I'm thinking about changing my 2nd chanring to a smaller one (2 chanring setup). I hear most people recommend to change the chain when changing the cassette.
The rule of thumb is: if you change a drivetrain part, anything in front of the changed part will work perfectly but anything in rear of the changed part may need to be replaced.
- New cassette: the old chain and chainrings work as they are in front of the changed component
- New chain: the old chainrings work (as they are in front of the changed component) but cassette may need to be changed
- New chainring: you may need to change the chain to a new component (as it's in the rear of the changed part), which in turn may necessitate changing the cassette too
Hence my question: should I expect to change other parts (chain? other chainring? cassette?) if I change my 2nd chainring?
Depending on how worn the chain is, it may or may not work.
If you don't need to change the chain there's no need to change the cassette. But if you needed to change the chain, this can in turn necessitate changing the cassette.
Whether or not the chain will work depends on how worn it is so it's impossible to say. It's wise to have a spare chain somewhere so you have a new chain if you need one. Similarly, it's wise to have a spare cassette too somewhere so you can install a new cassette right away.