted.  You can easily measure s and c on your board at home.  Then plug those numbers into the equation to find r.

13 minutes ago, barryj said:

what "edge angle" are you referring? 

How high you tilt the board.  Board flat on the ground = 0 degrees, board tilted all the way up = 90 degrees.  (But at that point you're not carving.)

[barryj]

2 hours ago, Jack M said:

Additional reading here.

Physics of a Snowboard Carved Turn

Great article Jack!

[st_lupo]

This is all fine and good, but my understanding is that the "secret sauce" of really good alpine snowboard design harmonizes (V)SCR and board camber.  I've assumed that Kessler's clothoid function is a 3D shape that ties the variable sidecut, with the boards camber line, so that at a given inclination you have a very optimized turn radius that can't be predicted by SCR alone.  

[Wolf]

Sean Martin did a couple of great videos explaining side cut and turn shape:

 

 

[big mario]

so I thought I would plug a few numbers from my big ol' 195 virus with its super secret clothoid sidecut to see what happens in that radius calculator. Flattening the board, and using a framing square and tape measure, I came up with some interesting numbers.  After converting from imperial to metric, the tip and tail segments came out to 14.63m, while I got an impressively small 9.75m underfoot.

Granted, this may not have the most accurate way to check but it gave me a nice ballpark, and a little insight on how this board turns. Ride lazy, and it makes huge turns, jump on it, and it will get surprisingly small.

My chord segments, in imperial #'s, 24'', and my Sagitta's where .125'', .1875, and .125

mario

Edited March 7, 2020 by big mario

[lowrider]

And when you jump on it you want to be wearing your big boy pants.

[big mario]

3 minutes ago, lowrider said:

And when you jump on it you want to be wearing your big boy pants.

Didn't bring em' to Montucky.  Soiled my lil' boy pants on day one run one. 

Boneheads got to know his limitations

 

[Rusty Edges]

Were they the brown pants??? LOL

[big mario]

Camo  bibs  

Mario

 

[snowwjob1]

24 minutes ago, big mario said:

Boneheads got to know his limitations

Chances are the tree would  fall down

[firepopa]

hi guys!
 if you do not know the radius of your board it is possible to calculate with the formula: R = (((C / 2) ² / F) + F) / 2,

or by drawing the arrow in relation to the rope  the arc on a drawing software.  unless your radius is made up of several radius .

in this case you will still have a fairly close measurement.

enjoy !

[ursle]

On 3/6/2020 at 12:32 PM, rwmaron said:

Would the radius or the diameter be 36’ in this example?

Timely, if the radius is 36', the diameter would be 72'

So a 12 meter radius board would have a 72' diameter if it were drawn on paper, of course, when weighted a board bends, making a 12 meter board capable of much less than a 72' diameter circle, rebound is the energy gained by a bent board being unweighted.

[lonbordin]

A little addendum to the SCR discussion from Ryan and Sean. Skip to 8:13 in the video.

 

[barryj]

38 minutes ago, lonbordin said:

addendum to the SCR discussion from Ryan and Sean.

Thanks LB!      A timely and informative addendum for sure!

[johnasmo]

With a straight edge and some feeler gauges, you can analyze the heck out of your sidecut.

Given 3 points on a plane, you can calculate the radius of a circle passing through them.  Mario and Jack have provided links to the math.  Do that at enough intervals and you can figure out what your fancy VSR is all about.  With just the effective edge and the sidecut depth you get one number, the radial equivalent approximation of the whole sidecut.

For VSR's that aren't easily described, I think that radial equivalent sidecut depth is a good way to talk about them.  Better than just saying an average radius.  Depth equivalent radius gives a good idea the shape it will form when high on edge.  So that's how we're sizing the Coiler Contras.  A Contra 12 has a sidecut depth equivalent to a radial 12, but is not radial.

Clothoid is nothing special, no magic to it.  It's a type of curve where the rate of change of the curvature (1/radius) is constant.  So a 10 - 13 clothoid goes from 10 at one end to 13 at the other such that the inverse of the radius is changing at a constant rate throughout that progression.  Like the path your car follows if you're turning your steering wheel at a constant rate.  But as soon as you change the rate or direction, it's not technically a clothoid curve anymore...  it's some other VSR curve.