Originally Posted by nodnerb
Thanks, that's good news. How about using a full 9 speed drivetrain(chain, chainrings, cassette) with 8 speed shifter and deraileur? Would I just have to tune out either the highest/lowest gear or would the shifting be all screwed up?
There is no such thing as a 8 vs 9 speed derailleur. The derailleur doesn't index, it just moves over a distance in response to cable pull. 8 speed and 9 speed systems have the SAME spacing between the biggest and smallest cog. 9 speed just squeezes one more in.
The indexing is handled by the shifter. And of course, the shifter is indexing over the spacing on the rear cassette. So to change from one to another, you need to change:
There IS such a thing as a 7 speed derailleur. You don't want that at all because the spacing for a 7 speed is different than an 8/9 speed. It IS possible to upgrade from such a system. But any bike that came as a 7 speed isn't worth upgrading.
Don't expect to see 10 speed on mountain bikes anytime soon. There is a big "retro" movement going on right now of individuals who feel that 9 cogs is one too many. SRAM has pushed it's 8 speed stuff up into the X.9 group. Mountain Bike Action ran an article this month on "downgrading" your bike to 8 speed.
Bottom line ... if you have an 8 speed, you probably don't need nine. It bends/wears easier, and snaps easier. It's easier to fall out of alignment because the indexing tolerances are smaller.