Here is a chart to find the "pull ratio" of many derailleurs that has to match with the shifter ratio which is what has been mentioned above and why the 4700 version will not mix with the 4500-4600 and some other older Tiagra groups. You need to know which model shifter you have before choosing a derailleur. Two Wheel Tools NOTE: This is the same chart that gets posted here occasionally but has been moved to a different host with a slightly different format but has the same info. (I liked the old format better)