Chain catching on the inside of the large chain ring on 2x7

cookci
cookci Posts: 25
edited February 2015 in Workshop
Hi,

When I'm on small small cogs the chain catches on the inside of the large chain ring... initially I thought it was catching on the front mech but its definitely the chain ring.

The only way I can think of fixing this would be to install a longer bottom bracket unless you can think of something else?

Its a 7 speed setup and the spacer is between the wheel and the back of the cassette... is that right?


Thanks
Christian

Comments

  • jimothy78
    jimothy78 Posts: 1,407
    cookci wrote:
    When I'm on small small

    Don't be.

    Use the small ring with the largest 5 sprockets, the big ring with the smallest 5 sprockets - even this will likely give lots of overlap in the middle - there's no reason to ever go anywhere near small/small or big/big.
  • cookci
    cookci Posts: 25
    So is this behaviour normal bearing in mind I only have 14 speeds to use

    cheers
    Christian
  • keef66
    keef66 Posts: 13,123
    It can be normal with some chainsets, especially on smaller frames.

    That doesn't neccessarily mean your chainline is correct though. The gap between the front rings should ideally line up with the middle of the cassette.
  • cookci
    cookci Posts: 25
    Is my spacer in the correct place i.e. behind the cassette?
  • jimothy78
    jimothy78 Posts: 1,407
    cookci wrote:
    So is this behaviour normal bearing in mind I only have 14 speeds to use

    No, it might not be normal behaviour for the chain to catch (have you actually measured the chainline front and back?) , but it's poor technique that's making it a problem.

    Regardless of how many/few gears you have, there's still duplicated ratios in the middle unless you're running a single chainring, and there's no reason whatsoever to be in small/small, as that ratio will be duplicated by one available on the big ring and a sprocket somewhere in the middle of the cassette, giving a much straighter chain.
  • keef66
    keef66 Posts: 13,123
    cookci wrote:
    Is my spacer in the correct place i.e. behind the cassette?

    Depends on the wheel / freehub and the cassette. Do you know what they are?

    I only have experience of Shimano wheels with 9 and 10 speed stuff. No spacer required for the former, but a spacer is needed with 10 speed cassettes, apart from Tiagra 4600 which has one built in.
  • cookci
    cookci Posts: 25
    Its a HG41 7 speed 11-28T


    Concept EX wheels
  • keef66
    keef66 Posts: 13,123
    I'm not familiar with those hubs, but Sheldon Brown has this to say on the matter:

    "Add a 4.5 mm spacer before installing a 7-speed cassette on an 8-, 9-, or 10-speed hub.
  • cookci
    cookci Posts: 25
    Sounds like its in the correct place then.

    maybe ill try a longer bottom bracket.

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