While waiting for Poborski to return to Whistler in June so I could assemble and tune several pair of race boots for the 1980-81 World Cup season I spent a lot of time thinking about how I could fit the foot differently from the conventional method of supporting the ankle with foam pads inserted between the ankle and the interior boot cuff walls and squeezing the sides of the forefoot together. After discovering that the forefoot of the boot tongue was applying little or no pressure to the instep of most skiers I was trying to find a way to pad the tongue so as to close the gap between the instep of the foot and the forefoot of the shell.
There are three challenges to attempting to pad the tongue of a conventional liner in order to load the instep with the forefoot boot closure. The stiff nature of the plastic and the inability to open the seam of the overlap very much require that the throat of the boot where the cuff transitions into the forefoot be ‘generous’. By ‘generous’ I mean that the instep has to be much higher than the height of the instep of the average skier’s foot in order to facilitate entry. In addition, the point where the forefoot of the boot rolls up into the cuff has to be much farther forward than the same reference in a street shoe. But the biggest challenge is that the shape and form of the typical boot tongue bears little resemblance to the asymmetrical shape of the instep of the human foot where what I refer to as the ‘dorsal ridge’ angles inward towards the ball of the foot from the crown of the midfoot.
In what turned out to be another disastrous experiment with Dave ‘Mur’ Murray I had used 2 mm thick sheet thermofoam to fabricate a custom tongue pad that was inserted into the Lange tongue body in place of the factory foam padding. The custom tongue was laminated from a number of layers of thermofoam heated and shaped to Mur’s shin and forefoot with each layer bonded to the layer below. The final assembly was ground to shape to reflect the corresponding interior shape of the shell. The fit of the final product was perfect. But Mur said the tongues made the flex of his Langes so stiff he could barely ski.
At first I was puzzled. What happened was totally unexpected. After researching the biomechanics of the tibial talar joint (commonly referred to as the ‘ankle joint’) I found out why the tongue made Mur’s boots stiff. The ankle joint is gliding hinge, not a fixed hinge like the hinge a door swings on. The implications of a gliding hinge in the ankle are that when the ankle dorsiflexes (the shin moves towards the toes) a reference point on the tibia moves closer to a reference point on the top of the foot. When this happens the centre of force of the shin pressing against the boot cuff suddenly drops down the shin. The effect is like someone kicking your feet out from underneath you. Not good.
Once I understood what was happening I decided to try and make a tongue for Pod’s boots that had 2 components, a shin component and a forefoot component. The 2 components would have a gap between them. They would be joined together with a flexible link. This would hopefully allow the 2 components move towards each other without binding and causing the centre of force on the cuff to move downward. Now all I had to do was figure out how to make the new boot-fitting tongue.
…… to be continued.