Join Date: Apr 2002
Location: Montréal (Québec)
Actually, if you upgrade from 9- to 10-speed, the only things you need to change are:
- chain (10-speed chain)
- cassette (10-speed cassette)
- shifters (10-speed shifters).
You don't ever need to change anything else.
Rear derailleurs will shift whatever you present them with, and front derailleurs are fine-tuned to what Shimano considers a "perfect" crankset. Since the 9-speed crankset and the 10-speed crankset have slightly different rings (40 vs 39 middle ring if I remember correctly), the new front derailleurs are shaped slightly differently. So using a 9-speed FD with a 10-speed crankset and STI shifters may result in slight rub on 1-2 extreme combinations.