The bottom bracket on a bicycle connects the crankset chainset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks. The bottom bracket fits inside the bottom bracket shell , which connects the seat tube , down tube and chain stays as part of the bicycle frame.
Bottom Bracket Standards and Terminology | Park Tool
What is a bottom bracket? Your bottom bracket connects your cranks to your bike in such a way that they can rotate freely as you pedal and put power into the drivetrain. Shell and spindle widths vary depending on the type of bottom bracket. If your bottom bracket is working well, you can pedal smoothly with minimal resistance.
Bottom Bracket -Traditional, Pro Quality, Tange - for 68mm BB shell width (normal)
The tables below give dimensions for threaded bottom-bracket shells and parts which thread into them. These parts can be:. As of , cartridge bearings are being used for most bottom-bracket bearing assembly replacements. Cartridge-bearing installation is simple; assemblies are available in several brands at various price points and with various spindle lengths.
The evolution of road bikes may have provided cyclists with frames that are lighter, stiffer and more aerodynamic, but there has also been a substantial increase in the number of bottom bracket and crank axle designs. The once ubiquitous threaded bottom bracket shell has given way to larger threadless designs while the diameter of crank axles has also grown. Both may have helped elevate the performance of contemporary road bikes but consumers have been left to contend with myriad options and some frustrating incompatibilities. In this post, Matt Wikstrom updates his original article from with a look at the range of bottom bracket and crank axle designs that are found on the market today and discusses the details that are important for matching one to the other.