Quick and Dirty
There are more or less two choices for bearing race material for bicycle applications; Bearing Steel (AISI 52100) and Stainless Steel (440C or 316C). AISI 52100 steel is by far more ubiquitous in the bearing industry and therefore will have a lower cost point because of sheer volumes produced. If one feels that their bearings will be exposed to water often, think cyclocross, then maybe stainless is a better option for you. But know that any bearing should be protected from most water/fluid ingress already and light rusting on the outside of the bearing does not inhibit performance.
You may also hear of Ceramic Races – commonly Silicon Nitride or Zirconia – but these are not optimal for a bicycle. They are brittle to install, do not like shock loads, and there is no chemical exposure or very high temperatures (think 800°C) on a bicycle. The cost to benefit or quirkiness is just not there. We suggest a logical ‘no’ to any discussion for full ceramics for bicycles.
Should I Choose Tool Steel or Stainless Steel for Bearings?
There are many details and aspects that we can cover, these are all very similar to our ball material discussion. As stated above, the main decision is between AISI 52100 steel and a common Stainless. Average material properties for either 440C or 316C stainless are less advantageous for bearings than AISI 52100. However, as long as the engineers designing whichever bike part you are interested in did their due diligence, then either material should be just fine.
The main caveat to this engineering note is bearing size being too small. This can happen, but would be rare. Let’s say a hub was designed with 605 size bearings, but the application is actually a mountain bike. Shock loads going off of a jump could potentially dimple the races of this bearing size. For this reason, we would suggest AISI 52100 races to gain the material properties that would support this abuse for what could be a potentially undersized bearing that cannot be changed. This circumstance would be rare at best.
Corrosion; or more commonly called ‘our friend’ RUST. Again, similar to our ball material discussion, some rust on the outside is not a huge deal. Also, a properly lubricated, protected, shipped, stored, and installed bearing should not have to worry about any corrosion for many months or years. All of this can be summed up to a trusted supplier.
- Do they have a temperature and humidity controlled warehouse?
- Do they have a specific shelf life for their bearings that if exceeded, the bearings are cleaned and re-lubricated before selling? (Verinent’s is 2 years on our shelf, this is much less than the grease life of most bearings of ~5 years. We do this to protect our customers because we do not know how fast the bearings will be used)
- Do they have consistent, accurate, and repeatable internal procedures for all aspects of the bearing cleaning, relubrication, and storage?
- Does their packaging suffice?
A trusted supplier will; ensure the bearing is ‘wet’ with oil, the grease is installed correctly per volume and location specifications, the seals are installed properly, and all packaging is done well and air tight while being protected from any extreme elements including sun, temperature, and humidity. This is all on top of the fact that they should be wearing gloves to prevent one of the top rust causers – the human hands. If your bike part/assembly is being re-built, we would ask that your bike shop technician wear gloves when doing the final assembly. This is a very low-cost step that prevents rust. As a frame of reference, a ‘wet’ bearing is not dripping with oil. A wet bearing is one that has a shine in light and feels slippery to the touch. Too little preservative oil and too much preservative oil can be a bad thing – there is a wide margin for error.
Bearing Material Specifications
Below are some general material spec’s for those who want to know some actual engineering numbers. Please note that these numbers are averages of readily available material spec’s. ‘Exact’ numbers exist per supplier of raw material and heat treated material, but variations for sure exist between specific suppliers. Please don’t send us an email stating that the number are wrong, but feel free to send us emails stating how great this information is! ha ha