Originally Posted by Thylacine
Round tubes are easy to fabricate, have excellent strength to weight characteristics, and take torsional loading very well, which is what you primarily get in a bicycle frame.
I-Beams are hopeless at dealing with torsion - they're only really designed to take bending in one plane.
What perterpan is talking about in terms of a smaller 3D truss is well illustrated in the Moulton folding bikes.
I take it then, that designs with lattice braces, like the Moulton, are strongest. What about multi-shaped tubing and tubes that are drawn with patterns, like Colnago's Gilco set or Coppi's 'For Three'?
I suppose that what I'm asking is, if one were to make a good, stiff structure for a folding bike (with 406 or 451, 20" wheels), what's the best way to do it? I've seen evidence that aluminum isn't good enough to take the stresses of such a small frame
and I'm thinking that titanium is the more obvious choice. I'd like to avoid steel because folders are commuting bikes and are subject to the wet more than most other types of bikes are, and because steel weighs alot (a lightweight folding bike is a blessing because it gets taken places other bikes never go and there's usually a number of staircases along the way).
I've posted a photo of the discontinued Soma Ti-Journey below. What do you think of it, in terms of its design?
Thanks,
DG1