Originally Posted by
mixtemaniac
How do you even distinguish between grade 100, grade 300 and grade 25 bearings on a bicycle? We're not talking wind turbines here. All things being equal, it would seem (and I'm no engineer) that other factors on the bicycle would effect the smoothness of the assembly. Like manufacturing defects on the cups & cones of loose bearing parts. In all these years I've never been able to tell the difference except when comparing a very cheap wheel (< $50 USD) to a high end racing wheel ($1000 USD+). Or something like a Chris King headset vs. department store headset.
What am I missing?
I think you're probably right that you might not feel a difference between low-grade and high-grade balls on a low-end wheel or headset (or BB). However, since there will be more variation in spherical roundness on low-grade balls, I wonder whether that may cause accelerated wear on cups and cones. The idea behind spherical "perfection" is that the pressure exerted along the races as the bearings spin will be even. Would uneven pressure as the balls roll around the race cause premature wear? Logic would say yes, but to what extent, I wouldn't be able to guess.