Telemark Talk / Telemark Tips Forum

Having not had the privilege to ever ski on a cable/spring type binding, I find myself wondering how it worked. Please forgive my ignorance here but as I think about the dynamics of one of these older systems as compared to a newer system such as NNN, Xplore, Meidjo, etc, I need some help in visualizing how the older binding worked. The simple diagram below lays out a Cable/Spring system. Not all the connection points are intended to be exact here. What I'm trying to capture is relative positioning.

Diagram A is the system in a relaxed, heel-down state. B and C show two possible configurations for a heel-raised state and I don't know which one is correct. In B, the toehold is fixed to the ski preventing the toe from lifting and keeping it rigidly fixed to the same plane as the ski. All the bending occurs in the boot. In C, the toehold is free to rotate about the front edge and bending can occur in both the toe of the boot and at the toehold-to-ski-edge.

The distribution of forces and moments and, by consequence, control authority, are very different for B and C and I'm really interested in which is correct. Thanks!

This is binding dependant. In some bindings, cable is routed horizontally from toes towards mid footsole, too. Then the cable / spring system connects from about midsole to behind heel. See image below for a diagram.

In the diagram, purple is cable, and blue lines show bootsole. A blue, dashed circle show heel location, when the binding pivots. I guess you get the idea.


In the design above, the spring gets stretched, when the heel is lifted. This presses front ski down.

If purple line would connect at heel, and spring would have no elasticity, the ski would rotate even more, when heel is lifted. It would be an alpine binding practically.

Here is also a photo of my first BC ski bindings (below). These are Swedish army bindings, which are probably optimized to keep rubber boots in place Swedish army skis are Wooden planks with zero sidecut.

On the other hand, the binding in the diagram above is optimized for downhill performance. It is a 22Designs Axl binding.


In B and C, do springs actually shorten, when heel is lifted? See first image in this thread. C looks a bit like a Voile Switchback binding (photo below). In reality, there seem to be three pivot points, actually, because bootsoles bend, too. The third pivot is actually illustrated in B and C, great!

Neither B or C is quite correct. Your cable is attached way too far forward. It’s actually attached well back of the boot tip. Also the binding toe plate doesn’t move up, except with the Switchback in free pivot mode.

Here is a super simplified example of types of forces at work:

When the upper part moves, the string eventually runs out of slack. With a cable binding, there is also a spring instead of a string, and the boot bending complicates things too.

Here is Voile Switchbacks in action, free pivot then binding locked down.



So, your diagram C and B is the Switchback in free pivot uphill mode, and ski downhill mode, respectively, except the cable is attached at the back of the toe plate. BTW, I think the Switchbacks were developed after NNNBC!

Nice looking skis DG. What are they?

Those skis are the original Voile Vector BC skis. 180 cm, 121-96-110, the original design.
There’s a groovy cartoon on them. Nowadays they have the Ultravector and V6 BC fishscale skis, similar specs, but more sedate graphics.

I thought I saw "Voile" on the ski but didn't recognize the graphics. My original Vector that I bought in 2015 has the topo lines on it. I like yours better.

For as good a ski as the original Vector is, the ultra vector has a better flex and is better balanced.

Thanks gents, for those clarifications. From what @tkarhu and @DG99 have said, and the diagrams and video, it looks like there are a wide variety of configurations. For the Voile Switchback ("Yeah, I've been ready for a while actually" ) it looks to me like when the toe plate is in pivot mode, all the spring/cable is doing is keeping the boot in the binding unless you manually force your toe onto the ski. Only when you lock the toe plate down do the springs start imparting moment to the ski. Interesting. Is this primarily a way to simplify the transition from kicking to skiing? All you need is a pole!

For @tkarhu 's Swedish Army Binding, it looks like the cable both retains the boot in the binding and provides some moment. My guess is that this would be a very simple system suited to the needs of ski troops as opposed to recreation which would likely want to be useful over a wider range of conditions.

I find myself wanting to make a simplified dynamics model of these systems and run it in Matlab/Simulink. (The first thing I'd neglect is sole bending other than at the toe. Too hard to model!) I think I'd find that the more recent toe-only force systems require more control authority and display greater sensitivity to input uncertainty and perturbations than a cable-spring system. (I.e., they are harder to learn, harder to control, and have a smaller envelope.) I don't know that I'll actually do this since I'd really rather be out skiing and I do similar things at work. And it wouldn't be helpful in design or sizing since the model would be too simplified to be used for generating any kind of specification. All it would do is verify what users have already reported.

Oh, it would also let me vary the configuration and put a stake through the heart of the physics debate!

Maybe worth it after all???

But it does leave me wanting to cobble together an Xplore/Cable frankenbinding and test it out for grins. There are a bunch of used cable setups available locally in the $150 range. From all I've heard I think I'd probably really like a 75mm cable system but I've played the find-used-boots game with motorcycles and it's just not fun for me anymore.

Incidentally, my wife views this level of interest in something like this as some kind of insanity and I'm going to take a wild guess that I'm not alone, here. Then again, warm houses during the winter, automobiles, and many other modern conveniences are due to this primarily, but not exclusively, male fixation on how things work. I hope that makes me a sexist. I try to check at least one box a day.

John, a cable can aid performance in 3 ways.

1) The cable assists in breaking the bellows. This assists the skier in getting the ball of the foot flat on the ski.

2) The cable adds to longitudinal stability of the ski boot interface. This happens in two ways.
A) When the cable is under tension, it assists in keeping the
boot in the same plane as the ski. If the boot heel were to.
move out of plane with the ski, spring tension increases,
directing the boot back in plane with the ski.
B) The Rotte ST cable is very laterally rigid on it’s own. It.
has very little play side to side. The spring cartridges also.
cradle my Alaska 75 boot.
3) An active spring transfers the energy expended lifting the heel
to the front of the ski.

I do not believe you are going to see a lot of benefit #3 from a leather boot. I believe the boot will fold before you see significant benefit.

But it does leave me wanting to cobble together an Xplore/Cable frankenbinding and test it out for grins. There are a bunch of used cable setups available locally in the $150 range. From all I've heard I think I'd probably really like a 75mm cable system but I've played the find-used-boots game with motorcycles and it's just not fun for me anymore.

Yah, that was done with NNNBC in ancient times. I don’t know why it didn’t catch on, I think maybe the system couldn’t handle the stresses very well? Compared to all the powerful “active” 75 mm cable bindings.

“Active” means relatively more flex resistance and “neutral” means less resistance, free pivot no resistance.

What you are proposing is basically the same as the TTS bindings like Voile’s or the more complicated Meidjo. A claw on the toe and a cable! Meidjo is like a holy grail, free pivot touring, active downhill flex, light weight, releasable. AFAIK! Very expensive set up, I don’t have.

A lot of the same principles are at work on the NTN bindings as 75 mm cables bindings.

People used to go uphill on neutral bindings like G3 Targas or 3 pins etc., but you are fighting the flex resistance there (like a hard flexor too on Xplore) so the free pivot became desirable. G3, Rottefella, Black Diamond, 22 Designs and Voile all had them in 75 mm. Just the Axl and Switchback left.

JohnSKepler wrote: ↑

Wed Jan 25, 2023 3:29 pm

I find myself wanting to make a simplified dynamics model of these systems and run it in Matlab/Simulink. […] I don't know that I'll actually do this since I'd really rather be out skiing and I do similar things at work. […> All it would do is verify what users have already reported.
Oh, it would also let me vary the configuration and put a stake through the heart of the physics debate!
Maybe worth it after all???

@JohnSKepler If you have time at some moment, it would be great to see an updated version of the first post diagrams, with the difference that the cables would be routed through somewhere around mid sole. Already, it is nice to have a summary of the lengthy Physics Debate content in this thread. Thanks