Hello Jan,
"It's amazing that constructeurs like Rene Herse persisted so long with the Cyclo, which shifted quite well, but was a terrible pain to set up - especially if you run the cables in the open, rather than in housing with tension adjusters, as was the British (and pre-war French) practice."
I'm asked the same thing why Rene Hers use so long Cyclo rear derailleur. I guess is for two thing 1) simplicity, when something is simple is light and reliable 2) Tension of chaine auroud 40's 50's was a strong debate, with a cyclo and the long spring, tension of chaine is constant and the freewheel roling-up is better.
i'm agree with you Nivex 5 speed is better but more heavier. To a better shift with a cyclo, the TA-Herse shifter is nice.
About triple chainring i think around 40's is very rare and 50's not common, and double chainring is usualy 50(49,48) and 30 enougth in 40's. I never see Duravia with triple chainring.
I think Rosa (1st type) was the 1st front derailleur, i see one on a 1934 catalog, probably the range is enougth to a triple and 2nd version not sure.
Regards
Jaouen BAZIN
wissous, France