Is Shimano RD-5800 rear derailleur compatible with a 7 speed cassette?
1 Answer
Nope. The RD-5800 is the previous generation 105 level derailleur that works with 11 speed shifters and cassette.
You need a derailleur intended specifically for 7 speeds. The only 7 speed models Shimano makes are in the Tourney range.
Apparently, at least for 7-9 speeds, Shimano road derailleurs are compatible with 7-9 speed shifters as the combination of shifter cable pull and derailleur ratio will index the cage correctly. This does not work for 11 speed though.
answered Apr 9, 2018 at 17:01
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I don't think so. The derailleur is not indexed (unlike the shifter) such that new a derailleur is compatible with old (7-speed) shifters. See blog.artscyclery.com/science-behind-the-magic/… Apr 9, 2018 at 17:22
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11-speed derailleur can be installed together with shifter indexed for 7 speeds, but the combination will not index correctly for 7-speed cassette. Check "derailleur ratio" under the link you posted. 10-speed road derailleur or any Shimano derailleur for 9 or less speeds will work.– ojsApr 9, 2018 at 17:32
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1Yes the shifter does the indexing, and pulls a certain amount of cable per sprocket, but the derailleur also has a derailleur ratio which is how much it moves the cage per cable pulled. AFAIK there used to be compatibility across different Shimano speed drivetrains, but 11 speed broke that. Apr 9, 2018 at 17:37
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@ArgentiApparatus 5800 was superseded by R7000 a week ago, so it's not really the last 105 anymore. Apr 10, 2018 at 2:33