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Truth In Ice:Net Pressure

Part 5 in a multi-part series on skiing/snowboarding on hard snow.

As the athlete glides from arc to arc, and as the angle between the edge of the platform and snow surface changes from one turn to the next, the load expressed on the platform (pressure) will also change. This overall (net) pressure rise and fall should be fairly consistent throughout each arc, and proportional to the edge angle.

This may seem simple in theory, but may not be so in practice.

It’s common for many hard boot riders to topple, or ‘cross over’ their boards as they move from one turn to the next. Many also ride with a significant amount of static leg flexion. Both can be due to equipment choice/configuration, and/or movement philosophy. These tendencies have implications for pressure development/management, in terms of where in the arc pressure is concentrated, how it develops, and how or if it can be utilized to shape the following turn.

During simple cross-over, the athlete’s center of mass (COM) will rise up and out of one turn, move across the platform, then drop into the next turn like an inverted pendulum. The platform will see a significant fall in net pressure when the board is flat ( COM at zenith), and a corresponding rise in pressure when the board is close to it’s maximum engagement angle near the last third of the turn; when the COM reaches the end of that trajectory.

There won’t be much bend to the board at turn initiation if the COM is too close to it’s high point. The actual turn must then start later, once the board begins to ‘see’ the rider’s falling mass. The net pressure peak is then delayed until the latter part of the arc.

On hard snow, abrupt late pressure increase can exceed the holding capacity of that surface and/or the ability of the working edge to maintain it’s purchase. On very soft snow, sudden pressure rise can cause the board to ‘punch through’ or sink, adversely affecting glide.

If a rider can flatten the ‘up and over’ trajectory of their COM from one turn to the next, they can also flatten the pressure curve and increase edge hold through load distribution.

The ‘simple’ way to do this is to incorporate some range of movement in the legs.

If a rider is fully compressed or otherwise non-compliant at the bottom of the turn arc, there are few options to remove pressure from that arc other than through deformation of the surface, violent rebound of the platform, or a combination of the two. On the other hand, if the rider is more extended in the legs before they reach that area of the turn, they might then use controlled leg flexion, followed by leg extension to relieve and then redistribute pressure , thereby increasing edge hold.

Once you have a means of relieving the pressure developed during a turn, some of the pushback or rebound from the platform can be constructively recycled/repurposed from one turn to drive the board into the next turn. Rather than lofting the rider from the surface at the turn connection, that same rebound can propel the board forward in contact with the surface. Forward propulsion of the platform is then harnessed to develop the turn arc sooner, and from there one can distribute pressure more evenly over both time and area.

The key is to extend from the transition rather than before the transition at a rate that provides suitable resistance to the board, without pushing the COM too far to the inside of the developing arc. This should propel rider and board forward out of one turn and into the next, rather than upward in between turns. This suggests that a rider should not be fully extended at the turn transition, nor fully compressed near the last third of the arc.

If you find that you cannot comfortably extend into the arc of the turn without affecting edge grip, the problem is most likely with your boot geometry. Most production hard shell snowboard boots have an excess of internal ramp. A ‘sinking/sunk’ posture allows the rider to temporarily negate the effects of this ramp, while extending or lengthening the posture will concentrate the overall pressure of the turn toward the front end of the board, inducing skid, or otherwise affecting bite and stability.

A large part of riding well on marginal surfaces is working the details. If you can recognize the origin, characteristics and basic management of the pressure that develops in a turn, you can better match that pressure and it’s distribution to the rise and fall of platform edge angle. From there, you can begin to match both to the terrain and the prevailing surface.

>Next:Fore/aft pressure

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