Originally Posted by
VegasJen
Not at all my intention. In fact, just the opposite. I want to make sure I only buy the part(s) that will work with what I have now. I have no intention of "reinventing the wheel" so to speak. If what I have works with an 8-speed cassette, then that's what I'm going to shop. No sense finding a 9-speed cassette/wheel, and then having to change the derailleur and shifter to fit.
If you have a 9 speed shifter, you will need a 9-speed cassette.
However, your existing wheel is fine with either an 8 or 9 speed cassette as the freehub is designed to work with 8, 9 and 10 speed cassettes.
Also, you do not need to change your rear derailleur if you change your cassette. Keep in mind that the total width of an 8 and 9 speed cassette is the same which is why the spacing between individual gears is different. But your derailleur doesn't care about spacing between individual gears, your shifter determines that. The derailleur is only "along for the ride" so to say.
It sounds like a 9-speed cassette is the only part you may need. NOTHING ELSE.