Originally Posted by
mtnbke
... your statement that Accushift is the same spacing as SIS isn't accurate, since each speed in the Shimano indexing world has its own cog spacing standard. Sure Shimano had SIS on 6sp Dura-Ace but that kit is almost a unicorn. To the point that Sheldon Brown doesn't even reference Shimano SIS 6-speed spacing on his freewheel/cassette crib sheet. Shimano 7sp SIS spacing and every Shimano spacing standard from 8-11 are not compatible with Accushift or "normal" 6sp.
Something I've wondered: Why in the world make the spacing different between different cogs? Is it just vendor lock-in? You've got a derailleur which I believe moves in a linear fashion, and a shifter with a circular groove for the cable to ride in. Given a certain angular movement of the shift lever, you should see the same linear movement of the derailleur pulley cage, right? If I'm screwed up in my thinking about one or the other, wouldn't a Shimano, SunTour, Campy, or other derailleur move in almost exactly the same fashion?
Please clue me in.