I have been looking at downward hanging (traditional) derailleurs and slant parallelogram derailleurs. The slants do seem to shift faster then the pendulous ones. I am trying to determine why. Some of the better shifting that was experienced with the slants of the 70's and 80's was plainly due to better chains and better construction of the derailleur itself. The rest of the difference is still something of a mystery to me.
Say we assume that the idea is get the jockey wheel to be close, very close to the cluster to increase the chain angle, in order to quickly catch on to the next cog. This is a reasonable conclusion because some of the fastest shifting rear derailleurs have the jockey wheel practically touching the cog teeth with less than a single link between cog and wheel. However, using a pendulous, (down hanging) system, you can still get the top wheel to come very close to the cog. The only difference I see is that with the down hanging system, the derailleur action happens further back where the chain tension and chain wrap is strong. Perhaps the slant system makes the change happen in an area where the chain is more flaccid, and thus more able to be pushed and pulled. If this is the case, then a down hanging (vertical system) could still have been created back in the 60's where the derailleur is indeed pointing straight down, but the "neck" has the whole assembly comming further forward toward the chainwheel.
To sum up: Was the faster shifting that was experienced with the advent of the slants, as a result of the slant design or other factors such as chain design, decreased spacing between the cogs with ultra 6 and the like, canted cog teeth, or just tighter construction in the derailleurs themselves? In any event, it seems that manufacturers would have quite naturally experimented with slight differences in derailleur design and found little benefit to slant style over traditional. This may have been the reason why Campy was slow to switch to slant style. Can such small differences in design even be legitamately copywrited? Garth Libre in Surfside Fl.