In a well-known St Kilda cafe the other day someone in gaily-coloured lycra was banging on about the wonder of ceramic bearings. Being naturally curious and in a work-avoidance frame of mind this arvo I found this:

From http://www.superflycycles.com/servle...plate=techinfo:

?Last but not least, ceramic bearings can generally be made more round than steel ones. The ceramic balls we use are Class 5 or better. The class of a ball bearing refers to its sphericity in millionths of an inch. Thus, our bearings are round to 5 millionths of an inch and better in many cases. In comparison, the best bearings that come stock in Campagnolo Record or Shimano Dura-Ace is Class 25. That means our ceramic bearings are at least 5 times more round which results in less rolling resistance?

This got me thinkin’ (instead of workin’). 5 times as round? Who taught these guys arithmetic? Hold that thought and work with me for a minute or two?

Consider a 1? ball bearing for the moment, because the arithmetic is easier. A 1? class 25 ball will be no more than 25 millionths of an inch, or 0.0025% out of round. Put another way, that?s 99.9975% spherical or better. A 1? class 5 ball will be no more than 5 millionths of an inch out of round. Put another way, that?s 99.9995% spherical or better.

Unless my arithmetic has gone horribly wrong, 99.9995% round is NOT ?5 times more round? than 99.9975% round. It?s more like 1.00002 times more round, but hey, what do I know? I never studied marketing maths…

(If you scale it down from our 1? ball to a ?? or 3/16? inch ball, the ratios stay the same)

Now all this extra roundness translates to about three hundred bucks for a chinese-made bottom bracket.

Fuck that, I’m round enough.