> The thin-walled tube of circular cross section is a most efficient structural member; it can resist tension or compression, bending, torsion, or the combinati

> The thin-walled tube of circular cross section is a most efficient structural member; it can resist tension or compression, bending, torsion, or the combination of stresses that are exerted on the frame of a vehicle. Although for bending in a particular plane an I-section joist may be more efficient, if bending load can be applied in any plane, then the thin tube is to be preferred. It is for this reason that tubes are used as a strut or compression member in which failure could occur by elastic instability, or bowing. For torsion there is no better section, hence the tube is the typical main transmission shaft of an automobile. The stem of the bamboo plant is an excellent example of the properties of a hollow tube ... I notice that many current bikes have flattened, non-tubular frame components. Why? Style? New materials? I would assume, knowing little about it, that the tube shape would generally retain its advantages regardless of the material. But perhaps the new material doesn't form tubes well?