I just finished working on a friends SIS rear deraileur. I have to say quite frankly, I'm ****** over the way deraileur tension wheel's bearings are designed. They don't hold lube, they are subject to high friction and wear because of the poor clearance, and they require way too much servicing. I've dipped my hands into skateboard repair and don't see why deraileur wheels don't use sealed bearing cartridges-- they last forever and require no servicing. Why hasn't a change been made?!!! If you say weight savings I'll kill you! There's no way weight justifies the pathetic performance and servicing time envolved with such a primitive bearing setup. By the way, I hate Shimano's SIS line and I apologize ahead of time for not having researched the archives for past discussions on this topic. I'm needing to vent. Again, REAR DERAILEUR WHEEL BEARINGS SUCK! Please bring fourth your comments. I'd be suprised if other mechanics don't agree. Later, FasterthanU P.S.- I have a little voice in the back of my head telling me that deraileur wheels have to be able to shift slightly in order to shift efficiently. Maybe this is the primary reason of it's design? STUPID BEARINGS!!!!!!!!!!