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On this SRAM Apex 1 derailleur, what does this barrel adjuster do?

What happens if I turn it clockwise/anti-clockwise?

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    FYI your B adjustment screw (silver screw above the barrel adjuster) is backed almost all the way out. It's not supposed to be like that. B screw adjustment is covered in the Park Tool video linked in my answer. Sep 21, 2018 at 19:24
  • Do you have a barrel adjuster on your brake levers? If brifters, probably not; they're generally on flatbar levers though. So for a bike with Brifters, this is the only fine adjust available.
    – Criggie
    Jul 20, 2021 at 5:54

2 Answers 2

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It lengthens or shortens the housing length to adjust the lateral position of the derailleur cage. It's used to adjust derailleur 'indexing' so that the chain sits properly on the cassette sprockets.

Mountain bike shifter units have barrel adjusters, road bikes use this one as well as having frame mounted or 'in-line' adjusters some where on the housing run.

This video from park Tool Company has a good visualization of how it works:

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Better than a long answer watch this video for a comprehensive explanation of the settings of the RD:

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    Video does have the answer, but link only answers are discouraged here. Sep 21, 2018 at 19:40

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