Index Categories:
Hub Engineering – Ceramic bearing upgrades
From:
Jens Dec 27, 2006, 1:15 PM
Question:
I sure wish those Zipp ceramic bearings were better.....I've now done 7 head-to-head rolling resistance trials between a Zipp 404 and a Z4 on 3 separate days. I've been looking for that extra watt or so that ceramic bearing advocates claim. The Z4 has lost all the trials except one. The average difference is .00009 Crr -- or about 1 watt at TT speeds.
Here are some test details:
* Tests were on rollers with front wheel stand and power measured with SRM professional
* Wheels were swapped on alternate runs
* Test speeds varied between 30 and 35mph
* Tires are same make and model. However, the tire on the 404 has a bump in it (that should make it slower, right?)
* The 404 tire has been glued on for several months longer with the same adhesive (albeit slightly different technique). The Z4, incidentally, has not improved in the 3 weeks since it was originally glued.
I really wanted to see an improvement with the Z4s. But it looks like adhesive technique and curing time may affect your wheel's performance more than highfalutin', expensive ceramic bearings......
Josh:
I think that Jens' study is great and really shows just how far we have come with steel bearings in the last 4 or 5 years. First of all, we still see about a 0.78 watt difference between the two using highly sensitive bearing testing equipment, that difference is for one wheelset or 6 bearings, but we also see a larger difference than that in using different types of glue, or even two of the same tires as production tolerances for all those things can add slight variation, such as a slightly thicker/thinner tread or more latex on the sidewalls.
Remember we’re talking about some very small numbers here and wringing the absolute last bit of performance out of the wheelset – the standard Zipp steel bearing already uses a ball that is more than 2.5 times rounder than a Campy record ball, and uses a lot of the other technology in the ceramic cartridge. And our ceramic cartridge is the finest ever used in cycling, you cannot find any other with similar specifications.
So my viewpoint on this is the same as it has been for a few years now...we have nearly acheived ceramic performance in our standard bearing, which I know sounds like a cop out, but our standard bearing is a Swiss made bearing that costs 15X more than a bearing from Asia, but look at the difference. There is a reason that I can buy a complete hubset from Asia for less money than the standard Zipp bearing set, and the ceramic pushes it up one more notch, but the differences are very small.
If it were me I would try to do this test using the identical tires without glue, and you will need to control the pressure very tightly, we use a gauge from the motor racing industry with 0.1 psi resolution for wind tunnel and similar testing... but even with that you are looking for a very small difference in a very complicated system...
Here’s the engineering white paper on the current state of Zipp bearing tecnology if you’d like to know more:
A Note on Bearing TechnologyIndex Categories:
Hub Engineering – Ceramic Bearing Upgrades
Hub Engineering – Machining tollerences and real-world effects
From:
BarbBikeTechie Nov 15, 2006, 10:01 AM
Question:
Should I consider Ceramic Wheel Bearings?I may need to replace the wheel bearings in my Lew (2000) with White Industries. With all the talk in ceramic bearings should I consider using them. If I am going to replace them now is the time?
Josh:
Like so many other issues in cycling, my answer has to start with “buyer beware”. There is a lot of misunderstanding about about ceramic upgrades that misses one critical point. Bearings are incredibly complicated to design and spec in a wheel and I would guarantee that the ceramic bearing problems most people are experiencing on the bike are due to using bearings in assemblies they were not designed for. In general, the ceramic ball is harder and lighter than steel. It isn't necessarily rounder or better unless you specifically spec it that way. As an example, the standard grade 10 Zipp steel ball is rounder than about 90% of the ceramic balls people are selling for bicycle wheels.
One huge market for ceramics is industry, where many of the uses are specifically for hot environments, or environments where lubricants aren't allowed or possibly the parts are subject to chemical exposure. So you have relatively low grade ceramic bearings that have no need for high precision (applications like furnace carts) and also don't need high speed, but need very high load capacity. It is common to see grade 40 and 50 balls for these applications. On the other end of the spectrum you have applications that are extremely high speed and sometimes also high temp, if you buy any car with a turbocharger chances are they are using ceramic bearings as speeds in a turbo can be well over 120,000rpm and get so hot that they glow, a perfect ceramic application. But you also see them in F1 and CART car wheel assemblies due to their light weight, low friction, and extremely high load capacity, or even in wind turbines where you have very high loads and relatively low speeds of only a few hundred rpms.
Clearly every one of these instances needs a very different bearing and the same is true with the bicycle application. Choosing an industrial grade bearing designed for high temp, or a marine grade bearing with tight seals and washout resistant grease designed for corrosion resistance are not going to get you any performance gain in your wheels or BB or whatever. Also to consider are internal clearance of the bearing, type of cage, grade of ball, ABEC or ISO rating of the races, race material, race surface finish and grind quality, and finally (and possibly most importantly) the fit of the hubshell into which the bearing is pressed.
I think the hubshell fit is a huge issue as manufacturers cut their bearing bores to specs that work best with their bearings. Since even high ABEC rated bearings have a relatively large tolerance for outer diameter, and since hubs from Asia can have very large variance, you can just have the wrong bearing in the wrong bore. I have seen bearing bore variance of as much as 0.002" between hubs and even high end hubs generally use a +0.0005/-0.0005" tolerance, combined with the ABEC3 outer diameter variance of 0.0003" you can have an interference fit of nearly 0.001” in high end hubs and over 0.001” in other hubs.
In machining terms these are huge numbers. You can fix that by using a bearing with large internal clearance, but then that bearing will be very loose in a well cut bore, which in some hubs may the the bore on the other side of the hubshell. Combine all this with variance in seal friction, grease drag, difference in ball cage design and materials, and you can easily end up with a ceramic bearing that it higher friction than steel. Granted, it will still last longer and have a higher load rating, but if it is higher friction, that really doesn't matter.
We have tested bearings 4 times now in 5 years with an independent lab in california the difference between our ceramic and steel bearing, as well as other grades of steel bearing, trying to find optimal grease type and quantity, optimal internal clearance of the bearing, etc., and when it is all designed to operate together (in this case our bearing bore tolerance of +/-0.0002”, the ABEC7 tolerance of +0.000/-0.0002” and our spec for internal clearance and grease, cryogenically tempered races polished to near optical standards, teflon cage, and high hardness bearing steel races (non-stainless)), the savings under load equate to 0.8 watt for 150lb rider compared to our standard grade 10/ABEC5 steel bearing.
Our standard bearing also shows between 0.5 and 1 watt better performance compared to a grade 25/ABEC1 with brass cage and standard seal, with that 0.5-1 watt savings being the result of about a 6 factors, mainly reduced seal drag, lower viscosity grease, teflon cage instead of brass, higher ball precision, higher race precision, and use of ultra hard bearing steel instead of stainless.
Anyway, no matter what wheels you have, you are almost always best replacing the stock bearings with bearings from the hub manufacturer as they will know what works and what doesn't, and there are so many small factors in bearing specification that it can be pretty easy to end up with a very expensive bearing that is slower than what you started out with.
You can find more information about bearings at:
Si3N4 (Silicon Nitride) Ceramic Bearings
http://www.zipp.com/Technology/HubTechnologies/Si3N4SiliconNitrideCeramicBearings/tabid/107/Default.aspx
Index Categories:
Hub Engineering – Bearing importance
Hub Engineering – Ceramic bearings upgrades
From:
Trigeak13 Jul 13, 2006, 8:34 PM
Question:
How good are ceramic Ball Bearings?I'm looking at the claims on FSA's web page. Ceramic bearing are the way to go or so they claim. What do you guys think? Does anyone have proof that they are faster?
If what they are saying is true I'm gaining about over 1mph over a 20k, this can't be. Right?
Josh:
It is not the ceramic that makes most ceramic bearings so good, but the ultra-precision tolerances that can be held with ceramics. However, just like steel balls, you can get ceramics in low tolerance grades at lower prices. These are generally used in high temperature industrial applications like furnace carts where the ceramic has the temp resistance necessary but only needs to be low tolerance.
Just looking at what is out there right now, almost every ceramic bearing you can find is actually less round than our standard steel ball bearing (granted we are using the highest grade steel balls of any company in this industry), so it always makes me cringe that somebody wasted $100 or even $200 of their money to put grade 40 ceramic balls in one of our wheelsets when we already ship them with grade 10 steel balls, so in effect you are paying all that money for a less round, lower quality ball, and the extra hardness of the ceramic can in no way make up for poor roundness. The only company other than us widely detailing their spec is FSA, they are using a grade 3 ball. By comparison we are using a grade 1 ball, (3 millionths of an inch variance vs 1 millionth of an inch) but to give you an idea, a grade 3 ball costs about $5 and a grade 1 ball of the same size costs about $15, so with ball bearings in general and ceramics in particular you really get what you pay for. By comparison, most mail order ceramics that I see people buying these days are using at best a grade 25 ball and even more common a grade 40 ball (a grade 40 ceramic ball costs about $0.30) this is the only way to get the costs down to those levels.
All told, the difference between our standard bearing and our ceramic is roughly 0.75-1 watt for the entire hubset (6 bearing cartridges), and the difference between our grade 10 steel ball and a Campy record or DA spec grade 25 ball is about 0.5-0.75 watts for the entire hubset.
Here some more info on bearings from our engineering white papers:
A Note on Bearing Technology