alig said:
I have a Shimano HG-50 9 speed 12-25 cassette
Rather than buy a new cassette, I'd like to know if I can remove the 25T sprocket and replace it with an 11T sprocket to make a 11-23
Do you really want an 11t cog?
Even if you're changing to a "compact" crankset, short of having legs like Robbie McEwen, about the only reason for the average rider to have an 11t cog on a ROAD cassette is if s/he is doing a lot of riding on mountain roads, or equivalent (i.e., long descents).
N.B. If you were to ONLY buy an 11t cog + 11t lockring (the diameter is smaller ... it can be used with a 12t cog, of course), then you will
still need a DIFFERENT 12t cog because the smallest cog on the stack is capped & cannot slide all the way onto the freehub body ...
Consequently, IMO, your least expensive option for an 11t cog + 11t lockring is to buy an 11t-32t LX cassette ... cannibalize the two components you want + the LX's 12t cog (or, whichever size SECOND cog you want) ... and, put the 12t, 13t & 25t from your road cassette in a baggie with the rest of the LX cassette.
BTW. On some of the Shimano's second tier cassettes, the portion that is pre-assembled as a unit are held together with a RIVET and in some cases a BOLT which has a 1.5 (?) mm Allen head. If the cassette is riveted, then you will have to grind the head (on the largest cog) off ... if it is bolted together, then unbolt it. UNLESS you are using a wheel which has an alloy freehub body, the bolts/pins which hold the larger cogs of the LX-or-105/whichever cassette are NOT necessary & are primarily to facilitate sliding the cogs-and-spacers onto the freehub body.