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Is there an easy, objective way to tell?

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marked as duplicate by Móż, Daniel R Hicks, jimirings Aug 8 '14 at 11:55

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

IMO this question is too specific and should be better phrased as "how do I tell the difference between short/med/long rear derailleurs". Otherwise we're opening ourselves up to a string of extremely specific questions like this one and yesterdays "is this long" one. – Móż Aug 8 '14 at 1:54

The objective way to tell is by calculating the total capacity and matching that to the make and model of the derailleur.

This has an excellent answer for calculating derailleur capacity.

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