Ceramic bearings: What's the point?

have you tried using plastic bb gun pellets? Work a treat

Or Solero Shots, winter use only though.

I use those little polystyrene balls you get in bean bags. It's like riding a full sus MTB!

Full Silicon Nitride 6001 at $99 each
http://www.vxb.com/page/bearings/PROD/Kit8150

I'm not completely convinced these would be viable in hubs, or that they could be pressed into shells which had been designed for steel housing cartridges, as the allowance for a proper interference might be different given the different material properties.

good point. I had no intention of getting those ones, found some other cheaper models:

^^^grade 5 full ceramic bearings at £50 last between 10-20 times longer than steel equivalent gotta make sense at some level.

Those are Zirconia, not Silicone Nitride. All the bicycle applications I've seen so far have been Silicone Nitride, so I'd be even more cautious about going out on a limb as yet untested by the likes of Zipp. Silicon Nitride is described as having abnormally high shock loading resistance among ceramics, which is probably why it has been selected over the cheaper Zirconia for bicycle applications.

my understanding on ceramic bearings is the way they are made and the materials used allow much tighter tolerances, which leads to overall stiffer components, which means more of what you put in goes to the back wheel and as there is less slop they will last a lot longer

my understanding on ceramic bearings is misguided and woefully inadequate.

Fixed.

ill get me coat then :-(

For low speed applications (all bicycle bearings are considered low speed), the key benefits are lower friction and longer life. Stiffness and clearance (which is what I assume you might have been grasping for with your comment about "tighter tolerances") don't come into it, as the contribution of bearing stiffness to system stiffness is trivial, and the closer clearance which can be achieved thanks to the greater roundness possible with ceramic balls is only of concern at high speeds. There is a small incidental benefit to weight weenies that ceramic (Silicon Nitride) bearings are lighter than steel ones.

Largely unsupportable claims are made by people trying to sell common, fairly cheap, hybrid ceramic bearings to cyclists at boutique prices. The upper bound for the total losses in all the rotating bearings on a properly maintained bicycle (wheels, cranks, pedals, derailleur pulleys) is about 10W at 40km/h, of which at most 80% can be saved by replacing all the bearings with ceramic. This is worth about 0.3km'h, or around 27s in a 25 mile TT (obviously much less at the sharp end of the field where they are doing over 50km/h, something like 12s). This could prove decisive in a race, but may not represent the best disposition of resources for a recreational or utility rider. For comparison, there are quite a few good quality wheels which are 8W worse than the best, aerodynamically, and some tyres which are considered race worthy which will waste 8W in rolling resistance compared with the best, so ceramic bearings are only one possible avenue to explore in the search for speed, and might not be the best place to start looking.

anyway, ceramic bearings were developed for really high temperatures and really high spin speeds in turbos and such like.
In an environment like that ceramic bearings make a huge difference, but not in bikes, the conditions are far too tame.

That's what they were developed for, but they still have the potential to make a race winning difference to competitive cyclists, just perhaps not the huge difference claimed by some marketing departments and not the biggest gains available to people who have not yet optimised other areas of their bike.

i'm leaving ceramic to the pro's and connoisseurs, where they belong.

[U][/U]meant tighter tolerances as in they dont expand under heat and thus can be made tighter which reduces wear but pretty much the same as wot you said
i speak motorbike better than cycling ;-)

Selling these things, i'm sure the manufacturers make a kiln.

I first came across ceramics aged 12 in RC cars and I couldn't afford them but wanted them.
I have fitted ceramic bearings to my BB and hubs on one of my bikes and it is amazing how smooth it is, you just role along like your riding on silk. Also I fill my tires with helium.

Helium? Pah! Go for hydrogen, it was good enough for the Hindenburg.

I fill my tyres with a mix of EPO and nandrolone.

Definitely hydrogen - lighter and lower viscosity.

Whipped cream reduces rolling resistance over double cream at sea-level.

The place where people comment on the ceramic making a noticeable difference (on the work stand, the actual power saving is all but undetectable on the road, and way smaller than the measurement resolution of your legs) is in the Campag Super Record BB, but that is all down to the fact that they do without rubber contact seals due to the above mentioned contamination-squishing properties of the bearings. You can get the same benefit on a bike with steel bearings by using shielded, rather than sealed, cartridges. The penalty is shorter bearing life, especially in wet or dirty conditions.

If I were going to use ceramic anywhere, it would be in the derailleur pulleys, because most stock pulleys use bushings rather than roller bearings, so you're upgrading an already high friction bearing to one which has very low friction and should stay that way in the horrible conditions to which they are subjected. Since the loads on these bearings are quite small, and they are not subjected to the shock loads which trouble every other bearing on a bike, you can use full-ceramic cartridges too.

Has anyone actually measured the difference between standard and ceramic bearings? I mean, proper scientific measurement that you can be reasonably sure that "they will save you 0.00002W" is likely to be true? Was talking to a bloke about them at the track and now obviously I'm curiouser and curiouser.

Ah, balls, just read your next post..
http://www.lfgss.com/post1128102-17.html

But then..
"The upper bound for the total losses in all the rotating bearings on a properly maintained bicycle (wheels, cranks, pedals, derailleur pulleys) is about 10W at 40km/h, of which at most 80% can be saved by replacing all the bearings with ceramic. This is worth about 0.3km'h, or around 27s in a 25 mile TT" is still 27 seconds faster.

"manufacturer CeramicSpeed stated that ceramic bearings can offer power savings of between 10 -12 watts and bring heartbeats down by 2 - 5 beats per minute.

Other reports found by the dailypeloton claim that power savings at 25 mph equate to two watts and that on an 8% climb the reduced friction is equivalent to a stationary weight saving of 340g (zipp.com). BikeRadar.com meanwhile report a claimed advantage of between one to four watts, again at 25mph."

http://www.dailypeloton.com/displayarticle.asp?pk=19501

So, what cost to save these 2-12W?

Off-topic, but interesting nonetheless:
According to the excellent book Bicycling Science, the difference between a plain plastic bearing and a good-quality traditional cup-and-cone ball bearing is 'smaller than the difference between a good quality tyre and an excellent one'. A plain bearing would be more susceptible to dirt, though.

Remember that how smooth a bearing feels in the hand is totally different to how it performs under load.

"These ceramic bearings roll so much faster"

I'm not interested in what they 'feel' like or any of that tosh.

I want to know for £x how much faster will they be. Then I can judge where in the pecking order of pricey performance part purchasing these particular pebbles place.

I'm not interested in what they 'feel' like or any of that tosh.

I want to know for £x how much faster will they be. Then I can judge where in the pecking order of pricey performance part purchasing these particular pebbles place.

At the bottom.

I'll bet my back teeth, shoe covers have a bigger effect.

They are lighter, last much longer, and spin nicely on the work stand. Thats speaking as someone that has 3 bikes with ceramic BB bearings. I'm an idiot when it comes to bike gimmickery.