A derailleur must match the shifter's speed count and actuation (cable or electronic); it provides the largest-cog limit the cassette then requires. The box prints the cage length; the pages print the rest.
- How do I know whether a part in this category fits my bike?
- Every part page lists the standards it requires and its computed verdict on each bike in the fleet, with its confidence and sources. An "unknown" verdict means we do not have the measurement on file — not that it fits.