Originally Posted by
dunkleosteus
So here's how I currently understand things, let me know if any of this is wrong, because I'm trying to (over)simplify the veritable profulgence of options here.
1. The number of speeds of a derailleur is an upper limit of the number of speeds it can actually run, like a 10 speed RD would be fine shifting across a 7 speed cassette, and so on.
2. The "number of speeds" of an indexed shifter is the number of clicky clicks in it, that's all. They are not compatible among different numbers of speeds.
3. A friction shifter can run anything.
I'm especially curious about number 3 because I'm thinking of using an old school friction shifter to control a modern 11 speed RD.
Cheers
1. No, actually the upper limit is determined by the amount of travel the RD can handle. As long as it can cover the full width of the rear cluster, you can use it. With a compatible shifter, that is.
2. Yes and no. The number of available clicks is the maximum, but you can use them for fewer speeds. I use 9-speed shifters with 5 and 6-speed rear clusters on some of my touring bikes. The remaining clicks are blocked out by the RD limit screw. As long as the shifter's cable pull matches the RD and cluster combo you are good to go.
3. Yes, but only so far as it can pull a cable. Especially older shifters with a smaller diameter "cable drum" will often reach the 180 degree position before the RD reaches the most inner cogs.