Quick and Dirty
Three main ball materials that are commonly found on the market are Steel (52100/100Cr6), Stainless Steel (440C or 316C), and Ceramic (Silicon Nitride or Zirconia). Steel balls are the most cost effective and are great for any general use. There is a small gain in corrosion resistance with Stainless Steel, however, don’t be fooled into thinking there are also large technical gains within the bicycle industry. Ceramic can gain a rider longer use after contamination, and some overall robustness to the bearing. Stainless Steel bearings would make sense for Cyclocross because of the frequency the bearing is getting wet. Outside of Cyclocross, a properly installed ‘Steel ball’ bearing will be great for a standard bicycle application. Feel free to step up to Ceramic balls for a little bit of robustness and bragging rights to your friends! (“Full Ceramic”)
Ball Bearing Materials
Let’s take a closer look at the three main ball materials that are readily available. The steel balls should be made of standard bearing steel which is 52100/100Cr6 Tool Steel. This material has been proven to be an exceptional bearing material for almost 100 years for all bearing precision classes. 52100/100Cr6 etc. have good rigidity/ductility, corrosion resistance, availability, etc. The Stainless Steel material utilized is commonly 440C, but 316C is also seen relatively frequently. Similar to 52100/100Cr6 tool steel, these materials are also often stocked which helps cost (but are still generally more expensive than 52100/100Cr6 bearings), and carry many similar properties to 52100/100Cr6, but also add extra corrosion resistance. Many people will pay extra for the Stainless Steel material within the bicycle industry to prevent corrosion. This is obviously much more beneficial for those who prefer puddles over pavement. Ceramic is a clear step up for ball material for multiple technical aspects. The two most common ceramic materials seen will be Silicon Nitride and Zirconia. We strongly suggest Silicon Nitride, the main reason for this is the regulation within this material vs. Zirconia. The main driver of this newer regulation is the vast medical uses for Silicon Nitride (think joints). This has created a very tightly controlled material and specs that the bearing industry has benefited from. Good Zirconia suppliers are out there, but they are harder to find than Silicon Nitride.
Corrosion of Ball Bearings
Corrosion of bearings within a bicycle application is probably going to happen at some point. For the most part is it nothing to be alarmed about. If a bearing has existing and mostly working seals and grease on the inside, then corrosion should probably not happen within the ‘inside’ of the bearing. This is where corrosion is a major issue, this will for sure cause rolling resistance (wasted Watts) and premature failure. A little corrosion on the outside however is not a big deal. Take a look at this picture, this level of outer corrosion will not inhibit performance in any way. The second picture obviously will but this is from negligence and almost never seen on a bicycle that is being used vs. sitting in the garage.
Proper installation will for sure prevent corrosion. We talk about this more extensively here, but we will make a couple of key points as well. Bearings should be ‘wet’ with oil on the outside and have grease on the inside of the seals to prevent any premature corrosion. A ‘wet’ bearing on the outside is not by any means dripping with oil. It means that there is a shine in the light and feels slippery. This is all that is needed. Trust in your supplier is what will insure proper grease fill volume AND location within your bearing. Also, a very key point, the natural production of oil on human hands is a large contributor to corrosion. Wearing some cheap rubber gloves or being quick and clean with your bearings can prevent much corrosion.
Property Differences of Ball Bearing Materials
This table outlines the specific property differences between the materials. Remember, this is a bicycle application that is not very severe, outside of contamination, for most of the bearings that are designed into bicycles. These material facts should be, and hopefully are, utilized by the engineers designing the hubs. End users, bike shops, etc. choice for different ball material should be quick and easy.
Is the bearing getting consistently wet?
Do I need to worry about robustness? Dust, dirt, grime, etc. getting into my bearing.
Is cost a factor?
What materials are readily available?