Doug Stephens wrote:
>Errr.... I've heard "Rapid Rise" is Shimano's trademarked name for what is
>actually called a "low normal" mechanism. So, are there any late 70's early
>80's "low normal" designs?
No, low normal derailers pretty much disappeared by the early '60s.
I recall it was very confusing converting to the use of high-normal derailers when I bought my first Hurét Alvit as an upgrade from the Benelux Mark VIII I had previously been using.
There is a rare and quite wonderful Sun Tour low-normal parallelogram derailer, probably dating from the late '60s. It's called the "Skitter" and it is a brilliant desgn.
It only has one spring, a coil spring. One end of the spring winds up the cage, the other end moves the parallelogram down toward the big sprocket.
This is not cool just because of its elegant simplicity, it olso serves to equalize chain tension! As the derailer shifts inward to the larger sprockets, the tension on the cage automatically reduces. As you shift to higher gears, the cage tension increases.
The result is that chain tension hardly varies at all from low to high gear, a feature unique to this design. (Most derailers cause there to be less chain tension when you're in the smaller sprockets, increasing the risk of chain jumping.)
These work _really_ well for their vintage (they're slant-pantograph design too) but they never caught on because of the "backwards" shifting.
I think the name "Skitter" might also have been part of the marketing problem...due to the font chosen, the "k" looked a lot like an "h."
Sheldon "Sun Tour Used To Have Some Really Good Ideas" Brown
Newtonville, Massachusetts
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