Bearing Q&A

A version of this article was originally
published in Triathlete Magazine

Since the August 2009 “Tech Support” on bearings was published, I’ve been asked some good follow up questions about choosing bearings and bearing ratings.

Question 1) “I’m not that technical.  What is the biggest thing to focus on when choosing a replacement bearing?”

Look for quality and reputation over material and ratings.  You get what you pay for and just being ceramic, like just being carbon fiber, does not always make something better.  A high quality steel bearing made with top quality materials, grain structure and race polishing will perform better than a basic ceramic (even if the ceramic is “rated” higher) bearing.  If a company like Ceramic Speed (the arguable inventors of ceramic bearings for bicycles) or Zipp (likely the earliest to offer ceramic options from the factory) is selling a high quality bearing for a certain price, you are not going to find that same quality bearing for significantly less money.  Even if two bearings are rated the same on paper, if one bearing costs less, the lower priced manufacturer cut costs in the quality and refinement of the materials.  These are things you can’t see or feel by looking at or spinning a bearing in your hand, but that are significant in how well a bearing works and lasts when it is actually being ridden under load.

Question 2) “Why do some companies list both an ABEC rating and a millions of an inch Grade rating?”

In the August article, I misstated that ABEC rates both ball and race tolerances and that millions of an inch Grade primarily applies to loose ball bearings only.  “Radial Run Out” in regards to ABEC ratings is not the roundness of the balls; it is actually a measurement of the consistency of the roundness of the groove in the race that the balls roll. ABEC standards only apply to race symmetry and tolerances and do not consider the roundness of the balls.  Grade, on the other hand, refers to ball roundness in either a loose or cartridge bearing and does not consider the race tolerances. Companies list both the ABEC (race tolerances) rating and Grade (ball roundness) because both ratings are important reflections of the tolerances in the bearing system as a whole.

Question 3)  “Why are some steel bearings more expensive than some ceramic bearings of a higher Grade?”

Bearing Grade is not what matters most.  Bearing Grade is universal across materials, so one Grade 10, regardless of whether the balls are ceramic, steel or silly putty, has the exact same tolerances/roundness as another Grade 10.

True bearing quality and performance comes down to the grain structure, polish and refinement of the materials used in the fabrication.  You can have very round bearings and races, but if they do not offer appropriate material integrity and finish for each other, they will not work ideally together.  For example, imagine you had two bearing systems with identical tolerances (Grade and ABEC ratings) and identical ceramic balls, however, one had races made of silly putty and the other steel.  When they are unweighted and properly lubricated, both bearings might spin well in your hand, but what happens when you apply weight?  The silly putty races deform, bind and grind to a halt immediately, while the steel still spins.

Now, let’s take this same concept of harder balls and softer races and apply it to common ceramic hybrid bearing construction.  If ultra hard Grade 5 ceramic balls are placed in super hard, fine grained ABEC 5 steel races with proper lubrication, they will resist binding, pitting and deformation and will roll smooth and fast together for a long time.  However, if you take these same Grade 5 ceramic balls and place them into ABEC 5 steel races that are not as fine grained and highly polished (softer), the substantially harder ceramic balls can wear the races much quicker.  The race will pit and the softer race can even crack under impact loading (actual riding).  The same thing can happen in full ceramic or full steel construction.  In fact, some manufacturers will not even use a full ceramic cartridge bearing at this time as they have not found a ceramic cartridge where the races are strong enough to meet their standards.

In addition to making sure the balls and the races are polished and hard enough to wear well together, the quality and tolerances of the seal design, the volume of grease in the bearing and its formula, and the purity and cleanliness of the assembly process matters as well.  Just like with carbon fiber construction, keep in mind that the easiest way to save money when building bearings is to spend less time refining the materials and assembly.

If you are choosing between a $25 Grade 10/ABEC 5 steel bearing offered by a manufacturer known for high quality engineering, materials and attention to detail or a $20 Grade 5/ABEC 5 ceramic hybrid from a supplier who sources their bearings from an unknown factory based in a country that may not recognize ABEC standards, the steel bearing will likely offer you higher performance.  As stated previously, look at quality and reputation over material and ratings when choosing replacement bearings or considering an upgrade.

Question 4) “My bearings are worn out.  Should I upgrade to ceramic bearings?”

On wheels, the answer is “Maybe”.  High quality ceramic bearings in combination with tight tolerances hubs (DT, Zipp…) are a great combination.  However, if you have high precision hubs and are wanting to keep bearing costs under $100 a cartridge, consider buying the very best quality steel cartridge bearing you can from a reputable manufacturer, as they will likely work better than a lower quality ceramic.  If your wheels do not have high precision hubs, consider saving yourself some money and going with the best Grade and quality steel bearings you can.  Less aligned hub shells actually require more bearing play to roll smoothly in the long-term and a high quality Grade 10-25 steel bearing will not only save money, but might work better and last longer than a tighter tolerance ceramic that may not be aligned in the hub shell as well as its tolerances require.

Partly because they use bigger bearings than hubs, just about all bottom brackets benefit from high grade steel or ceramic bearing upgrades.  Shimano, FSA and SRAM cranks (amongst others) have a fair amount of seal and bearing friction that is noticeably reduced with a high quality bearing upgrade in ceramic (Ceramic Speed, FSA…) or steel (Chris King, Hawk Racing…).  Because bottom brackets use bigger bearings than hubs, the tolerances and manufacturing precision don’t need to be as precise to gain the same performance.  Note that no matter how high quality the bearings, if they are not mounted flush, they are going to be held back and could wear prematurely.   Very few frames come from the factory with well faced bottom bracket shells, so make sure the shell is faced by a good technician before installation.

Ride hard and smart.

Ian

Originally published in Triathlete Magazine November 2009/Copyright © 2009