The Numbers Game: Bindings, Part 2

[Bruno Schull]

I have two remaining questions about how all this testing works.

1) It would seem that where the arm of the Wintersteiger machine presses on the boot would make a difference. is this true? Is so, how is this controlled during the test process?

2) Does the Wintersteiger machine print out force, torque, or indicator settings? When you get the little piece of paper that shows your bindings have been tested (I don't have one in front of me) what exact numbers are reported?

Ok, thanks,

Bruno

 

[Bruno Schull]

I thought I would try to answer LegacyGT's question. I don't think it's trivial. The answer is not immediately obvious. Some analogies used here to try to explain the difference between a high-quality and a low quality binding set to the same release vale are chairs, car tires, and bikes.

How about we just use bindings?

Consider two bindings in a pure lateral toe release as tested on a machine. Both bindings are set at a release indicator value of 7. Why would these bindings feel and perform differently?

One binding is very robust and stiff. When forces are applied, only the spring in the binding moves. The release values recorded by the machine therefore reflect only the movement of the spring. This binding will release at 7, but it will transfer forces precisely between the skier and the ski.

The other binding is made of soft flexible parts like cheap plastic, stamped metal, and, for sake of argument, jelly-like elastomer or rubber. When forces are applied all these parts as well as the spring moves. The release value recorded by the machine therefore reflects the combined movement of all the parts and the spring. The binding will release when all the elastic tension has been taken up from the parts, and the spring reaches the point where it releases. This binding will also release at 7, but it will not transfer forces precisely between the skier and the ski. This same would be true for heel release. It is clear that the flex and movement of this binding would effect how bindings feels.

Of course there are other things to consider (Boot compatibility, ease of entry, elastic travel, durability) but just in terms of why two bindings, one high quality and one low quality, both set to the same release value, would feel and perform very differently, I think this example helps.

Or at least it helps me.

All the best.

 

[Tony S]

OMG this thread is intense. I will go back and read the second half after another beer and dinner. I can't imagine, though, that any of the many remaining unread posts will out-do @cantunamunch 's reference to "second empire" vs. "circus duty" chairs in the now-locked ancestor thread.

 

[parkrat]

Well, "DIN" is skier shorthand for

ISO 9462:2014, "Alpine ski-bindings -- Requirements and test methods"
ISO 8061:2015, "Alpine ski-bindings — Selection of release torque values"
ISO 9465, "Alpine ski-bindings — Lateral release under impact loading — Test method"

which are standards.

So I am still confused about the point Phil is making. Is it that the torque level is specified but the value on the scale in the window is not?

ISO 8061 sets maximum torque release values as a continuous function of weight with adjustments for skier type and age. ASTM F-939 provides a discrete table which approximates the continuous functions in the ISO standard by mapping weight classes to skier codes and torque values. The specified torque values and lever arm, as determined by boot sole length, determine at what force the binding must release.

 

[parkrat]

They are methods how to test bindings and specifications...NOT the values that you get in the window.

ISO 11088:2018 Annex B does in fact provide a normative chart for the Z-mark(indicator position) in the window.

 

[parkrat]

Then where DO the values in the window come from? And why are so similar across brands?

After looking at the ISO 11088:2018 standard, there is in fact a normative table of indicator settings. From looking at three or four tech manuals I could find online, the manufacturers matched the ISO table exactly. The question isn't why they are so similar, but why do any alpine ski binding manufacturers, deviate from the ISO table at all. If you want to be precise about terminology, the indicator mark on the binding is referred to as a Z-mark instead of a DIN in the ISO standard.

 

[François Pugh]

ISO 8061 sets maximum torque release values as a continuous function of weight with adjustments for skier type and age. ASTM F-939 provides a discrete table which approximates the continuous functions in the ISO standard by mapping weight classes to skier codes and torque values. The specified torque values and lever arm, as determined by boot sole length, determine at what force the binding must release.

What's the function? What is the cost to buy the standard?

 

[parkrat]

What's the function? What is the cost to buy the standard?

For the upper limit:

1. if the mass of the skier is less than 70 kg:
   Mz =0,84⋅ms +4
2. b) if the mass of the skier is equal to or greater than 70 kg:
   Mz =0,69⋅ms +15

If you're under 10 or 50 or older, go down 15%.

 

[S.H.]

What's the function? What is the cost to buy the standard?

Standard Practice for Selection of Release Torque Values for Alpine Ski Bindings

AbstractThis practice establishes procedures for the selection of release torque values for Alpine ski/boot/binding systems. The recommended release torque is chosen based on skier type, age, and other factors such as adjustments for normal, discretionary

www.astm.org

 

[oldschoolskier]

This was discussed and very well explained on Epic many years ago on how binding forces work, including their faults and benefits by Rick Howell, it vanished when the lawyers made it be taken down. It is a shame it can’t be shared again as it was a true insight into bindings.

He also shared how different bindings while set and tested at the same release level, held differently and explained why some bindings over others need to be set higher (in some cases lots) to achieve the same hold (won’t mention names as it RH’s work) by preventing pre-release, it matches the practical knowledge for those that set their own bindings through experience.

For that Level 1 and 2 skiers, the DIN chart is a very good setting as it offers a decent balance release/retention, for those stepping beyond Level 3 and up (if you have to ask what “up” means you are still a 2) it is a good starting point and these few adjust up and down from there to achieve the desired balance as pre-release can be more dangerous in certain conditions than no release. Remember those that step beyond the settings take on full responsibility should it not work as expected and pay the ultimate price for it.

In safety issues like this if you have to ask, don’t!, leave it to the pro’s.

 

[fatbob]

In safety issues like this if you have to ask, don’t!, leave it to the pro’s.

Obviously as a contrarian I'll argue the opposite. If you have to ask you should have access to the information and enough guidance to make your own informed decisions. After all the "pros" aren't skiing with you, noting your style of skiing or experiencing the nature and feel of releases in practice.

And there are some seriously dangerous practices out there from pros. When in Whistler once my brother dropped his skis in for a service - basic grind and wax. Without drawing it to his attention because they had no data on the service ticket (guess the counter should have asked) they wound his DIN down to the bottom of the range (I assume for liability reasons????). Next morning we set out and he had a couple of pre releases on a mild blue run. If it had been a powder day and we'd gone straight up to the peak the result could have been far worse. Needless to say as we adjusted them back up at a workbench some "helpful" mountain host couldn't resist sticking his nose in to suggest we shouldn't be doing it. He got some anglo-saxon dialogue for his education as he bragged about good skiers being smooth enough to ski on a DIN of 1.

 

[François Pugh]

I'm with @fatbob . There are folks who would be safer doing what they are doing with much higher than the chart recommended settings who have (no clue) very little knowledge about binding settings. Of course they might be better off not doing stupid er... stuff or reckless stuff until they have more experience, but that doesn't change the fact that they do it nevertheless. Whether or not they should be doing it is a different question.

 

[parkrat]

I'm with @fatbob . There are folks who would be safer doing what they are doing with much higher than the chart recommended settings who have (no clue) very little knowledge about binding settings. Of course they might be better off not doing stupid er... stuff or reckless stuff until they have more experience, but that doesn't change the fact that they do it nevertheless. Whether or not they should be doing it is a different question.

I mostly disagree. A lot of prerelease issues aren't due to a low indicator setting. The AFD or toe height is improperly adjusted, the forward pressure is improperly adjusted, or the boot sole is worn out or covered in snow and not making a good connection to the binding. If a binding fails a torque test, it's time to trash it and buy a new binding. When you think about the starting point of the ISO standards, it's trying to estimate the moments required to fracture your tib-fib. This isn't going to change no matter how good of a skier you think you are or how gnarly the terrain is you ski.

 

[parkrat]

Obviously as a contrarian I'll argue the opposite. If you have to ask you should have access to the information and enough guidance to make your own informed decisions. After all the "pros" aren't skiing with you, noting your style of skiing or experiencing the nature and feel of releases in practice.

Style of skiing is already accounted for by selecting skier type and otherwise over-emphasized. The starting point is tib-fib strength. If you want a more accurate estimate of tib-fib strength than what ISO came up with, you would need a radiologist to do a bone density test. In absolute no-fall terrain, you might prioritize being able to self-arrest over broken bones and decide to go way above what ISO recommends. Just go into the tradeoff with your eyes wide open when you've effectively done this with your ski boots in a crash.

 

[fatbob]

Don't assume I'm arguing to crank up ( although if everyone obeyed DIN charts there would be very little actual need for bondings with DIN of 15,16,18 etc that are so lauded). I actually crank down relative to my weight and height because I'd far rather release easily than get my knee torqued badly in a crash. But I do like to know how much I've got to play with at my intended degree of aggression for the day. And yes I know how to set FP for all my bindings. Because ultimately the person responsible for my safety is me, not an unknown unseen shop rat.

 

[parkrat]

Don't assume I'm arguing to crank up ( although if everyone obeyed DIN charts there would be very little actual need for bondings with DIN of 15,16,18 etc that are so lauded).

I would argue there is close to zero actual need for a 18 recreational ski binding. Aksel Svindal would race 12 bindings for some events on the World Cup and he's 6'2.

 

[S.H.]

Aksel Svindal would race 12 bindings for some events on the World Cup

I am skeptical

 

[parkrat]

I am skeptical

Believe or don't. If you look at some of the high res photos of him holding up his skis after a race some of them clearly say 12 on the bindings.

 

[François Pugh]

I do not doubt the accuracy of their testing or statistics on femur strength, nor am I unaware of the many bad reasons for increasing the release setting instead of finding the problem. I'm just saying that in some rare cases, if you multiply the low chance of an otherwise survivable release at a chart level of 3 by the the high chance that a fall caused by that release will kill you at that speed in that place, a higher than 3 setting might be the better choice (given you wont be dissuaded from dangerous skiing).

 

[S.H.]

Believe or don't. If you look at some of the high res photos of him holding up his skis after a race some of them clearly say 12 on the bindings.

show me a photo of him with a ski he actually skied on (not handed to him by a rep in the finish or in a podium glamor shot) with a 12 on the bindings and I'll believe you, but ... WC athletes are rarely photographed holding up their race skis; they're usually photographed with a consumer ski that vaguely approximates a race ski for marketing purposes. Usually a completely different ski, binding, plate, etc.