Originally Posted by beyond
I've been following your work for years. Great stuff. Question:
Torsional stiffness - or really, the balance between that and longitudinal stiffness - is fairly important to how a ski actually handles. Your setup seems to measure longitudinal flex, although in your intro you mention torsional stiffness. Am I wrong about the setup, or if it's for longitudinal, do you have plans to measure torsion resistance?
I do measure torsion stiffness, but only on a few skis. The main reason I don't measure torsion for most skis is time and energy. One pair of skis take about half an hour in total (all geometry included flex, bindings on/off, plotting data etc.). I agree that torsion properties would be interesting, (and for other reasons than a lot of people think). The most torsionaly stiff skis we have tested was not the metal sandwich constructions, and the most torsionaly stiff skis scored low on general hard pack turning performance, (and so did the least torsion stiff skis). Torsion stiffness is like all other parameters of skis: too much is too much, too little is too little.
As you mention, Torsion stiffness is relevant to longitudinal stiffness, so it is all measured in the same machine at the same ski segments., numbers divided to a relative value.
When we measured the first skis in 2006, the ski market was all about fatter and fatter skis. What I discovered right away was that there is a direct link between ski width and torsional stiffness (naturally) this worked to such an extreme degree that I could sort the skis by width just by looking at the torsion stiffness data. (The first years skis varied from 70 to 140mm), the wider a ski gets the more torsionally stiff it is (compared to longitudinal stiffness). At the same time, fat skis need less torsional stiffness (because they are used in powder), that is why torsional stiffness is (probably) less important now than 20 years ago. The rockered and tapered shapes of today are even less vulnerable to variations in torsion stiffness, since the skis are already bent into the desired shape, and the distance between the extreme contact points is cut by 1/3.
Interesting subject, I might get more time to work in deep with these things in the future, time will show.. :)