What makes a good ball bearing a great ball bearing for bicycles? Part 1
Ball bearings are at the bottom of every spec sheet. They’re hidden in the bike, nobody is going to give you a thumbs up when you show up at the group ride with new ball bearings. Typically bike and frame manufacturers spend as little money as possible on bearings and at Kogel Bearings we understand why from a commercial point of view. A bike in a catalog or on a shop floor gains instant value with aero handlebars or a branded stem. Expensive bearings? Not so much.
Is this the sole reason why people typically do not care about their bearings? News flash! Ball bearings are at the heart of anything that turns on a bicycle. Wouldn’t it be great if all those circular motions were a bit more efficient, robbing you of a little bit less leg power?
Here are the key elements to making a great ball bearing:
The theory behind ball bearings is easy: rounder and smoother rolls better. Steel balls start off as a metal wire and after a lot of cutting, grinding and polishing, they end up as the shiny bits we recognize. The key to quality is in the finishing. The rough work is done by rolling the balls between two spinning plates, a process similar to rolling a ball of dough between your hands. In between these operations, the balls get heat treated to make them harder and at the end they are polished in a very similar machine.
The quality is often determined by the amount of time the balls spend in each operation. The roundness, size and surface smoothness defines the quality level, called grade. This number ranges between 2000 and 3. A lower grade number represents a tighter tolerance and higher quality ball. In bicycles any number between 300 and 3 is common.
Ceramic vs Steel ball bearings
Most ceramic balls in bicycle applications are made of Silicon Nitride (or Si3N4, if you’re a chemist). This wonderful material is harder than steel and can be polished to a much smoother and rounder ball than it’s steel counterpart. This in the end will cause less drag in the bearing. Another great feature is that the material does not rust, so even in a hybrid ceramic bearing, the balls cannot fuse to the races.
The downside of Silicon Nitride is that the balls are hard, but brittle. Imagine them being made out of compressed sand. Once the hard outer layer chips, or the ball breaks, it usually falls apart. This is very common in inferior quality balls and one of the reasons why ceramic bearings have a bad rep for their durability.
Cost is an aspect to consider. Quality ceramic balls are expensive to produce. Since the polishing of Kogel Bearings takes more than three weeks, it puts our bearings in another price bracket than any steel bearing. This higher purchase price is partially compensated by the longer bearing life of a quality ceramic balls vs a steel or 'cheap' ceramic ball.
- Ceramic balls can be polished to a mirror finish and have extremely tight tolerances as can be seen in this 6 inch diameter example.
Ball bearing production
Here's a cool Discovery Channel video of the production process involved in making radial ball bearings that are most common in bicycles.
In part 2 of this post we will speak more about the races, seals and grease used in a ball bearing. Stay tuned!
If you have any questions about Kogel Bearings, ball bearings in general or our Ball Bearing Adventures, please ask them either in the comments section below, one of our social media channels or by email via firstname.lastname@example.org. We will answer them in a highly professional, but not always scientific way. We do not shy away from many subjects. Please ask, we are here to answer.