Capacity Questions
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Capacity Questions
So, I would like to move to a Shimano Ultegra 9spd short cage derailler, but I'm not sure about the capacity. The derailler has a 29 teeth capacity. On my bike I'm running a super compact double (46-30) and a 12-27 cassette, thus--if I'm calculating correctly--I need a RD with a 31 teeth capacity. So, the question is whether I can use an ultegra short cage (they look SOOO much better than long cage models) with this set up?
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Probably. It's only a few teeth past the spec of 29t wrap. I have used a 50/34 and 12-27 with a standard shimano road deraileur. You need to be careful about setting the chain length.
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Now here's where it gets interesting. Use the big/big chain sizing method. That'll give you the shortest chain that will safely cover the big/big combination. That's important. Even though you may never consciously shift into that combination, if you ever accidentally do it with a too short chain, the result can be real expensive. A slightly slack chain in the little/little isn't nearly so troublesome.
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I've had no trouble with a Shimano short cage derailleur on 50/34 12/27 set up. Your 46/30 12/27 setup is the same amount of chain wrap. I think you'll be fine.