A bottom bracket is the three-body problem: it requires the frame's shell standard and provides a spindle standard to the crank. Both are listed on every page, and the crankset pages require the spindle in turn.
- 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.