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舊 2012-02-05, 13:39   #1
Mike
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Flatness of ski base

Flatness of ski base - how "flat" is enough?

You buy a pair of new skis, you perform a "true bar" test and found out the base of your base is not as flat as it should be - either slightly convexed or concaved, why?
Since the advent of wider shovels and cap construction, skis have more frequently arrived in shops with slightly concave bases (less occasionally, convex), especially near tips and tails. This is due to production, design and material challenges, such as: the inherent thinness of tips and tails; molded topsheet ridges, tubes and other design features; diverse expansion/contraction rates of various ski materials; and the way the ski‘cures’ between the time it leaves the factory and arrives in your local shop.
It is unlikely you will get the ski completely flat even after removing excessive material, and the consensus of top tuners is you don't need to. Try for at least 3/8" (9mm) of base flatness in from the edges and be sure to bevel the edges according skiing type and you will be fine.

How do fix the flatness issue?
Convexity, although not so commonly encountered, can usually be completely removed by hand or stone-grinding.
Concavity, on the other hand, sometimes cannot be completely removed without also removing unacceptably large amounts of base and steel edge material, especially when it's 1mm deep or more.

Greg Guras (owner of A Racers Edge in Breckenridge) addresses this issue by aiming to get bases flat across 2/3rd's of the ski width. On a 3" wide ski, for example, this would mean getting the base flat 1" in from each edge.
Jim Deines (owner of Precision Ski in Frisco) and Leif Voeltz (owner of The Fifth Season in Mt. Shasta) try to get bases flat at least ½” to ¾” in along each outside edge. If the ski still exhibits any unwanted edge grab after that, a very small additional amount of base edge bevel (1/2 degree or so) can judiciously be imparted near tips and tails.
Mike de Santis (Summit Ski & Snowboard in Framingham, Massachusetts, and former World Cup race service technician for Hillary Lindh & Volkl) deals with concavity by first belt-sanding bases to slightly remove high steel edges, then stone-grinding with sufficient pressure to counterflex concave base areas until a uniform structure appear across the full width of the ski. While the ski may still remain slightly concave afterwards when un-weighted, racers find it feels and performs like a flat ski once they put the skis on.
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舊 2012-02-05, 13:56   #2
Mike
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How does mon-flatness affect your skiing?
Your ski bases are most likely to be concave more than convex.
Concave bases will result in your skis getting stuck going straight down the hill, which will make it harder to slalom your feet back and forth.
Convex bases will wiggle all around, making it hard to control.


It appears that Atomics have more complaints about their base being concave more than others. Might be it is a flaw in their manufacturing process.
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