connyro wrote: ↑Mon Jan 02, 2023 1:06 pm
Let's try this: since you are the only user in the history of this forum to bring up the term "heel control" (do a search if you don't believe me) , maybe you could explain exactly what that telemark sking term means?
OK. Let me give this a “noodle” for a few hours. I suspect that whatever I offer will be pretty much the same that others have already provided on the control aspects of the cable (I felt many of those comments to be quite correct and well thought out).[/i]
I’ve been invited to comment on what I mean by heel control in the context of telemark skiing. There are two parts to this “heel control” which is what I believe cables on 3 pin bindings are bringing to skiing and “telemark skiing”, which is style of skiing that can be practiced by people wearing 3-pin bindings and boot systems.
What follows is restricted to what I’ve described above. It does not have anything to do with other equipment variations in bindings or boots.
I would like to preface my comments by saying that any reference to principles or laws of physics isn’t arrogance. On the contrary, it is my humble and complete acceptance of the superb work of others. So here goes…
This is a typical three pin binding and cable.
My crudely drawn red line is roughly the point where the rat trap locks down the duckbill. This is the furthest forward pivot point around which the can boot rotate around the longitudinal axis of the ski. Why? Because the rat trap (which is the exact term used by the inventor) and three pins bind the boot to the ski at this point.
The crudely drawn green line shows the rotational axis of the cable system. Most, but not all, cables use springs to maintain cable tension. For reasons I have already explained using the laws of motion, this arrangement does not apply any force to the ski. It’s purpose is to act as a control mechanism on the movement of the boot.
How does it do that and why does it matter to telemark skiing?
Before getting to that, we need to consider the human foot…
The human foot evolved from a climbing/grasping appendage to one suitable for walking. It retained a lot of flexibility but it’s musculature adapted to walking. So the phalanges shrunk and lost strength and the metatarsals gained considerable strength. This had a profound affect on the way the human foot functioned (i.e. transmitted force).
The main force bearing and force transmitting elements of the human foot are the ball of the foot (the point that lies between the phalanges and metatarsals) and the heel. Of these, the the ball of the foot is the forward most force transmitting element.
The phalanges (toes) can transmit force but they’re not all that good at it. Their primary function is balance control.
This is why a person can retain an ability to walk (transmit force to the ground) without toes, but lacks the ability to do so smoothly.
Big deal… So what?
Let’s look a three pin boot (not necessarily the one any of us would use for telemarking, but the angle of the photo is useful)
The forward most pivot point of a 3 pin binding is where the rat trap holds the duckbill. The flex of the sole of a boot has some give and flex, but the pivot point is still well forward. This is why boot soles show fatigue failure at that point.
This pivot point is not ideal because it is well forward of the ball of the foot. It is also well forward of the phalanges, which we know aren’t designed to transmit force (they control balance).
Cables shift the pivot point of the boot backwards, closer to the ball of the foot. They do this by controlling the centre of pressure of the boot relative to the ski by creating unequal forces on the sole of the boot…
The rat trap holds the toe. The point of greatest deflection of the boot is at the toe. The cable’s pivot point is roughly in line with the ball of the foot. Tension in the cables move the boot’s centre of pressure forward to somewhere between the rat trap and the cable pivot point.
This slight shift in pressure point helps the foot to transmit force more effectively onto to ski (through the binding). The force isn’t greater (force is still a function of skier mass and loading (“stomp”), but it’s application is now through the ball of the foot instead of the phalanges (which contribute to balance way more than the transmission of force).
So what about the heel? In an ideal world, the foot wouldn’t twist while skiing. But it does. So does the boot… especially in a 3 pin boot which NEEDS a flexible sole in order to “kick”. This flexibility is a problem. It is mitigated but not entirely eliminated by cables, which act as “stays” used to limit the lateral flex of a sailboat mast.
Unfortunately, their placement isn’t ideal. This is because the only practical place to attach them is to the trailing edge of the binding. They still play a role in heel control through resistance.
We all know that telemarking requires heel lift because there is only so much flexibility in the calves and Achilles’ tendon to accommodate how far we sometimes need to bend the ankle. Bending one’s knees to get weight over the front of the ski for balance and control puts our lower leg at an acute angle. The heel must lift to accommodate this in order to execute a telemark turn.
Even though the cable angles are not ideally placed for lateral control, they are designed to resist unequal side loading. This is why the back of cable straps aren’t simply wire… there is either a small clip or channel that helps centre the cable at the back of the boot. Again, it’s an aid, not a perfect solution.
This is what happens when a binding made for one particular purpose (classic XC skiing) is modified for another purpose altogether (telemarking).
Anyhoo… those are my thoughts on the matter. What I’ve offered in terms of the cable NOT transmitting force to the ski are supported by the laws of motion. What I’ve offered in terms of the cable using tension to change the manner in which the boot and foot apply pressure to the ski don’t (as far as I can tell) violate any of these laws.
Lots of words, lot of pictures. Freely given. How readers wish to apply it is entirely up to them.