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Shimano XT B-screw adjustment

mar_kmar_k Posts: 323
edited April 2012 in MTB workshop & tech
can anyone tell me what gap I should have between the cassette and the rear mech?

Posts

  • supersonicsupersonic Posts: 82,708 Lives Here
    6mm on the top cog (cog to jockey wheel)
  • mar_kmar_k Posts: 323
    Thanks, I havent adjusted it. it was set when I bought the bike however I have noticed quite a large gap.
    Certainly much bigger than 6mm.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Often are, not many know what it does!

    The other way is to adjust until you hear rubbing, then back off a bit until goes.
  • mar_kmar_k Posts: 323
    just adjusted it now, Thanks
  • kenikeni Posts: 3
    supersonic wrote:
    Often are, not many know what it does!

    The other way is to adjust until you hear rubbing, then back off a bit until goes.


    What does it do? I don't remember ever having to adjust one
    Keni
  • supersonicsupersonic Posts: 82,708 Lives Here
    Sets the derailer angle: optimises performance.
  • cooldadcooldad Posts: 32,599
    Changes the distance between the mech (jockey wheel) and cassette.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • cooldadcooldad Posts: 32,599
    Sorry opened too many pages again.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • bikaholicbikaholic Posts: 350
    The B-screw controls chain wrap around the cogs and the ease at which the RD cage moves up and down the cassette.

    More chain wrap means faster shifting.

    So, you want maximum chain wrap at the point where the cage moves freely (ie where the teeth of the jockey wheel does not touch the teeth of the cogs). This will be the optimum point.

    You adjust the RD by shifting onto the largest sprocket, keeping the cranks spinning, and then adjusting the B-screw until the RD jockey wheel runs smoothly over the sprocket teeth (the RD starts off in a jerky washboard motion and will smoothen out as the B-screw is screwed inwards).

    Repeat for each of the chainrings to find the optimum point. It may be 6mm or it may be not, but this method will find it.
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