Will my RD work with a different cassette?
I currently have a Shimano 8 speed RSX rear deraullier, I believe the model is RD-A416.
I currently have a 11-23 cassette but want to change it to 11-32, 13-32 or 13-34. Will my current derailleur work with the new cassette?
It probably won't clear the 32T and almost certainly won't work with a 34T large cog.
Shimano rates their road rear derailleurs to work with a 27T maximum cog size and generally they will work with a 30T and sometimes, but rarely, a 32T. It depends on the derailleur hanger on the bike too. If you want to be sure to clear a 32 or 34T cog, you need an MTB rear derailleur.
Any recommendations on a good MTB derailleur to get? I use my bike for commuting, day rides and touring.
I would like a nice derailleur but don't want to spend the money for XTR if its not needed.
XTR is overkill. Any of the Shimano lower line MTB derailleurs will provide excellent service. I'd consider LX or, at most, XT.
Are rear derailleurs rated for different speed cassetes? ie, will a Deore LX rear work with a 8speed cassette without issues?
Yes. Within a given manufacturer's models, the number of "speeds" is determined by the shifter so any of their rear derailleurs will work with any shifter/cassette combination. The shifters, cassette and chain must match but the rd is suitable for use with any.
Originally Posted by chemando
Required disclaimer: Shimano Dura Ace pre 9-speed shifters, etc, aren't compatible with older stuff but that isn't a issue for you.