>I've looked at a few Osgear equipped bikes (online) and it would
>seem that one can't use a front derailleur with a a rear Osgear
>derailleur because of the idler pulley mounted below the chainring.
>Am I wrong?
I can see your reasoning, but in fact, you can use a front derailleur with the Osgear Super Champion derailleur. Many pre-war Barra cyclotouring bikes used the Super Champion. Since the long tension arm can take up huge amounts of chain slack, he could use something like a 48-28 on the front, with a 14-22 or similar on the rear (4-speed), giving a very wide gear range.
The chain tensioning arm under the BB appears to have enough play to adjust for the different chainline when the chain moves to a different chainring on the front.
I haven't ridden a bike so equipped, so I can't comment on how well it works. I have ridden a racing bike with Super Champion and a single front chainring, and it worked very nicely. It's indexed, because racers were reluctant to try the new-fangled derailleurs. Oscar Egg figured that if he made it indexed, the racers would have less trouble shifting, and would adopt it more readily. The derailleur needs a lot of overshifting, so you shift two steps, then back one, and you have the next gear. It's much faster than stopping and moving the chain by hand, or even turning the rear wheel around...
Once the racers had been persuaded of the advantages of derailleurs, indexing fell from favor.
Barra combined the Super Champion with a Simplex shift lever, so he didn't have to worry about the cumbersome indexing and the frequent adjustments needed to keep it working smoothly.
How the world changes: Friction shifting used to be seen as an advance over old-fashioned indexing. Since indexing is the "classic" choice, does that make Shimano STI a "keeper of the flame" component?
;-)
Jan Heine
Editor
Bicycle Quarterly
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