Join Date: Sep 2008
Location: Loveland, CO
Bikes: Two LOOK 585s, one KG461
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Operator is right for 10 speed RDs. Unless you have some other use for an 11 speed RD, buying a medium cage 10 speed model would be cheaper and work perfectly. I even use a 10 speed medium cage with one of my 11 speed bikes, but I make a small alteration to the RD clamp bolt to increasse the actuation ratio.
The 11 speed RD has a slightly larger actuation ratio, but it will work fine with 10 speed. Only the 2010 models are guaranteed to work with a 29T large cog. Those models have a revised "B" screw mechanism that swings the cage further back to clear the 29T cog. 2009 models can be converted with one cheap part (#5-RD-SR004).
Some users manage to combine a short cage 10 speed RD with a 13-29 and get it to work, but how well it works depends on the frame. A longer RD hanger improves the chances of the upper jockey pulley clearing the 29T cog. The prefect chainstay length can add 3T of wrap capacity, compared to a worst case length.