Ski Builders Forum

Not having much luck with search. Can anyone point me to a thread or able to share info on how a ski flex for a given core profile will change with width? So far I've built only race-narrow (65-68 mm underfoot) carving skis for the icy east. Am about to start start some with 85 - 88 mm underfoot and am wondering if/how I'd need to change core profile to compensate. Thanks in advance.

I think you will need to change is for same flex, not sure though. http://www.junksupply.com/ski-calculator/

In the link you can simulate your build see what happens with flex.

Good luck!

Been a very long time since my new math days, but......

Not sure how to show special characters to give the formula for simple beam deflection, but the relevant point is that twice the width doubles the moment of inertia, so half the deflection, or twice as stiff. But thickness is cubed, so twice as thick increases the moment of inertia eight fold, so eight times as stiff. Right?

Scott

Thanks for replies - sounds about right. Got it figured from the ski flex .xls that's kicking around to make a decision on thickness close enough to try out.

Nice, is that the same as seen at junksupply? Else could you share?

Don't think it's the same - it's an Excel spread with active fields. PM me with email and I'll send it.

NM - Found the link on the old thread:

http://www.mediafire.com/file/w2zhdmuzk ... mmsexe.xls

thx!

So i quickly run a calculation in my calculation programm. This depends on the Layup and core so those values here are not 100% exact, but the difference is probably smaller than your production tolerances (no offense )

In general the stiffness is linear dependent of the ski width. So a 20% wider ski will be 20% stiffer.
To compensate you have to adjust the thickness. Here the stiffness of the face sheets is depending on the core thickness squared, and the stiffness from the core is depending on the thickness cubed.

for two skis to have the same flex, once with 66mm width to 86mm width, yellow poplar core, 400gsm UD glass, 400gsm biax glass on either side. ABS sidewalls and standard edges and base, you have to change the core thickness as follows:


1 => 0.81mm
2 => 1.73
3 => 2.65
4 => 3.57
5 => 4.49
6 => 5.41
7 => 6.33
8 => 7.25
9 => 8.17
10 => 9.08
11 => 10.00
12 => 10.92
13 => 11.83
14 => 12.75
15 => 13.66

hope that helps

Cheers, Reto