Ceramic bearings: what's the big deal and who are they for?
You’ll often find ceramic bearings featured in most articles about performance upgrades you can do to your bike. The reason behind this isn’t always made clear and with ceramic bearings, a significant investment compared to standard steel bearings it is worth understanding what you get by upgrading.
It is well documented that ceramic bearings have a lower rolling resistance but why is that, and how can you best look after them to get the best performance for mile after mile?
How are ceramic bearings made?
Ceramic bearings like the Eenox LS-10 series are made from silicon nitride. This material is a wonder for a whole range of mechanical applications with desirable properties for high-performance, durable bearings. Silicon nitride has incredibly high fracture toughness, abrasion wear resistance, and resistance to solid particle erosion.
Ceramic balls used within the bearing are made through a process of heating and moulding. The method commonly used is hot isostatic pressing. This uses a multi-axial press to ensure the uniformity of the final product.
In contrast, the process used to make steel and stainless steel bearings starts with steel wire being cut into small sections that are then cold-headed into a sphere. Cold heading is a process that hits both ends of the cut section of wire with a rounded form to create the steel balls..
Ceramic bearings are faster rolling
Ceramic bearings exhibit lower rolling resistance than standard 100Cr6 steel bearings due to several key factors.
The material properties of silicon nitride (Si3N4) ceramic balls contribute to a smoother surface finish, which reduces friction when the bearing components interact, leading to less energy loss during rolling. Over time, the harder ceramic balls smooth out the asperities of the steel raceways through a process known as "polishing." The polishing effect not only enhances the surface finish of the steel raceways but also minimizes microscopic wear particles, which can further reduce friction and improve the overall performance and longevity of the bearing.
The correlation between lower surface roughness on the raceways of a bearing and the lambda value (λ) is rooted in the concept of elastohydrodynamic lubrication (EHL). Lambda (λ) is a dimensionless parameter that represents the ratio of the lubricant film thickness to the combined surface roughness of the contacting surfaces. As the surface roughness of the bearing raceways decreases, the lambda value increases, indicating better lubrication conditions, reduced friction, and improved bearing performance.
The advantage of having a higher lambda at a lower surface roughness value (measured by a parameter known as Ra and Rz), is that the bearing can be lubricated with oil (or grease) at a lower viscosity value. Oil viscosity and bearing rolling resistance are inversely related in a complex way. Higher viscosity oils can reduce friction from surface contact by maintaining a thicker lubricant film, which is needed when the surface roughness is higher, but can also increase rolling resistance due to higher internal fluid friction. Lower viscosity oils reduce internal friction, lowering rolling resistance, but may increase friction if the lubricant film becomes too thin. With a highly polished raceway as a result of the ceramic balls, the bearing can be used with a lower viscosity oil, such as Eenox Showtime Grease, that will lower the rolling resistance and deliver higher speeds for a given unit of input power.
Additionally, ceramic balls are harder than steel balls, making them more resistant to deformation under load. This resistance decreases the contact area between the ball and the raceway, further reducing friction.
Lastly, the lighter weight of ceramic balls compared to steel balls also plays a significant role, as it lessens centrifugal forces during rotation, resulting in lower frictional losses.
These combined characteristics give ceramic bearings their high efficiency and low friction characteristics, allowing cyclists to achieve peak performance and speed.
Are all ceramic bearings created equal?
While ceramic balls offer significant mechanical advantages, not all ceramic balls are engineered to the same standard. Poor-quality ceramics can negate the benefits, potentially increasing friction rather than reducing it.
Critical quality control parameters for ceramic balls include material purity, uniformity, hardness, impact resistance, and even the cleanliness of the finished product. Below are optical + laser images of ceramic balls from three different manufacturers, revealing material contamination post-production.
This contamination, often residual lapping material not visible to the naked eye, is a byproduct of an inadequate cleaning process. Despite appearing minor, such contamination can severely impact performance; hard lapping particles left on the balls can damage raceways, accelerating wear and increasing friction—exactly the opposite of the intended effect.
This issue underscores why many lower-quality ceramic bearings fail to deliver the reduced friction expected. At Eenox, the approval process for ceramic ball manufacturers is exhaustive, involving both rigorous lab analysis and extensive validation testing that can span 12 to 24 months before approval is granted.
Due to our stringent quality control and validation processes, only a select few manufacturers meet the criteria to supply ceramic balls. This commitment to quality is evident in the superior performance of Eenox LS-10 ceramic bearings
They do require maintenance
Contrary to widespread belief, ceramic bearings are not completely maintenance-free. Some Industrial, fully ceramic bearings are however the hybrid ones found in bicycle components do require routine maintenance to keep them in good working order.
As a result of how hard the balls are, any dirt, dust or grit that manages to find its way past the dust seal and into the bearing can prove problematic. This is because the balls are significantly harder than the metal races. Any contamination will gradually over time wear away the races scoring and pitting them which will degrade performance and ultimately bring an untimely end to the bearing's life.
To extend the life of a ceramic bearing keeping them clean and well lubricated is advised. Removing the bearing, cleaning it with a bicycle-specific degreaser and reapplying the correct grease is not a big job but should be done routinely especially if you do a lot of winter riding in wet and dirty conditions.
Who can benefit from ceramic bearings?
Ceramic bearings have been shown repeatedly to offer a performance advantage by decreasing rolling resistance by minimising frictional losses within the spinning components of the bicycle. Fitting ceramic bearings inside the hubs or your wheels and in your bottom bracket can save between six and nine watts which is certainly not an advantage to be sniffed at.
For anyone cycling competitively, the advantage that ceramic bearings offer is hard to ignore, over the course of a road race or time trial nine watts could easily amount to the difference between making the winning move or finishing in the peloton.
Ceramic bearings aren’t just for those looking for a competitive edge, they are also a worthwhile upgrade for riders who do spend a lot of time riding in inclement conditions. Of course, as discussed the use of ceramic bearings doesn’t forego the need for routine maintenance but as ceramic bearings do not rust and are harder wearing they can be better suited to harsher environments. This could in the longer term save you money as you will only need to invest your time in keeping the bearings running smoothly rather than continuously replacing them.
Who should avoid ceramic bearings?
The first thing to bear in mind is that ceramic bearings are expensive if your bike is not optimised for efficiency, the six to nine watts that you might be saving will largely go unnoticed if there are other larger sources of rolling resistance such as incorrect tyre pressure or brake rub.
They are also not for people who are not familiar with fitting and removing bearings on their own bicycles. The routine maintenance that is essential to maintain optimal bearing performance is by no means difficult but if you foresee yourself heading to your local bike shop every time you need to lubricate your wheel bearings you are quickly going to wrack up a hefty bill that makes ceramic bearings uneconomical.
Where are ceramic bearings best used?
The best place for ceramic bearings on a bicycle is in the wheels. This is because they are subjected to the highest rotational forces and for the most part, are fairly stable in their loading.
Switching from steel to ceramic wheel bearings will also have a positive effect whenever you are moving regardless of if you are pedalling. This means that across the board a bike fitted with ceramic wheel bearings will always be a little faster than one with steel bearings. In the case of ceramic bottom bracket bearings, this is only the case when the cranks are turning and power is being applied.
Alex Hunt, Cycling Tech Writer and Eenox Engineers
About The Author
Alex loves all facets of the cycling world with a particular interest in cross country mountain biking and big adventure rides. He is a mountain bike coach and guide in the Forest of Dean.
