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The relationship between ski bindings and how ski boots fit them is always tricky. In the event of a fall, the ski needs to break away from the boot but the attachment between the boot and the binding needs to be strong enough, so the skis don’t come off in everyday skiing. So, how are ski boots attached to the bindings? And do your skis come off when you fall?
Ski bindings have had a long and complicated evolution. Early versions attached ski boots to the skis, but they wouldn’t break away in the event of an accident, causing numerous accidents. Through advances in technology and materials, ski bindings now perform reliably and are standardized throughout most of the world.
A very brief history of Ski Bindings
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The highly moveable AFD (Anti Friction Device) located in the toe piece allows for a smooth boot release without dirt, snow and ice effecting the release.
The injury rates of skiers in the 1930s were astronomical compared to today’s figures. A good proportion of injuries were caused by the bindings not disconnecting from the ski boots. Early bindings had a cable that wrapped around the heel of the boot and that was enough to put nearly a third of the European downhill team in the hospital.
Recreational skiers didn’t escape either and by the end of the season, statistics showed almost 10% of skiers were immobilized, with 50% sustaining lower leg fractures.
In the later 1930s Norwegian inventor, Hjalmar Hvam, spent a long time developing different bindings after he emigrated to Canada. His best development was a binding, wherein a fall the boot was released from the binding at the toe.
Initially, customers were suspicious but over time the mechanism was proven and Hvam went on to sell several thousand. Unfortunately, in 1946 larger manufacturers started to imitate his invention.
Mechanical engineer and keen skier, Mitch Cubberley, from New Jersey realized that the weak point in contemporary bindings was the connection between the soft leather boot heel and the cable going around it. The solution was to screw metal plates to the toe and heel of the ski boot to create a much firmer connection.
Various innovations over the years help to solve some of the further problems of bindings. However, even so, the number of casualties injured by poor release mechanisms was still high, even if they had reduced to some degree.
In 1961, a German rocket scientist, Robert Lusser, finally cracked the problem by completely redesigning the attachment of the binding to the boot. At the front, he used long, releasable toe-wings that gripped the boot’s upper toe and a spring-loaded releasable lever that clamped against the sole of the heel of the boot.
Many advances in boot binding technology have been adopted since these early beginnings. Friction plates, which reduce the friction of the base of the boot against the binding, and brakes, which automatically deploy when the ski comes off are now a routine part of binding manufacture.
How do Ski Bindings work?
Ski bindings have an important and difficult role to play in skiing. The connection between the ski boot and binding must be solid enough so that the skier can effectively transfer his leg movements to the skis.
However, at the same time, the bindings must be flexible enough so that if extra force is applied to the bindings, such as in a fall, the binding will release and allow the ski to go free.
If the ski doesn’t break away from the ski boot it can cause injury either by twisting the foot to cause a fracture or by the loose ski hitting the skier during the fall. So, ski bindings have a dual role, partly as a safety device but also as a mechanism to efficiently transfer the skier’s movements to the skis.
How does a Binding Release?
A typical ski binding has a toe cup at the front and a heel cup at the back. Ski boots are designed with a toe lip at the front, which slots neatly with the design of the toe cup. At the rear, the heel cup attaches to the base of the ski boot when the heel is pushed down into the binding.
Once in place, the ski boot will remain secured by the toe cup and the heel cup during normal skiing. However, if during a fall a twisting force is applied to the boot the toe cup opens, just enough to allow the ski boot to break free. The twisting force can be applied from either direction to release the boot.
In a different accident, forward force may be applied to the rear of the boot and if this is strong enough it will allow the heel of the boot to break free and release completely from the binding.
On some more technical bindings, the heel cup can also flex sideways in a similar way to the toe cup. This is actuated by a twisting force at the rear of the boot making the boot release from the binding.
Flexibility Settings for Boot Bindings
Boot bindings must transfer considerable forces from the legs to the skis. There must be a compromise between the tightness of the boot in the binding for good ski control but enough flexibility so that the boot can break away from the binding in the event of a fall.
The design of bindings enables the toe and heel to move around slightly within their housings. Often this movement is only about 5 mm, but it is enough to limit any vibration coming up through the skis, act as a shock absorber over rough terrain and prevent the boots from breaking away from the bindings accidentally.
The force required to make the toe and heel cup housings give way can be adjusted. Normally there is a screw adjustment at the front and back and a visual guide of the setting. When you hire skis from the ski shop the assistant will test each ski with your boot in place and make the correct adjustment. The calculation for the adjustment considers your weight, height, skier type (beginner through to advanced), age, and your ski boot length.
So, if you are heavier, you will need a tighter binding setting than a lighter person and similarly, if you are an advanced skier, you will be putting your skis through much stronger forces than a beginner so you will need a tighter setting, so the skis don’t inadvertently release.
The settings for ski bindings have been standardized to a German system, DIN, which stands for Deutsches Institut für Normung (German Institute for Standardization). This means the setting of ski bindings throughout the world is standardized, with a few exceptions.
The numerical setting corresponds with the tightness of the binding at the front and the rear of the boot. It’s always best to get an experienced technician to set the bindings for you.
An anti-friction device (AFD) is fitted to most skis. It is a small smooth pad located at the front of the binding near the toe cup. The AFD reduces friction if the toe cup is activated sideways in the event of a fall. It enables the toe of the boot to break away cleanly. Most AFD’s are manufactured with a low friction surface but some more advanced models use small roller bearings for easier movement.
The AFD also ensures that any sideways forces are transmitted into the toe cup and not directly down into the binding.