Please know that this project measures the resistance of the binding toe wings to opening, or what you could call the toe closure “strength.” It is tempting to call this the “spring strength” in lay terms, but that’s utterly wrong terminology so I’ll attempt to refrain. To get more specific, what is often called spring “strength” or “stiffness” is technically called “spring rate.” What I’m measuring is the force, in newtons, it takes to overcome the spring rate and open the binding.
In theory, the variations of binding opening resistance visible in my test results are from a combination factors, everything from the geometry of the binding wings to yes, the spring rate. For example, all tech binding toe springs have 3 “active coils,” but the wire diameter, length and overall spring diameter changes between brands and models. In the case of our binding with the most opening resistance (Plum Yak), the springs are clearly longer than others, thus allowing room for thicker wire.
The test involves beginning with the toe unit in the closed position, with a spacer (wood block shown in photos) to hold it in the same position as if clamped to a boot. The toe is then pulled open to the point just before the jaws spring open “over center” (as if you were opening the binding to step in or out). I also set my testing machine to fully open the jaws and the results were similar, though more variable due to the difficulty of preventing an extra jerk during the pulling open process. So again, the jaws are pulled open to just the point before they “trigger” open. We control this “pull distance” with a steel cable limiting strap, adjusted with a turnbuckle.
Our test machine uses a 2/1 pulley system, hence the sampling values in the chart are about 1/2 actual pull force (friction, acceleration of the pull and instrument tolerance causes variation). I included a set of spreadsheet cells with the newtons multiplied x 2 for those of you who are interesting in the actual force it took to pull the binding wings open. Quite a bit for bindings such as Yak!
Feel free to copy/paste our data but please don’t publish it, as it’s subject to revision as we refine our test methods and instrumentation. If you’ve got a spreadsheet formula you’d like me to try plugging in, please feel free to share.
Another thing this testing suggests is it’s good to store your tech bindings with the toe wings closed and the springs at their most uncompressed state, so the springs are less likely to take a “set” over months and years. According to my studies of coil spring physics, this is not as much an issue as some folks would have you believe, so don’t fret on it.
Lastly in terms of notes, you newcomers to WildSnow might wonder why the heck we’re going to the trouble to measure this? Two reasons. Most importantly, we have a theory that a certain kind of accidental binding release (pre-release!) can occur due to the tech binding toe wings opening while downhill skiing due to. Also, in our opinion you can enhance your safety in avalanche terrain by ski touring uphill with bindings that don’t require locking the toe unless you’re doing stressful maneuvers such as steep kickturns. In our field testing, bindings that rate higher in terms of opening force can in many situations indeed be toured without the toe locked, and we theorize they are less prone to pre-release.
I’m assuming the “classic” tech binding toe design will stay viable for a few more years (heck, it’s been what, 30 years now?), so we have refined our measuring system by acquiring a better instrument (digital pull force gauge). We desperately needed to figure out if 1.) Marker 10 & 13 are different from each other (they are) as well as how the vaunted Marker “6 pack” springs compare to a variety of other bindings (interesting, to say the least).
Bear in mind that consumer testing is showing that, Kingpin, ION and other high quality tech bindings appear to have adequate toe retention (with regards to accidental release due to toe wings/springs opening). But our testing reveals that larger aggressive skiers may want to pick the higher DIN version bindings simply because the toe spring strength is indeed higher, thus preventing pre-release due to the toe springs opening. For example, you can ski the Marker Kingpin 10 or 13 at a release value of 8, but the toe of the model 13 will have more holding force.
Indeed, the last sentences above might be the operative conclusion from all this work. Again, if you’re a larger aggressive skier, even if you don’t need the top highest DIN settings of the Kingpin or ION, you should consider using the higher DIN versions of these bindings simply because the toe wing closure will be more resistant to opening up and causing accidental release. And if you want a massive amount of force, Plum Yak is there for you (though I think it’s probably overkill for most people).
First surprise here was how much force it takes to pull open the Plum Yak. My system uses a muscle operated lever with 2/1 mechanical advantage to actuate the pull test, and believe me you could easily feel how much more the Yak resisted opening! I’m pretty sure this is a good thing, but with more than twice the closure pressure as most other tech bindings, one wonders about possible wear — and man, don’t get your finger in there when the Yak chomps down on your boot fittings!
Another surprise was the Marker Kingpin 10, with six springs, measuring as low as it did.
I measured each binding 5 times, threw out the lowest and highest numbers, then averaged the three remaining result numbers in the spreadsheet. The three numbers I used to calculate the average are displayed. Since this is intended to be a comparison I did not measure multiple toes from the same model. I did experiment with this and the measurements do vary a bit, and thus could be a tie breaker, but in my opinion the bindings are different enough not to need excessive attention to averaging multiple tests. Perhaps during summer we’ll triple the sampling.
Regarding variations of spring rate in same model binding, what that should tell you is, yes, if you want to run your bindings as “safety release” bindings, you need to test the release on a shop machine as variations in the toe opening resistance (as well as variations in the actual release machinery springs) will cause variation in the actual “DIN” settings. This is a known issue — even the DIN/ISO standards allow what I feel are rather extreme variations in release values compared to the numbers printed on the bindings.
Apologies if any of my math is off or spreadsheet messed up, corrections appreciated. Please bear in mind I am not an engineer and this is a totally amature endevor with quite a bit of opinion involved in how I set things up for testing and interpreted the results.
Thanks goes to Cripple Creek Backcountry here near WildSnow HQ, they supplied some of the bindings for testing.
This data is subject to revision as we improve our test methods. Apologies to engineers out there for our bastardization of terms such as “force” and “strength.” We do study up on this stuff but we write in lay terminology using terms of art. For specifics about the physics of “force,” check out http://www.physicsclassroom.com/class/newtlaws/Lesson-2/The-Meaning-of-Force