Originally Posted by gobucks
Given the same model ski, do you all think a longer ski would be easier, harder, or about the same to flex? My common sense tells me a longer ski, would be easier to flex. For example, it seems easier to bend a lead pencil that is full length, compared to trying to bend one that is half size. ...
Given the concern behind your question, overall flex is probably not the most relevant variable to be thinking about. Say you are considering a 170 vs a 190 in the same model. Eliminating the turned up tip and tail regions, what you really should be considering is if the center (say) 150 cm of the 170 ski is more or less stiff than the center 150 cm of the 190 ski.
Even if the mfgrs don't increase the overall stiffness as suggested in a previous post, if the skis are constructed the same, the stiffness of the two center regions will be the same. So, at best you won't buy anything by going longer. However, the situation is worse than this hypothetical break-even case.
The longer ski (of the same construction) will distribute your weight over more snow. Spreading the upward force from the snow out will mean that the center of the longer ski will actually have even less upward force on it than the center of the shorter ski, so the center of the longer ski will actually have a larger radius of curvature (as viewed from the side) than the shorter ski. This will make it more difficult to turn, not less.
Another increase in turning difficulty comes from the mfgrs usually beefing up the construction of longer skis for the reasons given in the previous post.
Another factor in increasing the difficulty of turning longer skis is that the "swing-weight" (aka, polar moment of inertia) of a ski goes up at least as fast as the square of the length, so the longer ski will be much more difficult to turn by pivoting, even if the tip and tail are completely off the snow (ie, on top of a mogul - not carving).
Probably, the final factor in increasing the difficulty of turning longer skis is that if you are trying to pivot them with the tip and tail in contact with the snow, even a small sideways drag a long way out from the center of the ski will be very hard to overcome, whereas the same force dragging over the snow closer to your foot will be easier to overcome. In addition, to pivot the skis by say 30 degrees, the tip and tail of the longer ski will be sweeping over much more snow (longer arcs) compared to the shorter skis.
All these factors (and probably more that I haven't thought of) are what make shorter skis always easier to turn than longer skis of the same construction.
Tom / PM