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Chainset swap, do I need to touch the front mech?

Discussion in 'Bicycle Mechanics and Repairs' started by GrumpyGregry, 12 Oct 2017.

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  1. GrumpyGregry

    GrumpyGregry More gruff than grumpy

    Location:
    West Sussex
    Saturday I plan to swap the SRAM chainset on the best bike for another SRAM one with carbon arms. Will be fitting it to the existing bottom bracket, which is a Hope with the usual Truvativ GPX adapters fitted.

    To my mind, with correct application of my trusty torque wrench the new chainset (same numbers of teeth, swapping compact for compact) should end up precisely located where the old one currently is and the sweet shifting front mech should need no adjustment.

    What says the hive mind? Should I postpone the swap to a day when I have losts of mech fettling time free or am I good to go?
     
  2. Threevok

    Threevok Senior Member

    Location:
    South Wales
    Front mech should be fine, should the chainline still be the same
     
  3. andrew_s

    andrew_s Veteran

    Location:
    Gloucester
    Any change will be in the in/out direction, but since both chainsets are SRAM, I wouldn't expect you'd need to do more than tweak the front mech limit screws slightly.
    i.e. a limit screw setting that stops the mech moving far enough to chuck the chain off the existing chainset may stop it moving far enough to make the change on the new chainset.

    Fiddling the limit screws takes a minute or 5 - if it won't change, undo the screw a bit, if the chain gets dropped, do it up a bit. Hopefully the screws will be labelled H and L for the high gear and low gear stops (I use Shimano)
     
  4. mjr

    mjr Wanting to Keep My EU Citizenship

    Whether you should leave it or not depends on why you're replacing it (is the old one still OK to use?) and whether you need the bike to work flawlessly (such as for an event).

    I think it should need no adjustment but always be prepared for it to need adjustment - hope for the best, prepare for the worst!
     
    Threevok likes this.
  5. OP
    OP
    GrumpyGregry

    GrumpyGregry More gruff than grumpy

    Location:
    West Sussex
    I am replacing it for no reason other than that I can. I do have time on Sat for a shakedown ride before doing something longer Sunday morning.
     
  6. Smokin Joe

    Smokin Joe Legendary Member

    Good man :okay:
     
    Threevok likes this.