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Kastle MX78 Turn Radius

post #1 of 21
Thread Starter 

Folks,

 

I have Kastle MX78 in a 176 length.  They have the KTI plate.  The ski has R18 printed by the width information

on the tails.  The question I have is do you think the KTI plate changes the turn radius or not?  And if so, what

do you think the radius is with the plate?

 

The plates stiffen up the skis and I really love them.  I was just wondering about the turn radius effect.

 

Mike

post #2 of 21

The marked radius is the radius of the sidecut with the ski unloaded.

When you bend it the radius decreases.

The KTI plate is intended to allow the ski to flex freely not change the bend radius.

That said, a good plate changes the feel of a ski by a lot.

post #3 of 21
Thread Starter 

Just joined and I learning stuff already... thanks!!

 

Mike

post #4 of 21

You can change any skis stated turn radius, depending on how much you bend the ski. 

post #5 of 21

Great skis, by the way.

post #6 of 21
Thread Starter 

Thanks.

 

I really enjoy the skis.  It is the first time in decades I am not on a GS race skis.  But

getting a bit older, I find pushing race skis in the woods, bumps or crud to be too much

work.  So I wanted a GS style all mountain ski that was easier to drive.  This ski doesn't

require the muscle of a race ski but still handles speed very well.  It remains stable up

and though 65 - 70 mph (per my IPhone ski app).  It holds ice very well.  It doesn't have the

powerful race ski snap.  But then again it doesn't take race ski muscle to load up in order

to snap.  Smooth, stable... the more you put into the ski, the more it gives back.

 

Mike

post #7 of 21

Many here believe the Kastle 78 is best in class winner and should be a great fit for your needs. If I remember correctly, the Kastle 78 has a dual radius in that the tip is has slightly lower radius than the tail. It promotes quicker turns while remaining more stable in turn completion due to the straighter tail. Or at least that what Kastle marketing claims. Most like the increased standheight the plate provides. Consensus of Epic reviews of the ski seem to prefer it with the plate and not skied flat. There is a lot of discussion of this ski on Epic if you want to do some searching.

 

BTW, there have been discussions about the accuracy of Iphone ski apps and their velocity readings. I would not bet the farm on their accuracy.

post #8 of 21
Thread Starter 

Ya to totally change the topic of the thread (my thread any way ;-) I have gotten completely bogus data on SkiTracks.  Got 80 mph on a couple runs where I was skiing very casually....no way!!  Definitely a blip.

 

But on early mornings when I am really flying, the results are very consistent run after run and day after day.  So for the app to be totally wrong, it would need to be consistently totally wrong... off by the same amount all the time.  Skiing with a large group (6-8 IPhones) and at very similar speeds, all with the SkiTracks app we all get results that make perfect sense.... I was a hair faster or slower and my results were a hair faster or slower than the guy next to me.

 

I also use MapMyRide on my bike.... and that is very consistent as well (same internal IPhone GPS). MapMyRide was actually slower than a buddies speedometer attached to his bike tire. (I believe MapMyRide was right and the tire speedometer was wrong) 

 

Lastly, I forget if is my Garmin Maps app or Google maps that show speed... but whichever it is, it is dead on per my car speedometer.  So are they perfect... no.  Do they give a pretty accurate representation if looked at with a skeptical eye.... I think so.

 

In anycase, I just threw it into my description of the Kastle MX78 to avoid the "do you really think you were going that fast" and provide a pseudo empirical data point so that when I say "speeds" people are not thinking Bionic Snowplow....  Look at it this way, if you believe 65 mph per SkiTracks is really 30 mph, then the Kastles are very stable at 30 mph....

 

I should probably post this in the Ski App thread...  ;-)

 

Mike

post #9 of 21
Quote:
Originally Posted by Living Proof View Post
 

If I remember correctly, the Kastle 78 has a dual radius in that the tip is has slightly lower radius than the tail. It promotes quicker turns while remaining more stable in turn completion due to the straighter tail. Or at least that what Kastle marketing claims. Most like the increased standheight the plate provides. Consensus of Epic reviews of the ski seem to prefer it with the plate and not skied flat. There is a lot of discussion of this ski on Epic if you want to do some searching.

Yep, yep, and yep. Except that it's now an elliptical radius, so both tip and tail are few m below midsection. 

post #10 of 21
Quote:
Originally Posted by beyond View Post
 

Yep, yep, and yep. Except that it's now an elliptical radius, so both tip and tail are few m below midsection. 

 

I always feel a deep sense of relief when Beyond affirms my thoughts!

post #11 of 21

"Elliptical Radius"

The mathematician in me takes offense to this sloppy use of language.

post #12 of 21

Agree. That's what Kastle calls it, believe it or not...

 

OP: The most important determinant of your turn radius is how far over you have your ski, actually. If you're not much engaging the ends of the ski, their radius doesn't matter. Which is how you can make long radius turns on a slalom ski. The second most important will be whether you bend the ski to a shorter radius. Then maybe the stated number on the ski. A plate only changes the leverage you can exert on the ski to change the edge angle.

post #13 of 21

A cone is a versatile object

Were "parabolic skis"  back in the 80s' really a mathematical parabolic shaped side cut ?  Or merely linguistic marketing term ?

 

post #14 of 21
Quote:
Originally Posted by ARL67 View Post
 

A cone is a versatile object

Were "parabolic skis"  back in the 80s' really a mathematical parabolic shaped side cut ?  Or merely linguistic marketing term ?

 

 I really like my MX78's. This picture gives me a headache.

post #15 of 21

think that Elan skis actually had parabolic-shaped sidecuts, at least back in the days of the ground-breaking SCXTM that revolutionized the shape of skis to come. I was working with Elan at the time, representing their skis and skiing on their "Elan Special Forces" team. Their official word was that the parabolic sidecut shape would actually bend into a rounder arc when tipped, pressured, and decambered for carving. An actual round sidecut, they claimed, forms a non-round arc when decambered. Makes sense to me. They certainly skied better than their previous generation of skis with "cycloid"-shaped sidecuts!

 

But I still wouldn't bet my life on the sidecuts actually being true parabolas. In any case, Elan also trademarked the term "parabolic" for their skis. I don't know if you can patent a curved shape, but I am pretty sure that most other manufacturers' skis did not have parabolic sidecuts, even though "parabolic" quickly became a generic term for any of the new breed of deep-sidecut skis. (Ironically, Elan used the term to describe the sidecuts on their more-conventional "straighter" skis at the time as well.) 

 

---

 

Here's the current draft of the entry for "Parabolic" from my upcoming (eventually--don't hold your breath) new edition of The Complete Encyclopedia of Skiing:

Quote:

“Parabolic” entered the skier’s lexicon shortly after the deep-sidecut revolution of the 1990’s, when the Elan Ski Company promoted its ground-breaking SCXTM models as featuring “parabolic sidecut.” Although Elan had trademarked the term—and in fact, used it to describe the sidecut of even their more conventional “straight” skis—”parabolic” quickly fell into common use as the generic, but inaccurate, term for any deep-sidecut ski. 


So, what is a “parabola”? A parabola is a specific “U”-shaped curve with unique properties, defined mathematically by quadratic functions like “y=x2.” A “conic section,” it is the curve defined by the intersection of a cone with a plane that is tilted parallel to the edge of the cone.

 

 Parabolas--conic sections formed by the intersection of a cone and a plane parallel to the side of the cone.

 


Parabolas appear often in our lives, from sports, to architecture, to dish antennas and old-fashioned headlight reflectors. An object like a baseball flying through the air—or a skier—follows a parabola-shaped trajectory. The main cables of a suspension bridge form a parabolic arc. (“Real” parabolas are only approximate, of course, due to small variables like air resistance, cable weight, and such.) The parabolic shape has unique properties in engineering, architecture, optics, and sound. 

 

 

 

Parabolas. (Top left) graph of a quadratic function, parabolic spotlight reflector, conic sections—the intersection of a cone and a plane parallel to the side of the cone, and a suspension bridge; (bottom left) supporting structure of the Tiehack arch bridge across Maroon Creek in Aspen; (bottom right) the trajectory of a cannonball, and the advertised shape of the sidecut curve of the pioneering Elan SCX ski—that gave rise to the generic but incorrect use of “parabolic” to describe modern deep-sidecut ski; and (top right), the trajectory of the center of mass of World Moguls Champion Patrick Deneen, flying off the kicker at Mt. Hood. (Note that real-life examples will only approximate a true parabola due to small variables like air resistance, cable weight, and such.)

 

In skiing, “parabolic” has become a common, but generally inaccurate, descriptive term for the shape of modern, deep-sidecut skis. The Elan ski company—a pioneer of deep and experimental sidecut shapes—introduced the term to promote its revolutionary deep-sidecut skis in the later 1990’s (although it used the term to describe the shallower sidecuts of some of its more-traditional skis as well). Elan claimed that, compared with a round sidecut, its parabola-shaped edges would form a more perfectly circular arc on the snow (and therefore carve a cleaner turn) when tipped, pressured, and bent into reverse camber.  Whatever the reason—whether the parabola, or merely the dramatically curvier shape—Elan’s new SCXTM (“SideCut Experimental”) skis ignited a revolution in ski design that we still benefit from today. As other manufacturers followed the trend toward deeper sidecuts, “parabolic” became a common generic term to describe the new shapes, despite Elan’s objections that it was their trademark, first, and that for most (if not all) skis, it was technically inaccurate.


Now, nearly twenty years since the “shaped” ski's public debut, deep-sidecut skis are the norm, at least for general use. Now, so-called “shaped skis” are simply “skis,” and it is the traditional shallower shapes that call for an extra adjective (“straight” skis) to distinguish them from “regular” skis. Now that deep sidecut shapes are no longer unique and trendy, “parabolic” has become less common as an industry buzz-word. But it’s still the word that, right or wrong, started the ““shaped ski revolution.” 

 

Were they really parabolic? If they weren't, I'm not sure that the few who actually know will ever tell!

 

Best regards,

Bob

post #16 of 21

^^^ I skied those (badly) for a few runs; the shop guy gave essentially the same explanation less elegantly. Think you're right about circular arc not staying in contact, although curious how a true parabola would differ in this regard from an ellipse, or from whatever Blizzard would call the 810 with its three curves. If you think about it, a parabola has maximal curvature at its apex. That would produce a ski that started and finished slowly but got around the belly of the turn faster. Hmmm. 

post #17 of 21
Quote:
Originally Posted by Bob Barnes View Post

think that Elan skis actually had parabolic-shaped sidecuts, at least back in the days of the ground-breaking SCXTM that revolutionized the shape of skis to come. I was working with Elan at the time, representing their skis and skiing on their "Elan Special Forces" team. 

 

It can't be long before we see Bob in a Dos Equis commercial on TV.

 

(I mean that in the nicest possible way, btw. Your post was very interesting, as usual.)

post #18 of 21
Quote:
The main cables of a suspension bridge form a parabolic arc.

 

 

 

I was going to comment here that the cables of a suspension bridge are really in the shape of a catenary curve, but then I got to the qualifying statement...

 

Quote:
(“Real” parabolas are only approximate, of course, due to small variables like air resistance, cable weight, and such.)

 

So I suppose I can't quibble too much here.  :duel:

 

As for the original shape of the Elan skis.  No idea.  Maybe Elan thought that "parabolic" sounded better than "catenaric"?

post #19 of 21
Quote:
Originally Posted by KevinF 

 

 

I was going to comment here that the cables of a suspension bridge are really in the shape of a catenary curve, but then I got to the qualifying statement...

 

Very cool. God, the geek in me loves the collective IQ around here. 

post #20 of 21

Yeah, some of you really know what's up... with civil engineering.

 

 

 

 

 

 

 

 

- just kidding.

post #21 of 21
Quote:
Originally Posted by KevinF View Post
 
Quote:
The main cables of a suspension bridge form a parabolic arc.

 

 

 

I was going to comment here that the cables of a suspension bridge are really in the shape of a catenary curve, but then I got to the qualifying statement...

 

Quote:
(“Real” parabolas are only approximate, of course, due to small variables like air resistance, cable weight, and such.)

 

So I suppose I can't quibble too much here.  :duel:

 

As for the original shape of the Elan skis.  No idea.  Maybe Elan thought that "parabolic" sounded better than "catenaric"?

 

Right, Kevin--if the cables were just suspended from towers and supporting their own weight, they would, in theory, form a catenary curve--like a string of pearls. But supporting the flat roadway of the bridge, they form a parabola (again, in theory, and assuming that the weight of the cables is negligible compared with the weight of the bridge).

 

VERY relevant to the turning radius of a Kastle ski, of course!  :cool

 

 ---

 

So back to you, parapapam (original poster). Welcome to EpicSki, where catenary curves and suspension bridges and conic sections have something to do with sliding around on snowy mountains!

 

In case you have not seen this graphic before, here is a representation of how sidecut combines with edge angle and pressure to bend a ski into "reverse camber" (on firm snow--it is an entirely different principle in powder). It is the shape of that bent ski that determines the actual "carving radius."

 

  Pressure on a tipped ski causes it to bend into "reverse camber."

 

 

The higher the edge angle, the tighter the radius of the decambered ski, according to the formula "carving radius = sidecut radius X cosine of edge angle. 

 

 The higher you tip it, the tighter it bends.

 

So the longest radius turn a ski can carve cleanly is its sidecut radius. A ski tipped to 60 degrees from the snow surface will (theoretically) carve a turn half its sidecut radius (COS 60is 1/2). And, theoretically, a ski tipped 90 degrees will have an infinitely small carving radius. Obviously, there are practical limits to these theoretical truths, as a ski flat on the snow cannot carve, and skis cannot bend into ridiculously tight, round arcs. But for typical edge angles, your Kastles with their 18m sidecut radius can cleanly carve a turn of a maximum radius of 18 meters, and can carve a much smaller radius turn than that when tipped to high edge angles and pressured accurately and sufficiently to bend them.

 

Best regards,

Bob

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