Dunno. I mean, with these types of bearings, the life expectancy is probably going to be on the order of tens of thousands of hours in good conditions, so the ingress of grit and grime is probably going to be the big X factor - riding in the rain/wet, over gravel and dirt, etc, will affect lifespan. FWIW, I don't think that I've had BB bearings go bad in under 10k miles.