Big ring shifting - what *am* I doing wrong??

munkster
munkster Posts: 819
edited May 2012 in Workshop
OK, seem to be having this issue on two different bikes now; front shifting working like a dream on the stand (almost like clockwork, very crisp!) but when actually ride on the road it really refuses to go onto the big ring. Seems that the way that "works" is if I lift pressure off the pedals, thus simulating turning cranks by hand, it'll shift up there.

Given this has happened on two bikes I've recently changed from standard to compact what am *I* doing wrong here?? Front mech limits all seem fine, height of mech seems fine, rotation fine. At a loss...

When "slack" the gear cable is taut but not *really* tight, perhaps about a cm of play if you push weedily with one finger. Tightening with barrel adjuster doesn't seem to make a great deal of difference. Changed gear inner, still the same.

Never had this problem with my MTBs, so am perplexed... If anyone can give me any suggestions on this (aside from "take it to the LBS", that may yet have to happen) I'd appreciate it.

Comments

  • mamba80
    mamba80 Posts: 5,032
    If shimano - turn H outer limit screw 1/8 counter clockwise and then another 1/8 if the first turn isn t enough.

    have a look on the Park tools website for any other adjustments.
  • munkster
    munkster Posts: 819
    H outer limit is (and was) as far outboard as it would go...

    ...and I have the Park book, the Zinn book, and the Haynes book so I'm fairly sure I've got all the adjustments. It's "just" a front mech right, what could possibly go wrong?! :roll: :shock:
  • Barbarossa
    Barbarossa Posts: 248
    They all do that sir! I wouldn't expect a front derailleur to shift without lifting off.

    Joking aside, I bought a cyclocross bike last year with a 36/48 and Tiagra front mech. It shifted really badly until I changed to an Ultegra CX70 mech - designed for the smaller 'big' ring. Maybe a stiffer, higher spec front mech would help.
  • Twostage
    Twostage Posts: 987
    As above, reducing pedal power to shift to the big ring is normal behaviour for me. Apparently one of the advantages of shimano electric gears is its ability to shift under load.
  • munkster
    munkster Posts: 819
    Interesting OK, point taken. Although lifting off/reducing pedal power is one thing but I'm having to almost lift feet off the pedals and let the cranks rotate freely for it to shift... That can't be right, shirley?
  • DaSy
    DaSy Posts: 599
    The fact that you have changed from standard to compact, can affect the position that the chain meets the inner plate of the front mech. Some have a raised area that pushes the chain up against the big ring. When it is mated with a smaller diameter ring, it can miss this raised area (does depend on what mech you have).

    Try toeing the mech slightly in or out, that can often improve things.
    Complicating matters since 1965
  • Twostage
    Twostage Posts: 987
    Yeh, you shouldn't have to really lift off just pause momentarily. If you have a quick link on the chain try taking the chain off and then dropping the DR into the smaller ring. Then pull the cable by hand to make sure the DR travels as far as you would expect. If it travels further than when you use the shifter then you might have to tighten the cable with the adjuster.
    I don't know what kind of chainset you have but it could be that the driveside crank needs tightening which would bring the chain rings closer in.
  • ineedalager
    ineedalager Posts: 374
    You say you changed from Double (standard) to compact recently. Did you move the front mech down for the smaller size big ring? I used to fit a 53 ring to my compact and had to move the front mech up to allow the mech to work correctly so if you go the other way the mech has to be moved down.
  • antonyfromoz
    antonyfromoz Posts: 482
    I might be completely off the point here - and, if so, I apologise - but is this a new crankset you are installing or second hand? The reason I ask is that I had exactly the same issue on my bike with an FSA crank where the chain would get caught between the front mech and the large ring when I rode the bike but on the stand, where there was no pressure on the chain, the bike would shift fine every time. I had taken the bike to several mechanics who had worked on adjusting the mech - and one who had found small cracks on the front mech that he said could also be causing the problem by flexing during the shift and not putting enough pressure on the chain - but even after the fine tuning and the installation of a new mech the problem persisted. Eventually we found it was due to the small pins on the back of the large chain ring being slightly worn and not gripping the chain enough to bring it up from the small ring even though they looked fine (only slightly worn) on inspection.
  • munkster
    munkster Posts: 819
    It's a new chainset but am considering a new front mech since the bike is second hand (it's the Mrs' and she's not that fussed so not "prime" components!) and the old one may have seen more action than I'd like.

    Front mech has indeed been moved down the seat tube. When shifting into big ring the FD has no further play either, in answer to the other Q.

    Will see if the new FD helps, assuming I can get it "cheap" on eBay! No Dura-Ace for Mrs M! (or me, for that matter...)
  • migrantwing
    migrantwing Posts: 385
    FD's are relatively cheap. Tiagra are around £12-20, 105 around £20-30.
    Ghost Race 5000 (2011) Shimano 105 Black
    Carrera TDF (2007)

    http://www.bike-discount.de/#

    http://www.bike24.com/
  • munkster
    munkster Posts: 819
    It's an 8 speed set up though, so am assuming I'll need an 8 speed specific one with the 'orrible fat chain it uses?
  • snoopsmydogg
    snoopsmydogg Posts: 1,110
    If its the same as mtb then I would have thought you could use a tiagra or sora fd with no issues.

    recently fitted a deore ** (cant remember which model) fd and 9 spd truvative triple front chainring to my 24spd GT mtb with no issues.