Real measurable benefit to ceramic bearings?

Question

Is there a real difference between riding on ceramic bearings and riding on stainless steel?

How would you measure it? Does it require it to be every bearing in the drive train, or will each set of bearings replaced improve performance?

Does anyone have real world experience with them to relate?

Edit:

I don't know if it matters on the bike, but I saw this today. If this is an indication of the difference in the level of friction resistance ceramic offers, then I'm in.

In the video:

The left pulley shown is Shimano DuraAce, the middle one is Campagnolo Record 11 speed. All three pulleys are fixed to 5Nm of torque at the axle bolt. And all 3 three have at least 1mm of play at the pivot, so there is no extra tension on the bearings compared to normal install in a derailleur. There is a difference in movement of about 18 seconds of spin in the video. It's crazy.

Answer 1

Short answers

Is there a real difference between riding on ceramic bearings and riding on stainless steel?

The power savings from using ceramic bearings compared to good steel bearings is almost zero.

How would you measure it? Does it require it to be every bearing in the drive train, or will each set of bearings replaced improve performance?

Yes, it is possible to measure the difference but it's not easy.

Longer answer

First, however, it depends a little on whether you're talking wheel bearings, bottom bracket bearings, or both. If you're interested in measuring the difference, the way you measure differs for the two. BB bearing drag would show up in differences in drivetrain efficiency, while hub bearings would show up as a component of rolling resistance. The difference, of course, is that drivetrain losses only occur when you're pedaling (not while you're coasting), while rolling losses occur as long as you're rolling (whether pedaling or not).

You can measure differences in no-load hub bearing drag by holding the wheel up in the air with a fork, using a home-made speed sensor jury-rigged with a reed switch connected to a digital voice recorder. You spin the wheel up, then record and calculate the difference in timing "clicks" as the wheel decelerates. Swap bearings, lather, rinse, repeat.

However, this would be in a no-load setting and you might think differences in bearing drag might be amplified in load-bearing situations. If so, you'd have to test that way. You could do it in the lab but it's also possible to do yourself, in the field, with the jury-rigged speed sensor.

First some background. The rolling component of drag is typically measured by the coefficient of rolling resistance, C_rr. (The coefficient of aero drag is C_d, which is usually multiplied by the front surface area, A, and described by the combined term C_dA.) C_rr can have a speed-dependent component, but at cycling speeds this is negligible so we can assume C_rr is constant. If so, the power demanded for moving a bike and rider at a given speed is pretty well known and understood. Rather than go through it all here, I'll point to a brilliant method that allows you to estimate C_dA and C_rr.

Now, if you do all of this, you'll find that for a typical bike, the total overall C_rr from all sources (tires, tubes, hub bearings, and typical "smooth" road surface) of around .005. The C_rr for really good tires on that same surface might be .0045; for really lousy tires the C_rr might be .006; and for a really rough surface the C_rr might go as high as .01. And, some context if you look at the power equation linked to above, you see that C_rr scales exactly like gradient in its effect on power so when the C_rr is .01, the effect on power is exactly like climbing a 1% grade. Likewise, an increase in C_rr of .001, due either to a different tire or to putative bearing differences, is just like climbing a grade 0.1% steeper.

Here's one more fact, also derivable from the link above: a rule of thumb is that at 25 mph on a flat hard surface, a cyclist in good aero position needs around 250 watts (an exceptional aero position is achievable with under 200 watts). At 25mph, a difference in C_rr of about .0005 is roughly equivalent to a difference in power of 5 watts. That is, a difference between a good tire and a very good tire is worth about 5 watts at 25 mph.

If you have done any field-testing of bicycle drag you'll realize that 5 watts difference in rolling resistance is pretty noticeable. Riders report that the difference between using ceramic and steel hub bearings is not noticeable.

Answer 2

I don't have the source at hand, but from what I've read, converting your wheel bearings to ceramic will net you something like a 1 W savings at racing speeds, thanks to reduced mechanical losses. A ceramic bottom bracket would result in less improvement.

Considering the rider is putting out 200+ W at racing speed, the savings are clearly minor. Additional savings may accrue from the much lighter wallet the rider is carrying.

Answer 3

I have ridden ceramic BB bearings. This is my one and only experience. They seemed to take a couple rides to break-in which definitely seemed odd. One of my training partners noticed the same thing, but in his case, it was after 90 minutes that the bearings seemed to spin freely.

I rode them for just shy of a year, which is approximately the same usage I get out of standard bearings. Based on the insane price and insignificant difference, I opted to go back to stainless.

The riding partner, I mentioned earlier, is on his second set after going back to stainless. If funds permit, I am open to trying again. It was not a bad experience in anyway. Another buddy has swapped all bearings including derailleur pulley bearings and swears by it!!

That's all I got!

Answer 4

Since the current answers are very road specific, I'll give my take on it for the disciplines I know.

Downhilling can benefit from them because they deform less under load, so in theory last longer. But in practice BBs and hub bearings in this discipline tend to fail from corrosion brought on by failed seals, and although ceramic bearings won't rust - the race will. The lower shock load isn't an issue due to long travel suspension.

For trials it really depends on how much of weight-weeny/rich you are. Ceramic bearings weigh far less than steel ones, so there's an instant benefit there. But, ceramic bearings are much less resistant to shock load so they will shatter, and because trials bike's are rigid, this will happen quickly.

Answer 5

The material that the bearings are made of is only one piece of the whole mechanical package. I've worked on bikes in the shop that had ceramic BB's and all sorts of steel. From a material point of view, ceramic has the possibility to be better, but as others have noted, you pay a large premium...and often they may not be the best anyway.

Think of it this way, oak makes a better table then pine. But pine is easier to work with and the resulting table might be smoother and put together better than the oak one...and cheaper at that. Likewise, there are steel BB's, hubs, etc. that are better than some of the ceramic bearing counterparts. I have my favorite and it's a decent priced steel (Hawk Racing), I have yet to see anything that is better on a bike that I've worked on.

Sidenote: Videos like the one shown should be taken with the grain of salt...it's marketing and the demo has been set up for a particular purpose. Talk with the guys at the LBS and get opinions from both sides of the counter (the mechanics and the customers).

Answer 6

Besides the supposed reduction in friction resistance some other issues have crossed my mind.

Let me bring two analogies - prosthetic hip joint replacements and car brake pads/discs combinations.

For the first one - a metal cup is used with ceramic head. Since ceramic is much harder than the metal, the metal cup wears out (the body can handle the metal ions and excrete them). Some time ago someone (source needed) came up with an idea to make the cup also from ceramics to prevent the wear down. The cause was that ceramic rubbing on ceramic (there is no possibility to grease the hip joint whatsoever, is it?) caused the ceramic particles being released to the body. Those were not excreted and caused serious health issues. What I'm getting to I'll explain in the moment.

Now about the brake pads/discs. For the pads there are different hardness of the pads available, and quite often the softer, the more expensive. Why would you spend more on softer pads if they wear out sooner, you may ask? The answer is simple - it's not the pads that wear out, it's both the pads and the discs. Thus the less the pads wear, the more the discs get ground off. And in turn, the harder the pads you use, the sooner the discs need to be replaced (extra costs and labour).

TL;DR; part starts here:

When using hardened steel cups with stainless steel balls it's the balls that wear out leaving the cups mostly intact. When tightening does't work anymore one would just replace (pretty affordable) balls.

When using ceramic ball bearings in hardened steel cups it's the cups that receive more wear as ceramic is harder. Then after the while not only one has to replace old ceramic balls but also replace worn out cups. Of course this does not apply if a complete ceramic cartridge bearing is replaced.