Originally Posted by
eja_ bottecchia
I would also like to know the answer to this.
Just what prompted the advent of compact cranks?
I didn't know, either. I found this
2008 article that covers the history.
Basically, when 9 and 10 speed cogs were produced, it allowed the same close gearing from 12-19 that the old 6 speed freewheels had, with additional larger cogs. And the shaped teeth and chain lift pins on the chainring allowed a larger difference in chainring sizes while still having good front shifting. Oh, and 11 tooth cogs were too small for the old freewheel bodies, but worked fine with cassettes.