We turned my wife's old Peugeot into a 1x 9. Used the small chainring which I believe is a 40 tooth. Matched it to an 11 -32 9 speed cassette and older Tiagra medium cage derailleur. I did it with the help of my LBS. works really well. The easiest gear is small enough to handle most of the hills we ride regulArly, most of which aren't too steep.