A Comprehensive Guide to Bicycle Wheel Bearings - Types, Sizing, Materials and Maintenance

Introduction

Wheel bearings are small precision ball or roller bearing assemblies pressed or sealed into the center of bicycle wheels. They consist of an inner and outer raceway made of hardened steel with many small steel balls or cylindrical rollers in between. This bearing construction reduces friction between the stationary outer race and the spinning inner race.

Wheel bearings' main purpose is to allow the hub and attached wheel to effortlessly rotate around the stationary axle. They take the radial and axial loads from pedaling and braking forces.

Bearings generate very little rolling resistance compared to a rubbing surface. By using a set of steel balls or rollers and races, bearings make the bicycle more efficient by minimizing rotational losses. They also absorb small impacts and vibrations to provide a smooth ride. 

What is a Ball Bearing?

Ball bearings are mechanical components that are designed to separate the bearing races using spherical rolling elements. These bearings utilize the rolling motion of the balls to bear axial and radial loads. The major components of a ball bearing include an inner race (labeled A on the left in Figure 3), an outer race (labeled A on the right in Figure 3), balls (labeled C in Figure 3), and a cage (labeled B in Figure 3) that prevents the balls from coming into contact with each other. They are commonly used in high-speed applications such as electric motors and gearboxes. You can learn more about ball bearings by reading our article on the ball bearing overview.

 Ball bearing components: inner and outer races (A), cages (B), and balls (C). credit from: tameson

What is a Roller Bearing?

Roller bearings, also known as roller-element bearings, work on the same principle as ball bearings, providing efficient support for loads while minimizing friction. The difference lies in their shape and construction. While ball bearings use spherical balls, roller bearings use cylindrical rollers, which can be cross or linear.

These roller-element bearings can have single or double rows of rollers, with double-row bearings being particularly good at carrying radial loads. Their versatility, available in various shapes and sizes, allows them to transmit radial and axial loads with minimal friction, making them a valuable component in a variety of applications.

Roller bearings are designed with cylindrical or barrel-shaped rolling elements, providing greater contact area with the raceway to carry heavy radial loads.

Roller bearings have cylindrical, barrel-shaped rolling elements. credit from: tameson

Bearing Sizing

If you need to replace your bearings, it's important to know how to size them properly. This requires knowing the ball diameter, which can be measured using an imperial set of verniers for loose ball bearings. Common sizes include 5/32" for headsets and pedals, 3/16" for front hubs, and 1/4" for rear hubs and bottom brackets.

When dealing with cartridge (sealed) bearings, understanding three key measurements is paramount: the outside diameter, inside diameter (bore), and width. These measurements, often printed on the bearing itself, are crucial for finding the right replacement. In the absence of these markings, verniers can be used for measurement. For instance, a bearing with dimensions of 30x42x7mm should fit SRAM/Truvative cranks in a BB30 bottom bracket. Additional markings like 6806 2RS can also aid in size determination. If you encounter similar numbers, a quick online search should yield the necessary sizing information.

credit from: rs-online

Bearing Materials

The choice of material for bicycle bearings is critical to their performance. Different materials can affect how long the bearings will last, how smoothly they rotate, and how well they resist corrosion. For instance, using high-quality materials such as ceramic or stainless steel can increase the lifespan of the bearings and reduce friction, leading to more efficient riding. Moreover, suitable bearing materials can prevent wear and damage, prolonging the overall life of the bicycle system.

Ceramic Bearings

Ceramic bearings have become very popular in cycling due to their exceptional properties. They are known for being highly strong, hard, and having low friction coefficients. These features improve speed stability, reduce energy loss, and enhance efficiency. Ceramic bearings minimize vibrations and resonance, providing smoother and more stable operation, particularly at high speeds. Moreover, their corrosion resistance ensures long-lasting performance, making them an excellent choice for cyclists who ride in wet or corrosive environments.

Chrome Steel Bearings

Due to their reliable performance, chrome steel bearings are a popular choice for bicycle components. They are strong and durable, capable of withstanding the loads and forces encountered during cycling. Although they may have slightly higher friction than ceramic bearings, steel bearings still provide satisfactory speed stability. Cyclists commonly select steel bearings for their cost-effectiveness, making them a practical choice.

Hybrid Bearings

Hybrid bearings are a type of bearing that uses both ceramic and steel materials. They are designed with ceramic rolling elements and steel races. Because of the integration of ceramic rolling elements, hybrid bearings provide better speed stability compared to all-steel bearings. The ceramic components reduce friction and heat generation, improving speed stability, while the steel races give the necessary strength and rigidity for stable operation. Hybrid bearings are particularly advantageous in high-speed applications that require a balance between performance and cost.

Bearings Maintenance

Before removing a bearing for inspection, it is important to document its physical condition and take photographs. After checking the remaining lubricant and collecting a sample for examination, the cleaning process should be done.

• A dirty bearing should be cleaned using two cleaning processes, such as rough cleaning and finish cleaning.
• It is recommended that a net be set on the bottom of cleaning containers.
• In rough cleaning, use brushes to remove grease and dirt. Bearings should be handled carefully. Note that raceway surfaces may be damaged by foreign matter, if bearings are rotated in cleaning oil.
• During finish cleaning, clean bearings carefully by rotating them slowly in cleaning oil.

Bearings are typically cleaned using a neutral water-free light oil or kerosene. If necessary, a warm alkali solution can also be used. It is imperative to filter the oil before cleaning to ensure it remains clean. After the cleaning process, apply anti-corrosion oil or rust preventive grease on the bearings immediately.

Brand Recommend

Shimano

Shimano is the industry-standard OEM supplier with a wide model range for all budgets. From the value-priced Alivio to top-shelf Dura-Ace, you get legendary Shimano quality assurance. Precise engineering delivers consistent spin life after life. As the creator of common bearing types like 6803, their specifications are proven to simply work.

CeramicSpeed
For those chasing marginal gains or operating in demanding conditions, CeramicSpeed bearings slice watts with less rolling resistance. Their flagship UltrALite employs a ceramic ball design that's 40% lighter than steel. This shaves rotational mass for quicker acceleration and decreased friction for more efficient power transfer. The fully-sealed cartridge also simplifies cleaning and re-lubing. While expensive, racers appreciate maximum efficiency.