Putting the Boot in…

Ski Boot & Ski Binding Compatibility

It’s a minefield out there – once it was all so simple! All ski boots fitted all types of bindings, end of story… simples. Admittedly ski bindings were nowhere near as sophisticated nor as safe as they are nowadays and neither was the range of manufacturers and models so varied.

Many skiers will prefer to leave the decision of ensuring all the ski kit used is compatible and maximises the safety achievable with various combinations to the experts in the retail store where you buy or rent your stuff. Ultimately though you will be responsible for your own safety so having a bit of an understanding of the products you’re about to spend hard earned plastic on is a useful thing. More importantly though is the knowledge and understanding that some combinations of boot and binding can be downright dangerous.

Alpine

If you ski only on pistes or groomed trails you’ll buy a downhill or Alpine binding and a ski boot fitted with an Alpine sole. This combo will also work really well for the skier who likes to ski off the pistes but has little inclination to hike uphill using skins on the base of the ski.

alpine-sole

The safety standard for this combination is set by DIN (Deutsche International Normung). The safety standard is focussed on the interface between the ski boot and the binding and how they react given particular stresses, twists and external forces. In other words, how the binding retains the skier on the ski or releases the skier when it all goes pear shaped beyond recovery. The level at which a binding lets the skier go from the attachment to the ski is determined by a number, known by many skiers as the DIN number but more appropriately called the Release Value. The recommended Release Value for individual skiers is arrived at by an equation that combines your age, your weight, your ski boot sole length and the type of skier you are (not what you’d like to be!). Not many skiers are aware of their own Release Value or that the ultimate responsibility for the set value is a personal one. Ask a Ski Technician to work it out with you and then remember it! The two main functions of a ski binding are to hold you securely on the ski and to release you from the ski before injury is caused. A correctly adjusted binding will also go to the brink of a total release but if it senses that pressures are reduced it will snap back into place. This is known as Binding Elasticity.

salomon-warden-can-be-used-with-AT-boots

The toe piece of a ski binding has elasticity built into rotational (sideways) movement and, in more sophisticated products, an upwards twisting movement. In combination with this elasticity the interface between the sole of the boot is integral to safety. The toe of the boot rests on top of a nylon or plastic anti friction device (AFD) which, in the case of an alpine binding, is fixed. Additional elasticity is offered in the heel unit which, when the ski is pressed into a reverse camber, will slide almost imperceptibly backwards to negate the pinching effect on the skiers boot that would otherwise occur. This is sometimes referred to as the forward pressure that the boot is subjected to when clamped between the toe and heel unit. Technically, it’s called longitudinal elasticity. An Alpine binding heel unit also has some elasticity in upwards release before it finally releases.

In general, Alpine bindings are only compatible with Alpine soled ski boots. But there are some exceptions…

Alpine Touring

Alpine Touring Norm (AT) is specifically for ski touring bindings and boot combinations. The two main differences from the Alpine binding are that the heel of the binding can be released to allow the skier to ascend on skis with skins stuck to the base of the ski and, most importantly, the AFD slides sideways when the toe of the binding releases. This is of great significance from a safety point of view. An Alpine Touring boot usually has a rubber sole with cleats or tread to enable comfortable walking and grip on all sorts of terrain.

AT-or-Touring-norm

The interface of the rubber on a static AFD would not allow the boot to slide smoothly sideways as it is way too grippy and as such does not conform to the standard DIN for Alpine bindings and boots.

sliding-AFD-on-Touring-binding

Another significant difference between the Alpine sole and the Touring sole is that the latter features a fairly significant curvature in the sole, again to allow for comfortable walking. This means that the lip of the boot that is retained in the toe of the binding is considerably higher than the flat Alpine sole and the range of adjustment of toe height on most Alpine bindings is not sufficient to accommodate an AT sole.

AT-versus-WTR-toe-height2
In general, AT norm ski boots are only compatible with AT norm bindings. Though there are exceptions…. notably an Alpine binding that has manually adjustable toe height and a sliding AFD.

salomon-guardian-MNC

AT binding norm is however, compatible with Alpine sole norm!

Doing your head in yet?

Well, there’s another permutation. Introduced a few years ago, it’s called WTR (Walk To Ride). The norm for this format of binding and boot sole is a TUV norm (Technischer Überwachungs-Verein).

Walk To Ride

For simplicity sake this can be considered an amalgamation of the two previous norms. On the binding side it features bindings with Alpine norm release with the added benefit of being able to go into ‘touring mode’. Boots that fall within this norm are a clever mix of rubber sole enabling comfortable walking but also incorporating an anti friction pad under the toe where it interfaces with the AFD of the binding. Boots in this category often have interchangeable sole types – Touring (AT) and Alpine, which is a much flatter sole. Removing and replacing just requires a screwdriver. Some AT sole units also come with inserts to accommodate a Low Tech or Pin binding.

WTR

WTR is a Salomon innovation and was originally conceived as a walk friendly sole that could be used with Alpine norm bindings, adding further walking comfort by introducing a releasable cuff into a more flexible walk mode.

Tyollia

Things have moved on quite a bit since the introduction of WTR a few years ago and more manufacturers have adopted the concept. If you’re big into backcountry adventure skiing, need the option to walk with skins on skis but want high performance skis, bindings and boots, WTR is the way to go. If you’re a travel-light-uphill-racing addict or more mountaineering orientated it’s probably fair to advise you to look at a different set-up more suited to lighter travel.

To be sure that the equipment you ski on is compatible in every way always seek expert advice from boot fitters and technicians trained to fit bindings to skis and boots to bindings.   Where safety is concerned no compromise is worth accepting.

When your brain has had a chance to recover and digest all this information we’ll take a look at Pin bindings.

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The Guide & Author

Nigel Shepherd has been a fully qualified Mountain Guide for 34 years and spends each winter exploring great places to ski both in Europe and other snowy mountains around the world… It’s not a job he’s going to give up very easily.