[Editor’s Note: There’s still a lot of confusion about bindings, and this 201 article is intended to give a general background on how tech and alpine bindings work. Much of this article is taken from Marshal Olson’s review of the Dynafit Beast 16, and we always intended to give this information its own dedicated space. So now, let’s talk about elastic travel, release values, and more.]
A Little Background on Elastic Travel and Release Value
The elastic travel of a binding is the single most important aspect of a ski binding’s ability to retain or release a skier from the ski.
Elastic travel is the amount of distance a binding can move before the boot clears (i.e., “releases from”) a binding. So, for example, if a binding has a 38mm elastic travel value, it can move 37mm and still retain the boot. In a 20mm travel binding, you can only move 19mm before your boot will release from the binding.
The weight of the binding spring will control how much work it takes to displace the binding a given distance. For example, if you have a 200 pounds-per-inch spring, it would require 200 pounds of force to compress the spring 1 inch, or 25.4mm.
You can then further tune the binding’s functionality by adjusting the “Release Value” of the binding—i.e. adjusting your binding up from a setting of, say, 8 to 10.
(Note: “Release value” is often mistakenly conflated with “DIN setting.” A DIN setting of “8” is a release value, but not all bindings are “DIN”—Deutsches Institut für Normung—certified.)
The release value of a binding is a measurement of the amount of “spring preload”—the amount of force required to move the binding initially.
Adjusting the spring preload does not affect how firm a spring is through its travel. The spring constant (lets say 200 pounds per inch) is exactly that—a constant for a spring.
So adding preload—e.g., cranking your bindings up from 8 to 12—simply means that the spring requires a higher force to initially compress it. It does not mean that the spring itself just got 50% stiffer.
In a binding with low elasticity, one must run a higher release value to compensate for the short release action of the binding to prevent unwanted release. By running a high release value on a low-elasticity binding, you are simply preventing the binding from entering its motion as naturally.
Doing this will certainly help to keep you in the binding, but it also introduces a higher likelihood of injury. In other words, cranking up the release value on a low-elasticity binding is a pretty sketchy fix.
A highly elastic binding allows a skier to use the binding at a lower release value, since they are relying on the travel (i.e., elasticity) in the binding to prevent unwanted release.
There is then less need to jack up the preload tension, because more elastic travel can occur, increasing the skier’s ability to recover from an awkward situation before (pre-)releasing. This promotes controlled support for recovery through the range of motion of the binding’s elastic travel, but also promotes a smooth release that is unimpeded by an overly firm initial resistance.
The Ideal Binding Trifecta
In a perfect world, then, one would ski a relatively heavily sprung binding with a minimal release value setting, with maximum elastic travel. This enhances the binding’s ability not only to release the skier from its hold, but also to retain a skier if recovery is possible.
Tech Toe Pieces vs. Alpine Toe Pieces
Traditional tech bindings such as the Dynafit Radical or Dynafit Vertical function very differently than alpine race-heritage bindings, and this difference is apparent on-snow.
Most tech bindings utilize a rigid connection between the toe piece of the binding and the boot tip.
Since the toe piece only has a few millimeters of elasticity (it doesn’t house a release spring), it can only tolerate a few millimeters of travel before release occurs. And since this inelastic connection between the boot and binding is also a metal-on-metal connection, tech binding toe pieces tend to transmit a massive amount of feedback to the skier.
(A few new bindings, which we’ll be reviewing soon — the Dynafit Radical FT 2.0, for example — feature some elastic travel in their toe pieces, but this is still relatively uncommon in the world of tech bindings.)
The toe of a typical tech binding is analogous to riding a fully rigid mountain bike frame: there is no elastic travel to absorb feedback, it offers no controlled support, it doesn’t smooth the ride.
An alpine race-heritage binding has a lateral spring in its toe that controls the motion of the boot relative to the binding/ski, with the boot gliding across an anti-friction device (AFD). In this way the toe of an alpine binding is analogous to a mountain bike with a front shock. The binding offers a much smoother ride without sacrificing any control over the shovel of the ski.
To combat the negligible lateral elastic value in a typical tech binding, many people opt to ski with the toe locked out, or the heel release value cranked far higher than they would on an alpine binding. Either practice artificially inhibits the binding from releasing per the manufacturer’s intentions.
Tech Heel Pieces vs. Alpine Heel Pieces
An alpine binding’s heel piece exerts both forward pressure and downward pressure into the heel of the boot. All alpine bindings have vector forces in both forward and downward directions, even if they are not independently adjustable (e.g. Rossi FKS).
The downward pressure in an alpine binding controls the release of the boot from the binding in a forward fall. This downward pressure prevents either upward or downward free play of the boot relative to the binding and ski by constantly pressing the boot tightly into the binding and brake assembly.
The forward pressure in an alpine binding manages the pressure of your boot into the toe piece of the binding and allows the heel piece to clear out of the way when you have a twisting fall. It also maintains a controlled connection between the boot, binding, and tail of the ski when the ski becomes deeply flexed.
These two forces combine to remove lateral and horizontal free play in the boot and binding system by keeping them under tension—not to mention the obvious safety release functionality.
To use the mountain bike analogy again: an alpine heel piece is the equivalent of adding rear suspension to your bike.
A tech binding only has spring resistance against upward boot motion. In order for the binding to release vertically, you have to overcome the retention spring by opening the two pins enough for the fitting on the heel of the boot to clear them and release. There is not any downward tension or forward tension present in a tech binding at the heel piece.
There is a 5.5mm gap between the heel fitting of the boot and the binding itself. When downward pressure is applied to the heel of the boot, the pins simply slide deeper into the heel fitting and close the gap between the boot and the binding. This free play prevents a skier from accessing the the tail of the ski, and creates a vague and disconnected sensation compared to how an alpine binding feels and behaves.
To compound this issue, the part fit between the pins of the binding and the tech fitting of the boot are imperfect. Since these parts are not held under spring tension, the pins and heel fittings can freely move relative to one another. This creates a further disconnect between skier and ski relative to a conventional alpine binding. On the workbench, you can twist the heel of the boot with the ski held flat and see the boot heel and pins moving relative to one another.
To finish the mountain bike analogy: a traditional tech binding effectively functions like a fully rigid mountain bike with a flat rear tire squirming all over the place. Conversely, an alpine binding functions like a finely tuned, full-suspension trail slayer: smooth, controlled motion on both ends.
NEXT PAGE: So What Does This All Mean On-Snow?