The size of loose ball bearings is determined by the diameter of the balls themselves, typically measured in fractions of an inch, such as 3/16 inch (4.7625 mm).
The exact size required varies depending on the specific component. Generally, it’s easier to replace the cones in loose ball bearings, while the cups, especially in hubs, are rarely replaced. If you need to service or replace the balls, ensure that the new ones are the same size as the originals. You’ll need a micrometer to measure the old balls, and brands like Park Tool offer specialized gauges specifically for measuring ball diameters.
Alternatively, you should be able to find the ball size in the technical manuals on the part manufacturer’s website. Generally, brands that use loose ball bearings tend to use the same size across their product range.
Deep Groove Cartridge Bearing Sizes
These bearings are typically measured by their outer diameter (OD), inner diameter (ID), and width, and sometimes have a common identifier like “61902.” With this information, sizes are generally expressed in the format “15x24x5mm” or similar. Standard parts often have corresponding universal identifiers, such as 6802 for the above bearing.
Using calipers, you can measure the bearing to easily find a replacement. Sealed bearings of this type usually benefit greatly from a bit of grease applied to them.
Headset bearings have unique characteristics, featuring angled raceways. Their size is typically expressed as “46.9x7x45°,” representing the outer diameter, width, and angle measurement of the bearing raceway, respectively.
In terms of performance, generally, the larger the balls within the bearing, the better. An increase in diameter positively correlates with increased contact area; more contact means a more even distribution of force, resulting in improved rolling performance and durability. In recent years, several major wheel manufacturers have started using larger bearings, and hub sizes have continued to increase accordingly.
Radial vs. Angular Contact Bearings
Two types of bearings are typically used in bicycles: radial and angular contact. In the image above, the radial bearing is on the left, and the angular contact bearing is on the right.
Radial bearings are the most common due to their lower cost. They are designed to bear vertical loads, such as those found in hubs, cranks, and bottom brackets. However, since these moving parts inevitably have non-radial force vectors, there is a slight performance trade-off. Therefore, radial bearings compensate by lowering tolerances.
In short, radial bearing systems have lower precision. They can only handle vertical forces without distinguishing between internal and external directions, and since they are less dependent on precise tolerances, they are suitable for more cost-effective applications.
Angular contact bearings require strict tolerance control, distinguish between internal and external directions, and, in terms of design, are comparable to traditional cup-and-ball systems. They support both radial and lateral loads in rotating parts but require highly precise housing bores to achieve proper fit and excellent rolling performance.
In most cases, angular contact bearings are the most suitable choice for hubs, cranks, and suspension. However, the manufacturing precision of many hub and frame brands is insufficient to meet the requirements of angular contact bearings. This high precision requirement is the reason brands like Industry Nine, Chris King, White Industries, Phil Wood, and Alchemy Wheel Works have earned their reputation.
What Makes a Bearing High Quality?
You’ll often see bearings labeled as "ABEC" followed by a number (e.g., ABEC 1, 3, 5, 7, and 9).
The ABEC standard encompasses the following criteria:
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Inner Diameter – Acceptable tolerance variation for the bearing’s inner bore size
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Parallelism – Width tolerance
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Radial Runout – Tolerance variation in the grooves where the balls sit
In short, the higher the number, the better the bearing quality. It serves as a general “good, better, best” measure. However, the ABEC rating doesn’t account for load capacity, ball precision, or material hardness.
Generally, ABEC 3 and 5 are suitable for all bicycle applications. Levels 7 and 9 are designed for equipment running at thousands or hundreds of thousands of RPM, which is overkill for bicycles.
Factors like sealing, material, and grease are more critical in determining the performance of bicycle bearings.
Quick Guide to Seals
Seals on bearings can be carefully removed for cleaning and fresh grease injection, but be aware that improper handling may damage the bearing. Cartridge bearings are generally sealed with two rubber seals, one on each side.
There are three main considerations regarding seals: friction, protection, and maintainability.
Friction is a primary point of debate. While less friction is ideal, a slight amount can offer protective benefits. The purpose of seals is to keep grease inside and prevent contaminants from entering. However, once contamination occurs, can you clean and service the bearing without damaging the seals?
For most high-quality bearings, such as those made by Enduro, each bearing is designed so the seal can be removed from the inner ring “using a small blade and a careful hand for servicing.”
What Types of Seals Are Used on Bicycle Bearings?
Labyrinth Seal on Shimano Rear Hub
Bearings on bicycles can feature single seals, double seals, or labyrinth seals. As the name suggests, a single seal is a simple cover attached to the outer edge of the bearing race. With only one seal, it may be more susceptible to contamination than more complex seals.
Double-sealed bearings have a second dust cover outside the main seal, making the bearing more resistant to contamination. Labyrinth seals provide a winding path that helps prevent dust and water from entering the bearing. This design helps expel contaminants before they can reach the bearing. While labyrinth seals can extend maintenance intervals, they may also add extra friction compared to simpler sealing systems.
What Are Bearings Made Of?
Bearings are made from a variety of materials, typically including chromoly steel, 440C stainless steel, XD15 nitrogen stainless steel, and silicon nitride (ceramic bearings). Generally, the harder the material, the better, but there’s a point of diminishing returns. If the material is too hard, it becomes brittle, loses toughness, and overly hard balls can increase wear on the bearing housing.
A balanced quality, along with the budget and servicing you’re willing to invest for performance improvement, are all factors that bearing brands need to consider.
What Are the Benefits of Ceramic Bearings?
Ceramic bearings are five times harder than steel bearings, resulting in less friction when they roll. Ceramic bearings are also manufactured with tighter tolerances, and the balls in ceramic bearings have better sphericity, requiring less lubricant and resulting in an overall lighter weight, which further reduces friction within the bearing assembly.
According to Hunt Wheels, replacing steel bearings in hubs and drivetrains with ceramic bearings can save 6 to 9 watts of power. However, ceramic bearings require more frequent maintenance than steel bearings. Industry experts agree that high-quality steel bearings outperform low-quality ceramic bearings.
How to Maintain Bearings
Like any moving part on a bicycle, bearings require maintenance and care. High-quality bearings may have longer maintenance intervals, but no bearing is truly “install and forget.”
Bearing maintenance typically involves removing the bearings from the bike and using a degreaser to remove old lubricant. At this stage, you can inspect the balls and bearing race for wear or pitting. If there’s significant wear or damage, replacement may be necessary. You can then re-lubricate the bearings and reassemble, or replace the balls if needed.
Proper installation also plays a crucial role in bearing lifespan.
For loose ball bearings, ensure the cup and cone are tight enough to have no gaps, but loose enough to allow effective rotation of the component. You may need to adjust multiple times to achieve this balance. Misalignment from improper installation of deep groove ball bearings is a major cause of premature wear; a professional bearing press tool can help ensure proper installation.
Additionally, if you're using angular contact bearings, they are typically distinguished by seal color to indicate orientation: black faces inward, and red faces outward.
Proper maintenance of bearings requires the use of suitable lubricants, which can range from thick waterproof grease to thin low-friction lubricants. Selecting the best lubricant depends on understanding your riding environment and consulting the relevant component manuals to find the most suitable option. Brand manufacturers often recommend their own branded lubricants, though these are typically more expensive than other brands.
The type of bearing system used, maintenance frequency, and the environmental exposure the system undergoes will determine the optimal lubricant choice.