Categorizing ski sidecuts?

How would you categorize ski turn size radii for the different types of skis we use today? Are there generally accepted cut-off points or ranges for the turn radius values? I know that there are "FIS legal" specifications, but what are they exactly?

So I'm wondering how you would fill in something like this:

Slalom/Carver (small turns): <15m radius
All-mountain (medium turns): 15m-20m radius
GS/Big Mountain (big turns): 21m+ radius

These are just estimated turn radius values on my part. I want to know when someone says this is "quick turning" ski then generally what turn radius values are considered quick turners (and so on). Are there additional categories that should be included?

Speaking for my part of the ski world I have the feeling that 15 meters are considered more "medium" than "short".
Of course, there are no sharp borderlines, but 13-14 meters seem to be the distinction nowadays with 15 belonging to the medium range already.
Similarly, there seems to be a tendency to consider everything above about 19 meters as "long".
Might not apply for Big Mtn/Freeride but since most retail "pseudo-GS" skis ("racecarvers") end up around those 19 meters this would be the line for skiers not using real GS skis.

I think it's all relative. My Explosivs with a 34m sidecut will snap off short turns just fine. Of course I wouldn't want them in a slalom course ...

Ok so heres my question. what will sidecut do to my skis? if its 14m what will that do? mean i can turn 14m how? from turn to turn ill go 14m or or when i d os turns there will be 14M between S sections?

None of the above.

A sidecut radius is the radius of the hypothetical circle that would "fit" into a ski's sidecut (in an un-flexed state) and follow the "curve" of the skis shape.

It's useful for baseline knowledge to compare models. However, it's important to know that radii are very seldom exactly accurate. This is because of 2 reasons 1) many manufacturers use shapes other than a circle (parabola, ellipse) to derive sidecuts, so the use of a "circlular" radius value is an approximation at best, and 2) there are different methods for measuring the radius. An example: many modern skis have the widest part of the ski above the contact point, off the snow - so if you were going to measure radius, where should you measure?

If you want more info, I'd do a search. I'm sure PhysicsMan has several good posts on this subject...

Woodee, I've used my Pistols (24m rad) on a human slalom at Big Sky. Amazing how some of the "gates" looked worried as I got into a tuck...

troutman - So my follow-up question to your post is: Can you use the manufacturers' ski radius spec to compare ski "turniness" between DIFFERENT manufacturers? OR are ski radius values only good for comparing skis between the models within the same manufacturer (like boot flex index values)?

I resemble that remark! :

'course, it could have been the look of those aircraft carriers on your feet!

IMO, the radius values are just an orientation point showing the approximate turn radiuses the particular ski will be comfortable with - supposing some expected flex, skier weight and skills.
Unfortunately - at least that´s what I see a lot around me the last couple of years - the ski radius has become (well, beside length) the main parameter skiers consider and discuss. I hate statements and/or advice like "you can´t learn to carve your turns with ski radius exceeding 13 meters" or "the 13 meter radius means a turn size of a swimming pool" which I already gave up fighting against.
The same skier might find a softer 15-m ski "turnier" than a stiffer 13-m (depends also on what you mean by "turnier"!)
It´s important to include especially the ski flex into considerations. Unfortunately, as mentioned above, most skiers learned to understand the (relatively simple) radius value to some extent but they can´t imagine anything under non-presented (and thus "non-existent") flex characteristics.
The result is they operate with radius as with the most important and relevant characteristics of a ski neglecting the fact that a ski is a sum/mixture of parameters which become realistic only with a person using them.

Hi - Replying to "Noodler" who posted <<How would you categorize ski turn size radii for the different types of skis we use today? Are there generally accepted cut-off points or ranges for the turn radius values? I know that there are "FIS legal" specifications, but what are they exactly?>>
Be careful with this "Radius" stuff.  It can lead you down the wrong path to an absurd conclusion.
Side Cut Radius is a fixed constant for the mechanical design of the ski.  It doesn't have much to do with the arc you can carve.
Skis have always had a sidecut. 
The difference today is that the manufacturers can make a wide ski that's both light and strong and can take a large side-cut without them flopping into an aeroplane-propeller twist.
You ski on the Bend Radius - not Side-cut Radius
When you ski on a carving turn, the path followed is the Bend Radius of the ski.  Not the Side-cut Radius.
You make the ski bend by applying a force to them when they are on edge. 
But this is again not the point in good skiing.
Look at the clean-cut apex of a GS race turn.  It's no more than a couple of metres radius at the apex. But the Sidecut radius constant on the ski is 27 metres for a FIS-Legal Man's GS Ski.

Maths gives the beautiful truth:
This if you look at angular acceleration, is constant angular acceleration.  In other words the rate of change of direction is constantly increasing or constantly decreasing.  In maths, look up constant angular acceleration and you will find a parabola which is part of an ellipse - not a circle of a given radius.
In GS, the path they make is an arc of an ellipse, not an arc of a circle.  A circle has an angular acceleration of Zero.
If you are carving a circular arc, you are doing the "Park-And-Ride".  Static skiing.
Great GS Racers never Park-and-ride.  No, they start a turn and progressively tighten the turn-radius up to the apex.  Then they progressively relax the turn radius continuously.  It's called "Working the ski".  Making it bend.
Quick Test
To get an Idea of what radius your ski will carve, try this:-
Pick the ski up by the tip and rest the tail on the snow.
Hold the Tip and push the middle of the binding away from you to bend the ski.  Look at the ski and see it's bent into a reverse-cambered curve. That's the radius that it will carve-turn if you can get them loaded-up on max edge.
Sidecut Radius Limiting Turn Radius?  No.
To prove this to yourself, stick a pole in the snow.  Pace out 15 metres on the snow.  It is collossal! Are you believing that this is the Turn-radius  you will be limited to with a pair of 15m Sidecut skis?!
Also - remember Remember the full side-cut diameter is twice the side-cut radius.
I advise: Never use the terms "Turn-Radius" and "Side-cut-radius" interchangeably.  They are completely different things.  Side-cut is a mechanical invariant property of the ski.  Turn Radius is a continuous variable and it depends on how good you are at making the ski bend when you ride it.

Happy carving!
All the best
Davey (Scotland)


Edited by Davey - 11/5/09 at 3:31pm

When you are skiing on a flat hard surface and tip the ski as you force the edge to remain in contact with that surface the ski must bend.  Try it with a model "ski" cut out of a stiff sheet of paper in an hour-glass shape and you will understand. The path traced where the edge of the ski meets that hard surface will approximate a curve whose radius is cosine of the tipping angle of the ski multiplied by the side cut radius of the ski. 

All other things being equal, a smaller radius ski will bend easier into a smaller turn because it is designed to make that turn under design loading conditions taking speed and skier weight into account.  Racing skis won't be as easy to bend into a turn as other skis because they are designed to only bend into that turn shape under racing speeds.

Typically slalom skis are about 13 m, GS now 27, but were 21 for a while, cheater GS around 18, Cross skis between SL and GS (even though most x-skiers used gs skis as I understand it).

Ski radius does not limit the size of the turn you can make, but it does limit the size of the turn you can carve in a pure arc; you can't arc a turn larger than the sidecut radius of the ski, and you may not have sufficient force to bend a long radius ski designed for high speeds and longer radii into a tight turn.

If you are in deep 3-d snow, the sidecut radius affects bending of the ski via other more complex means than the cosine rule above.

Just a wild guess but I'd suppose that Noodler has gotten a satisfactory answer or just lost interest in the last 4 1/2 years.

SJ

Holy friggin' dredge up an old thread Batman.

Yeah...  I've kinda got a handle on this in the past 4.5 years!  WTF

Yes Jim, but Noodler isn't the only one reading this thread.

Yes It's Davey again.
Hi Noodler.  It was an old post wasn't it? But side-cut radius limited turns is still a current myth people choose to believe.

Hi Ghost
The theory that you can't carve a ski tighter than the sidecut radius is not correct in my humble opinion.
What your paper template model theory is proving is that if you park and ride a ski on a static circular arc, you get limited.  But that's no surprise, is it?
If you are working the ski like an expert and get a cos of (for instance) 84 Degrees - well you are talking rTurn of one-tenth of the rSidecut even by your cos formula, but it is not as simple as that.  It isn't a circular arc.  It's a net effect of the combination of ever-decreasing circles.

I'm attempting to show by observation that the parabolic track carved in the GS Course by a skilled racer can allow them to carve perfect tracks that have a progressively Decreasing radius up until the shortest radius at the apex.  Then the tight radius progressively increases again - allowing the linear speed to increase. 
Illustration
Look at these GS race railtracks below. (skis are 21m rSidecut)

• First-off it isn't a circle.
• Second, it's tight.  Looks like about 1.5m to me. 
•  

There is no way that the minimum radius seen here is limited by the ski.  If you load up the ski from tip through middle through tail on an ever-increasing edge-angle, you can carve clean tight parabolic arcs of an ellipse.  See below.
You see: The simplistic calculations are for angular acceleration of zero.  i.e. a circular arc.  Make a parabola with a constant (nonzero) angular acceleration (Means angular velocity (rate of change of direction) is speeding up and slowing down), and you arrive at a tight apex radius like in the image below.
I have spent years trying to understand what the coaches have been trying to teach me.  I've discovered that they are regurgitating error-based theory that they haven't worked through.
Going back to first principles with the Classical Newtonian mechanics is a revelation.  This is where the racers get their slingshot out of the gate.  It won't work when you make plain semicircles. 
Cheers, and happy carving!


Edited by Davey - 11/5/09 at 3:29pm

What I'd like to know Davey, is if you can manage to write a post without putting up a link to youcanski.com? In your three posts so-far, it looks like you're not capable of leaving the elaborate spam out of your otherwise potentially useful posts.

3 for 3 so-far...

Wow. My nose starting bleeding after reading this

Edited by The Squeaky Wheel - 11/5/09 at 4:12pm

Sorry Helluva
You didn't like the urls, and think it's spam. So:-
The links to the other sites removed from 2 posts based on your advice.  Sorry, I can't edit Squeeky's post.  The one who quoted my entire post only to put a one-liner as comment.
Has anyone else got anything to say?  Any more witty nicknames?
Was it you, Helluva who came up with the "A critic is a legless man who teaches running. " hilarious quip?

Actually, I kid you not, I've just come back from a lecture by a legless man on track-running, rock-climbing, skiing, Ice climbing, Trekking up 6,000m Mt Killimanjaro, canoeing, sailing, marathon running and sky-diving.
His name's Jamie Andrew and I found it inspirational.
And there's more, he's got no hands either!  He lost hands and feet to frostbite whilst climbing in Argentiere, France, Europe.
I'd give you a url, but look it up yourself !

Davey

HI Davey,

Actually we are more in agreement than you think.

I said you could easily carve a turn smaller than said sidecut radius, simply by tipping the ski.  I never said you had to carve circles.  You tip the ski more and more as you approach the apex and then less and less as you leave, thus carving a decreasing radius turn on the way in and an increasing radius turn on the way out.  If you tip up to say to 70 degrees you can arc a beautiful 4.5 m turn.  If you want to turn harder than that you can carve an arc, but the arc will be a bit ragged.  The shape is up to you and how quickly you tip and untip the ski.  I only conceded that there was a limit to how far you can bend a stiff long radius ski.

I still maintain that you can't make a pure arc  turn radius greater than the side cut radius of the ski.

^^^ You may be great at math, but humor is not your strong point.

I removed the link you mention above.
Entire thread quoted because it's easier to hit the quote button than to try and edit your drivel

To Ghost:
Thanks for your thoughtful reply.
Especially "I still maintain that you can't make a pure arc  turn radius greater than the side cut radius of the ski.".
I think you're correct. Especially for the deep side-cuts. Sorry I mis-read your original post and then I thought you must have put greater instead of less.
It's a valuable point.  In our organisation, there is a big fuss from the aspiring instructors who are being told not to turn up for tech exams with skis of side-cut radius less than 17.5m.  But they shouldn't complain.  It's easier to carve the longer turns.  And they'll learn that long skis can carve tight turns too.
Cheers
D

Radius of a carved turn is interesting for what it is, but when we want a quick ski we are usually not thinking of railed turns. We are thinking of a quick, definite response for dealing with tight terrain, and that often involves a slide or a check. In these situations I like a ski that has qualities such as liveliness, spring and snap, rebound, stiffness with responsiveness. That usually involves the properities of the core and overall construction more than sidecut, IMO anyway.

Davey, in this interesting classic thread there is some discussion as to whether sidecut, or even edges, are necessaryat all for "carving" - at least on a non-infinitely hard surface:

http://www.epicski.com/forum/thread/17714/get-off-those-edges

Thanks for the link Martin.
Lots of good stuff by Physics man.
However
I think that sometimes the assumptions made for carving calcs are limiting real skiing.
PM's calcs are great, provided the edged ski is propped equally on its widest points and reverse-cambered to the max extent.
However, If the ski is weighted towards the forebody, the forepart of the ski will bend more like a cantilevered beam, causing an extra influence on the bend of the ski.
I suppose this doesn't count as "Carving", but it's how an old-school ski bends.
I think there is a case to be made for the thought that the ski grips on a kind of mini "Wall of death" banked track.
If your snow is soft enough, the edge isn't so important.
I like my razor edges on that summer glacier at es Deux Alpes for my 08:45 first run, though!
Thanks again
D