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Apr 23 2018

2-pin Tele Springs: Size Matters

Size matters. J Nicol checks to see if these springs measure up.

Size matters. J Nicol checks to see if they measure up.

While the effect of cable pivot location tends to dominate the sensation of a tele tech binding, the next strongest binding component of the tele sensation comes from the springs used. To some extent you can trade one for the other; meaning a stiff spring and a forward pivot are somewhat equal to a soft spring with a pivot farther back. It’s not an exact replacement, but more importantly, the further back you put the pivot the longer spring you need so it doesn’t compress too far too fast. Therein lies the limit with a real heel 2-pin tele binding — springs that limit how deep you can tele. So let’s take a closer look at the cable rods, heel throws, and springs.

Cable Rod limits

Homebrewed cable rod connection for DIY TTS.

Homebrewed cable rod connection for DIY TTS.

If you go with Voile springs and cable rods, or Kreuzspitze springs and rods, you will be able to fit any size boot but need a post to hook them on to, like Kreuzspitze or B&D. Voile’s sizing system of — long and short cable rods, plus long and short spring cartridges and long and short yokes for the heel lever, and heel levers — will fit pretty much any boot with a forward pivot (< 60mm). I did not run through the numbers for Voile like I did with OMG. If you have a small foot, and want an aggressive pivot, plan to shorten or add threads to the short cable rods and make sure the yoke is the short version. If you want lots of spring travel too (with small feet), go with Kreuzspitze. This is pretty much the same system as Voile or OMG except the springs are universally longer so you can flex further before limiting out. The difference in travel distance is only millimeters, but that translates to extra degrees of forward rotation.

The OMG system has fewer miles on it so I took the time to map out what combinations of short and long cable rods work with Voile’s standard and long springs for each boot size. As the tables below show, for a 60 mm pivot you can fit small to large boots (mondo 22 – 28, BSL: 275-310) with a small cable rod. For size 28.5 and larger, you need the large cable.

In the tables below green cells mean the specific combination of cable rod and spring for each column will fit that size boot for the pivot location of each table; red is outside the cable size range, while orange is on the edge but might work.

Cable/boot compatibility for 49mm pivot, 20mm heel post:

49mm Pivot Short Rod/Std Spg Short Rod/Long Spg Long Rod/Std Spg Long Rod/Long Spg
Cable Length 220-245mm 240-265mm 245-290mm 265-310mm
298.8 mm 30-30.5 30-30.5 30-30.5 30-30.5
286.3 mm 29.5-30 29.5-30 29.5-30 29.5-30
278.6 mm 28.5-29 28.5-29 28.5-29 28.5-29
269.9 mm 27.5-28 27.5-28 27.5-28 27.5-28
261.3 mm 26.5-27 26.5-27 26.5-27 26.5-27
253.7 mm 25.5-26 25.5-26 25.5-26 25.5-26
245.7 mm 24.5-25 24.5-25 24.5-25 24.5-25
238.1 mm 23.5-24 23.5-24 23.5-24 23.5-24
230.5 mm 22.5-23 22.5-23 22.5-23 22.5-23

Cable/boot compatibility for 61mm pivot, 20mm heel post:

61mm Pivot Short Rod/Std Spg Short Rod/Long Spg Long Rod/Std Spg Long Rod/Long Spg
Cable Length 220-245mm 240-265mm 245-290mm 265-310mm
287.2 mm 30-30.5 30-30.5 30-30.5 30-30.5
274.7 mm 29.5-30 29.5-30 29.5-30 29.5-30
267.0 mm 28.5-29 28.5-29 28.5-29 28.5-29
258.4 mm 27.5-28 27.5-28 27.5-28 27.5-28
249.8 mm 26.5-27 26.5-27 26.5-27 26.5-27
242.2 mm 25.5-26 25.5-26 25.5-26 25.5-26
234.3 mm 24.5-25 24.5-25 24.5-25 24.5-25
226.8 mm 23.5-24 23.5-24 23.5-24 23.5-24
219.2 mm 22.5-23 22.5-23 22.5-23 22.5-23

Cable/boot compatibility for 73mm pivot, 20mm heel post:

73mm Pivot Short Rod/Std Spg Short Rod/Long Spg Long Rod/Std Spg Long Rod/Long Spg
Cable Length 220-245mm 240-265mm 245-290mm 265-310mm
275.7 mm 30-30.5 30-30.5 30-30.5 30-30.5
263.2 mm 29.5-30 29.5-30 29.5-30 29.5-30
255.6 mm 28.5-29 28.5-29 28.5-29 28.5-29
247.0 mm 27.5-28 27.5-28 27.5-28 27.5-28
238.6 mm 26.5-27 26.5-27 26.5-27 26.5-27
230.9 mm 25.5-26 25.5-26 25.5-26 25.5-26
223.0 mm 24.5-25 24.5-25 24.5-25 24.5-25
215.5mm 23.5-24 23.5-24 23.5-24 23.5-24
208 mm 22.5-23 22.5-23 22.5-23 22.5-23

Cable/boot compatibility for 85mm pivot, 20mm heel post:

85mm Pivot Short Rod/Std Spg Short Rod/Long Spg Long Rod/Std Spg Long Rod/Long Spg
Cable Length 220-245mm 240-265mm 245-290mm 265-310mm
264.2 mm 30-30.5 30-30.5 30-30.5 30-30.5
251.7 mm 29.5-30 29.5-30 29.5-30 29.5-30
244.1 mm 28.5-29 28.5-29 28.5-29 28.5-29
235.6 mm 27.5-28 27.5-28 27.5-28 27.5-28
227.1 mm 26.5-27 26.5-27 26.5-27 26.5-27
219.6 mm 25.5-26 25.5-26 25.5-26 25.5-26
211.7 mm 24.5-25 24.5-25 24.5-25 24.5-25
204.3 mm 23.5-24 23.5-24 23.5-24 23.5-24
196.8 mm 22.5-23 22.5-23 22.5-23 22.5-23

The tables above only determine whether the cable/spring combo will fit the boot for a “standard” height tech toe, meaning pins 27 mm above the ski deck with a heel post 20 mm high. Notice that small boots only work for pivot positions forward of 65mm with short cable rods. If you use a higher toe (G3′s Ion) and subsequent heel post, even fewer small boots will work unless you shim the cable post from below.

Even though the OMG short cable rods have 45mm of thread on the ends (1¾”), the spring cartridges will hit the bend in the rod at around 25mm (1″) of thread depth. That’s why the short rod cable assemblies only show 25mm of adjustment range in the tables above. Nonetheless, for average sized feet, the short rod with either spring should fit fine for most pivot locations.

Springs: Size matters

In practice the factor making a TTS binding fun to ski is how far you can lift your heel before the springs limit out. In general it is easy to show that you get more range of motion with a forward pivot and/or a spring with more travel distance, which is typically a third to a quarter of the total length.

It doesn’t take long to realize springs for a 2-pin tele system need a larger compression range, particularly for stiffer springs, than are available from Voile’s springs built for 75mm bindings. This is more true for guys with boots larger than 28.5 that want a stiff spring. You can figure this out yourself by solving for the intersection of two circles using quadratic equations, or sketching it out with an accurately scaled graph and a compass.

Determining the limit of heel lift by drawing the intersection of two circles; the radius of the heel throw about the toe pins, and the radius of the stretched cable where the spring is limiting out.

Determining the limit of heel lift by drawing the intersection of two circles; the radius of the heel throw about the toe pins, and the radius of the stretched cable where the spring is limiting out.

If you take the time to calculate it you will find that for stock 75mm springs, with a travel distance of approximately 35mm, you will feel the spring begin to limit out in the range of 30° to 39° depending primarily on the pivot location. Further forward yields a 39° limit, and an aggressive pivot further back only 30°. You can add a degree of mobility for smaller feet, or subtract with larger.

Increase the spring travel distance 10mm (~⅜”) and the range improves almost 10°, from 30°–39° for an inch of compression (1″=24.5mm), to 37°–50° for 1½” (~35mm). Again, a higher range of motion before limiting out the further forward the cable pivot is and the smaller the boot, or less as the pivot moves back and boots get longer.

Estimated boot range of motion with standard and long springs.

Spring TD Std: 25mm (solid @ 35mm) Long: 35 mm (solid @ 45mm)
Pivot sz 24 (BSL:275) Sz 30 (BSL:333) sz 24 (BSL:275) Sz 30 (BSL:333)
47 mm 39.4° 38° 49.7° 48.5°
85 mm 30.9° 30° 37.7° 37°

The angles computed above are not the limit to your leg range of motion. First, there’s another 10mm of spring compression available, which should allow another 10° of rotation. Plus you can add in the flexibility of the bellows and cuff to increase leg mobility another 35°–40°. Depending on how deep you go, that may be enough. I used compression values less than the max because the spring compression forces change exponentially as you approach max compression, and non-linear when they go solid. You might experience more range of motion than my numbers indicate, but only for brief moments, like in a crash or a deep knee tele bounce.

Response from those who have tried the longer springs is they provide enough range of motion, but they’re too soft. One person I know combined the soft feel with an aggressive pivot and they like the sensation. For reference they like Switchbacks.

Compression travel distance for Voile/OMG/Kruezspitze springs

Mfg   Soft Medium Stiff
OMG / Voile voile-std-spring_5x 45mm 39mm 35mm
Kreuzspitze Kreuzspitze Switchback Backcountry_5x 48mm 42mm 37mm
G3   35 33 30

Compression travel distance for 22D Axl springs

An early prototype of an Axl based 2-pin tele binding.

An early prototype of an Axl based 2-pin tele binding.

Mfg Axl Long Axl Stiffy Axl Std
22D 65mm (2.57″) 64mm (2.53″) 50mm (1.99″)

To be more useful/acceptable to a larger number of tele skiers the entire cable system needs to be engineered from scratch, not using conveniently available cable systems developed for side-routed 75mm bindings (Voile, Targa, Cobra, etc.). One consequence of longer springs will be additional weight.

Heel Lever

voile_hardwire_lever_540x540 omg-heel-lever bomber-heel-lever
Voile – GOOD OMG – BETTER Bishop – BEST

The final component you need to pay attention to in the cable assembly is the heel throw (or lever). Most are designed to work in the heel groove of a 75mm boot. This groove is absent on NTN boots, forcing the lever to be up on the heel step. The net result is many heel levers designed for 75mm boots don’t close with a resounding snap on the heel step. It might hold and it might not. At some point it’s bound to fall off unexpectedly. And it feels sloppy so the the springs engage unevenly.

The good news is the heel lever for OMG cables works beautifully. In fact, there’s only one heel throw I’ve tested that snaps on tighter; a Bishop heel lever. The Voile black heel lever works well, but it doesn’t snap as snug as the OMG. Same for a Cobra heel lever, if you can find one. G3 Targa levers do not work well, nor do the Voile heel levers prior to 2014 (grey). It doesn’t hurt to be creative; Nviglio found a BD crampon heel lever worked well. To work properly the heel lever needs to be over center when snapped onto the heel.

Shimming

Shimming may be required for the cable block, or the toe, or the heel, depending on how much ramp angle you like. Do you like your foot level when you’re standing on your heels, or do you prefer your heel raised above the toe and if so, by how much? The answer to that question will determine how much you may need to shim underneath the bellow of the boot so it doesn’t sag when standing flat. Whether you shim above or below the cable block depends on how active you want the binding to be.

Remember, one millimeter down is like two back. If you want to increase activity, shim above the cable block. To reduce activity, shim beneath. This is another way you can fine tune the power delivered in the cable in combination with selecting a stiffer or softer spring. You can shim the toe, the cable post, and heel post up or down to achieve the final desired effect. The higher the pins on the toe, the more shimming you can expect to create. For instance with a G3 Ion toe you will need to shim the cable post at least 10mm to prevent the boot bending when standing flat, probably more depending on your ramp angle.

Conclusion

As you’ve realized, embarking on a DIY telemark binding project is not trival. However, building your own 2-pin telemark binding IS possible, and if you plan it well, the results will be satisfying, especially for the turn earners among you. For this sort of system to gain larger acceptance it is clear that the cable assembly, from the adjustability of the pivot location to the range of motion and tension allowed by the springs needs a serious overhaul. But for those who don’t mind tinkering, the future is here today.

As an example, consider what one intrepid engineer put together.

Jason Quinata’s POLR binding.

Granted, this is the same engineer that gave us Flick-Lock® adjustable ski poles, so this is not an example of amateur hour, but a pro using his passion to build a 2-pin tele trap. However, the tools exist for you to do likewise.

Related Posts
2-pin Tele Chronicles: State of the Art
2-pin Tele Chronicles: Picking your toes
2-pin Tele Chronicles: Use the Force Luke
2-pin Tele Chronicles: Cobbling the Cable
Calculate the intersection of two circles

© 2017


  • Rene-Martin

    Wow, great stuff Craig, I’ll keep tis post as a reference for sure

  • Andrew Nock

    This is awsome, but pondering it all since it first came out, I finally saw the analysis is ‘missing’ looking at the impact of the height in which the rear clamp holds the rod to the boot back. Wow. If we move it up the spring begins to start out with a steeper angle. Importantly, the change in rod length from the boot-heal-on-ski to boot-fully-raised is shortened. Since we need less change-in-length for boot movement, we can increase pre-compression when the the boot is in down position. This means more ‘immediate’ activity when the heal rises the first couple inches. This all is especially important for big feet.