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What is best edge angle for max grip - Page 2

post #31 of 51
Quote:
Originally Posted by Davey View Post

 

For Example:

(Do a "Google" for engineering calculations for inclined railway tracks. (I found this if it's of interest) There is only one unique speed for a given angle of track banking where the force of the weight of the locomotive goes at right angles down into the tracks. 

Our skis make grooves like railtracks.  But we can vary the angle of inclination of the track - unlike the loco driver who must regulate speed exactly for every curve.)


You achieve this choice of speed and angle by feel.  If it isn't right you make subtle adjustments to the inclination, the speed, the radius of turn.  You change speed by choice of line. You don't need to throw them sideways.


Well done Davey.  Just want to highlight the problem with tipping too much isn't sliding down the track (or icy on-ramp) like the train engineer's problem.  You can make that groove at any angle higher than the critical angle because sliding down the groove doesn't derail you; it just helps put more pressure on the bottom of the groove (and your knees).   However if you try and turn too tight for your given speed, your critical angle will become higher than your current tipping angle given your current speed.  If you try and make a 2g turn at 50 mph, you will need to tip your skis to resist the forces while balancing on the skis (preferably the inside edge of the outside ski), and the ski will try and dial up a turn according to the (cosine (tipping angle) X side cut radius) formula.  It will not succeed; it will skid along at some wider radius.   If you hit a bump and the ski momentarily digs in, you're toast.  

 

And also,

 

Quote:

Originally Posted by Bob Barnes View Post


How can a ski hold LESS well when tipped to a higher edge angle?
Because edge angle on the snow plays such a significant role in the carving radius of a turn, too much edge angle can actually cause a ski to hold less well than "just enough" edge angle. Especially at high edge angles of 45 degrees and up, a slight change in edge angle can have a tremendous influence on the ski's carving radius. For example, an edge angle (on the snow) of 60 degrees (cosine = .5) creates a theoretical carving radius of one half the ski's sidecut radius. Increasing the edge angle just 15 degrees further from 60 degrees to 75 degrees (cosine = .26) nearly cuts the theoretical carving radius in half again--about one quarter of the ski's sidecut radius! When the ski bends into a tighter radius arc than the turn the skier is trying to make, it will not carve--or hold--nearly as well as when tipped to the optimal angle. Conversely, if you let the ski tighten the turn to whatever radius it bends into, it will cause a dramatic increase in the g-forces (centrifugal force) caused by the turn. That can cause the snow itself to break away under the load, and can also increase the stress on the body, making it more difficult to sustain the intense force--either way resulting in the ski skidding because of too-high edge angles.

 

Edited by Ghost - 11/8/15 at 6:16am
post #32 of 51

Good thread to resurrect, Davey, and a great contribution to it! Thanks--let the discussion continue on these often misunderstood concepts! I'll quote your post so that it re-appears on the new page of the thread for easier reference.

 

Best regards,

Bob

 

 

Quote:

Originally Posted by Davey View Post
 

To Krazzy Legs :-

 

SkiRacer55  has it well explained.

Quote:
Originally Posted by Krazzy Legs View Post
 

What is the edge angle that allows for the most edge grip. If a ski is put on an edge angle higher then 45 degrees would it not start to lose grip past the 45 degree angle ?

I would add:

The answer to the question "What is best edge angle for max grip?" is: It depends on the radius of the turn and the speed.
Also, we assume you are attempting to carve cleanly on a hard surface.  That means all the "ah-but" stuff people throw in about snow quality, depth, temperature, what you ate for breakfast - can be assumed to be irrelevant.
 

The answer is: as has been covered above:  It doesn't matter what the slope angle is (up to the limits of carving that is), or how far over you are leaning.

Here's why:- You cut your own groove.  Your ski bears down on this groove at 90 Degrees to the "wall" of the cut groove.
If that isn't happening, then you're skidding. :-)


I look at it like this:

For each unique combination of forward speed and radius of turn you try to make; you need to have chosen the one and only edge angle in order to hold and not break away.

 

For Example:

(Do a "Google" for engineering calculations for inclined railway tracks. (I found this if it's of interest) There is only one unique speed for a given angle of track banking where the force of the weight of the locomotive goes at right angles down into the tracks. 

Our skis make grooves like railtracks.  But we can vary the angle of inclination of the track - unlike the loco driver who must regulate speed exactly for every curve.)


You achieve this choice of speed and angle by feel.  If it isn't right you make subtle adjustments to the inclination, the speed, the radius of turn.  You change speed by choice of line. You don't need to throw them sideways.

 

Equipment

Quote:
Originally Posted by Krazzy Legs View Post
 

I was trying to figure out how wide of a ski to buy. If I buy to narrow when high on edge the boot will drag through snow. If I buy to wide There is to much leverage for putting the ski up on edge quickly. So no sense in going any wider then that which would allow for max edge grip.

How wide of a ski to buy?

For instance - in the top levels of ski teaching exams, you have to choose one pair of skis. You can't nip back to the lodge to change.

On piste, your skis have to allow you to ski precisely , but also ski bumps and offpiste in all sorts of variable conditions.
So:-

I'd say: Go for a longish GS "Oversize" cut.  Long (e.g 180cm - 185cm) to give you support in the deep.  GS (e.g. 21m Recreational GS Sidecut radius). The longish sidecut radius? that means you can "separate the concerns" of establishing grip separate from carve turning a variable arc. 
It also means they're not too wide underfoot - so this is faster edge-to-edge.  ("Disadvantage" is they don't float high in powder.  But that allows a more skilful 3D turn in powder where you move like a dolphin, diving deep and getting the vertical dimension up to the surface again.  If the ski is long enough and "oversize" (not competition cut), the ski will work well in powder for intermediates).

 

Carve Turn Range

GS Skis can carve a bigger range of radii than a ski of short sidecut radius. (Ski starts to carve at RTurn=RSidecut.  Then tighter as you lean them over in the turn.).
See this link to get the bend radius created for a particular edge angle applied during the turn for a  family of skis of different sidecut. (The assumption is reasonable that the bent ski will carve that radius out on the snow. As the angle is varied during the turn, the bend radius changes continuously during the turn).

 

GS skis if made to grip early using ankle pressure laterally, can then be leant over solidly as much as you can go to make continuous, tightly carved progressive arcs of decreasing and then increasing radius.
Once you have the edge gripping at the top of the turn, you can progressively apply edge angle at an increasing rate to get your chosen direction. 
At high edge angles, you'll carve a 5m radius turn at the tightest part of the arc.  Once you have that new direction you can quicky reduce the edge angle and avoid grinding at the end of the turn.  This means you don't need collossal strength at the end of the turn; you'll carry more speed into the next turn and have plenty of time to feel for the new edge, grip, then whack-on a big edge to nail the next turn.
 

This isn't park-n-ride circular arc skiing. (Constant-radius long-arc). That would be an intermediates' turnshape and that's limited because at higher speeds, you'll never release the over-pressured outside ski at the end of the turn until you slow down a bit.


 

The GS Shape is for more accomplished skiers - It's dynamic, fast, grippy and will give control of speed and direction in the carve like a real expert. 
 

 

If you go for short, tight sidecut skis, you have to be super-quick to establish the early grip.  You won't have time to do this if the ski is already whacking into a 10m curve on the slightest inclination.

post #33 of 51

Touching on another commonly misunderstood edging concept here that I submit does not contribute to edges holding less well when tipped too high (as other factors do, described earlier). It is true that the further we incline into a turn for balance against increasingly high G-forces, the greater the percentage of the force applied to the edge pulls parallel to the slope, and the less the percentage of that force pulls down toward the slope. But the important thing to remember is that this is the result of the lateral forces increasing, not of the perpendicular force decreasing. If you weigh 100 pounds, there will be 100 pounds of force pulling down no matter what your edge angle, and no matter how much "G-force" pulls sideways due to the turn--assuming you are in balance.

 

So yes, you are more likely to skid sideways with these high edge and inclination angles in high-speed, "high-G" turns, simply due to the greater lateral forces. But not due to less force pulling down toward to the snow.

 

Best regards,

Bob

post #34 of 51
Indeed bob. But you will only slide out if the resulting force vector is angled lower then the edge angle.

In my experience this is usually all about balance. If you are in balance then the above situation is extremely unlikely to ever be an issue, just watch Ted ligety! Most people who get wash out on highly edged ski are probably out of balance to the inside which reduces outside ski engagement regardless of the edge angle.

Also folks that try to pivot or steer the ski into too much steering angle can run into an issue with high edge angles.
post #35 of 51

http://www.nytimes.com/video/sports/olympics/100000002705897/on-giant-slalom-ted-ligety.html?playlistId=100000002688038

 

Jump to about :55 seconds.

 

The narrower ski will go on edge more quickly and more easily.  Consider the ankle a simple ball joint and the angles run from that ball joint out to the edges.  The narrower the angle, the less leverage working against you putting it on edge.  The wider the angle, the more force working against you edging it.

 

We need to remember, while Ted is a great ski racer, Head was the first to develop a GS ski to the new specs that really worked well.  Combine that with Ted's skill, and it was a winning combination.  The next year Atomic and others figured out how to make a GS ski that carved equally well at those specs, and Ted had some real competition.

post #36 of 51

More easily, SSG, I agree--and more effectively for gripping as well, for the reasons you described. But could you explain your understanding of how a narrower ski would go onto edge more quickly than a wider ski?

 

Best regards,

Bob

post #37 of 51

K.I.S.S.

post #38 of 51

Takes less tipping then a wider ski.

post #39 of 51
Thanks for offering your opinion, CVJ, but what I'm asking for from SSG is for him to explain his understanding of how a narrower ski changes edges or "gets on edge" more quickly than a wider ski. He's got me curious.

But while I'm at it, I'll ask you the same question--what is your understanding of why a narrower ski "takes less tipping" than a wider ski?

Best regards,
Bob
post #40 of 51

My experience tells me it is true; skinny skis swap edges quicker.

 

Thinking about it, I can understand how body parts that must move in harmony with the edge change have less distance to move.  Based on my engineering (over :D) education, I can also see based on applied torque, rotational inertia and moment of area that more time will be needed to go from tipped 30 degrees to tipped 30 degrees in the other direction.

post #41 of 51
Actually, the tibia angle is exactly the same whether you have a narrow or wide ski, assuming a rigid boot or ski.

It is true that the knee travels more to reach the same angle on a wider ski.
post #42 of 51
Quote:
Originally Posted by Ghost View Post
 

My experience tells me it is true; skinny skis swap edges quicker.

 

Thinking about it, I can understand how body parts that must move in harmony with the edge change have less distance to move.  Based on my engineering (over :D) education, I can also see based on applied torque, rotational inertia and moment of area that more time will be needed to go from tipped 30 degrees to tipped 30 degrees in the other direction.

 

The underlined bit is the key.  Wider skis have the boots further from the edge being engaged, with a longer lever.  The boot mass thus has to be moved a further distance to accomplish the same change of edge angle as a narrower ski.

post #43 of 51


Our goal in edging both wide skis and narrow skis is not to create a given tipping angle, but to balance the CoM over the edge.   

Tibia angles might be identical at the same tipping angle, but the position of the CoM will not be.     At any given tipping angle, the CoM of the skier on the wider ski will be further towards the outside of the turn.    
 

Therefore, to balance the CoM above the edge, the wide ski skier has to have greater tipping angles than the narrow ski skier.     Creating those greater angles is what slows the transition down (in comparison).

post #44 of 51
Quote:
Originally Posted by borntoski683 View Post
 

 

The underlined bit is the key.  Wider skis have the boots further from the edge being engaged, with a longer lever.  The boot mass thus has to be moved a further distance to accomplish the same change of edge angle as a narrower ski.

Don't longer levers generally provide MORE leverage.....seems opposite here with a wider ski. In the case of a narrow ski the boot alignment  much closer to the edge, the more force is available to the edge....NO?

 

Because it is not a lever!  With a lever you are applying force to one end to get the opposite end the opposite direction.

 

On a ski you trying to get the force to move the edge in the same direction as the force applied.  In other words your trying to apply downforce not pressing down to move the edge up!

post #45 of 51

leverage reduces the force requirement while greatly increasing the RoM needed to make the movement.

 

In the case of edging a ski, the leverage kind of goes both ways...its exactly this same leverage that causes the resultant force vector to try to lever the ski back to flat rather then contribute to tipping it.  We might be able to argue that its easier to tip in terms of the force required, but its also easier for those forces to untip it.  Which wins?  depends on whether you're talking about the weighted ski or the unweighted inside ski...but in either case the RoM required to make the movement is greater with a wide ski then a narrow one and this extra RoM takes time to complete...and as cantunamunch just talked about..there is also the aspect of balance...  You have to angulate more on a wider ski in order to find balance on the inside edge...which means not only do you have to move the Boot more to achieve a certain edge angle, but you will have to move the upper body the opposite direction more as well....

post #46 of 51

So what you're saying is you are NOT using a lever to edge the ski...you fighting a lever to keep the ski from not edging.  There is a difference.

post #47 of 51

In this case the lever is the shin which becomes relatively shorter as its tipping base platform widens. So, the narrower ski will deliver more leverage to the shin which will require less torque to roll in and back out. The interesting aspect to the wider ski which requires more torque to roll in but also, as well, back out which makes edge locking a wide ski such a pleasure. This dynamic is significant on the rare model touting both a deep sidecut and wide waist such as the Skilogic Occam's Razor, the gone but not forgotten B5 and a very few others. This is the only shape "type" that also delivers a lot of boot clearance with high tipping, not so much for consideration of booting out as these aren't race models but for reducing "boot drag" inherent with certain snow surface depths and densities such as crud. 

post #48 of 51

It doesn't really take much force with narrow or wide skis to tip the skis.   It just takes quite a bit more RoM to tip a wide ski, then a narrow one.

 

If you disregard the resultant force vector, it requires very little force to tip a ski on edge..nothing that poses a problem..not for wide skis and not for narrow skis.  But it does take quite a bit more RoM to tip a wide ski and balance on it.  Yes gravity is pulling on your body and pulling your  weight into the lever and that would create more untipping force which you would have to fight against in order to tip, but ideally you eliminate that aspect by angulating to bring the resultant force vector directly to the edge, thus reducing the force required to tip or untip to something that is very insignificant, but nonetheless requiring more RoM.

 

But the problem is the RoM required to do that..is significantly greater with wider skis.

 

As the turn progresses, the resultant force vector increases, which means that if you aren't angulated enough over the ski, the resultant force vector will be trying to push the ski the opposite direction then what you are trying to hold it or tip it more even...so the force could become greater....UNLESS you angulate enough, then that levering force will be mitigated to almost nothing...but again...lots of RoM to do that and perhaps over edging and over angulating and other oddities which are not happening on narrower skis.

post #49 of 51

I agree with you that in terms of quickness, Longer RoM of the boots is what is taking the time up and not torque.

post #50 of 51
Quote:
Originally Posted by Krazzy Legs View Post
 

What is the edge angle that allows for the most edge grip. If a ski is put on an edge angle higher then 45 degrees would it not start to lose grip past the 45 degree angle ?

 

I was trying to figure out how wide of a ski to buy. If I buy to narrow when high on edge the boot will drag through snow. If I buy to wide There is to much leverage for putting the ski up on edge quickly. So no sense in going any wider then that which would allow for max edge grip.

 

Did not read any other answeres so I might be repeating stuff. Anyway, if you want maximum grip on a hard surface you need to go for a ski with a narrow waist. You also need to have a narrow boot and to use a lot of lifter plates. I think the boot and the lifter plate issues are overlooked. Makes a huge difference.

post #51 of 51
Quote:
Originally Posted by tdk6 View Post
 
Quote:
Originally Posted by Krazzy Legs View Post
 

What is the edge angle that allows for the most edge grip. If a ski is put on an edge angle higher then 45 degrees would it not start to lose grip past the 45 degree angle ?

 

I was trying to figure out how wide of a ski to buy. If I buy to narrow when high on edge the boot will drag through snow. If I buy to wide There is to much leverage for putting the ski up on edge quickly. So no sense in going any wider then that which would allow for max edge grip.

 

Did not read any other answeres so I might be repeating stuff. Anyway, if you want maximum grip on a hard surface you need to go for a ski with a narrow waist. You also need to have a narrow boot and to use a lot of lifter plates. I think the boot and the lifter plate issues are overlooked. Makes a huge difference.


Yes!  And if you go over a bump mid-turn at speed while dragging your your boot toe (leaving two lines per ski as tracks) and land in the snow, no biggie, but if you land on hard ice you will boot out, which could have painful and expensive consequences.

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