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I have changed my front crank set from 42 to a 48 tooth ring. I am having difficulty setting up the front mech. The problem I am having is that the (don't know the name) tail? the box frame bit at the back of the mech is painfully close to the large cog. Whilst this is working I have no faith in in it remaining in place, if is does slip the results could be nasty. So in performing this change is there a specific front mech change that I also need to perform?

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  • @srank Good to see you've started on the review queues. There are some (possibly useful) resources on meta :-)
    – andy256
    Commented Oct 5, 2016 at 6:12

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with a bigger chainring you may simply need to install the front mech higher up the seat tube.. The outer part of the 'cage', if correctly positioned should be just a couple of millimetres above the biggest chainring when you change up.. Not sure this answers your question but i hope so...!

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  • I agree with @ian but one additional thing that will probably become apparent if it is an issue is you will have to loosen your front deraileur cable to make the adjustment, depending on how far you have to move the front mech up the seat tube you may need a new cable... on some small frames (and depending on the type of derailleur) you may not have enough adjustment space on the seat tube before hitting the water bottle cage braze-ons in which case you may need a new (different clamping style) front derailleur.
    – dafew
    Commented Oct 4, 2016 at 13:04
  • Another problem may arise with the teeth difference of the chainrings. (number of teeth on big ring - number on smallest ring) It needs to be within the specifications of the FD, typically it's around 20 teeth for three ring set-ups.
    – Carel
    Commented Oct 4, 2016 at 17:40
  • Correct - raising the FD to reach the new bigger chainring may stop it reaching the little chainring. On a double this is normally fine, on a triple it could be a show-stopper. I simply avoid cross chaining, so when in little chainring I'm always on a big cog.
    – Criggie ♦
    Commented Oct 4, 2016 at 23:20

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