Introduction
One of the most controversial topics in cycling is whether or not steel or ceramic bearings is superior. Marketing has often claimed that ceramic bearings reduce drag and last longer. The question is whether or not this is true? This article will give you a detailed explanation of ceramic vs steel bearings, as well as how they compare.
As a side note, we will be talking about cartridge bearings as they are the norm in hubs, since they require lower maintenance, are easier to swap, lighter and more compact, and usually have better sealing. Some cartridge bearings can wear out faster though, which will be covered in this article.
At Particle, we use exclusively S&S steel and ceramic bearings.
Internal Construction
While we refer to the bearings used in cycling applications as ceramic, the truth is that they are actually hybrid ceramic, meaning just the balls are ceramic. As opposed to ceramic bearings, steel bearings contain hardened steel balls and a steel inner and outer race.
The ball bearings are ceramic, while the inner and outer races are made of steel. Ceramic bearings usually have C3 clearance. The clearance used in steel bearings is typically CN. Bearing clearance is a measurement defining the gap between the inner race, outer race, and balls. This clearance is important as a proper one prevents a bearing from seizing when it inevitably heats up and expands.
Cages used on both kinds of bearings is also different. Cages keep balls spaced out properly within the bearing. On quality steel bearings, the cage is made of a piece of pressed metal, which is riveted between the balls. This is a costly method to produce a bearings, but it reduces friction and improves stiffness. With virtually all hybrid ceramic bearings, cages are typically made of composite or rubber cage. It snaps in and holds the ball spacing. Under high loads, this type of cage has is more likely to deform or even pop off causing noticeable friction.
Our S&S steel bearings use quality steel races.
External Construction
Bearings have either non-contact seals, contact seals, or one on each side. Contact seals touch both the inner and outer races to maintain the seal. This leads to a friction loss. When ridden, this isn’t as noticeable, but there is a difference. Non-contact seals offer less drag, but are more easily contaminated with water or dirt.
Our bearings use a mixture of a contact facing outwards and non-contact seals facing inwards. This give our bearings both the benefits of non-contact and contact bearings, allowing them to be both high performance and long-lasting.
Bearing Friction
One of the most important things to understand about the rolling resistance from bearings is that the balls themselves play a very small role. The truth is that bearing seals cause the most frictional loss, roughly 60%. Grease causes roughly 30%. Finally, cage friction, ball deformation and raceway deformation cause the remaining 10%. These numbers are a close approximate, and there are slight variations depending on the bearing itself. Ball deformation contributes roughly 3% of the overall friction loss, though in reality, the difference between ceramic and steel bearings is roughly 10% of 3%, meaning a savings of approximately 0.3% everything else being equal.
However, there is a caveat, which is ceramic bearings in virtually all cases have snap in cages, which in general produce more friction than pressed metal cages, reducing efficiency.
As far as performance, steel and ceramic bearings have similar overall rolling resistance, with ceramic having a very slight edge in general with everything else being equal.
Bearing Life and Changes in Friction Over Time
One of the most overlooked parts of bearings is how quickly they can wear out. While ceramic balls are significantly harder than steel races, they can much more easily wear into the softer steel races. This leads to a gradual increase in rolling resistance over time.
The truth is that some hybrid ceramic bearings have good rolling resistance, and some do not, as differences are primarily based on seals, grease, and to a smaller extent cage friction, rather than the balls themselves. Non-contact steel bearings and some ceramic bearings hold the top spots for rolling resistance out of the box, however after a period of time, ceramic bearings get overtaken by high-quality steel bearings.
Extending Bearing Life
At Particle, we put a strong emphasis on not just the bearings we choose, but also keeping the bearings free of contamination. Protecting bearings from the elements is extremely important, as they will last significantly longer.
We have chosen our hub supplier carefully. Our AR1 hub shells and axles have been machined to 0.005mm and 0.003mm tolerances respectively, making them among the most precise ratchet hubs hubs available. This results in lowered rolling resistance and improved longevity, as bearings are subject to less stress. The hubs uses labyrinth sealing and double layer contamination barriers, significantly reducing the likelihood of ingress, protecting bearings and ratchets from the elements.
Why are wheel spin tests a poor way to evaluate smoothness?
While it is common for people to judge the smoothness of a hub by spinning a wheel in their hands or on their bike, this does not reflect how well a wheel will spin when out riding.
First, hubs experience radial and axial loads from your body as well as cornering forces, which affect bearing performance and friction.
Second, what you are really seeing is the momentum of a wheel and not bearing resistance. A heavy rim or tire can spin longer even if the hub has high friction. A light wheel on the other hand may stop quickly even if the hub is smooth.
Third, hubs with little grease or grease that is not viscous enough may spin well but wear quickly under real-world stress.
For those without proper testing equipment like a dynamometer, real world test could be done by coasting on a slight downhill with different wheels, though such tests should be taken with some skepticism as the environment is not controlled.
Which should you choose?
The truth is you cannot go wrong with either steel or ceramic bearings. For those wanting longevity and long-term low rolling resistance, we recommend steel bearings. For those who want a slight edge and are fine with changing bearings more often, ceramic bearings are for you. The S&S bearings we use are quality, and when paired with our AR1 hubs, you won't have to be worried about performance, contamination, or rolling resistance.