Bottom bracket bicycle

The right bottom bracket for your bicycle must be compatible with both the frame and the crankset. In this category, you will find various Shimano bottom brackets and bicycle bottom bracket units with square taper, Octalink, and Hollowtech II interfaces, as well as versions for threaded and press-fit installation. Before ordering, please compare the full model designation and all relevant dimensions with your existing bottom bracket and the manufacturer's specifications for your drivetrain.

Finding the right bottom bracket for your bike

When choosing, it is not just the type of bike that matters. First, you must determine whether the frame has a threaded bottom bracket or a press-fit interface. For threaded bottom brackets, the thread standard and shell width are crucial. BSA versions with 68 or 73 mm and Italian ITA versions with 70 mm must not be confused with each other simply because of a similar size.

Selecting Shimano bottom brackets by crank interface

Square taper, Octalink, and Hollowtech II are different systems and are not interchangeable. The Shimano BB-UN300 series models in this category are square taper bottom brackets and are available with various shell and axle lengths. For Octalink versions like the BB-ES300, the crank must be specifically designed for the corresponding Octalink system. Shimano bottom brackets such as the BB-MT501 and SM-BBR60 belong to the Hollowtech II system, while the SM-BB94-41A is designed for a press-fit interface.

The existing crankset therefore determines a significant part of your selection. Check the model number of the crank and the old bottom bracket. Matching the brand alone does not guarantee compatibility between different Shimano systems.

Correctly distinguishing shell width and axle length

Specifications such as 68 or 73 mm refer to the width of the bottom bracket shell on the frame for many threaded bottom brackets. Values such as 110, 113, 117.5, 118, 122.5, or 127.5 mm refer to the axle length for square taper and Octalink cartridge bottom brackets. A different axle length can change the position of the crank and therefore the chain line. For this reason, do not automatically choose a shorter or longer version, even if the thread and shell width seem to match.

For a secure identification, you will generally need:

• the complete model number of the existing bottom bracket and the crankset
• the installation type: threaded or press-fit
• the thread or press-fit standard of the frame
• the shell width of the frame
• for cartridge bearings, the required axle length and crank interface

When should a bicycle bottom bracket be checked?

Play in the crank, rough rotation, or noises while pedaling can indicate a worn or incorrectly installed bottom bracket. However, similar symptoms can also be caused by pedals, crank bolts, chainrings, or other drivetrain parts. When in doubt, have the cause checked before ordering a replacement part. Further components can be found under bicycle spare parts. Support for diagnosis and replacement is offered by the bicycle service provided by Fadu Bike in Vienna.

Frequently asked questions about bottom brackets

Which Shimano bottom bracket fits my bike?

Compare the frame standard, shell width, crank interface, and the full model designation. For square taper or Octalink bottom brackets, the intended axle length must also be correct. The name Shimano alone is not sufficient, as several non-interchangeable systems are offered.

Are "Tretlager" and "Innenlager" the same thing?

In retail and search queries, both terms are frequently used for the crank's bearing unit. However, the specific design type, dimensions, and compatibility with the frame and crank are the decisive factors for ordering.

Can I replace a 68 mm bottom bracket with a 73 mm model?

Not automatically. The shell width, frame standard, crankset, and installation specifications must be checked together. Use only a combination intended by the respective manufacturer.