Choosing a bottom bracket can be confusing. Aside from shell width and spindle length, you also have to consider bottom bracket standards and types. From their size to construction, different manufacturers offer different bottom brackets. You need to find one that suits your bike.
To find the right bottom bracket, it would be best to remove the bike’s crankset to measure the inner diameter of the bottom bracket shell. To help you make the right choice, read on and we’ll talk about some of the most common types of bottom brackets.
What is a Bottom Bracket?
The bottom bracket is a bearing system between the cranks. It sits inside the bottom bracket shell, which is one of the parts of the bike’s frame. It connects the frame to the chainset. One of its main functions is to ensure that the cranks make a smooth turn. With the recent advancements in technology, bottom brackets have evolved. Some of them are now cups or bearings only.
The time will come when the bottom bracket will wear out and require a replacement. This is when it can get confusing for most people. Finding a bottom bracket compatible with your bike can be difficult because of the different types of bottom brackets.
In the older models of bottom brackets, all that you need to do is use two spanners in opposite directions to improve smoothness. With today’s sealed bottom brackets, you will need a replacement once they no longer turn smooth.
The Most Common Types of Bottom Brackets
Clueless about the bottom bracket standards and types? Identifying bottom brackets can be difficult because of having too many options. Below are some of the most common.
1. Threaded Bottom Brackets
Bottom brackets are available in two broad categories, and threaded bottom bracket is one of them. As the name implies, these will thread into the bottom bracket. It is not suitable for all bike frame materials. Instead, this is only for metal. If it is made of any other material, then you will need a bonded metal insert, which should have threads.
This type of a bottom bracket can be further broken down into three categories.
Adjustable Cup and Cone
In this type of bottom bracket, you will see two tool fittings positioned on the drive side of the bike. One has a notched lock ring, which will separate it from the cup. One of the best things about this is that it allows adjustment of the bicycle bearings.
Also called and integrated spindle system, it has threaded ends or cups, which will be the ones securing the bottom bracket into its shell. There is one unit that holds the spindle and another that screws it.
Thru-bearing systems, also called external bearing, has a cup and cartridge bearing. The latter can be in or out of the shell. It is threaded into the frame of the bike. The crank spindle, meanwhile, passes through the bearings.
2. Press Fit Bottom Brackets
The frame shell of this bottom bracket has no threads but has a smooth bore. It has cups or adaptors on the shell. This is what will create an interference or press fit. The pressure from the interference is what will hold the bracket in place.
Not all press fit bottom brackets are the same. They are available in several types, including those briefly mentioned below. They differ in terms of their sizes, especially the diameter of the bore.
It goes by many names, including BB86, BB92, BB121, and Shimano Press Fit, among others. The nominal width of the shell in this bottom bracket can vary, and this is indicated by the numbers at the name. The inside diameter of the bearing can range from 24mm to 30mm.
With this type of a press fit bottom bracket, the diameter of the inner shell is 42mm, which represents the number in its name. The bearings of the bottom bracket will vary from one kind to another, but it will range from 24 to 28.99mm.
Like those mentioned above, the number in the name also refers to the frame shell bore, which is 46mm. This is the diameter of the smooth bore inside the frame. Its cartridge bearing has an aluminum or plastic adaptor, which presses into the shell of the bottom bracket.
3. English Bottom Bracket
Also called BSA, this is the most popular from the types of bottom brackets you can see in today’s bikes. This is also a kind of a threaded bottom bracket. It has a 68mm wide shell if it is in a road bike. On the other hand, if it is fitted in different types of a mountain bike, then the width is 73mm. It can also be 83mm or 100mm.
4. Italian Bottom Bracket
This bottom bracket has a threading of 36mm x 24 threads per inch. It has right-hand threaded sides. It is quite rare to find a bike nowadays with an Italian bottom bracket. If there is one problem with this bottom bracket, however, it would be that there is a likelihood of undoing itself since it has a standard thread on the non-drive side.
5. French Bottom Bracket
Like the Italian bottom bracket, this is also a rare find nowadays. This threading standard is deemed obsolete. It has a right-hand threading on both sides. The shell has an approximate diameter of 34mm.
Q: How do I know what bottom bracket do I have?
To know what bottom bracket you have, you have to first remove the bottom bracket bearings from the frame. This will give you a better view and identify the bottom bracket that your bike has. Inside and outside the shell, you will find codes, which will make identification easier.
Q: Are bottom brackets universal?
Bottom brackets are not universal. The size of the bottom bracket shell is one thing that makes them different. Make sure that you know the different bottom bracket standards to find one that best suits your needs.
Q: What is a 73mm bottom bracket?
A 73mm bottom bracket means that the bottom bracket shell has a width of 73mm. This is the size that will suit the shell of the bike. It is what dictates compatibility. This kind of bottom bracket is common in mountain bikes.
Q: Do all cranks fit all bottom brackets?
Not all cranks will fit all bottom brackets. This is why you need to find out what size is most suitable for your bike. This is also why there are several standards and types based on your needs.
Q: Are all bottom brackets the same diameter?
Not all bottom brackets will have the same diameter. This will depend on the type of bike that you are using. In mountain bikes, it is common for the bottom bracket to be 73mm in width. On the other hand, in the case of road bikes, the width is 68mm.
Globo Surf Overview
Bicycle manufacturers have introduced several types of bottom brackets in recent years. Anyone looking for a replacement should be familiar with the bottom bracket standards, including those mentioned above. As a part of routine bike maintenance, consider checking and replacing the bottom bracket to ensure smoother performance.