Hello Garth -
Your questions are good - but hard. I can't address most of them, but I humbly offer the following.
Sun Tour patented the slant parallelogram design in 1964, and defended it zealously until it expired in 84. Yes, it was technologically superior. As practical evidence of this, all of the major derailleur manufacturers adapted the design after the patent lapsed. Most of them (but not Campy) did so immediately. Campy apparently resisted copying others for the sake of pride.
The slant style maintains the same relative chain-jockey-wheel-cog geometry over the whole range of gears. Constant chain gap, the distance from the jockey wheel to the cog measured along the line of the chain, is the key. Shimano improved the concept to enable index shifting.
Frank Berto has an excellent treatment of this topic in his book "The Dancing Chain".
I have experimented with a modern Shimano XT derailleur matched with an old Suntour 5 speed freewheel. The shifting is crisper than with a Cyclone GT. Both are slant parallelogram designs but the XT has both pivots spring loaded, which I believe is the major reason for the better shifting. I have found the biggest difference in (friction) shifting ease is the step from slab-sided cogs to shaped cogs like Uniglide (good) or Hyperglide (better).
An aside - when people say their Nuovo Record derailleur shifts as well as a modern slant parallelogram derailleurs, I always have been surprised and skeptical. However, in retrospect, I believe these folks may racing types (or live in Florida) and use "corncob" close-ratio rear cogs. With wide ratio cogs (used by persons like me described more commonly as "old" or "chubby" than "fit") I believe the difference is significant.
I hope this shines a little light on your questions.
Skip almost "all I know is what I read in books" Echert Renton, WA
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At 04:17 PM 11/9/01, you wrote:
>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.