Bottom Bracket

BOTTOM BRACKET

The bottom bracket (BB) is the bearing assembly housed in the bottom bracket shell of the bicycle frame. It allows the crankset spindle to rotate smoothly. It is one of the most frequently serviced components on a bicycle, as it is exposed to high loads, and on flat-mounted designs, to contamination from dirt and water.

Types

• Threaded (BSA): The most traditional type. The cups with the bearings screw into the threaded bottom bracket shell. Very serviceable and reliable.
• Press-fit: The bearings are pressed directly into the frame's bottom bracket shell, which has no threads. Common on carbon frames for weight savings. Can develop creaking issues.
• T47: A newer standard combining threaded reliability with wider shell diameter for increased bearing size and stiffness.