When it comes to bottom brackets for bicycles, there are two main types: threaded and press fit. Each type has its own set of advantages and disadvantages, so it's important to understand the differences between them to make an informed decision when choosing a bottom bracket for your bike. Here are some of the most popular models for each type:
A. Italian thread, all threads are positive threads, with outer diameter 36mm and the pitch 36*24TPI. It is very rare, and it needs to be matched with the central axis of special regulations.
B. BSA English thread, the thread is positive and negative, with outer diameter 34.798mm and pitch 1.37*24TPI. The width of BB is mostly 68 and 73mm, one of the most traditional BB standards.
C. Press-fit BB30, 30 represents the diameter of the chainwheel axis (the diameter of the integrated chainwheel axis represented by Shimano is 24mm), the BB Width is 68mm, and the inner diameter is 46mm. It adopts a short length of 30mm diameter aluminum alloy shaft; the bearing is directly pressed into the frame (generally, there will be an aluminum embedded part on the carbon fiber frame, because the method of pressing the bearing directly into the carbon fiber is not ideal). At present, it is difficult to find a real BB30 frame, because PFBB30 will be easier to use.
PF30/PFBB30：It is the same as the chainwheel used in the BB30 mentioned above, but the bearing is not directly pressed in, but pressed into the nylon sleeve in advance before being pressed into the frame. This can make installation easier, and the manufacturing cost and processing difficulty of the frame will be lower, because the tolerance becomes larger and the requirements for the lathe are reduced. The composite cup ring with fixed bearings can make up for the slight BB tolerance and help minimize the "squeaky" noise under the BB30setting.
BB386EVO：This is a relatively updated standard and claims to be able to create "the best full compatibility specifications" for the future. Initially, the BB width of road bike was about 68mm or 73mm. BB386 has raised this standard to 86mm, which allows the frame manufacturer to design a wider and harder BB to improve transmission efficiency. However, this also requires a longer chainwheel axis, which is called BB386EVO with this specification. Although BB386 cranks must be used on some frames, because they have a wider central axis, the BB386 chainwheel sets can also be used on BB30 and PF30 frames, as long as a gasket of the appropriate thickness is added.
D. Press-fit BB90/95, As for the BB90 system (trek exclusive) and the BB86 system (giant, Lapier, etc.) in the same period, it also adopts an indented central axis design. The bearing size is still the original 24mm, but the bearing spacing is pulled to the widest, especially the BB90 system.
E、Press-fit BB86/92，PF BB86 is developed on the basis of BB90. The only difference is the BB,its width is 86.5mm. Most of them still use ordinary all-in-one dental plates.
Finally, T47: This specification began in 2015. This is a new threaded BB caliber specification. They try to combine the advantages of pressing into the central axis with the advantages of easy-to-install threaded bottom bracket. This specification is called T47. In short, it uses the same thread style as the BSA bottom bracket, but the diameter is larger, which is suitable for bearings and axes under the BB30 specification.
Although this specification has not been widely adopted, it may be used as a backwards compatible way and become a standard in the future. Here, if you think what you see is the standard for all bicycles, it is very good, because it is enough.
Generally speaking, the best way to buy expensive crank sets or power chainwheel sets is to buy options with a longer axis.
Because you can adapt the long axis through gaskets or central axis modifications, but if the axis is too short, your choice is very limited. ( This is also one of the reasons why the BB30 specification tooth plate can't be sold in the second-hand market).