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short-cage or medium-cage

Old 06-09-08, 09:06 AM
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jprestley@comca
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short-cage or medium-cage

I'm doing a build using new 10-speed Ultegra with a Shimano compact crank and a 12-27 cassette. I know Shimano says to use a short-cage rear der for double cranks, but wondering if the medium-cage would be better given the wide gear range.
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Old 06-09-08, 09:24 AM
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The short cage derailleur will handle a 27 tooth cog and a 29 tooth total wrap. Your 12/27 (15 teeth) + a 34/50 crankset (16 teets) total 31 for the total tooth #. A medium cage with a total tooth capacity of 37 would be a better choice.
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Old 06-09-08, 09:39 AM
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I second the use of a medium cage RD. Campagnolo recommends a medium cage for the 50-34 compact double and 13-29 cassette. While you might be able to get away with using a short cage, the shifting will be smoother with the medium cage.
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Old 06-09-08, 07:12 PM
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The shifting will likely be similar. However, the medium cage (road GS) will minimize/eliminate the chain from dragging on the upper pulley when in the 34/12 and 34/13 combos (edit: statement based on the numbers provided by maddmaxx above). I'm guessing you'll want to use those combos sometimes, so I'd go with the GS.

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