Bottom brackets: 68, 73, and the shells that are not BSA

BSA, sometimes called English, is a threaded shell. Road bikes are often 68 mm wide. Mountain bikes are often 73 mm. A kit that says 68–73 can span that with spacers. A kit that says 68 mm does not automatically grow. Measure the shell, not the model year of the bike.

What the catalogue motors actually ask for

• Bafang BBS02B: BSA 68 mm in the record here.
• Bafang BBSHD: BSA, commonly 68 to 120 mm depending on the version sold.
• Tongsheng TSDZ2B: BSA 68 mm.
• Pendix eDrive 300: BSA 68 or 73, and it sits on the non-drive crank rather than replacing the whole spindle the way a BBS does.
• CYC Photon 2, Photon Pro and X1: BSA 68–120 and BB92.
• add-e: clamps at the bracket and uses the chain you have. Clearance is the fit, not a spindle length.

Press-fit shells — BB86, BB92, PF30 and the rest — are not BSA. BB92 is on the CYC card because the maker published it. It is not a licence to press a BBS into a carbon press-fit frame. An insert is a different configuration, with its own creak and its own inspection.

Chainline comes after the shell is right. The lockring sets the motor’s angle and the ring’s offset. A chain that climbs the cassette under load is a line problem or a worn cassette, and it will feel like a motor fault.