Maya Ellison
The plastic sleeve inside the bottom bracket of a bicycle is designed to keep water and dirt from getting into the bottom bracket from inside the frame. While some cyclists have questioned the need for the plastic sleeve, others have found it useful for keeping the bearings inside the bottom bracket dry and clean. Modern bottom brackets have plastic cups that are pressed into the frame, which helps to accommodate manufacturing tolerances and reduce the risk of creaking.
| Characteristics | Values |
|---|---|
| Purpose of the plastic sleeve | To keep water, dirt, rust, and swarf from getting into the bottom bracket |
| Plastic sleeve's compatibility with modern bottom brackets | Modern bottom brackets should be fine without the plastic sleeve |
| Plastic sleeve's importance | Depends on the riding conditions and the frame of the bike |
| Bottom bracket types | Threaded, Press-Fit |
| Bottom bracket length | Typically between 68 mm and 73 mm |
| Bottom bracket shell diameter | Varies by standard, e.g., 30 mm for BB30, 41 mm for PF41 |
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What You'll Learn
Plastic tubes prevent water from entering the bottom bracket
The plastic tube inside the bottom bracket is designed to prevent water from entering the bottom bracket and damaging the bearings. Water can enter the bottom bracket in multiple ways, including through the seat tube, spray from the rear wheel, and riding through puddles. While the plastic tube may not completely seal the bottom bracket from water, it can help to reduce the amount of water that enters and extend the life of the bearings.
Some people choose to install an external bottom bracket without the plastic tube, especially on road bikes, as they believe it is more important to prevent dirt and debris from entering the bottom bracket rather than water. However, others argue that the plastic tube is necessary, especially in wet conditions, to prevent water from entering the bottom bracket and causing damage.
The plastic tube is typically found in bottom brackets with cutouts, and most modern bottom bracket shells do not require the plastic tube. The plastic tube is usually installed between the bearing cups or bearing assemblies to keep water and dirt out. It is important to follow the manufacturer's instructions when installing the bottom bracket to ensure proper installation.
Additionally, it is recommended to use waterproof grease or marine grease to protect the bearings from water damage. Regular maintenance and draining of water from the bike after riding in the rain can also help prevent water damage to the bottom bracket. Overall, while the plastic tube may not completely seal the bottom bracket from water, it can provide some protection and reduce the amount of water that enters, helping to extend the life of the bearings.
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They also stop rust and dirt from entering
Bottom bracket plastics, also known as bottom bracket protectors or cable guides, serve multiple purposes. One of their essential functions is to prevent rust and dirt from entering the bottom bracket area.
The bottom bracket area of a bicycle is susceptible to dirt, grime, and moisture buildup due to its proximity to the ground and constant rotation of the cranks. Over time, this can lead to corrosion and premature wear of the bottom bracket components, affecting the performance and longevity of the bike.
The plastic guards act as a protective barrier, covering the bottom bracket and shielding it from external contaminants. They create a physical barrier that traps dirt and grime, preventing them from coming into direct contact with the sensitive mechanical parts. This barrier also helps deflect water and moisture away from the bottom bracket, reducing the chances of rust and corrosion.
Additionally, these plastic guards can make cleaning and maintenance easier. They can be easily removed, providing access to the bottom bracket for thorough cleaning, lubrication, or component replacement. By keeping the area relatively enclosed, they help contain lubricants or grease applied to the bottom bracket, ensuring their effectiveness and reducing the need for frequent reapplication.
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The plastic cups in press-fit bottom brackets reduce creaking
The plastic cups in press-fit bottom brackets are preferred by frame manufacturers, but consumers tend to prefer aluminum cups. The plastic cups are used to insulate the cups from the shell and to prevent creaking. While they can be effective in reducing creaking, they are not a perfect solution. Over time, the dimensions of the plastic cups can change, causing them to no longer fit as tightly, which can lead to creaking. Additionally, the use of grease or retaining compounds is often necessary to reduce creaking, but these are only temporary solutions.
The plastic cups in press-fit bottom brackets are designed to provide better manufacturing tolerance and reduce creaking. This is achieved by housing the bearings in plastic cups, which are then pressed into the frame. This type of design is known as PF30 and is commonly used in high-end bikes. The use of plastic cups allows for greater rigidity and reduced weight, making it a popular choice for many cyclists.
While the plastic cups can help reduce creaking, it is important to note that they are not a foolproof solution. Some cyclists have reported issues with creaking, even when using press-fit bottom brackets with plastic cups. In some cases, the creaking may be due to the use of adapters, which may not have exact-matching tolerances. Additionally, the plastic cups themselves can change dimensions over time, leading to a less secure fit and potential creaking.
To further reduce creaking, it is recommended to ensure proper reaming of the bottom bracket shell to achieve a consistent round shape and proper diameter. This ensures a better fit between the cup and the frame. Additionally, treating plastic and carbon surfaces with a primer, such as Loctite, can improve adhesion and help reduce creaking. However, even with these measures, creaking may still occur, and it is often necessary to experiment with different solutions to find what works best for each individual bike.
Overall, while the plastic cups in press-fit bottom brackets can help reduce creaking, they are not a guaranteed solution. The effectiveness of plastic cups depends on various factors, including the specific design, manufacturing tolerances, and the age of the cups. Cyclists may need to explore different options, such as using retaining compounds or primers, to find the most effective way to reduce creaking in their press-fit bottom brackets.
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Plastic spacers are used in some bottom brackets
The plastic spacers are usually flimsy plastic tubes that connect the cartridge bearings on each side of the bottom bracket. While they may seem superfluous, they can prevent water damage and contamination from rust and other debris from the frame. Some people have used cardboard as a substitute, but this is less effective at keeping moisture out.
The need for a plastic spacer depends on the type of bike and the conditions in which it is ridden. For example, a road bike may not need a plastic spacer as it could trap heat and dust. In contrast, a mountain bike with a cut-out in the BB shell may benefit from one to keep the bearings dry.
Some bottom brackets, such as the Shimano Hollowtech II and SRAM GXP, use plastic cups to house the bearings, which are then pressed into the frame. This design improves manufacturing tolerance and reduces creaking.
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Plastic tubes are not necessary for all bottom brackets
The plastic tube inside the bottom bracket is not necessary for all bottom brackets. It is designed to keep water, dirt, and rust from getting into the bottom bracket and contaminating the bearings. However, some riders have expressed that it is unnecessary if you do not ride in wet conditions or if your frame does not have an opening between the seat tube and the bottom bracket.
For example, one rider on the Cycling UK Forum shared that they do not deliberately ride in the rain and questioned how much water could get inside their bottom bracket during the few times they ride in wet conditions. They also pointed out that there is nothing to prevent water from entering the outside of the bottom bracket, so protecting the inside with a plastic tube seems unnecessary. They also mentioned that on a road bike, the plastic tube might trap heat and dust instead.
Another rider on Bike Forums shared a similar sentiment, questioning the need for the plastic tube if they are not riding in the rain. They also noted that water can enter the bottom bracket through drain holes, and while it is easy to work with external bottom brackets, it is better to install the plastic tube according to its design and instructions.
It is worth noting that modern bottom bracket designs, such as the BB86/92 and PF30 standards, use plastic cups to house the bearings, providing better manufacturing tolerance and reducing creaking. These plastic cups are then pressed into the frame. However, this design can lead to issues if the fit between the plastic cup and carbon shell is not good enough, as it can cause unwanted movement and creaking.
In conclusion, while the plastic tube is not necessary for all bottom brackets, it can be beneficial in certain conditions, such as riding in wet weather or having a frame with openings between the seat tube and the bottom bracket. Riders should also consider the potential for water to enter through drain holes and the possibility of trapping heat and dust in road bikes. Ultimately, it is up to the rider to decide if they want to install the plastic tube based on their specific circumstances and preferences.
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Frequently asked questions
The plastic sleeve inside the bottom bracket is designed to keep water, dirt, rust, and other debris from getting into the bottom bracket and contaminating the bearings.
If you are riding in wet conditions with a frame that has an opening between the seat tube and the bottom bracket, then yes, you need the plastic tube.
The plastic tube should be installed according to its design and instructions. It is important to choose a bottom bracket that is compatible with both the crankset and the frame of your bike.
