I came across this article the other day and thought it would be good to share. All the guru’s on here probably know about this stuff already and may well flame me for pea-roasting or maybe for any inaccuracies contained within.
Anyways it has assisted my understanding greatly but be warned, it’s a long spiel. And a off a triathalon site…
Bearing Breakdown - Slowtwitch.com
Some extracts to pique your interest:
You’ll find that cartridges are often referred to as “sealed” cartridge bearings. They are filled with grease (similar to their cup-and-cone counterparts), and do feature a seal on either side. However, one should not assume this system is actually more sealed than a cup-and-cone. It just doesn’t work that way. In fact, the typical seal on a cartridge bearing isn’t so much a seal, as a deflecting shield against air, dust, and ambient moisture. In order to truly seal a cartridge system, they must have some sort of labyrinth seal on top of the cartridge’s own seal – similar to the old cup-and-cone. But – not all cartridge-using products have this.
There is another misnomer out there that ceramic bearings are unilaterally more durable than steel. The ceramic material itself is harder than steel – yes. So the ball bearings could be called more durable. However, there’s a catch. Most ceramic cartridge bearings on the market are actually hybrid ceramics – meaning that the balls are ceramic, but the surrounding races are steel. So these tough, durable ball bearings are housed in comparatively soft steel. If you use anything but a perfectly round ball bearing in this system, it is actually less durable than a full-steel cartridge. A very hard but non-round ceramic bearing will literally chew up a steel race in a very short order of time (think of it like little rocks or pebbles rolling around in there).
The other big hidden caveat in ceramic bearings is the fact that nearly every single one on the market uses lighter seals and grease than their steel counterparts. Why is that? Because the customer now has an expectation. An expectation that – ceramics are better and faster, and they should feel that way out of the box. When you plunk down a few hundred bucks for these things, our purchasing minds expect that we got our money’s worth. Nobody wants to feel like they’ve been “had”. This being the case, that bearing needs to feel absolutely-positively like greased lightning when you spin it with your fingers. With what we’ve learned, you now understand that very little of this perception actually has anything to do with the ball bearings inside that cartridge. At best, you got new bearings that were slightly rounder than your old ones. At worst, you got about the same as your old bearings. The reality is that any new bearing just doesn’t have that much drag. We can all thank the cavemen for inventing the wheel, ‘cause round things still work great today! The biggest part of your wattage/speed gain from the special bearings is simply because the outer seals are usually a light-contact or non-contact design, and the grease is less viscous. Non-contact seals have a “zero clearance” fit between the races. A full contact-seal has an interference fit, where it actually presses in to place and causes some drag (and seals the bearing better).
Good read, thanks for posting.