Tri-radial Sidecut Comments? Thoughts?

Question:
I have been doing a little reading about tri-radial sidecuts on snowboards
as a late. Never Summer just released a new model which touts this
"technology". (the Titan if people are interested) A few questions is this
regard.

Is this a new "technology"? or has it been around for a few/many years?

Any personal experience with a board which has a tri-radial sidecuts?

Does this "tech" make sense from a theoretical carving standpoint?

Thanks for all comments.

Ed

Is this a new "technology"? or has it been around for a few/many years?

Different sidecuts along different sections of the board is not new, it's
been done for a while.

Any personal experience with a board which has a tri-radial sidecuts?

I am pretty sure my old Salomon FRS had a *bi-radial* sidecut, with a bigger
sidecut fore and a tighter sidecut aft. At leas, that's the way it looked
to the naked eye, and it sure behaved like it was shaped that way. It was
a fun board... but I had to be really on my game to get from toesdie to
heelside without breaking my arc.

Does this "tech" make sense from a theoretical carving standpoint?

This would be a great quetsion to ask at www.bomberonline.com. Many people
there will give you a better answer than I can.


Mike T

Mike T wrote:

I am pretty sure my old Salomon FRS had a *bi-radial* sidecut, with a bigger
sidecut fore and a tighter sidecut aft. At leas, that's the way it looked
to the naked eye, and it sure behaved like it was shaped that way. It was
a fun board... but I had to be really on my game to get from toesdie to
heelside without breaking my arc.

My Nitro Naturals also had a tighter sidecut (smaller radius) at the
back. The theory is that you get smooth carve initiation using the front
of the board (high radius) and a snappy finish as your weight moves to
the back of the board (smaller radius). However it was difficult to
notice much with my Nitro other than its stiffness.
I did some quick estimates on the Never Summer board and tighter sidecut
at the back will be visually noticeable - I reckon the edge will be a
few milimetres shifted due to the tighter radius.
In terms of the theory the ideal shape is a mix between a sine curve and
a circle - in my view it's as close to the arc of a circle as makes no
difference. This is because the sidecut is the arc of a high radius
circle and the different types of curve you could put through the front,
midpoint and back of the edge come out very similar. I believe Sean uses
a symetrical (fore and aft) quadratic sidecut still.
In terms of the practice, I would look at the sidecuts of the winning
raceboards - e.g. Donek and others. If they don't have a sidecut that's
tighter at the back then it's probably bull****.
Iain

Sean Martin wrote:

If you are using a tri-radial sidecut with the same radii in the tip and
tail of the board and another in the waist, the performance will be a bit
better depending on the relationship between the sidecut at the waist and at
the tip and tail.

The Never Summer Titan board with "tri-radial" sidecut has radii of 8.9,
9.7, 7.6 at the tip, center and tail respectively. Interestingly the
tighter radius at the tip compared to waist is the opposite to what
would be achieved with your parabolic cut. For my Natural they called
the tighter tail a progressive sidecut.

ID's Sinusoidal curve is a very intriguing idea that was discussed here
several years ago. It makes an assumption about one single ideal turn and
edge angulation. If we all made turns at a 45 degree angulation all day
long, it could produce interesting results. There are some flaws as it
doesn't consider torsional flex or if the board itself is bending to a
complimentary curve and fuly supporting the edge along it's length.

Agreed torsional flex is not considered - but I'm guessing that on race
boards you're trying to minimise it. In terms of the board bending, if
it's carving a circle on the snow, then the the complimentary curve of
the board is an elipse, regardless of edge angle.
The theory (maybe best not to dig it up ;-) showed that with an edge
angle close to 90 degrees, the sidecut shape should be sinusoidal; and
with edge angle close to zero it should be circular.
But the most *intriguing* result was that because the sidecut radius is
large compared to the length of the board, the difference in the
resulting edge position between the sinusoidal, circular *and* parabolic
sidecuts was of the order of one tenth of a millimetre! I still believe
that the snow won't know the difference!

In the
end, there are multiple solutions to every engineering problem. What I've
found to work best given our approach is a parabolic sidecut combined with a
very specific flex pattern.

To my mind, the flex is the clever bit! One thing Sean showed me: take a
snowboard and test it's flex against the floor. It should bend into a
nice progressive curve - it's worrying how many boards show sharp
changes of curvature because that can't be right

Iain

But the most *intriguing* result was that because the sidecut radius is
large compared to the length of the board, the difference in the resulting
edge position between the sinusoidal, circular *and* parabolic sidecuts
was of the order of one tenth of a millimetre!

I asked Bruce Varsava from Coiler about his sidecut shapes and he pointed
out that the difference between parabolic, elliptical, and circular was
indeed teeny and that he prefers to solve the edge grip problem by tailoring
the flex.

In the
end, there are multiple solutions to every engineering problem. What
I've
found to work best given our approach is a parabolic sidecut combined
with a
very specific flex pattern.

Speaks to what Sean said about different solutions to every problem.... e.g.
Coiler and Donek. I will say this - the Coilers I've ridden are much damper
but nowhere near as lively as the Doneks I've ridden. When it comes to
alpine boards, I find Coilers better suited to isolating the rider from
variable snow surfaces, and Doneks more snappy and more fun. I'll always
have at least one of each in my quiver!

Mike T

Sean Martin wrote:

ID's Sinusoidal curve is a very intriguing idea that was discussed here
several years ago. It makes an assumption about one single ideal turn and
edge angulation. If we all made turns at a 45 degree angulation all day
long, it could produce interesting results. There are some flaws as it
doesn't consider torsional flex or if the board itself is bending to a
complimentary curve and fuly supporting the edge along it's length.

Sorry, guys. Got to thinking about this again. Sean talks about
assumptions and flaws and I want to come back on that. First
assumptions: we made no assumption about ideal turns and edge angles.
The assumptions we
* the edge of the board forms a circle on the (flat snow)
* there is no torsion in the board (more on that in a bit)

I won't labour the detail but from that you can quickly show that the
board will be bent into an elipse. As Sean points out, the theory shows
that the ideal sidecut shape will vary with edge angle - but that's not
a flaw in the theory, it just happens that the solution to the problem
is not as simple as we might like! Indeed the solution can't be
represented as an equation, but it can be solved numerically - which I
did. So there's bad news and good news...
The bad news: the ideal sidecut shape varies with edge angle and you
can't write an equation for it
The good news: the difference between the edge-angle-dependent ideal
sidecut, and both circular and quadratic sidecuts is miniscule - as
supported by Mike's chat with the Coiler guy. So both of these are close
enough to ideal as makes no difference.

With regard to board torsion, the effect will be to reduce edge angle at
the tip and tail. Radius of turn increases with decreasing edge angle so
to compensate for torsion you might want to increase the curvature -
i.e. decrease the sidecut radius - at the tip and tail. Interestingly
this is the opposite of what a quadratic sidecut achieves!

Iain