I have a question regardings rubber sealed vs.
metal shielded bearings: I have only experience
with one unicycle with metal shielded bearings (the type that is
often called 6203ZZ or 6203Z2). After just 20km outside the
bearings were creaking because they were full of dirt.
After exchanging the bearings with a rubber sealed type (6203RS2)
I don’t have any problems anymore.
So, why does anybody use metal shielded bearings if rubber sealed
bearings can last so much longer? Are there some advantages for the metal shielded type that I don’t see?
yep - but not in unicycling.
If you’re making a low friction joint then you want to cut down the rolling resistance as much as poss. open and sheilded bearings only suck-up a fraction of the energy that sealed bearings do.
A good example is on soap-box cars where open ceramic bearings are being used - there’s no seal and no oil even so they are as free-spinning as poss.
They have to be re-built after every meeting but that’s the price you pay.
Also - I have some track-bike hubs which run a bearing that is open to the elements - again for the same reason, this one however is lubricated by a small ammount of very very light oil.