Stiffness for different sizes

[motoman]

Dear forum users,
I have a question concerning stiffness for skies or snowboards.
If we use the same materials for instance for 5 different sizes of the same model of sky or snowboard we will have different flexible characteristics. 146 cm and 162 cm board will bend differently when we apply load in the middle of span (concerning case with two supports).
Does it mean that we have to play with wood or or some extra reinforcement?

Thank you in advance.

[MontuckyMadman]

Either or either.

[skidesmond]

Dear forum users,
I have a question concerning stiffness for skies or snowboards.
If we use the same materials for instance for 5 different sizes of the same model of sky or snowboard we will have different flexible characteristics. 146 cm and 162 cm board will bend differently when we apply load in the middle of span (concerning case with two supports).
Does it mean that we have to play with wood or or some extra reinforcement?

Thank you in advance.

Depends.. If you want the 146cm board to ride like the 162 then yes (or vice versa). I don't do that. But I do keep the same binding area length the same for all of my skis (360mm). I don't know if the commercial builders try to adjust the wood core to ride/ski the same for a given set of dimensions and varying ski/board lengths.

[motoman]

It seems that only way is to experiment using method of errors and trials.

[MontuckyMadman]

If u add composite u can add atiffness but at the cost of adding significant weight. Adding core thickness you get a much better stiffness to weight ratio so depends on what you want. Everyone wants lighter. But its tricky a bit of core thickness goes a tri long way.

[motoman]

Operating wood thickness seems the best option.
And still there definitely exist way to do this, since commercial producers solve this problem somehow.

[agiocochook]

Somewhere in the forum -- maybe somebody can point to it -- there's a spreadsheet based flex (deflection) calculator. It shows both amount of deflection under a particular load and the deflection profile. The way I've found it most useful is by inputting a ski with the kind of flex I'm looking for that I've already made and then playing with the profile dimensions for a ski I'm designing until I get what I'm looking for relative to the "base" ski.

I vary both the thickness profile (all three sections) and the max core thickness (I always taper to 2mm tip and tail). For the thickness profile, I usually start by adjusting each section proportionately to the difference in running lengths compared to the base ski. From there I tweak the profile to get the shape of the deflection curve where I want it. Then I play with the core thickness to adjust the amount of deflection, again relative to the base ski.

[vinman]

The shorter the ski the thinner the core needs to be. This will also depend on what weight fiberglass you are using.