Originally Posted by
3alarmer
700 c is more easily interchangeable with a stock tubular rim.
Otherwise, I think you're right...27's work fine if you put alloy
rims and good tires on them. Maybe even preferable in some
applications.
As people have accepted the idea that more speeds = better,
the rear cluster has grown from five to ten and counting.
I think I saw the first six speed rear clusters about late 70's,
but I'm told some people had them earlier. All those cogs gotta
go somewhere, thus wider spacings.
I think advances in derailleur design and the wider ranges made possible had something to do with it, too. Late 70s, early 80s seems right IME. Haven't a clue about any sizes after that.
As for the former point of rim size, as non-UK European makers became more known in the late 60s, so their preferred metric size became more common.