Originally Posted by taguy4

Why do pulleys sets nowadays have a different upper and lower pulley whereas on older derailleurs like this used the same pulleys for upper and lower? I've read posts on this and apparently the upper pulley is supposed to be a "guide pulley". I'm thinking Shimano might have started this trend possibly when they introduced SIS: I have an older Shimano 600 pre-SIS derailleur and it has matching pulleys, and then I have a 600 "tri-color" derailleur that has the two different pulleys on it. Can the older derailleurs like my Campy one use the newer style pulley sets that have the dedicated guide pulley, and if so is there a benefit in using them?