We have two broad flavours of shifters: indexed and friction. Indexed shifters are probably the ones you're most used to, they became ubiquitous in the late '80s after Shimano made them work quite well and they're super friendly when learning to cycle. They simply click into the right spot and stay there when everything is well-adjusted.
Friction shifters are a bit of an anachronism, but some die-hards are still slowly developing them and keeping them on the market, and we appreciate that: there's a calm confidence that comes with using a good friction shifter on a long ride, and it's only about 5% more difficult than indexed shifting. They're also impossible to adjust wrong and it's easy to mix parts.
If you're an indexer, you should match your shifter to your cogs, chains and derailers. Also:
- 7-8-9-speed work the same across all the brands, and you can use almost any derailer.
- 10-speed systems need to match quite closely, and brands don't mix. Road and MTB only sometimes mix.
- 11-speed: can't mix anything, road and MTB totally separate.
- 12-speed: I'm sure you can guess.
Friction shifters can do whatever, but struggle with SRAM 10-speed and up and all other brands' 11-speed and up. They weren't ever really intended to put up with that nonsense.
