Road vs MTN BSA Bottom Bracket

Road Vs MTN BSA - Bicycle Parts Direct

Threaded Bottom Brackets

Threaded bottom brackets use a shell with internal threads to hold threaded parts. The frame shell may be threaded directly at the shell, or there may be an insert installed that has internal threads. Typically threads are BSA (1.37″ x 24tpi), Italian (36 x 24tpi) or French (35mm x 1). Most of the current bottom brackets available from Shimano, SRAM, FSA and Campagnolo use external bearing cups. Wheels Mfg offers an external bearing cup bottom bracket for both road and mtb bottom bracket shells. The term BSA stands for Birmingham Small Arms, a British company that produced bicycles, cars and other durable goods.

BSA Road

  • The BSA Road Shell width is 68mm.
  • Shell threads: BSA 1.37 in x 24 TPI
  • Drive side cup is left-hand thread
  • Non-drive side cup is right-hand thread

BSA Road

BSA Road

BSA MTN

  • The BSA Road Shell width is 73mm.
  • Shell threads: BSA 1.37 in x 24 TPI
  • Drive side cup is left-hand thread
  • Non-drive side cup is right-hand thread

BSA MTN

BSA MTN

Road external cranks and their bottom brackets don’t use any spacers between the cups and the shell. Mountain external cranks have longer spindles and the bottom brackets generally come with spacers to accommodate both 68 and 73mm shells.

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