Introduction

Today, let's talk about the T47 bottom bracket standard and take a look at the various models introduced by major brands.

2021 could be considered the year when the T47 standard began to shine in the cycling world. Specialized launched the 2021 S-Works Tarmac SL7, and Trek introduced the Emonda SLR and SL series. More importantly, Trek plans to popularize this standard across more of its road bike product lines in the future. T47 first appeared in 2015, and back then, many thought it was just "another new standard." However, it is now gradually becoming a focal point in the industry and could become increasingly significant in the coming years.

But when it comes to bottom bracket standards, can't we make things simpler? Many cyclists wish the specifications for bottom brackets and cranksets could be less complicated because having too many options can be a headache!

 

ICAN Graro Equipped with T47 

This is why we want to delve deeper into T47. While it has many advantages, it's not easy to understand. On one hand, it involves various specifications and options; on the other hand, major brands have their own interpretations and practices when it comes to its application. Even more troublesome, it attempts to be compatible with a bunch of existing standards, which are already quite chaotic themselves. (If you're interested, you can check out the summary at the end of the article.)

 

What is a T47 Bottom Bracket?

T47 bottom bracket installation

What exactly is a T47 bottom bracket? Essentially, it can be understood as an improvement on the PF30 bottom bracket shell by adding threads. The inner diameter of the PF30 bottom bracket shell is 46mm, and after threading, the specification becomes M47 x 1.0mm. The drive side uses a left-hand thread, while the non-drive side uses a right-hand thread, which is a standard British thread design.

Why do we need T47? In simple terms, it's to solve the issue of bottom bracket noise. Press-fit bottom brackets (like BB30, PF30, BB86, BB92, etc.) offer good rigidity and wide bearing setups, but they require extremely high manufacturing precision for the frame. If tolerances exceed even slightly, noise can occur. Many brands have tried to address this by "gluing" the bottom bracket to the frame, but this is more of a temporary fix rather than a long-term solution.

The development of T47 can be traced back to 2015, developed by Chris King and other industry professionals. The design's intent was to combine the advantages of both press-fit and threaded bottom brackets - maintaining the stability of threaded bottom brackets while being compatible with the crankset specifications common to press-fit systems. Thus, it was named "Threadfit T47," which sounds like an "evolution" of the press-fit bottom bracket.

The name "T47" comes from the thread size - 47 x 1 millimeters. This standard is applicable to frames equipped with a T47 bottom bracket shell. Although the name is simple, its practical application isn't as straightforward to understand. T47 bottom bracket shells come in various width versions, requiring users to choose the appropriate model based on specific frame dimensions. Moreover, T47 can also be compatible with some cranksets originally designed for press-fit bottom brackets (like BB30 or PF30), making this standard even more complex.

T47 aims to bring more stability and compatibility to bottom bracket systems while addressing the noise issues associated with press-fit bottom brackets. However, its introduction has also increased the diversity of bottom bracket standards. Whether it will truly become the industry standard remains to be seen with time.

Original Drawing of T47

 

Types of T47 Bottom Brackets

This section will introduce several common types of T47 bottom brackets.

FIRST Components offers bottom bracket designs for both traditional 24mm and 30mm axle cranksets. These bottom brackets can be installed either internally or externally, catering to various needs.

Each model comes with spacers of different sizes to accommodate a wider range of cranksets. For instance, in the picture, you can see two types for 24mm axles: the one at the top has aluminum sleeves, while the one at the bottom has plastic sleeves. The plastic sleeves can also be drilled, making it easier for internal cable routing through the bottom bracket shell, thus simplifying installation.

Internal Installation vs. External Installation

There are two ways to install the bearings of a T47 bottom bracket: one is to place them inside the bottom bracket shell, and the other is to install them "externally" around the outside of the bottom bracket shell, as seen with the right-side component. The choice largely depends on personal preference; there's no absolute right or wrong.

With the rise in popularity of integrated cranksets, 24mm axles, and external bearing cups, the bottom bracket can use larger bearings. This not only extends bearing life but also increases the rigidity of the crank axle due to the larger diameter of the hollow axle design. For traditional BSA bottom bracket shells with an inner diameter of 34.8mm, the initial upgrade was from a solid axle to an integrated axle with external bearings, which significantly enhanced performance.

In contrast, the T47 bottom bracket shell has an inner diameter of 46mm, which is 11.2mm larger than BSA, allowing for even larger external bearings. For example, the outer diameter of sealed cartridge bearings is 30mm, traditional external bearings are 40mm, while the internal sealed bearings for T47 reach an outer diameter of 42mm, 2mm larger than traditional external bearings.

In summary, both internal and external installation methods have their pros and cons. Although there isn't a significant performance difference between internal and external components, you can choose your installation method based on your needs and preferences.

These internal bottom bracket cups with aluminum sleeves are threaded into the drive side. If you are particularly concerned about weight, you can opt to remove the sleeves, but this will reduce protection against water and grit. Sacrificing a bit of weight for a higher risk of water or sand ingress into the bottom bracket is not a wise choice.

Be Cautious to Avoid Cross-Threading

If the frame's bottom bracket shell is machined with sufficient precision, installing a T47 bottom bracket is quite straightforward: you just need to screw the bottom bracket cups into the shell and tighten them with the correct tool.

However, there is a risk of cross-threading with threaded bottom brackets. To prevent this, make sure the threads of the bottom bracket cup are perfectly aligned with those of the bottom bracket shell before screwing it in. Even if it appears aligned with only slight resistance, cross-threading can still occur.

T47 Bottom Brackets are Much Larger than Traditional Threaded Ones, Making Them More Prone to Misalignment Due to Incorrect Angles. To ensure proper alignment, you can use a little trick:

Start by turning the drive-side bottom bracket cup counterclockwise (left) for a few turns, then turn it clockwise (right). This goes against the threading direction and helps the threads find the correct position. When alignment is successful, you might feel or even hear a "click" or "thump," indicating that the threads have engaged properly.

Usually, you'll need to turn it back and forth a few times until you're sure it's completely aligned, then tighten the drive-side cup all the way clockwise.

For the non-drive side, do the opposite: start by turning it clockwise (right) a few turns, then counterclockwise (left) to align it.

Once you feel the threads engaging smoothly, you can complete the installation.

The image shows the T47 bottom bracket wrench provided by ICAN Cycling, suitable for T47 bottom brackets. 

Precautions Regarding Torque for T47 Bottom Brackets

For internal T47 bottom brackets, you'll need to use the tool on the far right; the left tool (Y30) is for installing external bottom bracket cups, which will be explained in detail later.

The flange provides a surface area of only 2mm, so when applying force, the tool must be kept parallel to the flange to maximize leverage. Since the flange's surface area is just 2mm, during tightening, the tool must be kept parallel to the flange to achieve the best leverage. The recommended torque range for tightening is standard for threaded bottom brackets: a minimum of 35 Nm and a maximum of 45 Nm.

How can you tell when you've reached the proper torque? Generally, if you tighten with full force using regular effort, you'll exceed 35 Nm. This tool is designed in such a way that it's not easy to over-tighten due to excessive force. It's recommended to wear gloves or wrap the tool handle with a soft cloth to both improve grip and protect your hands, then apply appropriate force to tighten the bottom bracket cup fully.

This image shows an example of a plastic sleeve, which can serve as an alternative to an aluminum sleeve. If you are very strict about weight, the plastic sleeve is a lighter option. 

24mm External T47 Bottom Bracket

The external bearing version includes two bottom bracket cups and an aluminum sleeve.

The sleeve is threaded onto the drive side. Alternatively, you can choose to install just the bottom bracket cups.

Compared to the internal T47 bottom bracket which only has a 1mm tool slot, the external T47 bottom bracket cups provide a 5mm clearance, making it easier to use tools.

Complete Assembly Diagram, Equipped with a 30mm Crankset.

T47 24mm Adapter Sleeve

You can add a 24mm adapter sleeve option to components designed for a 30mm axle. Each adapter sleeve has an outer diameter of 30mm and an inner diameter of 24mm.

By applying even pressure on both sides of the adapter sleeve, you can install it into the bottom bracket cup with a 30mm inner diameter.

The fit of the adapter sleeve is quite tight, but it won't be too difficult to install or remove. To remove it, simply clamp the bottom bracket cup with a vise, and then gently and evenly tap the inner edge from the other side.

The aluminum sleeve can be threaded onto the drive-side bottom bracket cup or permanently fixed to it.

On the non-drive side, the connection between the sleeve and the bottom bracket cup relies on a crucial component—a rubber seal ring, which is embedded in the end groove. Without this seal, the connection would be too loose, leading to noise during riding.

The seal ring is very durable, but if it ages or gets damaged, it can be easily stretched into place for replacement, making it very convenient.

T47 Asymmetric Bottom Bracket

An asymmetric bottom bracket can adjust the height of the crank axle, thereby changing the position height of the cranks and pedals. While adjusting the height, it also affects the chain tension. Therefore, an asymmetric bottom bracket can be used not only to adjust the riding posture but also to tweak the chain's tightness, achieving two benefits at once.

The T47 bottom bracket, with its larger size, is particularly suitable for some special types of bicycles, like tandem bikes, offering a wide range of applications.

This design draws inspiration from the popular BSA asymmetric bottom bracket by FIRST Components. Its core feature is an off-center component where the sealed bearings inside can rotate within the main housing, which has a unique hexagonal structure.

Here, the crankshaft is almost at the top position.

During adjustment, it's necessary to rotate both the drive side and the non-drive side simultaneously to ensure parallelism at both ends of the axle. If the sides are not synchronized, it will get stuck and cannot be adjusted.

The asymmetric bottom bracket is rotated to near the bottom position.

By evenly tightening three of the six 2mm hex bolts at the vertices of the hexagon, you can prevent the inner housing from rotating.

The large holes at the other vertices of the hexagon are used for the tool to install the bottom bracket cup — the curved end of the tool hooks into these holes to leverage the flat edges for operation.

 

T47 Bottom Bracket Geometry Dimensions

Label	Drive Side	Non-Drive Side	Shell Width（mm）	Notes
T47-68 (T47 or T47 External)	M47x1.0	M47x1.0	68	This is a very popular standard, mainly used for custom bicycle frames made of metal.
T47-86 (T47i or T47 Internal)	M47x1.0	M47x1.0	86.5
T47-85.5 (T47i)	M47x1.0	M47x1.0	85.5	This standard is exclusive to Trek. In most cases, it is interchangeable with T47-86.
T47A-77	M47x1.0	M47x1.0	77.5 (See Notes)	This housing is asymmetrical, with the drive side matching T47-68 and the non-drive side matching T47-86. It is almost exclusively used for Felt and Factor bicycles.

T47 Bottom Bracket Variants

 

Disadvantages

Weight Issue

For most cyclists, the biggest drawback of the T47 bottom bracket is its weight. A typical T47 bottom bracket weighs about 180 grams, and to install a T47, aluminum inserts or sleeves are needed inside the bottom bracket shell, adding another approximately 100 grams. That sums up to around 300 grams in total. In comparison, a BB86 bottom bracket weighs only 95 grams, and a PF30 is just 130 grams, making the weight of the T47 a significant consideration.

Tool Issue

When it comes to tools, the installation and removal of T47 bottom brackets can be quite a headache. Especially for specific T47 variants where the bottom bracket shell width can reach up to 86.5 millimeters (similar to BB86), but the flange where the tool grips is very thin, only 2 millimeters thick. This makes it easy for the tool to slip or even damage the threads during operation. Brands like Trek, Felt, and Factor have indicated they will use these T47 variants, but the issue of tool compatibility remains a concern that needs special attention.

T47 shows two versions, 68mm and 86.5mm, with clear differences in the tool drive flange.

 

For comparison purposes, here are pictures of the Chris King Threadfit T47 interfacing with Shimano and the Hambini T47 interfacing with Shimano. It's worth noting that the narrow tool flanges are not there to provide clearance for the cranks but to make manufacturing simpler and cheaper.

Chris King Threadfit T47 with a small transmission side flange

 

 

ICAN's Non-Drive Side T47

Advantages

Ease of Installation
One of the biggest advantages of a threaded bottom bracket system is its convenience both in installation and use, especially for average users. With the right tools, installing and removing a threaded bottom bracket is straightforward. Unlike press-fit systems, you don't have to worry about the bottom bracket shell not being round enough, as the threaded design inherently avoids this issue. Of course, aligning the threads on both sides might still be a challenge, but this can be addressed with alignment sleeves (for example, the Hambini bottom bracket comes with this feature).

Good Compatibility
For some lower-cost or custom metal frames, the T47 bottom bracket is an ideal choice. Especially the 68mm variant of T47, which is very suitable for these types of materials and manufacturing processes.

Performance

Friction Loss

In a setup where T47 is paired with Shimano, the friction loss is slightly higher than with a BSA setup paired with Shimano. This is mainly due to the different bearing specifications used: T47 employs 6806 bearings while BSA uses 6805 bearings. Although the difference is small, it can be measured.

 

Stiffness Comparison

Stiffness is another factor to consider. A BSA setup with Shimano shows better stiffness performance because its bottom bracket design has a smaller size and more precise manufacturing tolerances. In contrast, press-fit bottom brackets, like BB86, perform better in terms of stiffness since some of the load can be directly transferred to the frame, enhancing overall stiffness.

 

Conclusion

The T47 bottom bracket, as a solution combining threaded and press-fit systems, has been gaining more attention in recent years. From being initially viewed as "just another new standard" to becoming an important choice in major brand product lines, the adaptability and advantages of T47 have solidified its standing in the industry.

Its strengths lie in easy installation, strong compatibility, and particularly outstanding performance in certain special types of bikes (like tandems). However, T47 also has its downsides, such as the heavier overall weight and the higher precision required for tools, which might affect some users' decisions.

Although T47's performance in certain aspects (like friction loss and stiffness) might not match traditional BSA or press-fit bottom brackets, it attempts to strike a balance between stability and compatibility. Especially for riders with custom metal frames or those looking to resolve bottom bracket noise, T47 is certainly an option worth considering.

In the future, as the industry further optimizes and embraces the T47 standard, it could become the preferred choice for more brands and users. However, for cyclists wanting to try this standard, selecting the right configuration and tools remains crucial.

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