In the previous article, we dove headlong into the wide world of sidecuts and learned how sidecut shape (radial or progressive/quadratic) and sidecut radius affected the shape of a turn. Sidecuts are great for helping a ski rip an arc, but no ski alone will ski itself with a little input from the skier. When thinking about how a ski will perform while checking it out in a shop, how a skier's input makes a ski behave can be read in terms of the flex pattern of the ski.
Ski flex is what all those dudes standing around a ski wall and bending skis while talking about Jon's lastest kangaroo flip are testing. A ski makes a turn when the skier puts energy into the ski by bending it. The flexed ski deforms into an arc that cuts into the snow in a carve. This is all well and good except for a little thing called Hooke's Law. If you haven't lost your high school physics from brain damage yet, you'll recall that any force put on a springy object will have an equal and opposite force that wants to push that object back into its original shape. So, any ski that you bend will want to return the force you put into it and how a ski does this provides the energy to shoot the ski from one turn to the next.
The first way flex affect's how a ski skis is in straight up longitudinal flex, the amount of force it takes to bend the whole ski into an arc. Imitate your favorite ski connaisseur and pick up a ski, perhaps a 192 Volkl Race Stock GS ski put your hand on the boot center mark and push. The ski probably won't bend very much. Now try the same with something like a Salomon Pocket Rocket and watch the ski bend like a wet noodle. A stiff ski takes more energy to bend, and this means two things:
1. It takes more force to deflect the ski, so it will be more stable and predictable in high force situations (read here maching down early morning frozen baseballs of doom).
2. The ski can store more energy when flexed, and has the capability of releasing an equally huge amount of energy back into the skier.
So if you're a 230 pound linebacker who loves bashing hardpack at ludicrous speed, a set of Adamantium-strong planks will suit you better than a pair of wiggly boards that would kill it under a 150lb powder dancer. But for both of these folks, how the ski returns the energy is just as important as how the ski flexes under stress. This is where flex pattern comes in. A ski doesn't just flex up and down at the same rate all over. The tip, midsection and tail all can flex in different amounts for different reasons, and the whole ski can twist lengthwise as the skier applies an outward force against the snow while on edge.
The most often tweaked parts of a flex pattern are the tip and the tail flex, and they do different things. As a skier puts pressure forward on the ski to make a turn, the tip begins to flex. How quickly and easily this deflects is what gives a ski its "dive" into a turn. A softer tip will initiate into that turn more easily and smoothly, but will deflect equally easily when encountering chunks of mank and filling-removing chatter. At the opposite end of the turn, a reverse of events happens to the tail. As the ski arcs through the turn, more load is placed on the tail and as you start into that next turn, the tail unweights and releases this load back into the skier, making the ski spring back into the next turn. If your a racer, this gift of energy vaults your skis underneath you and around the next gate. These stiffer tails are also great for stomping landings regular or switch off of drops and tables but can be wily and unpredictable for a novice.
Penultimatly (word of the day), we come to that twisting flex I mentioned before. When a ski is on edge and carving, the skier pushes out and down on both edges of the ski. This force is only opposed on the edge of the ski that is in the snow, and as a result the unsupported ski flexes in the direction of the push, setting up a torque within the ski that will twist it along its length. This torsional flexion is something of importance to both Ice-Coast (what what...the right side of skiing represent), and Left-Coasties alike. A torsionally stiff ski will have better edge hold on steep and/or icy slopes while a twistier ski will porpoise buttery smooth in the dope white stuff.
So all this flex (admittiedly one of the more confusing aspects of ski design) affects the activity of a ski into, in the middle and out of a turn and how a ski will feel in different conditions, speeds and loads. "Sha," all you park rats must be saying, "I don't care bro, I be too steezy to care." Not so fast Tanner, the last bit flex affects is how a ski gets into the air. A ski can either give all of its flex back at once, "poppy"-like, or give it back slowly and smoothly making it feel "damp". A ski with a wood core, perhaps with the the pop-inducing steroid carbon will be quick and nimble releasing its energy all at once to launch from one edge to another or into a sweet cork 9. A damper ski, maybe a a foam core with fiberglass, aramid or kevlar woven in will be a little gentler, being more predictable and silky feeling while losing some livelyness.
So all these 3-dimensional forces and counteracting forces on a ski make it twist, bend and deform in different ways and the amount of energy it takes to do this in different places produces a set of characteristic reactions that causes a ski to act like it does on the snow, whether its a bruiser big-mountain ski, a laser-like GS ski, a super steezed jib machine or a forgiving and friendly grom setup. So use the flex, Luke. It's like a personality test for a ski.
Next Time:
"I see your Schwartz is as big as mine...": Ski Length and why it matters.
When in doubt, air it out,
Geoff
www.alpine-sports.com
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