Ski Builders Forum

Hi,

I am new to ski design! I was thrilled when I saw a post about homemade skis in the Make blog.
I am an engineer who loves all things outdoors and snowboarding and skiing are some of my favorites. I read through the section on ski design and it is clear that some of the performance qualities of skis are affected by their basic geometry, but I am not not clear on how does torsional and longitudinal stiffness affect the behavior of either skis or snowboards. The reason I ask is that I have been studying composites for a while and by controlling the directions of the fibers in the composite one can tailor the stiffness to a certain extent.

-Rui

Anyway by tailoring a composite I believe that it would be possible to arrive at a design that has the "right" torsional vs. longitudinal stiffness, if there is such a thing.

ps: My skiing and snowboarding experience is very much limited to New England where most of my skiing and boarding is on groomed (icy) slopes. I've ventured a couple of times (quite a few years back) to Tuckermans Ravine but that's the extent of my back country skiing.

Simply put, torsional flex is evil. It twists the ski under pressure so that the skier has less control, making the basic turn much harder and requiring more effort.

The flex along the length of the ski is more of personal preferance, and is also dependant upon conditions. It doesn't really matter. Im sure someone can explain this better.

Hi Rui,

Welcome to our forum and thanks for visiting SB.com -- we all hope you find it useful and fun.

The subject of stiffness -- both longitudinal and torsional -- is complicated, and for the most part like FREESKIER_FIVE-0 has indicated, is based on personal preference, for example the longitudinal flex. I would add that the torsional flex be minimized to enhance things like edge hold and the ability to 'steer' the ski. But at the same time, there's lack of data out there to suggest design rules, for instance, how much stiffness? One would also have to factor in the user, the conditions, and other variables, too.

We've built skis with a wide variety of flex patterns and I personally don't think there's one ultimate value. It depends on the use, conditions, etc. But there are basic design rules, for example, a stiffer ski for the hardpack and a softer ski for the powder. My suggestion for those who start out building skis, identify a commerical ski that you like, then try to mimic it. Granted you can't mirror it exactly, you can do a lot by guessing the core dimensions and tracing the sidecut. The core dimensions has a huge impact, but so does the glass layer; however, we don't play too much with that and stick to the usual 22 oz triax. In terms of weight, we've found that the core material (i.e., wood species) also makes a big difference too when all the other layers are kept constant.

Say, since you're an expert on composites, would you mind sharing your knowledge to the community? (this also applies to others out there with the same expertise.) This is such an interesting subject. Maybe we can create a question and answer thread related to composites.

Keep us posted on your progress! Best of luck and have fun!