I'm going to be trying out a new drivetrain on my bike, replacing the cassette and my smallest chainring. I used a park chain wear tool to look at the chain last week and it shows no sign of wear after 2,500 miles, and the cassette seems fine too.
Should I replace the chain anyway?
I will keep the old cassette and switch it back on whenever I'm going to do really hilly rides, as it has a lower gear on it (11-34 vs 12-30). So if I do change the chain, should I keep the old chain and use that when switching to the old gearing or would it be ok to use the new chain? There's only a 4 tooth difference so I think I can get away with using the same length of chain as long as I'm careful to avoid severe cross-chaining.