Originally Posted by
machinist42
The G25 bearing balls I use have a Rockwell hardness in the 60s, while the races in my hubs are hardened into the 70s.
(Replacing the races is not only often not possible, when it is possible it is a pain in the b***s.)
What ball bearing races are hardened to 70+ HRC? It's hard to get that kind of hardening response from any steel. Off the top of my head 52100 or 440C are in the 60's as quenched. I really don't know what toughness has to do with bicycle ball bearings as I've almost never seen one crack, but generally speaking toughness tends to be inversely related to hardness for this kind of application.
Also as an aside heavy wheels are going to tend to spin for a long time because of the flywheel effect.