Originally Posted by
SoSmellyAir
Having both RD pulleys "perfectly vertical" also depends on using a cassette that is officially within specifications and the B screw adjustment.
The B screw adjustment? Seriously? That has absolutely nothing to do with sizing a chain. It almost sounds like you don't know what the B adjustment screw is for. And of course the cassette has to be within the limits of the derailleur capacity. Duh.
Feel free to argue with Shimano if you must:
RD-7700
God, for some reason you guys make sizing a chain the most complicated thing about bikes.