The bottom bracket shell of a bicycle is the part of the frame where the spindle of the cranks go through. The bottom bracket and spindle together form the foundation of the drivetrain on your road bike or mountain bike. All the different standard dimensions can make it hard to determine what kind of bottom bracket shell your frame has and what bottom bracket bearings you need. How can you even tell what bearings and bottom bracket shell your frame has? This extensive how-to explains exactly what you need to do in order to service and replace your bottom bracket bearings yourself.
FREE U. For those who are looking to upgrade the cranks on your mountain bike, or just need a replacement bottom bracket , it's very important to make sure you get the correct bottom bracket for the job. The two major dimensions that differentiate bottom brackets of similar types are the shell width and spindle diameter. Hopefully, we can help clarify some of the more common bottom bracket sizes so that upgrading your cranks can be a simpler process. Because there are so many different bottom bracket variations, we think it is very important to always match the manufacturer of the cranks and bottom bracket to ensure the proper fit. English Threaded.
By BikeRadar. This comprehensive guide tells you everything you need to know about bottom brackets — from a breakdown of all the bottom bracket systems available and their compatibility with one another to how a bottom bracket works and how to stop a bottom bracket creaking, this guide has it all. Below we rundown each of the major bottom bracket systems currently available, along with advantages, disadvantages, notes on compatibility, and some input from their proponents on why they exist:. Modern, external cup threaded bottom brackets are among the most common of standards. Square taper bottom brackets also fit in most shells designed for external cup bottom brackets, but to keep things simple, we will only cover the modern standard here.