Originally Posted by
Road Fan
BG, minor point - the A and B markings are for rotating the parallelogram so that it can have a straight position like an NR or SR, or a slanted position like a SunTour. I think the slant parallelogram design was still under patent protection in those days, so companies had to be tricky about how they competed with it, or pay up to SunTour. Example: DuoPar.
No, the Suntour patent expired in 1984 and the Campagnolo Chorus came out in 1988, Shimano OTOH was waiting in the wings with their SIS system; the slant parallelogram combined with their Centeron pulley was released in 1985 and took the market (it should be noted that Shimano used the drop parallelogram for years, which resembles the slant parallelogram but still used an in-line parallelogram as to not violate Suntour's patent; when Campy released their Rally derailleur that used the same drop/ in-line parallelogram the European market scoffed thinking is looked like a Japanese design, which explains why Campy redesigned it as a drop in-line parallelogram for V2) . Campy was very slow to adapt the slant parallelogram, and released several in-line parallelogram innovations with their C record; the Athena lateral slant parallelogram and Croce d' Aune sliding control arm. The Chorus was a slant parallelogram in either the A or B position, the A position have a 5 deg slant and the B a 30 deg slant.