A bottom bracket is an important component of a bike’s drivetrain, responsible for the smooth rotation of the pedals. There are two main types of bottom brackets: cartridge bottom bracket and cup and cone bottom bracket. In this article, we’ll focus on the latter.
A type of bicycle bottom bracket that uses a set of loose ball bearings and a cup-and-cone design to allow the bottom bracket axle to rotate smoothly within the bottom bracket shell of the frame. It was the most common type of bottom bracket used before cartridge bottom brackets came to the market and it’s still being used on many types of entry level and children bicycles.
What are the parts of a cup and cone bottom bracket?
This type of bottom bracket consists of:
Fixed cup
The drive-side cup is a threaded component that screws into the right side of the bottom bracket shell and holds the cup-shaped race for the ball bearings.
The main job of the drive-side cup is to support the bottom bracket axle and the crankset, while also allowing the crankset to rotate smoothly around the axle.
Adjustable cup
The adjustable cup on the non-drive side of the bottom bracket is a threaded component that screws into the bottom bracket shell on the left side of the bicycle frame. Its primary function is to provide a means of adjusting the preload on the bottom bracket bearings and ensuring proper bearing alignment.
The adjustable cup is called “adjustable” because it can be rotated to adjust the amount of tension on the bottom bracket bearings. This tension, also known as preload, is critical to the smooth operation of the bottom bracket and can affect the durability and longevity of the bearings.
The adjustable cup is typically turned clockwise to increase preload and anti-clockwise to decrease preload. It must be adjusted carefully to ensure that the bearings are not overly tightened, which can cause premature wear and damage.
Bottom bracket axle
The bottom bracket axle is a component of a bicycle’s drivetrain that connects the cranks to the bicycle frame. It is essentially a long, cylindrical rod with a square cross-section where it attaches to the crank arms.
The job of the bottom bracket axle is to transmit the power generated by the cyclist’s pedaling motion to the rear wheel through the chain. As the cyclist pedals, the bottom bracket axle rotates, causing the cranks to turn, which in turn drives the chain and ultimately propels the bicycle forward.
In addition to transmitting power, the bottom bracket axle also helps to maintain proper alignment of the crankset and prevents the cranks from wobbling or flexing during use.
Bottom bracket axles come in various lengths and each has a unique code engraved on the axle.
These codes are explained here:
| Axle code | BB shell width | Asymmetrical axle length | Corresponding symmetrical axle |
| 3H | 68mm | 113mm | 113 |
| 3K | 68mm | 117.5mm | 119 |
| 3N | 68mm | 120mm | 124 |
| 3NN | 68mm | 124mm | 124 |
| 5N | 70mm | 122mm | 125 |
| 3P | 68mm | 119mm | 122 |
| 3S | 68mm | 124.5mm | 127 |
| 3T | 68mm | 123mm | 130 |
In order to address issues with chainline some old-school bottom bracket axles are asymmetric.
Chainline refers to the alignment of the chain as it runs between the chainring and the rear cassette or freewheel. In some cases, especially with certain types of cranksets or frames, the chainline could become misaligned, causing issues with shifting performance, chain wear, and overall efficiency.
By making the bottom bracket axle asymmetric, with one side longer than the other, bike manufacturers were able to adjust the chainline to a more optimal position. This helped to improve overall performance and reduce wear on the drivetrain components.
When replacing the bottom bracket axle make sure that the longer section of the axle sits on the drive side.
Two sets of ball bearings
Between the cups and cones are ball bearings. They are the components of the bicycle bottom bracket that allow the bottom bracket axle to rotate smoothly within the bottom bracket shell of the frame. They can be either loose ball bearings or caged ball bearings, and are 1/4″ in size.
Their main job is to reduce friction and wear between the bottom bracket axle and the bottom bracket shell, while also supporting the weight of the rider and transmitting pedaling forces to the rear wheel through the chain.
Loose ball bearings are individual balls that are placed within the cup-shaped races of the bottom bracket. They share the load better than the caged bearings and wear slower however they can be more difficult to remove and install as you have to deal with each bearing separately. The number of loose ball bearings in each cup is 11.
Caged ball bearings are pre-assembled sets of ball bearings that are held together in a metal cage. They are easier to remove and install however because there are fewer of them they do not share the load as well as loose bearings and may not last as long.
Lockring
The lockring is a threaded component that screws onto the adjustable cup on the non-drive side. Its main job is to hold the adjustable cup in place and prevent it from moving or rotating during use. The adjustable cup is used to adjust the tension on the bottom bracket bearings, and it needs to be held in place once the correct tension has been set. The lock ring provides a secure and reliable way to do this, by threading it onto the adjustable cup and tightening it against the frame.
Servicing a cup and cone bottom bracket
They need to be serviced regularly to keep the bearings spinning smoothly. Over time, dirt and grime can build up, which can cause the bearings to grind and wear down. Worn or damaged bearings can lead to excessive friction, noise, and reduced efficiency in the bicycle drivetrain,
Tools required for a cup and cone bottom bracket replacement
To service this type of bottom bracket, you will need a few tools:
- Fixed cup wrench.
- Lock ring spanner.
- Adjustable cup spanner.
- Pin spanner. Some older adjustable cups have holes and the pins on the spanner fit into them. To remove the adjustable cup slot the pins in the pin holes so that you can unscrew the cup anticlockwise.
- Crank extractor
- 14mm socket spanner or a 8 mm allen key
- Adjustable spanner
- Flat head screwdriver
- Grease or anti-seize
- Cloth or a paper towel
Replacing a cup and cone bottom bracket.
Here are the steps to service a cup and cone bottom bracket.
Preparation
- Put the bike in a stand.
- If you have a bike with front gears then move the chain onto the smallest chainring.
- If you have a single-speed bike or hub gears then use a 15mm spanner to undo the rear wheel nuts and move the wheel in the dropouts to slacken the chain.
- Remove the chain from the chainring and rest it on the bottom bracket shell.
- If you have crank dust caps then remove them with a flat-head screwdriver.
- Using a 14mm socket spanner or 8mm allen key remove the crank bolts anticlockwise.
- Before you screw the crank extractor into the crank make sure that the bolt part does not stick out of the nut part.
- Now, using your hand, gently screw the crank extractor into the crank arm on the drive side. If the tool is not screwing in then don’t force it as you may damage the thread. Remove it and repeat the process until the tool sits in the threads properly.
- Once the tool is in place use the adjustable spanner to tighten the nut part of the crank extractor.
- Now screw the bolt part of the extractor with your hand all the way in.
- Hold the crank in one hand and, using an adjustable spanner, screw the crank extractor clockwise until the crank comes out.
- Now remove the left-hand crank arm.
- Measure the axle length. Double-check this measure as the axles differ from each other only by a few millimetres and it is important to get the exact replacement.
Removing a cup and cone bottom bracket.
- First, remove the lockring on the non-drive side. Fit the lock ring spanner in the lock ring’s slot and undo it anticlockwise.
- Once loose remove it from the adjustable cup.
- Now slot the pins of the pins spanner in the pin holes on the adjustable cup or fit the adjustable cup spanner on the raised 16 mm flats and unscrew it anticlockwise.
- Remove the adjustable cup and remove the axle.
- Fit the fixed cup spanner on the 36mm flats on the fixed cup on the drive side of the bike and unscrew it clockwise.
- Once loose remove it from the bottom bracket shell.
- Clean the threads in the bottom bracket shell.
Fitting a cup and cone bottom bracket
- Remove the bearings from the bottom bracket cups and clean the cups, bearings, and axle.
- Check the bearings, the axle, and cups for wear and if required replace them.
- Add some grease to the bottom bracket cups.
- Place the bearings in the cups and add a bit of grease on the top of the bearings.
- Apply a small amount of grease or anti-seize to the threads in the bottom bracket shell.
- Grasp the fixed cup in your hand and gently screw it anticlockwise into the bottom bracket shell on the drive side.
- Once in place, using the fixed cup spanner, tighten it anticlockwise.
- Place the axle in the bottom bracket shell.
- Now grab the adjustable cup and gently screw it clockwise into the bottom bracket shell on the non-drive side.
- Use the adjustable cup spanner to tighten the adjustable bearing cup clockwise until there is no play in the axle but it can spin freely.
- Using your hand, fit the lock ring.
- Fit the lock ring spanner and the adjustable cup spanner. Tighten the lock nut clockwise making sure that the adjustable cup stays in place.
- Check if the axle spins freely and that there’s no play. If required, loosen the lock ring and adjust the adjustable bearing cup until you’re happy, and retighten the lock ring.
- Once the bottom bracket is secured, you can reinstall the crankset. We have a great article here to help you with fitting crank arms.
- if required refit the crank dust caps
- Place the chain on the chainring.
- For single-speed and hub gear bikes re-tension the chain. Our article here will guide you through this task.
Can I replace a cup and cone bottom bracket with a cartridge bottom bracket?
Yes, you can replace a cup and cone bottom bracket with a cartridge bottom bracket. In fact, many newer bikes come with cartridge bottom brackets as standard. Cartridge bottom brackets are generally easier to install and maintain, as they require less frequent servicing and are less prone to dirt and grime build-up.
If you’re considering replacing your old fashion bottom bracket with a cartridge bottom bracket, be sure to check that the new one is compatible with your bike’s frame and crankset. Most cup and cone bottom brackets sit in a 68mm shell. The only exception are bottom bracket shells with Italian thread. These shells were usually 70mm.
Make sure that the axle on the cartridge bottom bracket is the same length as the old one.
You will also need a 20-spline bottom bracket tool.
- Fit the bottom bracket unit on the drive side. Screw it gently with your hand anticlockwise until it sits in the bottom bracket shell.
- Fit the 20 spline tool and tighten the bottom bracket with your hand as far as it goes.
- Now hold the tool with one hand and using an adjustable spanner tighten the bottom bracket shell.
- Repeat the process on the non-drive remembering that the bottom bracket cup screws in clockwise.
- Refit the cranks.
Conclusion
servicing a cup and cone bottom bracket is an important part of bike maintenance. By keeping the cups, cones, and spindle clean and lubricated, you can ensure that your bike’s bottom bracket runs smoothly and efficiently. And if you’re looking for a simpler maintenance solution, consider replacing it with a cartridge bottom bracket.
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