Matching bottom-bracket shell width does not guarantee that a replacement will fit. The new unit must match both the frame's attachment standard and the crank spindle. On an e-bike, an integrated sensor or drive-specific assembly may add another requirement. If the cups or crank will not seat as instructed, stop rather than forcing them or removing spacers to gain room.
Match the frame side before the width label
The shell is the frame opening that holds the bottom bracket. Its width describes only one part of that opening. You also need to know how the bearings or cups attach to it.
A threaded shell and a press-fit shell are different starting points. Even within either group, the exact thread specification or bore diameter matters. A replacement advertised for the same shell width can belong to a different standard.
Check the frame documentation and original part markings. Do not identify the standard from the appearance of the exposed cup alone. Some arrangements look similar from outside but locate or attach differently inside the frame.
If a threaded part will not engage as specified, do not assume it merely needs a stronger wrench. If a press-fit part seems wrong, do not use the press as a sizing test. Either approach can turn a returnable wrong part into a frame repair.
Match the crank side separately
A bottom bracket that fits the frame may still be wrong for the crank. Confirm the spindle diameter and interface, plus the required axle length where the design uses a separate axle. The frame-side match does not answer those questions.
For example, a cup may seat properly while the crank spindle cannot pass through the bearings. That points to a crank-side compatibility check, not a reason to press harder. Conversely, a spindle sliding through does not prove that the crank will clamp, preload, or align correctly.
Keep the specified seals, spacers, and installation sequence intact. Removing a spacer because the crank otherwise seems too wide can conceal a wrong combination.
If the original assembly contains a pedaling sensor or is part of the drive system, confirm the approved replacement with the bicycle maker. A plain mechanical unit with similar dimensions is not an equivalent substitute.
Order from the complete specification
Before another purchase, collect the frame identifier, crank identifier, original bottom-bracket code, and the applicable service drawing. Ask the supplier to confirm both ends of the fit: frame to bottom bracket, then bottom bracket to crank. Include any sensor requirement.
If that information is unavailable, a shop should identify the installed system before you order. For the wider inspection and service schedule, see the maintenance guide; this is a replacement-fit decision, not an invitation to machine the frame.
When comparing electric bikes, ask whether drivetrain replacement parts can be identified from the bicycle's records. A clear service route is more useful than a single familiar dimension.
