Originally Posted by
63rickert
Bicycles are not light load applications. Stand a 200# rider on a 6-3/4" crank arm and that is a lot of torque. At super low rpm, which is worst case for maintaining lubrication. Add in that everything on a bike is underbuilt and nothing remains in alignment. If it ever was in alignment.
I don't think torque is the issue for the bearings. I think the issues are bearing speed, radial contact pressure, and axial force, calculated in consideration of worst-case static misalignment (frame or BB shell not aligned or poorly bored/threaded/finished; poor tolerances) and dynamic misalignment (flexing of BB and chainset due to pedaling and road bump stresses).
And a clear industry criterion for "heavy," a definition of proper design margin versus life, and a good understanding of how the options in material properties figure in.
Then we can talk. I'd like to know how to margin BB design and impose a sealing/lubrication strategy that would give 30 years/100,000 miles in a utility bike like a classic roadster. Maintenance free, guaranteed durability.