I've long admired Mike Barry's work, but on this one I'd agree with Kent Sperry: I just don't see any logic in the Campy Sport. It seems that there was an unverified myth that the chain bends required for two pulleys added a bunch of friction, and that was the problem that the one-pulley Sport and its peers tried to fix. This would not have been a hard test to run (dynamometer). But, they lived by the myth, as far as I can tell. Mike suggests that they were adequate for the purpose (town bikes with narrow ranges). Indeed, my Sport is stamped "16 a 22 denti." But the fundamental design flaw is that it must pull away from the fw cog in the lower gears, so it contacts fewer teeth and wears them more quickly.
Of course, the other hidden cost was that Campy dropouts all had to have an extra hole drilled as the spring stop for the Sport, until it was dropped about 1961 (?). For the minor savings of one pulley wheel and a pivot, they imposed a cost on all their dropouts, for the few high-end bikes that might get that poor derailleur. I'm sure that it's possible to set up a bike with the Sport, but Mike's example is not a gear range that excites me as an alternative to single-speed.
But, our difference of opinion on this derailleur might just mean that I'm missing something.
harvey sachs mcLean va
++++++++++++++++++++++++++++++++++++ The esteeed constructeur Mike Barry wrote: Harvey Sachs ridicules the Campag Sport single roller rear derailleur. The Sport was perfectly good for the purpose for which it was designed, that is Italian "around town" bikes with three sprockets, typically 16-18-20. There must be thousands of such bikes on the streets of Italy today, many of them still running around with those 1950s three speed derailleurs. Trouble is that North Americans couldn't understand why the Sport wouldn't handle a much wider range of gears than it was designed for. It wasn't a cheap version of the Gran Sport but a derailleur aimed at a much different market. A market just about unknown in North America. <snip>
and Kurt Sperry responded: The Sport was a stupid idea because it couldn't do anything that a 2 pulley couldn't and it couldn't do things a two pulley could. There was no upside to single pulley designs, hence their quick and permanent demise. I'll bet the sprung upper pivot even cost more to make compared to an unsprung equivalent than the amount saved by using one less pulley.