Off the top of my head, I seem to remember that when derailleur's were first invented, there were still die hards that raced on single speeds in the TDF. After the guys with ders starting winning, then I think most guys started using ders.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1