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Has anyone ever written a definitive story, not theoretical or speculative, about why the bike industry embraced sloping top tubes on road bikes? There are have been hundreds published that deconstruct pros & cons, but I don't recall one that authoritatively reported the history.
My hypothesis: The dominant reason is that manufacturing fewer sizes while arguably fitting everyone as well makes huge economic sense. And as a second lever, it makes sense to outfit pros, who already want small frames for performance reasons. Everything else is relatively minor
I will be honest. I have always held the opinion that road bikes with flat or nearly horizontal top tubes look better. I suspect many younger people, who have been around bikes with sloping top tubes their whole life, feel differently.
One (more) reason I love the gravel/bikepacking phenomena—frame bags. I think they have the potential to shift the overall road-bike aesthetic back toward horizontal. Possibly wishful delusion.
Another unproven hypothesis: I think this top-tube issue has driven interest in the handbuilt brands and NAHBS bike porn, because the best of these bikes look modern but still invoke a classic style that many big bike companies have left behind.
I'll wrap up this thread with one more unproven hypothesis: For 90% of road bike riders, the most important metric is joy. The objective of a bicycle is to inspire love, to fill a rider with beauty. I think the average $400 fixie captures this better than most $1500 road bikes.
