It seems many new road bikes have gently curving top tubes. I'm wondering if there is a functional reason for this, or if it's just cosmetics.
I'm no engineer, but I remember being taught that a round tube was generally the most efficient structure for strength to weight. These were modified by butting because bicycling doesn't stress tubing equally - some areas need more strength than others, so they were given greater wall thickness than areas of the tubes that needed less strength.
To further put strength where it was needed, round tubes were ovalized in different ways in different areas.
How am I doing so far? (Like I say, I'm no engineer - just a curious guy who is trying to figure things out.)
So now see all these bikes with curving top tubes and wonder why?
It's particularly pronounced on mountain bikes where some top tubes resemble the profile of a boomerang or banana. Is that for standover clearance, cosmetics, or something else? It seems as if there would have to be extra material added to match the strength of a straight tube. Strength is necessary, but weight is bad.