A physics lesson about Snowboard turn shape: Part 1


Hi I’m Sean Martin President and Founder
of Donek Snowboards in this video I’m gonna explain how the different side cut shapes
that we’ve produced can affect your riding in order to ensure that everyone watching
is one the same page I’m gonna start with some basic concepts and then progress through
some demonstrations intended to provide background information necessary to the discussions finally
I’ll show you how the different side cut shapes that we offer can affect the shape
and dynamics of the turn almost anybody’s whose purchased a snowboard has taken a look
down the side of the board like this bent it like that now there’s a good reason for
that some of you may or may not know what it is but that reason is because these two
things define very very key features in the snowboard the combination of curvature on
the side of the board and the degree to which it bends defines the ease of lack of ease
with which you can carve a turn let me demonstrate okay so if you’re standing on your board
your flattening it out bending it a little bit and when we make a turn we tip the board
up on edge now if we tip it a little bit we can see a curvature created with the contact
point between the edge and the snow the surface we’re riding on and as long as we use the
correct technique the board is gonna travel right along the path generated by the edge
so the steeper we angle the board you can see the curvature keeps getting tighter and
tighter so we get more and more curvature and therefore we carve a tighter turn so the
more we angle that board the more force we put on that board the tighter the turn that
board creates okay I’ve moved outside because I want to be able to demonstrate some basic
physics principals and I don’t have enough room in the studio so what were gonna look
at is the forces that a snowboarder sees while he’s riding the way we’re gonna do that
I’ve got a simple little contraption here just a frame that holds my go pro camera and
then what we got here is a weight here suspended by a rubber band so what you’re gonna see
is that rubber band stretching and coming out you can see my little device going around
in circles here and you’ll be able to see in the side frame here what’s happening
what IM gonna do to begin with is I’m gonna speed things up and go even faster and you’re
gonna see that rubber band really stretches alright now what I’m gonna do is slow things
down a little bit not too much and what’s gonna happen is I’m gonna tighten my radius
by pulling on my string with that slowing down the speed alright so let’s do that
again so if I maintain the same speed but shorten the radius that I’m turning at you’re
gonna see that that rubber band stretches a little bit more and we see a greater centrifugal
force both these things are key your speed the faster you go the greater the centrifugal
force you see the tighter the radius you go the greater the centrifugal force now let’s
look at a couple other things the primary problem with the last demonstration is when
we’re snowboarding we’re not on a horizontal plane we’re on an incline plane so what
we’re gonna look at next is what happens to the forces as we traverse through our turns
on an incline plane lest see if I can get this going and you can see that running on
an incline plane here here what your gonna see here is that the forces are greater at
the bottom of the turn and at the top of the turn this is a really really key element to
what happens to a snowboard when we go through a turn okay I’m back here in the studio
and I’ve got my little pretend snowboarding slope set up that we can draw on and look
at some of the things we’ve learned and see what the results are now the first thing
I want to talk about though is how most manufactures describe the side cut of a board you will
find that most of the time if you look at the specs of a snowboard is how most manufactures
describe the side cut of their board you’ll find that most of the time if you look at
the specs of a snowboard you’ll find they list a radius for this curve now if you don’t
know what that means it’s essentially just this curve is a section of a circle pop up
of a little graphic if you were to continue this curve indefinitely it would actually
come back and hit the end of the snowboard via circular shape that being said lets return
to what we found what we’ve been observing and have a look at what’s happening through
a turn one of the most important things we’ve observed is that as our speed increases while
we’re going through a turn the centrifugal force or the force we’re applying to the
snowboard increases as well so faster speed means greater centrifugal force the other
things that’s important is a smaller turn or a tighter turning radius means greater
centrifugal force the other thing we’ve observed is at the top of our turn this is
our turn up the top we have a relatively small centrifugal force and at the bottom we have
a relatively large centrifugal force and in between its gonna be a little bit bigger its
actually building okay this is because of a number of factors if you recall we said
greater speed means a greater centrifugal force well up here we’re going relatively
slowly but we’ve come down a hill here and our speed has increased and increased therefore
our centrifugal force down at the bottom is increasing what else is happening well when
we showed you earlier that when you tilt the board at a steeper angle the board bends more
and our turn gets tighter well because our centrifugal force or our force being applied
to the board has bene increased we have to lean into the turn more which means we’re
tipping the board at an angle more which means what we’re tightening the radius so our
turn is getting a smaller radius down the bottom then it was up top a very big radius
because we’ve tipped the board further over on edge our forces have combined and helped
us make an even tighter turn there is one other factor here that explains what’s going
on we’ve got the force of gravity pulling us down the hill up here at the top of the
turn the force of gravity is fighting or detracting from our centrifugal force so our centrifugal
force is small over here in the middle of our turn its not having an affect other than
to pull us down the slope and make us go faster down here at the bottom in addition to this
increased speed increased angle reduced turning radius we’ve also got the force of gravity
pushing on the board as well making us bend it even more so all of these factors combine
to result in a low force medium force and a very large force on the board which means
a very large turning radius up here a medium turning radius down here and a very tight
turning radius down here so we can very easily represent what that turn shape actually looks
like its big at the top tighter tighter tighter getting very very small towards the bottom
so this is what happens when we use a circular radius on the side of the board because nothing
is changing with respect to the shape of the board and all of these forces are getting
bigger and bigger towards the bottom now a lot of free carvers really like this turn
shape they like it because what happens is as they go through the turn as they progress
the board is bending a little and more and more and more until they get to the end of
the turn and then boom they release all that energy you use the board like a spring board
to launch them through the air into the next turn so if that’s the type of turn you like
to make well then a single radius side cut is really possibly what you want we can do
a similar thing with some of the other side cut shapes but it will generate this type
of turn shape and that type of building of energy towards the end of the turn and then
the ability to release all that energy and cause the board to sling shot you in to the
air and you can start you r next turn well the next question becomes what happens if
this isn’t right for me well if you look at a race this isn’t right at all in fact
a racer wants a turn shaped completely opposite from what we just saw they want a turn that’s
tight at the top and longer and longer at the bottom why cause if there’s a gate let’s
say right here they want to make a rapid direction change at the top of their turn and accelerate
to the turn or to the next gate that’s down here somewhere so a rapid direction change
an acceleration is what they want to create well the question becomes how can we create
something like that well with a different side cut shape or with board engineering well
we have to look at one other factor that’s occurring in your turn and that is where’s
your weight as the turn progresses so if you look at a typical snowboarder when they start
their turn up at the top the forces that are going to generate the centrifugal force needed
to generate a carve turn aren’t there they’ve got to create them themselves so what they
do they tend to do lunge in in front of the board or distribute or displace their center
of mass towards the front of the board so instead of bending the entire board their
bending just a portion of it and by doing so they can initiate a turn and begin that
carve turn and as their turn progresses we’re going typically slowly through the turn shifts
towards the tail of the board so what we can do is bury the radius of the side cut form
the tip of the board to the tail and we do that very simply the same technique drew that
carve it’s what we call a continuously variable side cut radius and it gives a very smooth
continuously variable side cut radius and the ability to very smoothly and effectively
adjust your turn shape depending upon where you weight is on the board there are a few
companies using variable side cut radiuses these days frequently referred to as VSR and
what they’ll do is use a combination of radii so you might start with one radius here
and progress to a second radius and that’s the tale of the board and there’s a mark
change or a very visible change in the shape of the curve there so what can be done is
you can use more than one one radius so you might go to three so you go your first radius
and then a transition radius and then your big radius at the other end so that smooths
things out a little bit what we do at Donek is we use something we refer to as a continuously
variable side cut radius and that involves a radius that changes continuously down the
length of side cut so you’ve got a very even transition from one radius to the other
over the entire length giving a tremendous amount of variability in your trend shape.

Antonio Breitenberg

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