Ceramic Bearings?

Are these a good investment for a roadie trying to improve?

Not really. You won't see a huge, if any, performance difference. There are other things you can do/change to net performance gains.

I sell loose ceramic balls for campy and shimano hubs on ebay. While there is a small difference it isn't going to rocket you up the standings. Really the guys who will get the biggest gains are the guys who are well trained and already got good gear. You are looking at a small % improvement, and unless you are at the point that every last little counts, then most of what you will gain is prestige and physiological.



If you buy name brand bearings, you are going to pay a lot, and for that same money you could buy some racing tires, or put that money towards a good mid range set of wheels.



If you already have good tires, nice wheels, good frame and running gear, then ceramics could be the next place to look for a bit of non organic speed.



Really if you are looking to improve, working on the engine is the best place to get more speed.

In the end really value is what you think of it. If you have the money and you think its worth it, then go for it. If you are on a tight budget and need to buy the name brand stuff, probably other options would be better value.
I'm sure plenty of people in here would give ceramics a go if the price was more to thier liking. I sell a few sets each month on ebay at a much lower price than the name brand kits, but not anywhere near enough to give up my day job!!

Thanks for the advice. I'm new to the game (18 months) and started off with very good equipment. So I guess it's just something else to spend money on?

Thanks.

I'm of the opinion that ceramic bearings don't make much if any improvement, but they don't do any harm either. In a bicycle, the actual bearing losses throughout the wheels and drivetrain amount to a total of ~10 Watts at 40 km/hr. This is an estimate based on my testing. The wheels are around a Watt each. So if you're putting out 250 Watts at 40 km/hr that works out to ~0.5% of your energy lost to wheel bearing friction. Even an improvement of 10% will give you back less than 0.1% or 250 mW. That's really and truly nothing.

Here's another way to look at it. How does a bearing cause friction losses and how does ceramic improve that? Let's simplify a set of cartridge bearings by imagining the individual ball bearings are between two flat plates of steel. The plates can move freely as they slide on the rolling bearings. Any friction is due to hysteresis losses in the bearings or plate. That is, the bearing or the plate deforms a little bit under the stress and you don't get that energy back. Therefore the uniformity of the bearings and plates (races) goes a long way to reducing this friction. That is, perfectly round bearings don't introduce areas of higher stress/hysteresis loss.

How can you improve this? Rounder, smoother bearings with smoother races will help a lot. You can simply buy better grade bearings. You can use bigger bearings to increase the surface contact area and reduce the stress, which is why some designers like external bottom brackets - bigger bearings. You can also use harder materials such as WC or ceramics. But both the bearing and the race need to be of the same material or you're just transferring the load stress and deformation onto the bearing race, reducing the amount of improvement.

What swamps all these lossses? The bearing seals that are designed to keep out water and grit. I'm pretty sure they cause as much or more friction than the bearings themselves. This is one of the (many) reasons why Campy likes the old square style inboard bottom brackets and Shimano refuses to give up cup and cone bearings in their wheels. Few or no seals to wreck bearing performance. In fact, you could make further improvements by getting rid of the thick weather proof grease and running a light oil instead. Yes, running with light oil and no seals means regular maintenance on a daily/weekly basis, but the improvements would be far, far greater than going to ceramic.

One last note. Why were ceramic bearings developed? Ceramics are very useful beacause thay are dimensionally stable through a wide range of temperatures. That is, at 1000'C they won't grow in size and bind in the bearing race. They can also withstand much higher loads without premature wear. Neither applies to a bicycle...

So yes, they probably make an improvement, but it is a small one. And if you really want ceramic bearings in your bike, why not? Enjoy!

John Swanson
www.bikephysics.com

John, fine summary. However, I was surprised at your estimate that wheel bearings could account for as much as one watt per wheel. On a properly-adjusted hub, particularly one with low-preload cartridge bearings and no axle seals, that figure seems high to me. Would appreciate if you could provide more details/discussion of how you arrived at this estimate. Thanks.

Thanks. My estimate was based upon some of the measurements on my site. Going through the data, for a front Ksyrium ES, the total bearing friction is almost 0.6 W. I figured that for worst case loading, etc, you could just estimate and round it up to 1 Watt.

The measurement I make includes the coefficients for stiction, bearing friction, and aerodynamics so it's easy to separate out the different elements and get a fairly precise calculation at any speed. If you're interested in the measurements and analysis, I'd encourage you to read the paper on my site. I'll be happy to answer any questions.

John Swanson
www.bikephysics.com