bottom bracket

From earlier bicycle designs, when it was a separate piece bolted onto the bottom of the frame. In modern designs the bottom bracket shell (or housing) is an integral part of the frame.

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bottom bracket (plural bottom brackets)

1. (cycling) A bicycle part that connects the crankset (chainset) to the frame and allows the crankset to rotate freely.

   Synonym: BB

   Holonyms: spindle, bearing

   • 1972, Richard Ballantine, Richard's Bicycle Book, New York: Ballantine Books, page 139:

     The chances are excellent that some of the material will fall down the seat tube and get into the bottom bracket, where it will make mincemeat of your crankset bearings (thought seats were simple, hah?).

   • 2009, Dennis Bailey, Keith Gates, Bike Repair and Maintenance For Dummies, John Wiley & Sons, →ISBN:

     Crucial to the crankset is the bottom bracket. Of all the bearings on a bike, the bottom bracket is the one that has to bear the heaviest load. Not only does the bottom bracket have to spin while you pedal, but it takes the force of all the twisting and turning that occurs during pedaling.

• spindle

• bottom bracket on Wikipedia.Wikipedia