I have a 2011 Crosstrail with the stock Tourney (48/38/28 front) and Altus (7-speed 12-32T rear).
I though I read somewhere that all deraileurs have the same range of motion and that the only difference between a 7-/8-/9-/10-speed is the indexing which to me seems to be done by the shifters themselves. When searching on Amazon, I notice that even among the same model name (Alivio) that they sell them as 8- or 9-speed versions. Even more confusing is that some of the front deraileurs are sold as "7/8-speed," as well (I know the Tourney will work with at least an 8-speed, because my wife's bike has the same one). The question is can I keep my crappy stock deraileurs and just swap to new shifters, a new cassette and a new chain? If that's the case, I could get Alivio 9-speed shifters, cassette, and 9-speed chain for around $90, or 10-speed Deore for around $130 on Amazon, which seems like a reasonable price for the improvement. Ultimately I would like to get matching and upgraded front and rear deraileurs, which would be another $60 or $90 respectively. Has anyone ever done this, or am I just wasting my time?
I guess I should put out there that my goal is to have the same gearing as my wife's 3x8 (48/38/28 and 11-32T). I found a 7-speed HG41 (11-28T) for $16 but I sometimes tow my 6 year old on a trailer bike and (rarely) the 32T gear actually gets used. As for why I was looking to move to a 9- or 10-speed, it seems a waste of time and money to only upgrade the 1 additional cog (from a 7- to 8-speed).