Relation of contact point to widest point of the ski

[Cadman]

I am curious whether anyone has done some experimenting on positioning the contact point at different areas around where the blend curve and the side cut meet up at either end of the ski. I am interested in finding out if this effects the way the ski hooks up or is it more about the thickness profile or a combination of both.

I know that on the old design skis, I noticed that the contact point at the tail was always closer to the widest point of the ski than at the tip.

Do you think that the contact point can be on the sidecut before it goes into the blend curve and if so, how does that effect the ski performance?


https://www.flickr.com/photos/123805078 ... 992617800/

[MontuckyMadman]

well its makes the running length shorter the turn sees to finish faster and you have more skid potential because if you continue the turn you loose contact.
Purely my feeling when skiing a ski like this.
If the ski id soft enough or the snow is soft enough or the rider is big enough he can make the ski do almost anything but generally the ski feels shorter and the turn feels shorter and the ski is less stable when running flat at speed.
My .0002Cents

[knightsofnii]

i dont know about skis, but any time i had a snowboard where the widest part or inflection point of the curves was not beyond the beginning of the tip rise, it resulted in a board that had a LOT of bite and was very grabby.

since then i always make sure that the tip/tail rise starts prior to the widest part or the inflection point, or both really. i also try to make the radius of the initial turn in of the tip shape as large as possible so its a good blend with the sidecut and not so much that it causes a problem when the board is leaned over.

sorry i dont have any numbers or science to back this up.

[pmg]

If the widest point of the ski is closer to the binding then the tip contact point (e.g. the ski getting narrower before the tip contact point), the ski will get more hooky and "bumpy".
When the ski is flat, every little little irregularity on the ground will push your ski a bit to the left or the right. Just imagine the very extreme case: riding a triangle. Every minibump or other irregularity u hit will be on the left or the right of the ski and push your ski in the other direction.
Of course, if the ground is soft, you wont feel any of this. And if you have a widest area in which the contact point is located, it surely wont make any problems.
But: If the ground is harder, you want to have more effective edge. When building the skis normal (widest point after the tip contact point, seen from the bindings), you will get additional effective edge if you edge up the skis. When building it the other way, you wont gain any additional effective edge, what will make the ski more "slippery" on hard ground.

Looking at your picture, it seems to be a pure powder rocket. In this case I seriously doubt you will feel a difference.

Thinking about the additional edge when edging the ski up: Of course this can be overdone as well. Just stand on a slalom ski and you will know what I mean. Little beasts always wanna go somewhere where you dont ;)

As Doug, I try to get a smooth transition from the sidecut to the tip curve, so that none of the two effects (nervous flat ski vs. nervous ski as soon as its a bit on the edge) appears.

[pmg]

By the way, it is quite hard to determine what is meant with "before" "beyond" "after" and so on. Seen from the tip to the tail, from the tail to the tip, from the binding to the ends?
Is there a forum standard about this?

[pmg]

Kästle has the same thoughts:

http://www.kaestle-ski.com/en/products/fx/fx94-1947/

[gozaimaas]

i dont know about skis, but any time i had a snowboard where the widest part or inflection point of the curves was not beyond the beginning of the tip rise, it resulted in a board that had a LOT of bite and was very grabby.

since then i always make sure that the tip/tail rise starts prior to the widest part or the inflection point, or both really. i also try to make the radius of the initial turn in of the tip shape as large as possible so its a good blend with the sidecut and not so much that it causes a problem when the board is leaned over.

sorry i dont have any numbers or science to back this up.

+1
I start my very gentle nose rise 100mm i from the end of the effectice edge. Too steep of anose rise will also make it feel grabby as when on edge this area is forced to cut through the snow but is does so at a different angle to the direction of travel.

[gozaimaas]

I built this to test this theory, the side cut extends will into the nose rise.
I am yet to test it.

[pmg]

Too steep of anose rise will also make it feel grabby as when on edge this area is forced to cut through the snow but is does so at a different angle to the direction of travel.

Nice explanation!

[b2therye]

Correct me if I'm wrong but if you mold a ski/snowboard with the unweighted contact points being the widest part of the side-cut; when the weight of the skier/snowboarder is applied the contact points both move inward on the ski making the end contact points inward of the widest point on the ski/snowboard?

this would only apply to skis/boards made with camber and the end contact points wouldn't move too far inward but wouldn't that be enough to make the ski/board less hooky?

[gozaimaas]

I cant get my head around that question

[pmg]

when the weight of the skier/snowboarder is applied the contact points both move inward on the ski making the end contact points inward of the widest point on the ski/snowboard?

This is what actually happens with every camber ski. Its not so much about the location of the widest point, but more about the camber shape.

e.g. a raceski: The camber line gets "steeper" until it gets very close to the contact points, and then turns up into the shovel/the end quite immediately. Lets say the "counterturning" starts less than 5cm before the contact points.
Like this hardly any contact length is lost when pressure is applied to the ski. Very useful for hard pistes, but not nice for soft or deep snow.

vs. the camber profile of the Völkl Code or most of the K2 skis having a "All terrain rocker":
The camber line gets "steeper" as well (seen from the binding), but begins the transition into shovel/end much earlier and smoother. The counterturning starts more than 20cm before the contact point.
Like this the ski rockers a bit when pressure is applied to it, making the skis good allrounders: floating more and turning easier in soft and deep snow, yet still have a good performance on hard pack due to camber.

Have a look at the 2 links, 1st is the classic raceski, second the Allrounder. Try to visualize yourself what happens when pressure is put on the middle of the ski:

http://www.voelkl.com/skis/technology/o ... amber.html

http://www.voelkl.com/skis/technology/o ... ocker.html

[SHIF]

Correct me if I'm wrong but if you mold a ski/snowboard with the unweighted contact points being the widest part of the side-cut; when the weight of the skier/snowboarder is applied the contact points both move inward on the ski making the end contact points inward of the widest point on the ski/snowboard?

this would only apply to skis/boards made with camber and the end contact points wouldn't move too far inward but wouldn't that be enough to make the ski/board less hooky?

Yep.

Contact point and running length are two different things. Contact point is basically useless, it doesn't mean anything. When you place a pair of skis bottom to bottom in the shop, it's the point where they contact each other. But when you decamber the skis the contact points move closer together. That's the true running length. If you make a cambered ski profile using three tangent arcs with the middle arc being the camber of the ski, that arc length is the true running length of the ski.

I think extending the sidecut radius somewhat past the running length is important, at least in the tip of the ski. Thus the widest part of the ski is off the snow a small amount (assuming firm groomed snow). Some ski designs over exaggerate this, for example the Rossi E98.

Another thing to remember is the widest part of the ski shape is actually on the tip/tail curves and somewhat beyond the effective edge or actual sidecut radius (assuming the tip/tail curves are made tangent to the sidecut radius).


Cheers,
-S

[b2therye]

Sorry goz, what I meant was when there's no weight on the ski it looks like blue line and the contact point and the widest part of the ski is the dashed line



then weight is applied shown by the red and then the contact point is the red dashed line and the widest part of the ski is still the blue dashed line

its a real crude drawing that i did quickly but i think it conveys the point

interesting that your link for kastle skis has the the tip contact point inward of the widest part of the tip but has the tail contact point outward or after the widest part of the tail

i didn't think of the widest part not being on the sidecut radius, that's definately a trap for young players, i guess instead of thinking about the widest point of the ski/snowboard you should be thinking about the endpoints of the sidecut radius.

how far inward of the sidecut radius to you start your running length?

[falls]

Pretty much all of the skis I have made I have ended the sidecut radius 1-2cm beyond where the camber arc ends or where the tip/tail rocker starts in regards to flat camber skis.
I then use a blend curve to blend the sidecut to the tip/tail shape so I also have the actual widest part even further away from the end of the sidecut's ends.
In addition to all this I think it is really important to do some detuning in the tips/tails as even if your design helps reduce hooking a detuned edge will help reduce it even more.

I have only found one pair of my skis hookey and the same for a pair I made for a friend, but once the tips got detuned a little they were great.

In a ski with a long rocker (eg. 30cm tip rocker length) I have extended the sidecut a long way into the rocker (say 10-15cm). I think as the rocker isn't too aggressive that when ypu edge the ski you can still engage this whole length of sidecut and have a pow ski that carves much better than something like as armada JJ that has a really short sidcut (therefore smaller radius). The Line EP pro is built along these lines. You can also still accommodate some tip and tail taper which is nice too for pow skiing IMO.