SKI BOOT EVOLUTION AND OUR PHILOSOPHY

In the simplest terms, skiing requires boots that support the foot, ankle and lower leg while providing feedback to the skier and allowing forces to be transmitted from the skier to the ski that would otherwise be impossible or difficult to apply.

 

Early ski boots where made from leather, then plastic-coated leather, and eventually settled on “rubbery”  injection molded plastics, which have been use almost exclusively since the early 1970’s.

 

Early Composite Boots 

There were some attempts to use fiberglass in the 1970’s, notably the Raichle Red Hot and Henke . However, the rigid nature of the materials made it impossible to build a boot using the overlap front entry design preferred by racers.

 

More Recent Attempts 

Recently, some boot makers have attempted to use composites to build competition ski boots for their sponsored World Cup skiers. The resulting boots had fantastic performance, but suffered many problems that prevented their successful use. They were prohibitively expensive and difficult to manufacture; entry and exit of the foot was nearly impossible, and; they proved to be too fragile for reliable use.

 

Other attempts to use composite materials in ski boot construction have included composite inserts which are over-molded during the traditional injection molding of thermoplastics. For example, a small shaped plate of composite material is placed in a modified ski boot mold and traditional “rubbery” materials are then injection molded over the insert to make it an integral part of the boot. The weight and stiffness advantages of the composite materials are nearly erased by the heavy, rubbery thermoplastics that fail to efficiently transmit the forces they were designed to carry.

Why Composites? 

Composites are phenomenally stiffer and stronger than thermoplastics. Designed properly, 1.5 mm of composite material can have the same strength and feel as 6 mm of conventional ski boot material with half the weight and much greater support.  The challenge in using such a stiff material is to take advantage of its super stiffness in edging forces, but still allowing for natural fore/aft ankle and leg movement. This stiffness in tension and compression versus the flexural stiffness or resistance to bending is called “in-plane stiffness.”.

 

The Effect of "In-Plane Stiffness" on Boot/Ski Performance 

With traditional materials, you cannot isolate the in-plane stiffness, so a boot with sufficient edging stiffness is either too rigid fore/aft, or compromises by making the boot sidewalls overly deflect or bulge. These deflections require the skier to make edge angle adjustment continuously as loads increase and decrease. They also lead to edge “chatter.” As the boot sidewalls deflect in response to turning loads, the ski edge angle is reduced to the point where the ski disengages with the snow, then the sudden release of the loads causes the boot to relax and returns the ski to the original edge angle, which causes the loads to build up again, deflecting the boot sidewalls, and so on, and so on.

 

The frequency and amplitude of this cyclical “chatter” are dictated by the mass of the ski boot and the in-plane stiffness of the boot sidewalls. By reducing the mass and increasing the stiffness one can increase the frequency and more importantly reduce the amplitude of the “chatter.” If one goes far enough in this direction the amplitude will always be less than the ski edge engagement with the snow and there will be no “chatter” at all.

 

The bottom line is that a properly designed composite boot will be 30% to 50% lighter, thousands of times stiffer in tension and compression with the same flexural feel as a conventional TPU ski boot.

 

If a Composite Boot is so Great, Why hasn't anyone done it before? 

The high in-plane stiffness presents a problem. In areas of the boot where there is a lot of compound curvature, the in-plane stiffness contributes to flexural stiffness and makes these areas very resistant to any deflection. Fortunately, this has little or no negative effect on performance, fit or feel. It does, however, make getting the boot on and off your foot very difficult due to the fact that one of areas of the boot with the most severe compound curvature is the instep area of the foot, precisely the area that must deflect the most to open to the boot enough to get your foot to pass through the throat of the boot. This is also a problem with all conventional thermoplastic front entry boots, but not nearly as severe.

 

The ski industry has tried to address this problem for decades with various designs. In the 70’s and 80’s rear entry boots solved this problem with a mechanical solution that allowed the back of the boot to pivot open, thus widening the throat sufficiently to allow easy entry. In the 80’s the poor performance of the rear entry boot was recognized and Lange developed a mid-entry boot with a more conventional, high performance, shell and an upper that could tilt back enough to gain easy entry. It was sufficiently successful that it displaced the rear entry boot from the market. However, the extra mechanical parts had a negative impact on performance and the market, unwilling to compromise on performance, eventually returned to a front entry design and accepted the entry problem as a necessary compromise.