by DMF on Wed Nov 08, 2017 3:17 pm
Let's just for the sake of argument take a purely scientific approach here, just for a minute...
Let's assume that it is pretty much physically impossible to produce a steel ball that is absolutely perfectly round, because we know this to be true. And let's also take into consideration that steel balls are at a microscopic level anything but smooth, the surface on ball bearings is under microscope pretty rough, and add to this that steel balls are pretty soft and subject to deformation under use in a bottom bracket.
Now, let's consider making a ceramic ball, first of all it is quite possible to get it pretty much perfectly round, measurably rounder than any steel ball. This is a fact, I'm not making that up. Then let's assume that it won't deform under pressure of, let's say, your legs pushing down on it...
Now, let's say the ceramic balls are perfectly round and the steel balls are not, then there is no point in measuring the microscopic differences between individual steel balls as these measures will vary depending on which side of the same ball you measure. Not perfectly round, remember?
You are able, technically speaking, to make a ceramic ball just about perfectly round, but the fact of the matter is that it is seriously difficult (impossible) to make several balls the EXACT same size, they will come out of polishing in slightly different sizes...
Here's the trick though, without naming the big ceramic brand who actually does this, it's quite possible to sort all the inconsistencies in size by their inconsistency and there by achieving pretty much perfect tolerances thru having all the same undersized balls in one bearing and all the same oversized or otherwise inconsistent balls in another bearing, making every individual bearing "perfect".
Now take a scientific approach here, could there not be a difference, albeit a small one, to this level of possible perfection?
Also, power meters don't lie and NO ONE, has EVER, gotten anything but a measurable drop in watts with upgrading every bearing on the bike to high quality ceramics. But just swapping the BB and nothing else? That's more about a buttery feel in the pedal stroke. Just like you won't drop 1kg with a change to carbon handlebars, but carbon everything will.
I will say though, that as friction in bottom brackets go, the quality of the frame dictates a lot, and I've seen a lot of really horrible tolerances from both open moulds to really high end brands.