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LiquidFeet

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You don't have to be at the critical angle; you just can't go past it....
....EDIT: if someone has access the the critical angle gif it sure would help the explanation.
I don't have a gif, but I've got this explaining Platform Angle. Is that what you mean by "critical angle"? C2 shows what happens when you "go past it." Assuming hard snow.
Bob Barnes' Platform angle graphic.png
 

WxGuy

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I don't have a gif, but I've got this explaining Platform Angle. Is that what you mean by "critical angle"? C2 shows what happens when you "go past it." Assuming hard snow.
View attachment 98808
OK, I'll bite. How is "Platform Angle" defined in this usage? Which "Platform" is being referred to?. And what are the red arrows (vectors?) indicating?

Enquiring minds want to know!
 

François Pugh

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The red arrow is the force the skier is exerting on the ski directed (having a direction) through the supporting ski. The X represents the skier's centre of mass. The force depends on the turn force and gravity.

So long as the ski is tipped enough that the line of action of the force and the tipping angle of the ski is such that the line of action of the force (red arrow) and the ski's surface make an angle less than or equal to 90 degrees, the ski will not slide out of its groove.

So long as you tip the ski enough for the given turn forces and position of your centre of mass (the critical tipping angle for that situation) to ensure an angle between ski and red arrow of less than 90 degrees your ski holds.
 
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Andy Mink

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There are tradeoffs, as with anything, between longer and shorter radius skis. I think (believe? feel?) that a shorter radius ski is easier to make longer turns than vice versa. However, some short radius skis can get twitchy going straight at speed. Again, as mentioned above, the WHOLE of the ski shape comes into play here. For example, the DPS Alchemist 100RP has a 15 or 16 meter radius. It will turn short or long depending on your preference. It also has a relatively short effective edge when cruising. The fairly pronounce rocker, plus the tip shape, can make it feel pretty nervous on hard pack, IME. A DPS Alchemist 79 Trainer has a longer effective edge relative to the ski length but a similar radius. It is much more stable at speed going straight on groomers. It has a much more traditional shape with just a little rocker.
 

LiquidFeet

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OK, I'll bite. How is "Platform Angle" defined in this usage? Which "Platform" is being referred to?. And what are the red arrows (vectors?) indicating?

Enquiring minds want to know!

"Platform angle" consists of two lines, as does any angle. One is across the ski, from its left side to its right side. The other line goes from the edge of the ski that's in the snow up to the center of mass of the skier. That angle needs to be 90 degrees or less for the ski to not skid across the (hard) snow.

Note that the "edge angle" of the ski to the snow is irrelevant. Example: one can make railroad tracks in the snow at a very low edge angle.

Adjust platform angle by moving where your center of mass is, not by changing your ski's edge angle to the snow. In other words, angulate out over your outside ski if you want it to not skid.

That said, angulation sometimes increases ski-to-snow edge angle, but in this case that would not be your goal. Reducing platform angle to 90º or less would.
 
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LiquidFeet

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Another way to adjust Platform Angle is to bring the inside foot closer, more up-under you. The inside foot will bring the outside foot along with it. When both feet are closer up-under the CoM, this reduces platform angle on the outside ski without the skier having to move the CoM by leaning out.

Last season (and in previous seasons) this has been my preferred way of dealing with the relationship of CoM to BoS. I move my feet from close-up-under, to out-and-around, then back close-up-under. In SRTs this feels distinctly like moving the feet in a sideways figure eight beneath the torso. This is a different movement pattern than what people usually describe, and definitely a different conceptualization of how balance and grip can be managed. I like it better.
 
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cantunamunch

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This last season this was my preferred way of dealing with the relationship of CoM to BoS. I moved my feet under me, from up under, to out and around, then back up under. This is a different movement pattern than the usual, and definitely a different conceptualization of how balance and grip can be controlled.

...brings me back to my Bongo Board point in the "retraction" semantics thread. The Bongo board angle is de facto your platform angle.

Now, how does one go about doing a cross-over on a Bongo?
 

Marin

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Something else that needs to be remembered with turn Radius is risk.

The smaller the radius the greater the risk at higher speed of catching an edge (tune not withstanding). This is most noticed on shorter length skis.

So the idea zone for speed vs turn ability vs risk is somewhere between 16+m and below about 20m. Larger to smaller from this range shifts the balance.

Again as @Philpug stated these are only guides not absolutes.
Not all skis like that , as Phil mention in post #12.
Try Fisher The Curv GT and you will see.
I am 6 feet , My Fisher The Curv GT skis are 168 with 14m radius , My average normal skiing day is speed is 50mph, this season I hit 65mph and did not have any problem handling it at all, not even one sec felt difference in balance. As we know this is triple radius ski so it really matter of construction of the ski.
 

oldschoolskier

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Not all skis like that , as Phil mention in post #12.
Try Fisher The Curv GT and you will see.
I am 6 feet , My Fisher The Curv GT skis are 168 with 14m radius , My average normal skiing day is speed is 50mph, this season I hit 65mph and did not have any problem handling it at all, not even one sec felt difference in balance. As we know this is triple radius ski so it really matter of construction of the ski.
Very short ski for those speeds. I would suggest that this despite doable with a ski like this it not a good idea. For a ski to have that tight of radius it will have shape no matter how it is constructed and therefore put you at risk as the rear edge can catch leading to a world of hurt.

Again, speaking in general guidelines, not a good idea.
 

Marin

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Very short ski for those speeds. I would suggest that this despite doable with a ski like this it not a good idea. For a ski to have that tight of radius it will have shape no matter how it is constructed and therefore put you at risk as the rear edge can catch leading to a world of hurt.

Again, speaking in general guidelines, not a good idea.
Just Demo them and you will see what I am talking about , they are different animal.
I got that size because of the short Slalom turns , which I love to do it .

Here is vieo I got it 2 years ago , this is 45-50mph:
 

oldschoolskier

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Just Demo them and you will see what I am talking about , they are different animal.
I got that size because of the short Slalom turns , which I love to do it .

Here is vieo I got it 2 years ago , this is 45-50mph:
In comparison to my SL’s if they where edged like that you’d be doing twice as many turns. I suspect that they have earlier rise tip and tail which slows down the turn in. My son has a set of Rossi’s which are similar, extremely pleasant to ski and while a nice ski (something I might consider when I get older), just not responsive enough for me.

IMHO early rise tempers the ski responsiveness which allows for easier progression of turns at speeds (race skis are starting to do this just a little) down side is that it can lead to false sense of security and if it catches it will catch you completely off guard.

Just be aware if you ever get a more aggressive tune (or hanging burr) you could be in for an injury. 168 at the speeds you suggest is an injury in the making.
 

Marin

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In comparison to my SL’s if they where edged like that you’d be doing twice as many turns. I suspect that they have earlier rise tip and tail which slows down the turn in. My son has a set of Rossi’s which are similar, extremely pleasant to ski and while a nice ski (something I might consider when I get older), just not responsive enough for me.

IMHO early rise tempers the ski responsiveness which allows for easier progression of turns at speeds (race skis are starting to do this just a little) down side is that it can lead to false sense of security and if it catches it will catch you completely off guard.

Just be aware if you ever get a more aggressive tune (or hanging burr) you could be in for an injury. 168 at the speeds you suggest is an injury in the making.
Rossi's are way different , plus they use Rocker at tip, Those Fishers are full camber .
And no they do not have early rise tip and tail, pure carving ski.
I have been skiing with them 2 seasons and know very well how they can handle. Like I said try them on and you will see what I am talking about.
They are really unique. I do not think anyone made something like Fischer did to those. It took almost 3 years to build this ski. It has triple Radius that you really can go form Shot, Medium and Long turns with out noticing any difference.

For speed , I always say ,Skis not skiing and controlling situation, it is person who skis on them.
 
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cantunamunch

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Which knee thread?

 

Primoz

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My Fisher The Curv GT skis are 168 with 14m radius , My average normal skiing day is speed is 50mph, this season I hit 65mph and did not have any problem handling it at all
It's not that it can't be done, but it certainly can't be done comfortably. I did 100km/h (close to your 65mph) with some long(er) GS like turns with my SL skis (WC stock), so it's not that it can't be done. I would say I ski quite ok, and even for me, it's not really best feeling on world doing that. Skis are anything but stable at such speed and at such long turns (or straight line), especially when you are used to GS or SG skis. So personally I think, regardless of what marketing of certain company is trying to sell you, that for such skiing, there are better and more appropriate types of skis, then short SL or SL like skis.
 

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