Originally Posted by
nomadmax
Bunkie
I'm not an engineer but I have stayed in a Holiday Inn
I would say the chief reason larger pulleys are touted as "better" is that they reduce the angle/bend of the chain when it goes around the pulleys, thereby reducing friction. I'm sure they have some kind of fancy bearing in them that further reduces friction but I don't know that to be a fact. As far as increasing chain wrap, it would be the same as it was with smaller pulleys; only a greater distance between the pulleys (center to center) would do that.
I remember seeing an infrared video from this research project www dot georgeron dot com slash 2007 slash 11 slash bicycle-efficiency-boosters dot html . Despite several searches, it doesn't look like it is available anymore. It showed a little heat on the chainring, a little more heat on the cassette, and the most heat on the jockey wheels. The heat generated is directly proportional to the angle the individual chain link has to turn to go around that pulley.