Chain Falls between front sprockets

TimmyBob Posts: 2
edited March 2012 in Workshop
Hi all,

I used to be a member of this forum many moons ago, but it seems to have migrated and I can't reactivate my old account. Anyway I'm having problems with one of my bikes. It's got a compact front chainset and a Shimano 105 derailure with 10 speed chain. When changing from the large front to the small sprocket the chain frequently gets stuck between the sprockets. It's extremely frustrating as I loose drive and it's almost impossible to get it back onto either ring without stopping and physically correcting it.

I've taken the bike back to the shop numerous times and they've never been able to fix it. I'm starting to think the the compact chainset isn't suitable for the width of chain? Anyone got any suggestions on how this can be resolved without me buying a new chainset?


  • Surprised your LBS could not pin point the issue. It could be that the front mech is not shifting far enough over to put the chain onto the smaller ring. This is usually sorted by adjustment of the limit screws on the front mech. But I would expect a competent bike mechanic to check this.

    The other thing it may be is that you have too big a difference in the size of your 2 front chain rings. I have a similar issue when I fit a 38t to my chainset when I go to France to climb the mountains. The jump from 53 to 38 is just enough to cause the chain not to locate on the inner ring. As soon as I revert back to the 39t the problem goes away. However if the chainset is stock from the shop I would be surprised if there were a mismatch.
  • desweller
    desweller Posts: 5,175
    I'd take the chainrings off and place them on a flat surface to make sure neither of them are dished or something like that. Sounds very odd.
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  • rake
    rake Posts: 3,204
    on some sets, the granny ring is slightly offset to the mounts, it may have been fitted the wrong way around. try turning it over. i did this to use a 8 speed chain on a 9/10 speed set to get more space between the rings. id say it gives between 1&2 mm difference at a guess.
  • bobgfish
    bobgfish Posts: 545
    Shimano tech docs will pinpoint if one of the chainrings is fitted the wrong way around. The large generally has the number facing out and the small has the number facing in. Also they are generally only put on in one spot to aid shifting.
  • fleshtuxedo
    fleshtuxedo Posts: 1,856
    I had the same problem with a shimano R700 compact chainset once I'd swapped the inner ring for a (TA) replacement. Turns out the chainset needs shimano rings or it throws a hissy fit. Worth checking your rings and cranks are compatible.
  • on-yer-bike
    on-yer-bike Posts: 2,974
    I had this with a Campag Centaur compact 10 speed. Never got to the route of it, neither did the LBS.