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Ski Turn Radius

post #1 of 18
Thread Starter 
(This was first posted on the Instruction Forum.)

I've been thinking quite a bit about stated Turn Radii as it's on most skis now. I have both 16m and 13m skis. As I've found this is NOT the turning radius of the skis. Think about it. that's 40-50 feet, (and if that's the radius, then the diameter of the circle is 80-100 feet!) Slalom skis have a turn radius of much less than that.

What this metric is, as the link below explains, is the radius of a circle that the sidecut would be a part of with the ski layed flat. The turn radius of a ski is a completely different thing, created by 3 elements; the sidecut, the amount the ski is pressured and thus decambered, and the edge angle. This makes perfect sense as you can tighten up a ski's turning radius by pressing down hard on it and bending it into a tighter arc. There is no "natural" turn radius of a ski, only a range.

So all this hooey about turning radius is flawed, as it is only one component of the turn size that a ski makes. My Atomic SX:11's are stiffer, and don't tighten up their turns as much as my Fischer RX8's thus making the difference between them much more than the numbers reflect.

See this great piece on the physics of it. http://www.math.utah.edu/~eyre/rsbfaq/physics.html
post #2 of 18
If anybody anytime claims that the ski radius ("sidecut radius" if you wish) equals the turning radius (or "radius of the turn") it is misunderstanding.
I only thought that after almost 10 years of ski radius being used this information and distinction had become generally known.
post #3 of 18
Checkracer is right. In fact, the topic of the distinction between sidecut and turning radii comes up at least several times a season here on Epic. There has been lots of previous discussion on this topic. A search for posts which includes all three words, "sidecut", "turning", and "radius" turned up 115 such posts in 87 separate threads. Many of these are relevant.

Tom / PM
post #4 of 18
Thread Starter 
So should I not have posted? Was that article I linked to linked to before? Have there not been about 10,000 Metron reviews? Was there enough snow in the PNW this year?

Of course searching through 87 posts that match a group of words that someone might not have been looking for would have had the same effect and my sharing that info with them was uncecessary I guess.

I constantly hear people talking about the "natural turning radius of this ski" and have never seen this concept questioned in a post. Even if the search function of the forum was more user friendly, I still don't think I'd see this - as to flex patterns and it's effect.

Oh and I think I've see too many posts saying "This has been discussed before, use the search function" Do a search on those terms and see how many postings come up.

Sorry, just a little pissy today. If my thread is boring to you why do you feel a need to in effect tell me I shouldn't have posted it?
post #5 of 18
post #6 of 18

Long, tedious personal observation.

Quote:
Originally Posted by SkiMangoJazz
So should I not have posted? Was that article I linked to linked to before? Have there not been about 10,000 Metron reviews? Was there enough snow in the PNW this year?

Of course searching through 87 posts that match a group of words that someone might not have been looking for would have had the same effect and my sharing that info with them was uncecessary I guess.

I constantly hear people talking about the "natural turning radius of this ski" and have never seen this concept questioned in a post. Even if the search function of the forum was more user friendly, I still don't think I'd see this - as to flex patterns and it's effect.

Oh and I think I've see too many posts saying "This has been discussed before, use the search function" Do a search on those terms and see how many postings come up.

Sorry, just a little pissy today. If my thread is boring to you why do you feel a need to in effect tell me I shouldn't have posted it?
Well, smj, I for one think it's an interesting topic and a fun variation on other threads.

This is actually something I was giving some thought to a couple of weeks ago. We had been in a prolonged dry spell and I was pretty much skiing my short slalom skis every day.

One particular day they had groomed a little side run that most people miss the entrance to, and the conditions were perfect for practicing carved turns. I'd be the first to admit that I've got a long, long way to go getting my carved turns right, but these conditions were so good that I was able to make some pretty good turns. It was very smooth, very hard snow, really consistent, with a "Jackson Hole Blue" pitch. What was great was that no one else was skiing this run so I was able to go back again and again.

So, each trip back I could plainly find my tracks from the previous run. I was deliberately trying to make as clean, round, and short a turn as possible (for me) on my 11m turn radius Dynastar Omeglass Speed 63's (165cm). "Clean" means that the tracks of the turning ski(s) should be sharp grooves - that's the goal. "Round" means that my goal is to get as close to linking perfect half-circles as I possibly could.

One time, curiousity got the better of me and I decided to "measure" the diameter of one set of what I thought were my best turns. Starting at the transition I sidestepped down the fall line through a full left turn and a full right turn. I tried to make my sidesteps as close to three feet as possible and simply counted my way down the hill. I admit this isn't at all precise, but years ago I did some work that required me to be fairly accurate at knowing how long a three-foot step is, so just humor me.

When I was done, I had counted 34.5 steps over two full turns. That would be a diameter of 17.75 YARDS per turn. If a yard is .9144 meters, that means the diameter of my turns was 19.4 meters, and the radius would be half that or 9.7 meters.

Now, that is absolutely as good as I can make what I believe is a pretty pure carved, linked turn. The conditions were perfect and I was trying as hard as I could. I'm sure many here on Epic could do shorter-radius linked carved turns in those conditions, but I was barely able to decrease the radius of my turns versus the "design radius" of the skis.

I would dearly love to have been able to see Ben Raich making turns in that same situation.

Bob
post #7 of 18
Thread Starter 
Bob, that is a fascinating story. I would have thought that the turns would have been much shorter than that. I have seen beautiful round carved turns from a lift (not mine!) that my guess is they were about 15 feet in diameter, maybe 20. That is then three times as small as yours, thus about 3 meter turns. I wonder what they were made with?

Any skiers out there have an idea of the size of their tightest round turns?
post #8 of 18
It also depends on the snow and flex of the ski. A stiff ski in very soft snow may not even carve as tight as it's sidecut radius. It is the snow presuring the ski that forces it into the turn after all.
post #9 of 18
Quote:
Originally Posted by Bob Peters
I would dearly love to have been able to see Ben Raich making turns in that same situation. Bob
A highly interesting post, Bob.
I remember having seen Benni Raich skiing leisurely with his slalom skis last (or maybe the year before) spring. He was just privately on a neighboring glacier, no training, no gates.
The angles he reaches without any visible efforts are awesome.

Which takes me three weeks back when I watched Freddy Nyberg training GS before WC finals (I reported somewhere here). GS skis are nor SL skis but the tracks he was leaving were amazing too. I´m sure there was a substantial difference between his ski and turn radii.

SMJ,
nobody said you should not have written what you had. No harm done, what you wrote is true.
Repetitio mater sapientiae.
post #10 of 18
Thread Starter 
Quote:
Originally Posted by checkracer
SMJ,
nobody said you should not have written what you had. No harm done, what you wrote is true.
Repetitio mater sapientiae.
Thanks Checkracer. Just being touchy I guess.

I was curious about "Repetitio mater sapientiae" so I Googled it and found

repetitio mater studiorum es (Repitition is the Mother of Learning) what is "sapientiae" ?

Steve
post #11 of 18
Oops.

It may be that I make better turns than I do math calculations. 34.5 yards divided by 2 is 17.25, not 17.75. It's not horribly significant and only drops my "calculated turn radius" to 9.4 meters instead of 9.7.

SMJ:

I've spent a lot of time this winter looking at tracks.

It's not at all uncommon to see short-radius carved tracks in the snow, but they often seem to be on shallower slopes, more "forgiving" corduroy, or tend to be for three-quarters of a turn rather than linking full, round turns. I see this shape track ) carved well fairly regularly, but I almost never see this track C (if you were to cut off the little indented squiggles). I would submit that it is magnitudes more difficult to do the "C" track because of the forces that build up in the lower quarter of the turn. Also, making the ) turns quickly leads to very, very high rates of speed that even on my mountain become unsafe (for other people around) in a hurry.

I very seldom (actually I'm being tactful, essentially never is a better way to put it) see a continuous set of ultra-low-radius tracks. Now maybe that's because very few skiers are even interested in that kind of skiing here at Jackson Hole, but I spend a lot of time watching for carving skiers and the tracks they make.

Come to think of it, "carving" has got to be about the most abused term in skiing these days. You hear it used constantly, but you almost never (on my mountain, anyway) see skiers actually carving turns. I mean linking more than a couple of actual full-track carved turns down a moderately steep, moderately firm ski run.

I see racers and ex-racers doing it. Other than that, practically nobody.

Bob
post #12 of 18
Quote:
Originally Posted by SkiMangoJazz
...

(Repitition is the Mother of Learning) what is "sapientiae" ?

...
High-school Latin was a long, long time ago, but I believe it would have some kind of reference to wisdom or awareness.

Bob
post #13 of 18
Thread Starter 
Quote:
Originally Posted by Bob Peters

I've spent a lot of time this winter looking at tracks.

Bob
As have I - fun, eh?
Quote:
It's not at all uncommon to see short-radius carved tracks in the snow, but they often seem to be on shallower slopes, more "forgiving" corduroy, or tend to be for three-quarters of a turn rather than linking full, round turns. I see this shape track ) carved well fairly regularly, but I almost never see this track C (if you were to cut off the little indented squiggles).
Bob
Those turns I saw were on a shallower corduroy slope, but what impressed me is they were C turns. I tried to figure 8 them on that run and my turns were more ) snakelike. I never forgot those marks in the snow.
post #14 of 18
Repetitio mater sapientiae (the boastful piece of Latin was from me):

yes, wisdom
homo sapiens should be a wise creature (not like us discussing tracks, radii and sïmilar impractical things)
post #15 of 18
Thread Starter 
Quote:
Originally Posted by checkracer
Repetitio mater sapientiae (the boastful piece of Latin was from me):

yes, wisdom
homo sapiens should be a wise creature (not like us discussing tracks, radii and sïmilar impractical things)
Ah, but skiing can involve great wisdom - (2: the trait of utilizing knowledge and experience with common sense and insight)

We are wise. Anyone who side steps down a section of a slope to measure the number of 3 foot segments in a pair of turns is definitely seeking wisdom.
post #16 of 18
And I was stupid enough not to have remembered I had a 2m tape measure in my backpack when admiring those tracks of Nyberg...
post #17 of 18
hey thanks for this post! that would have never came to my attention if it wasnt for this post. now i have a better understanding of skis, and there's no way i'd have searched about this topic.
thanks!
post #18 of 18
Thread Starter 
Strider, you're welcome.

Physicsman, I apologize for my overreaction to your post. Stuck at home on a beautiful Sunday unable to ski because my fiance insisted I stay home for her eat to much Easter brunch.
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