Originally Posted by
HillRider
For index shifting the floating upper pulley allows fast reliable shifts even if the cable adjustment or cassette cog spacing isn't perfect.
Also, Shimano isn't the only one with floating pulleys. Campy uses them too. I assume SRAM does also but I've never used their rear derailleurs so I'm not sure.
For friction shifting, the float is a non-issue but why do you think non-floating pulleys are more "frictionless" than the floating type?
Sealed ball bearings. Pretty hard to make a floating pulley with sealed bearings. Can be done - like in a self-aligning pillow block - but haven't seen anything like that available.
Actually, the float is more important with friction shifters, because it's a pain to dial it in precisely. I have a rain bike with friction and a nice bike with brifters, so I know. I'm saying I did this on my own bikes. I would never do it on a client's bike. I don't ride Campy, but I assume they're at least as accurate as Shimano, where at least the Ultegra group is plenty accurate enough to dispense with the float.