full guide: Bottom bracket standards & types

In the history of bicycles, we have seen many standards for bottom bracket systems and different types of bottom brackets. Most of them are still being widely used today. Suppose you are trying to explore all the bottom bracket standards, bottom bracket types, and how the standards have been evolved from generation to generation, you will probably find the answers here.

This diagram contains all the commonly used bottom bracket standards/types since the emergence of the bottom bracket, as well as the upgrade path for the bottom bracket:

In the following context, based on the diagram above, I will introduce every single bottom bracket standard and type and how the standards have been updated and evolved from generation to generation. Regarding performance, T47 is far superior to the original BB for OPC. However, all structural upgrades from BB for OPC to T47 were not completed in a day. Let me briefly introduce how the bottom bracket has gradually evolved from its original simple structure to its current state through slight changes in the detailed structure.

Here is a guide for the evolution history of bottom brackets and what we are going to discuss in the following context：

Phase 1:BB for OPC combined with three different spindles

We will start with the first generation of bottom brackets, called bottom brackets for one-piece crank (BB f/ OPC), also known as one piece crank BB / American BB / Ashtabula BB. FYI, It’s the best seller in SUMLON’s product line. Here are 2 versions of it, one with caged bearings and the other with sealed bearings. It looks like this when it’s disassembled.

BB for OPC has many other names, including one-piece crank bottom bracket, American Bottom bracket, and Ashtabula bottom bracket. BB for OPC is almost the most ancient version of the bottom bracket system ever. But it’s still widely used and works well in low-end bicycles. It’s cheap and easy to manufacture.

Usually, when we talk about one piece crank bottom bracket, we mean the cup set, including cups, bearings, cones, washers, and a locknut. This cup set can be combined with several kinds of spindles to be a whole bottom bracket system. The most commonly seen combinations are 1. BB for OPC with one-piece crank, 2. BB for OPC with Thompson cottered spindle, and 3. BB for OPC with square nut style spindle. BTW, unlike BB86 or T47 with a short bottom bracket type name, these combinations don’t, which means that if you would like to quote these combinations, you will have to use the long phrase such as bottom bracket for OPC with square nut style spindle. In case you want to see how they respectively look like:

BB for OPC is a bottom bracket standard, a.k.a. cup and cone bottom bracket. The corresponding frame shell standard is defined as 51.5mm / 43mm BB shell inner diameter (ID), press-fit type connection between BB and BB shell, and 68mm/73mm shell width. So, the definition of BB for OPC standard would be the bottom bracket system that fits the frame shell standard above and contains two press-fit cups, two bearings, two cones, two washers, and a locknut. BB for OPC could also be the bottom bracket type name. Other BB-type names include the one-piece crank bottom bracket, American Bottom bracket, or Ashtabula bottom bracket. So, if you are searching for it on Google, you should try the American / Ashtabula one-piece crank bottom bracket + 51.5mm / 43mm / 68mm / 73mm. Speaking of the ones using sealed bearings, usually, we use the term sealed bearing American bottom bracket.

Phase 2: The appearance of thread-fit BB and the detachment of the spindle from the bottom bracket

(1) Japanese spindle and cups – 3S/3T/3P/5S/3R/5T/5P bottom bracket

After knowing the three combinations mentioned above, let’s focus on the BB for OPC with square nut styles spindle among them. The structural design changes that have played an essential role in the historical evolution of the BB system are limited, including the connection between the spindle and the cranks (cottered, square taped, or splined), the connection between the bearing cone and the bearing cup (loose bearing, caged bearing or sealed bearing), and the connection between the cups and the BB shell (thread-fit, direct-fit or press-fit). Based on the first-generation BB system, which is BB for OPC with square nut style spindle, engineers’ first thought was to improve the connection between cups and BB shells, upgrading it from press-fit to thread-fit. Boom, here it is—Japanese spindle and cups.

This new redesign helps maintain the usability of the BB system after it is disassembled for maintenance. Without professional tools, cups in BB for OPC are not easy to remove from the BB shell. Even if dismantled, it will cause irreversible damage to the BB shell. The threaded cups will not have this issue. Meanwhile, compared to BB for OPC, the bearing cones in the Japanese spindle and cup system have been integrated into the spindle. The removal of independent cones resulted in a significant reduction in costs. The factory only needs to squeeze out two circular structures during the production of spindles to serve as bearing cones.

The new system has swapped the positions of cups and cones, integrated cones into spindles, and, most importantly, changed the connection between cups and BB shells from press-fit to thread-fit. The following video will explain how the 3S bottom bracket works to fix the spindle and allow it to rotate freely.

Japanese spindles and cups are bottom bracket standards. The corresponding frame shell standard is BSA or ISO, which specifies a shell width of 68mm/70mm and 1.37in*24TPI thread-ed shell inner face. Japanese spindles and cups standard refers to the BB system, which fits a BSA threaded BB shell and has a Japanese spindle, two threaded cups, and caged ball bearings. The 3S/3T/3P/5S/3R/5T/5P bottom bracket are the types of the bottom brackets. Taking 3S BB as an example, it has a 49+50+46mm axis, a 16mm spindle OD, and a 1.37in*24TPI threaded cup.

(2) Square taper

The square taper is one of the most common bottom brackets. The square taper is up grated from Japanese spindles and cups. The Japanese spindle and cups system and the square taper are products of two different eras. But please trust me, they are basically identical. The difference between them is that the bearings have been changed from caged/loose ball bearings to sealed bearings, and the manufacturer added a sleeve between the two cups for waterproofing and dust prevention.

Of course, there are square tapers that don’t provide sleeves, such as the Shimano Exage BB-M450. It uses roller bearings, BTW. We must know that applying sealed bearings is one of the most essential milestones in the evolution of the history of bottom brackets. Unlike the back-and-forth switch between press-fit and thread-fit in history, the application of sealed bearings is an improvement that old standards have never threatened.

From a structural perspective, you can see almost no difference between the Japanese spindle and cups system and the square taper. However, due to the application of sealed bearings, there are several small structural changes. Compared to the loose/caged ball bearing system, which requires cones and cups as inner and outer races, the sealed bearing comes with inner and outer races for the balls. So, after applying sealed bearing, the cup and cone no longer have to be used as races. So, the manufacturer completely removed the protruding structure that initially served as a cone on the spindle and transformed it into a simple limit structure that restricted the movement of the sealed bearing. The interior of the Cup is no longer curved but only serves to fix the remaining parts, ensuring they stay inside the BB shell.

Square taper is a bottom bracket standard. The corresponding frame shell standard is BSA/ISO threaded, which specifies a 68mm/73mm shell width, 1.37 inch BB shell ID, and 1.37in*24TPI threads. Under square taper BB standard, we can find so many different types of bottom brackets. They have different spindle lengths, such as square taper for 110.5 / 113 / 118 / 120 / 122.5 / 124.5 / 126 / 127.5mm spindle length. Manufacturers will not assign a name to each square taper with a different spindle length. Just use “square taper + (shell width) + (spin length)” as the keyword when you try to look for the specific square taper on Amazon.

(3) splined bottom bracket – Octalink and others

Before the appearance of Octalink, the diameter of the spindle was always 16mm. Increasing the diameter of the spindle is considered an effective way to improve the overall stiffness of the BB system. For this reason, Shimano launched Shimano Octalink based on the square taper. Octalink replaced the 16mm spindle with a 22mm hollow spindle. 8 splines on the 2 spindle ends are used to increase the joint capacity of the connection between the spindle and the cranks. As you can see, the differences between square taper and Shimano Octalink are the diameter of the spindle and the 8-spline design at both ends of it.

You can tell from its name that Shimano Octalink has 8 spines. Other manufacturers then launched ISIS bottom brackets (10 lines) and Power Spline bottom brackets (12 lines) to avoid Shimano’s patents. These bottom brackets are collectively referred to as splined bottom brackets. (see above)

Splined bottom bracket is a bottom bracket standard. The corresponding frame shell standard is also BSA/ISO, defined as BB shells with 68mm/73mm shell width, 1.37in*24TPI threads, and 1.37inch shell ID. Splined bottom bracket standard definition: a bottom bracket system that fits a BSA threaded BB shell and contains a splined spindle, sealed bearings, thread-fit cups, and a sleeve. According to the different number of splines, there are several types of splined bottom brackets, which are Octalink (8 splines), ISIS Bottom bracket (10 splines), and Power Spline Bottom bracket (12 splines).

(4) External BSA threaded BB

The appearance of splined bottom brackets has made cyclists realize the importance of increasing the diameter of the spindle. To further increase the outer diameter of the spindle, a new bottom bracket standard that fits spindles with larger OD has been introduced to the market. Under the new bottom bracket standard, engineers removed the spindle from the bottom bracket system and used more oversized sealed bearings based on splined bottom brackets. The new BB standard we are discussing here is the commonly used external BSA threaded bottom brackets. The emergence of external BSA-threaded BB is absolutely a milestone. Since then, almost all bottom brackets no longer contain spindles. Various manufacturers have also introduced larger diameter spindles, including SRAM GXP 22-24mm spindle, Shimano 24mm spindle, DUB 29mm spindle, and Cannondale 30mm spindle.

Interestingly, the spindle did not become an independent commercial component. On the contrary, the spindle, chainring, and crank arm have become an entirely new combination. A rigid connection exists between the spindle, chainring, and drive side crank arm. The chainring and the two crank arms were independent products in the past. In short, the emergence of External BSA-threaded BB officially started a history of integrated BB.

This bottom bracket standard is called External BSA threaded BB or Outboard BSA threaded BB. The corresponding frame shell standard is BSA/ISO, defined as BB shells with 68mm/73mm shell width, 1.37in*24TPI threads, and 1.37in shell ID. External BSA threaded BB standard definition: a bottom bracket system that fits a BSA threaded BB shell containing two threaded cups with bearings and a sleeve. External BSA threaded BB can be the general name for all external BSA threaded BB types. Speaking of bottom bracket types, external BSA threaded BBs can adapt to different spindle specifications, such as GXP/24mm/DUB/30mm. So the BB type would be BSA-24, BSA-DUB, and BSA-30. Please note that any one of them is universal for 68/73mm shells because you can use washers or choose different sleeve lengths.

Phase 3: Direct-fit bottom bracket was applied, but it turned out to be not that successful.

(1) BB30 direct-fit and derivatives

In 2006, the emergence of the BB30 direct-fit standard brought press-fit back. BB30 direct fit is a bottom bracket standard jointly promoted by Cannondale and FSA. This is a straightforward bottom-bracket system. The parts are two sealed bearings, two retaining clips, and some dust covers and washers. This system allows cyclists to use a 30mm ultra-large spindle while significantly reducing the weight of the entire BB.

The 30 in the BB30 direct fit standard refers to Cannondale’s BB system using only 30mm spindles.

Then, Cannondale developed the BB30A direct-fit standard and the BB30A-83 direct-fit standard. Cervelo launched a similar BBright direct-fit standard. But under BB30 direct-fit and its multiple derivative standards, the bottom bracket we use is interchangeable: the bearing and clip kit (42*30*7mm bearing + clip), or you can also call it the direct fit-30 bearing kit.

BB30 direct-fit and its derivative standards, such as BB30A direct-fit, BB30A-83 direct-fit, and BB-right direct-fit, are all bottom bracket standards. They correspond to different frame shell standards. The frame shell standard corresponding to the BB30 direct-fit bottom bracket standard is a press-fit shell with 42mm shell ID and 68mm road/73mm MTB shell width. Compared with the frame shell standards corresponding to the BB30 direct-fit BB standard, the frame shell standards corresponding to BB30A direct-fit, BB30A-83 direct-fit, and BB-right direct-fit specify different shell widths of 73mm road/78mm MTB, 83mm, and 79mm, respectively. So the definition of BB30 direct-fit standard is a bottom bracket system that fits the press fit shell with a 42mm shell ID and a 68mm/73mm shell width, and it contains only two 6806 sealed bearings and clips. Except for shell width, BB30A direct-fit, BB30A-83 direct-fit, and BB-right direct-fit have similar standard definitions. As discussed above, under these standards, we use the same bottom bracket type: the 6806 bearing and clip kit (42*30*7mm bearing + clip), or you can also call it the direct fit-30 bearing kit.

(2) BB90 and BB95 – direct fit bottom bracket from TREK

TREK developed its own direct-fit standards – BB90 standard and BB95 standard. They both press bearings with an outer diameter of 37mm directly into the frame shell, like Cannondale’s BB30 direct-fit, BB30A direct-fit, BB30A-83 direct-fit, and BB-right direct-fit standards. However, the BB90/95 standard specifies different shell widths (37mm) and inner diameters (90mm/95mm). Moreover, the BB90/95 standard does not specify the use of clips.

BB90/95 is the bottom bracket standard. Its corresponding frame shell standard is a direct-fit BB shell with 37mm shell ID and 90mm/95mm shell width. So, the definition of BB90/95 is a bottom bracket system that fits the direct fit BB shell with 37mm shell ID and 90mm/95mm shell width and contains two sealed bearings directly pressed into the shell. The bottom bracket type name is BB90/95 as well.

Now you know all the direct-fit bottom bracket standards. They are BB30 direct-fit, BB30A direct-fit, and BB30A-83 direct-fit standards from Cannondale, BBright direct-fit standards from Cervelo, and BB90/95 standards from TREK. The first difference among them is that the BB shell ID corresponding to the BB30 direct-fit, BB30A direct-fit, BB30A-83 direct-fit, and BBright direct-fit standard is 42mm, while the BB shell ID corresponding to the BB90/95 standard is 37mm. The second difference is that BB30 direct-fit BB, BB30A direct-fit BB, BB30A-83 direct-fit BB, and BBright direct-fit BB use clips, while BB90/95 bottom bracket does not.

Phase 4: Press-fit BB gradually replaced direct-fit ones and became the mainstream

(1) BB30 press-fit (PF42) and derivatives

The BB30 direct-fit standard removed the bearing cup and pressed the bearings directly into the frame. In most people’s opinion, this design by Cannondale is not really successful. Direct-fit bottom brackets require extremely high precision in frame manufacturing, and direct-fit BBs are prone to causing abnormal noise and irreversible damage to the frame. So, a group of direct-fit bottom bracket standards represented by BB30 were ultimately replaced. Engineers have added bearing cups and sleeves to the direct-fit bearing and clip system. The new standard is called BB30 pressure-fit or PressFit-42 (PF42). The BB30 direct-fit standard and BB30 press-fit standard both specify that the inner diameter of the BB shell should be 42mm, the shell width should be 68mm/73mm, and it can support a more oversized spindle of 30mm. The difference is that the BB30 press-fit standard bottom bracket has bearing cups and supports all spindle sizes of 24mm, GXP22/24, and DUB.

You can disregard the distinction between BB30 direct fit and BB30 press fit. They all belong to a more significant standard, namely the BB30 standard. The frame shell corresponding to BB30 standard is press fit shell with 42mm shell ID, and no shell width is defined. Any bottom bracket that fits the BB shell mentioned above can be named BB30 bottom bracket, no matter whether it’s direct fit or press fit. Under the BB30 standard, we have BB30 direct fit, BB30A direct fit, BB30A-83 direct fit, BBright direct fit, BB30 press fit, BB30A press fit, BB30A-83 press fit, and BBright press fit standards, which correspond to different frame shell widths and have different ways to connect BB and frame shell. But overall, they will all be installed into BB shells with an inner diameter of 42mm.

BB30 press fit, BB30A press fit, BB30A-83 press fit, and BB-right press fit are bottom bracket standards. They are also the bottom bracket types. The difference lies in the fact that BB30 press fit, BB30A press fit, BB30A-83 press fit, and BB-right press fit respectively correspond to 68mm road/73mm MTB, 73mm road/78mm MTB, 83mm, and 79mm shell width.

(2) BB86 & BB92 – PF41 from Shimano

Benchmarking BB30 press-fit BBs, Shimano introduced its PF41 bottom bracket standard. The PF41 standard includes two sub-standards, BB86 and BB92. The frame shells corresponding to the BB86 standard and BB92 standard are press-fit shells with 37 ID and 86.5mm/91.5mm shell width, respectively. So, the BB86 bottom bracket is a bottom bracket that fits the press-fit shell with 37 ID and 86.5mm shell width and contains 2 bearings, which are pressed-in composite or aluminum cups (37mm OD) that are, in turn, pressed into the frame. Meanwhile, BB86 and BB92 are also bottom bracket types.

(3) PF46 (aka PF30) from SRAM and its derivatives

In fact, the PF46 (PF30) standard is not an improved version of the BB30 press-fit standard. Instead, it was introduced on the basis of BB30 direct-fit standard directly. It was launched in 2009, which is a bit earlier than the BB30 press-fit standard, to solve the problems of the BB30 direct-fit bottom bracket system. Just like the BB30-press-fit standard, PF46 presses the bearings in cups and then presses the cup into the frame. The launch of PF46 bottom bracket system aims to address the strict dimensional tolerances and related manufacturing cost issues of BB30 direct-fit BBs. The only difference between PF46 and BB30 press-fit is that the PF46 standard adopted a 46mm cup OD instead of 42mm.

In summary, PF46 is a bottom bracket standard. Under its corresponding frame shell standard, the BB shell should be a press-fit shell with 46mm shell ID and 68mm road/73mm MTB shell width. So, the PF46 standard defines a bottom bracket that fits the press-fit shell with 46mm shell ID and 68mm road/73mm MTB shell width and contains 2 bearings which are pressed-in composite or aluminum cups (46mm OD) that are, in turn, pressed into the frame. BTW, PF46 is the bottom bracket type name as well.

PF46 (PF30) standard has several derivatives. We have PF30A, PF30-83 (PF30Ai), OSBB, BB386/BB392 and BB-right for 46mm shell ID. There is not much difference between them and the PF46 standard. The difference lies only in the fact that these derived standards correspond to different widths of the BB shell. Take PF30A as an example. It corresponds to a frame shell standard that BB shell should be a press-fit shell with 46mm ID and 73mm road/78mm MTB shell width, which is 5mm wider on the non-drive side than that in PF46 standard. So, under PF30A standard, except for containing 2 bearings, which are pressed-in composite or aluminum cups (46mm OD) that are in turn pressed into the frame, the bottom bracket system should fit a wider shell width, which is 73mm road/78mm MTB. The same applies to other derived standards. PF30-83 (PF30Ai) adopted 83mm shell width. OSBB adopted a 61mm shell width. BB386 adopted 86.5mm shell width. BB392 uses a 91.5mm shell width. And BB-right for 46mm shell ID uses 79mm shell width.

Phase 5: The problem of creaking in press-fit BBs is hard to solve, and thread-fit BBs came back

Since the emergence of BB30 press-fit, press-fit has become the mainstream. Thread-fit has faded out of people’s sight for a long time. Threads have recently returned due to their advantages, such as low noise and easy maintenance. There are still not many new thread-fit standards and products available. We are going to talk about BB386BSA, BB292BSA, and T47 here.

(1) BB386BSA and BB392BSA

The BB386BSA/BB392BSA standard is not an entirely new standard, and it is essentially an external BSA threaded BB standard with a specific shell width. Under their corresponding frame shell standard, the BB shell should be a BSA threaded (1.37in*24TPI) shell with 86.5mm/91.5mm shell width. So, under the BB386BSA/BB392BSA standard, the bottom bracket should be compatible with a BSA threaded (1.37in*24TPI) shell with 86.5mm/9.15mm shell width and should be an external BSA threaded BB.

(2) T47

The T47 standard is an improved version of the PF46 standard. The only difference between T47 and PF46 is that under the T47 standard, the connection between BB and BB shell has been changed from press fit to thread fit precisely by adding a layer of 1mm thread to the outer surface of the PF46 cup and turning the corresponding thread on the inner surface of the PF46 BB shell so that the BB shell can adapt to the cups with threads. By simply doing that, You will get a T47. The advantages of T47 bottom bracket are easy to maintain and reduces creaking. Of course, the T47 bottom bracket also brings some drawbacks, such as the risk of thread damage, causing the frame to be unusable.