I just got a new wheelset and am considering upgrading my Dahon Eco to a 9 speed rather than fit my 7 speed cassette. Besides a cassette and shifters what else do I need to get?
The Eco has a Tourney rear derailleur, would I need to change it?
Does the chain need to be changed to a thinner 9 speed one?
Do I need to change the crank/chainwheel?
What wheelset? This could be important in determining if a 9sp would even fit.
To convert from 7sp to 9sp, you would need
* Different hub (7sp freehubs are no good for 8/9sp cassettes)
* 9sp chain (10sp also works well)
* 9sp shifter
The derailer will work. The Tourney is rock bottom entry-level, so getting a few levels higher will be well worth it. (If you were in Australia, I have a spare Alivio.)
Cranks and chainwheel will be fine.