I'd like to try an eight speed system on my 9 speed hard-tail mountain bike (Raleigh M80). Can I just replace the 9 speed cassette and chain (SRAM 950) with 8 speed (e.g., SRAM 850 cassette and 68 chain) and leave the 9 speed shift levers? (I've heard the 8 speed system was better in some ways.)
2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
What ways have you heard the 8 speed system was better? I've only heard that the 8 speed chain is beefier and thus less likely to break and the shifters are less complex and thus more robust. If you aren't breaking 9 speed chains, I wouldn't worry about it. You could always go test ride an 8 speed bike at the LBS.
If you really want to try 8 speed on your exact bike, you'd need the chain, cassette, and an 8 speed rear shift lever. You could probably get a 9 speed rear shift lever to shift an 8 speed cassette but any benefit of the 8 speed shifter is lost then.
Not to mention that chain rub can become an issue with 9-speed front derailleurs and the wider 8-speed chains. I find 9-speed to be superior in most respects anyway, except that the parts are more expensive.