Lifespan of anything is just a guess, as I guess we all acknowledge. I have one wheelset with 6500 hubs that I check a lot for roughness, and I would say I overhaul it at least once a year. At 9250 approx. miles they feel perfect, ideal, as new, at last overhaul with fresh 25 grade bearings and grease, in December. I don't know that there is an upper limit before breakdown in other words, a REAL LOT, but when it goes.............bang.... you're not freewheeling any more. I should probably overhaul the freehub and pawls soon.