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The limitations of carving

post #1 of 16
Thread Starter 
 I've spoken before here about the importance of possessing good steering skills. We've just put a new entry on our glossary that explains the turn shape limitations associated with carving. I plan to do an article on this, but in the meantime I thought I'd throw this up here for you folks to have a look at. It shows pretty clearly what I'm referring to. If you have any questions about it, feel free to hit me with them. 

A big thumbs up to Janis (Little Tiger) for the great drawing. 

To have a look at the entry, go to this link and see "Carve Zone". http://www.yourskicoach.com/YourSkiCoach/C.html

post #2 of 16
Excellent!
post #3 of 16
Good point Rick, but I think it is important to point out that the maximum carved radius is not given by the sidecut. This is only close to the truth at very low speeds. As soon as you have some speed you have to edge significantly in order to carve and then the maximum radius will be smaller.

I did a quick calculation and without checking my results I think that the maximum radius is given by R cos( asin( V^2/(gR))) (if using metric units)

A bit over the top perhaps, but in practice it means that a short radius ski will have a very limited carve zone at high speed. Similarly a large radius ski will have a very limited carve zone at low speeds.
post #4 of 16

Great recource your glossorary Rick. Thats something I have been wanting to do for quite some time myself. The videos really make all the difference. I have some comments regarding the clips but nothing major. I think that you should limit the cross over/through/under to only over/under. I dont see the need for "under" in your glossorary. Anyway, that is a bit off topic but since you asked....

Jamt, check out PhysicsMan side cut calculator and the discussion that goes with it:
http://www.epicski.com/forum/thread/2681/physicsman-s-ski-sidecut-radius-calculator

How tight the ski turns is really a blend of many different components but you are right, the ski usually turns tighter than the geometrical sidecut since the ski always bends. I dont think anybody ever measured how wide the turn radius acutally is. On my racing skis I have the Marker Piston Plate and it helps the ski to bend and makes the turn radius smaller without sacrifying edge hold. I can carve both wide and tight arcs with my skis but I cannot ski a GS course. There the limitations step in. For an overall great carving ski on gromers I reccomend a normal SL type ski. Preferable a true or close to real racing ski. Stay away from cap skis.

IMO the two most important limitations of carving is that you cannot vary the turn radius by much and there is very limited speed controll. If you ask me you cannot ski safely and with much enjoyment if you do not posess any kind of steering skills. With steering I mean turning where the skis are not locked onto their edges and carving. There are pople that think they can but the fact is that these people are actually steering all the time and not carving at all. Check out my threads 5y back on people that think they carve but they dont .

post #5 of 16
Not bad.  Of course to carve the sidecut radius the ski would have to be flat, so the largest radius you can carve is less than the sidecut radius, but close enough.

Jamt,
Notice RicK left speed out of it.  A wise move. 
If you want to include kinematics, then the radius that you get from sidecut is modeled by Cosine( tipping angle) multiplied by sidecut radius.  However in order to hold the forces, the ski has to be at an angle greater than the critical angle at which point the net force due to gravity mg down and acceleration into the turn, mV^2/(RCosine(tipping angle)) in the direction that points parallel to the slope and towards the turn centre. The Setting the critical angle equal to the tipping angle should give you the maximum turn radius at any speed.  Your equation might be right, or not.

I haven't got time to do it now.
post #6 of 16
Thanks Ghost, that's what I used to derive the formula but I think I did something wrong becuase the values inside the asin can be greater than 1. I'll check it later when I have time.
post #7 of 16
Quote:
Originally Posted by Ghost View Post

Not bad.  Of course to carve the sidecut radius the ski would have to be flat, so the largest radius you can carve is less than the sidecut radius, but close enough.

 

Thanks for pointing that out Ghost! Its important to understand that the turns made at 30km/h with a SL ski with 12m radius are in fact turns with much tighter radius if they are cleanly carved.
post #8 of 16
Thread Starter 
 Thanks, Carl!

Jamt, you're absolutely right.  Because of needed tipping and bending the maximum turn radius will not be exactly that of the ski's sidecut radius.  But like Ghost says, it's close enough when just trying to explain the basic concept to people new to the topic.  

tdk6, i like the 3 classifications (cross under, over, through) because it allows me to describe not only transitions in which you disrupt balance via pressure transfer (cross over and cross through), but also by changing edge angles (cross under).  Cross under is much like the over steering concept you presented here a while back.  Like over turning the bicycle handle bars causes the bike to cut under the body, and the body thereby to tip into the new turn, adding edge angle without changing your state of angulation causes the ski to cut dynamically under the body.   The sensation of doing this is so distinct, it really needs a term all its own.  
post #9 of 16
I liken cross-under and cross-over to flying low and flying high, not too sure about that cross-through term.  Bonus, with flying you can use the analogy of the skis being the train on the railroad tracks as you fly past.
post #10 of 16
cool picture. 
post #11 of 16
Quote:
Originally Posted by Rick View Post

tdk6, i like the 3 classifications (cross under, over, through) because it allows me to describe not only transitions in which you disrupt balance via pressure transfer (cross over and cross through), but also by changing edge angles (cross under).  Cross under is much like the over steering concept you presented here a while back.  Like over turning the bicycle handle bars causes the bike to cut under the body, and the body thereby to tip into the new turn, adding edge angle without changing your state of angulation causes the ski to cut dynamically under the body.   The sensation of doing this is so distinct, it really needs a term all its own.  
 

I liked the definitions of cross over and under in the telemark book I gave a review of earlier this season (cannot find the thread). It considered them to be the same. I tend to agree with it although the terms here at epic has taken a different meaning: ILE/OLF. I can live with that but I dont understand the cross through consept. In the telemark book the cross over/under referred to what we here consider to be a cross under transition. ILE is not really a cross over transition since the body is not crossing over, it is vaulting over. A cross over would be the body being pushed hard across the skis insted of the skis crossing hard under our body. Kind of hazy in the borderlines. Thats why I think its a good thing to consider them the same. Or use the ILE and OLF consepts. In your video I could not understand the difference between cross under and through.
post #12 of 16

Rick, are you suggesting that you cannot change turn radius unless you do some steering? I ask because one can easily carve a fairly clean line with the shovel of the ski while letting the tail drift out of the carve. That tightens the turn (as would more tipping), but there is really no traditional steering involved.


 

post #13 of 16
Far be it for me to shed any criticism but the inside ski track looks like it is drifting a little. Epic experts said it was a pencil thin line.
100_0614.jpg
track3.jpg
post #14 of 16
I agree with slider, the inside foot does drift a hair but nicely hooks back up.  I also would like to know if the discussion is about adjusting the turn radius without steering?  Is there also a difference in steering to an edge or guideing to an edge?  Either way in my opinion there really isn't a difference between the two except for the intesity.  If we are truely moving to the future of a the new turns, there has to be a change in our shins and femurs which in turn will add some guideing towards the new turn hence adding some amount of steering in every carved turn.  If you are moving across the cuff of the boot say going from 10 to 2 or 11 to 1 again your adding a mount of guideing to the skis even if we are coming out of a deep carve.  Our picture above also shows this where you can see the tips of the skis engaging at the top of the turn allowing the shape of the ski to start working in our favor.  I think that this is where all of the "steering" is happening and for all arguments stops until it is time to start thinking about the new turn (with the assumption that we are not always thinking about turns that are happening 2 turns down).  We could make a carved turn if we just simply come straight up and over our skis but that throws us into an off balanced position and does not allow us to fully use these great peices of legal cheating in skiing.  I could be way off base but this is what I think of as I carve my turns down the hill. 
post #15 of 16
TomB,

The point is that turn radius can be adjusted without steering, WITHIN a range.  Beyond that range, steering or brushing will be required.
post #16 of 16
Thread Starter 
Quote:
Originally Posted by borntoski683 View Post

TomB,

The point is that turn radius can be adjusted without steering, WITHIN a range.  Beyond that range, steering or brushing will be required.

That's exactly it.    
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