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Turn Radius And Skidded Turns

post #1 of 13
Thread Starter 
You know how sometimes you never think about something and then for some reason one day you do, and even though it seems pretty basic and you should understand it fully, your want to make sure you aren't missing something? This is one of those times.

I understand the effect of a ski's turn radius on your turns when carving. I just want to make sure I understand it well enough with regards to steered or skidded turns and I think it doesn't matter or matter that much. I say this because when you consider things like pivot slips, It feels like the length or weight of the ski has more to do with the ease of pivot slips. Whether I use my 176 cm 21.2M TR skis or my 160 cm 12.7M TR skis, pivot slips are pretty much the same.

If your are primarily using the bottom of the ski to make your turn and not getting the ski on that much of an edge angle, isn't length a bigger factor than TR?

Just trying to make sure I'm understanding this correctly.

Thanks,
Ken
post #2 of 13

I'll contribute the the question.  

 

I have an old pair of 1080 twin-tips, which I consider my rock skis.  Doing any kind of pivoting on them is much, much easier than doing the same on any of my other skis.  This assumes all the skis have been tuned with the same sharpness and side angle.  They have a similar turn radius (14m) to the other skis I use.  What's up with that?  

 

I've always thought those 1080s must be torsionally floppy, and maybe also longitudinally limp.  They have that light colored base on them, which I understand is more appropriate for park skis but I don't know why, not the black base that is more normal.  They are the easiest skis I have for skiing bumps.  They don't like to hold an edge on typical New England ice.  I have a friend who skis on old twin-tips of about the same era who has never felt a true carve.  I blame his skis as holding back his learning.  Should I?

 

So to frame this as a question, does rigidity/floppiness of flex, both torsional and longitudinal, mean more than turn radius when comparing riding an edge/carving vs brushing/skidding the skis along the snow in a steered turn?

post #3 of 13

There are waaaaaaaaaaaaaaaaaaay more things than just sidecut and edge angle that play into the slarve of a turn.  

 

Of course length will play into the pivot as a function of swing weight- in which you will only notice a difference once a ski goes outside your range of comfort and everything below that will all feel the same essentially.  Also the camber profile and tip/tail shape will play into how well you're able to pivot slip the ski.  If the ski has a square tail and lots of camber it will be infinitely less intuitive in a pivot slip.  Conversely, if it is a ski that has not so much camber and a round or twin tail or tail rocker such maneuvers will be a relative breeze.  

 

Sidecut makes very little difference in moves like that specifically because you aren't employing that dimension physically.

 

For slarving a big turn, it's all in the tips and tails.  The way the ski initiates and finishes a turn is mostly dependent on the tips and tails and making a nice smooth slarve will be much more comfortable on a ski that has an upturned or round tail.  

 

As for LiquidFeet's question:

 

"So to frame this as a question, does rigidity/floppiness of flex, both torsional and longitudinal, mean more than turn radius when comparing riding an edge/carving vs brushing/skidding the skis along the snow in a steered turn?"

 

Absolutely.  The sidecut can be anything, but if the core or layup lacks the rigidity to hold the edges down into that radius then it's all for naught.  It's the noodle effect- when you go to drive the tips into a turn and they just sort of fold in half and want to make about a 3m turn instead of the advertised 17m or whatever.   You need to match your core materials and layup to the size and intensity of the turn shape it's being mated with for the size of the rider or else you're wasting your time.  

 

Also if the ski is so stiff that your body weight can't really get down into the meat of the turn, it's going to feel shitty and you still won't get the advertised radius either.  

     

 

 

At least that's how I see it...  It makes sense in my head anyways haha

post #4 of 13
Quote:

Originally Posted by Do Work View Post

 

...the camber profile and tip/tail shape will play into how well you're able to pivot slip the ski.  If the ski has a square tail and lots of camber it will be infinitely less intuitive in a pivot slip.  Conversely, if it is a ski that has not so much camber and a round or twin tail or tail rocker such maneuvers will be a relative breeze.  

 

Sidecut makes very little difference in moves like that specifically because you aren't employing that dimension physically.

 

Sounds about right to me.  The profile (rocker/camber) is going to make a big difference.  I would also expect that a more radical sidecut or more aggressive tune (especially in terms of base bevel) would make a ski more 'grabby' at low edge angles.  If the ski is perfectly flat against a very-close-to-perfectly-flat groomed snow surface, the edges won't matter at all.

 

Quote:
The sidecut can be anything, but if the core or layup lacks the rigidity to hold the edges down into that radius then it's all for naught.  It's the noodle effect- when you go to drive the tips into a turn and they just sort of fold in half and want to make about a 3m turn instead of the advertised 17m or whatever.   You need to match your core materials and layup to the size and intensity of the turn shape it's being mated with for the size of the rider or else you're wasting your time.  

 

Also if the ski is so stiff that your body weight can't really get down into the meat of the turn, it's going to feel shitty and you still won't get the advertised radius either. 

 

Ski stiffness is relative to factors like:

 

  • Your mass
  • Velocity
  • Turn radius
  • 'Natural' radius of the ski
  • Camber/rocker profile of the ski

 

If a ski is too stiff, it won't decamber enough to match the desired turn radius, and it will not carve cleanly.  If a ski is too soft, it will 'fold up' or decamber *too* much, and will also not carve cleanly.

 

There are also geometric limits related to the 'natural' radius of the ski and the edge angle relative to the slope.  Edge angles are further constrained by speed -- if you tip too much you'll fall in, too little and you'll be catapulted out of the turn (or at least be unable to carve and start skidding sideways).  LeMaster goes into this in some detail in "Ultimate Skiing".

post #5 of 13

Also add the skis tune into the equation:

 

Are the bases convex, concave or flat?

What is the base bevel on the skis?

What kind of base structure?

How much camber?

Where are the bindings mounted fore & aft?

 

All of these things play a significant role in how the ski pivots, skids, slarves, slips & stivots.

 

JF

post #6 of 13

I guess I don't get this thread.  To me the point of smearing or skidding a turn is to customize the shape and radius of that turn to whatever/wherever the skier wants it to be OUTSIDE of the side cut radius range.  You should be able do that with any size or shape of ski depending on the ability level of the skier.  You're either carving the arc at whatever angle and speed larger or smaller within the geometry of the side cut, or you're smearing/skidding something entirely different as needed.  The length is more useful with regard to stability at higher speeds where as the side cut shape, flex, tune, etc.. sets the compass arc for different pre-determined radius ranges while on edge.  You can also do this with parts of the turn instead of the entire turn.

post #7 of 13
Thread Starter 
Quote:
Originally Posted by crgildart View Post

I guess I don't get this thread.  To me the point of smearing or skidding a turn is to customize the shape and radius of that turn to whatever/wherever the skier wants it to be OUTSIDE of the side cut radius range.  You should be able do that with any size or shape of ski depending on the ability level of the skier.  You're either carving the arc at whatever angle and speed larger or smaller within the geometry of the side cut, or you're smearing/skidding something entirely different as needed.  The length is more useful with regard to stability at higher speeds where as the side cut shape, flex, tune, etc.. sets the compass arc for different pre-determined radius ranges while on edge.  You can also do this with parts of the turn instead of the entire turn.

 

This is more in line with what I'm after.  Let me rephrase the question"

 

On a perfectly groomed intermediate slope with only 1 fall line, a intermediate defensive skier (turns by not going there anymore) is on a 160 13M SL race ski.  The skier then returns to the same slope that has been re groomed (it's my question I can do what I want) but is now skiing on a 182 23M GS Race ski.  On both runs, the skier skis the same way; defensive turning.  Both pairs of skis have a fresh tune and same base structure.  Edges on both pairs are at 1/3.

 

What will the skier notice that is different between the two runs?

post #8 of 13
Quote:
Originally Posted by crgildart View Post

I guess I don't get this thread.  To me the point of smearing or skidding a turn is to customize the shape and radius of that turn to whatever/wherever the skier wants it to be OUTSIDE of the side cut radius range.  You should be able do that with any size or shape of ski depending on the ability level of the skier.  You're either carving the arc at whatever angle and speed larger or smaller within the geometry of the side cut, or you're smearing/skidding something entirely different as needed.  The length is more useful with regard to stability at higher speeds where as the side cut shape, flex, tune, etc.. sets the compass arc for different pre-determined radius ranges while on edge.  You can also do this with parts of the turn instead of the entire turn.

 

 

Minutia obsession.  It's fun.  smile.gif

post #9 of 13
Quote:
Originally Posted by L&AirC View Post

 

This is more in line with what I'm after.  Let me rephrase the question"

 

On a perfectly groomed intermediate slope with only 1 fall line, a intermediate defensive skier (turns by not going there anymore) is on a 160 13M SL race ski.  The skier then returns to the same slope that has been re groomed (it's my question I can do what I want) but is now skiing on a 182 23M GS Race ski.  On both runs, the skier skis the same way; defensive turning.  Both pairs of skis have a fresh tune and same base structure.  Edges on both pairs are at 1/3.

 

What will the skier notice that is different between the two runs?


A more radically sidecut ski should be more 'hooky' and resistant to sliding sideways, so on that basis the SL ski would be harder to ski "defensively".

 

But a longer ski would have a longer moment arm to resist pivoting (the distance from the foot to the front/back of the ski), so on that basis the GS ski would be harder to ski "defensively".

 

So kind of a mixed bag, at least in my armchair analysis.  Which factor would dominate might depend on other things, like the tune, the skier's weight/size, how fast they are going, and what shape of turns they make.

post #10 of 13
Thread Starter 
Quote:
Originally Posted by Matthias99 View Post


A more radically sidecut ski should be more 'hooky' and resistant to sliding sideways, so on that basis the SL ski would be harder to ski "defensively".

 

But a longer ski would have a longer moment arm to resist pivoting (the distance from the foot to the front/back of the ski), so on that basis the GS ski would be harder to ski "defensively".

 

So kind of a mixed bag, at least in my armchair analysis.  Which factor would dominate might depend on other things, like the tune, the skier's weight/size, how fast they are going, and what shape of turns they make.

 

Good point.  I guess the closest way to compare lengths is of the same model in different lengths. 

 

Good to go.  The basis of my question has been answered.

post #11 of 13

The effect of having a smaller side cut radius is a little bit like having grippier tires.  The Torsional and longitudinal rigidity (at the given displacement from the undistorted shape - i.e. including the effect of camber profile in the current stress-displacement relationship), etc. is like the suspension and steering shock absorbers. 

 

When you adjust your turn via fore-aft pressure distribution and tipping angle, it is easier to make the tips/tails dig in with the shorter sidecut radius.  That means you don't need quite as much tipping angle or quite as much pressure to be delivered to the front of the ski (or to the rear for that matter) to get it to bite in.  All else being equal, and it never is, the shorter side cut radius ski will be easier to smear with on that groomed surface.  The shorter turn radius is a little like power steering, provided the skier IS using tipping and pressure distribution to control the skis and not just pushing and torquing them around by brute force.

 

Length, is a straight linear relationship, longer length generally requires more skill, but if the skill is there, the longer length makes it easier.  It requires more to get the pressure all the way to the tip, but the resultant torque, once achieved is greater.  It's like having a steering wheel that goes around three turns lock-to-lock, instead of one and a half.  Shorter ski = quicker steering ratio.  It is easier to fine-tune the turn with the longer ski.

 

Stiffer ski is easier to smear the turns on if you have the skill, as it transmits your forces directly to the tip/tail as per your instructions; softer is more forgiving if you don't have the skills, as it also transmits mistakes and more importantly results of putting an edge wrong.

post #12 of 13
Quote:
Originally Posted by LiquidFeet View Post

I'll contribute the the question.  

 

I have an old pair of 1080 twin-tips, which I consider my rock skis.  Doing any kind of pivoting on them is much, much easier than doing the same on any of my other skis.  This assumes all the skis have been tuned with the same sharpness and side angle  (You mean base edge bevel angle, since side edge bevel has no effect on the ability to pivot/skid/redirect, side edge angle only comes into play once the ski is up on edge).  They have a similar turn radius (14m) to the other skis I use.  What's up with that?  

 

I've always thought those 1080s must be torsionally floppy, and maybe also longitudinally limp.  They have that light colored base on them, which I understand is more appropriate for park skis but I don't know why, not the black base that is more normal.  They are the easiest skis I have for skiing bumps.  They don't like to hold an edge on typical New England ice.  I have a friend who skis on old twin-tips of about the same era who has never felt a true carve.  I blame his skis as holding back his learning.  Should I?

 

So to frame this as a question, does rigidity/floppiness of flex, both torsional and longitudinal, mean more than turn radius when comparing riding an edge/carving vs brushing/skidding the skis along the snow in a steered turn?

post #13 of 13
Quote:
Originally Posted by LiquidFeet View Post

I'll contribute the the question.  

 

I have an old pair of 1080 twin-tips, which I consider my rock skis.  Doing any kind of pivoting on them is much, much easier than doing the same on any of my other skis.  This assumes all the skis have been tuned with the same sharpness and side angle  (You mean base edge bevel angle, since side edge bevel has no effect on the ability to pivot/skid/redirect, side edge angle only comes into play once the ski is up on edge).  They have a similar turn radius (14m) to the other skis I use.  What's up with that?  

 

I've always thought those 1080s must be torsionally floppy, and maybe also longitudinally limp.  They have that light colored base on them, which I understand is more appropriate for park skis but I don't know why, not the black base that is more normal.  They are the easiest skis I have for skiing bumps.  They don't like to hold an edge on typical New England ice.  I have a friend who skis on old twin-tips of about the same era who has never felt a true carve.  I blame his skis as holding back his learning.  Should I?

 

So to frame this as a question, does rigidity/floppiness of flex, both torsional and longitudinal, mean more than turn radius when comparing riding an edge/carving vs brushing/skidding the skis along the snow in a steered turn?

Thanks, Atomicman.  

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