Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Same term influences both bending and torsional stiffness, back in the day we called it moment of inertia, but a lot of people call it second moment of area.
you're misreading your data. It's hard to state without making some nit-pickable error, but you have to use more material in a square to get more stiffness. Granted, if all you have is a limited amount of space (and that space is square) and are willing to go with more weight, you can get a stiffer tube. The twisted tubes really give up the advantage of the square because their outer dimension is more like a round tube.
The other issue with square corners is the potential for cracking, which has been reported on some frames. Additionally, for thin-wall tubes, the beer can bending modes may significantly reduce stiffness.
Last edited by unterhausen; 03-16-11 at 11:56 PM.