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Triple chainring problems

Discussion in 'Bicycle Mechanics and Repairs' started by Crackle, 27 Feb 2008.

  1. Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Just fitted some new chainrings to my triple. Inners still the same but the middle and outer are smaller. I have moved the mech down and sorted out most problems.

    The one left is inner to middle. If the chainline isn't straight it doesn't want to know. Anyone any ideas? It's a Tiagra triple, only the Shimano inner ring left, the middle and outer are Stronglights now. Once I find my crank remover the inner will be Stronglight too.
     
  2. 02GF74

    02GF74 Über Member

    why replace the innner? these are usually steel so last much longer than the alloy middle and outer rings.

    are you saying you cannot shift up or down onto the middle ring?

    the derailleur position for the middle ring is set by cable tension and there is a ferrule on the shfter (I am talking mtb) or on the down tube for road bike with STI. you need to adjust this.

    also the outer most side of the derailleur needs to be parallel with the chain rings and when looking from the side, about 1 mm gap between bottom of the cage and the biggest ring.

    hmmm, the penny has dropped - since you have moved the position of the derailleur, who have in effect altered the cable length hence it is no surprise you are getting problems shifting.

    if you cannot get the adjustment using the adjuster, you need to alter cable length by undoing the cable clamp bolt, setting cable length and doing it up again.

    it is a pallaver but what can you do?
     
  3. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    They're all being changed to alter my gearing so 30 tooth to 26.

    No I've altered the cable tension and used the knurled adjuster to fine tune it. None of the stuff I've read describes issues with inner to middle, which is why I'm scratching my head.

    The derailleur is parallel and I'm not getting any chain rub, so everything else works. It changes when the chain line is straight but drops between when it isn't. I'm sure it's an adjustment I've already made but just not got it quite right. I've already done this once when I changed the outer ring. Well the LBS did but got the adjustment completely wrong.
     
  4. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Actually, after doing a bit of thinking, I might just raise the derailleur height by a mm or two....
     
  5. fossyant

    fossyant Ride It Like You Stole It!

    Location:
    South Manchester
    Got it there - should be a bit of a gap.... once mechs are sorted, it's fit and forget.....but a bugger to get it right !
     
  6. bonj2

    bonj2 Guest

    must be done in order:
    1) mech position - in line with outer ring and outer cage plate 2mm above it
    2) limit screws
    check 1 and 2 correct by shifting by pulling cable by hand
    3) connect cable so that it is just tense with mech on granny ring position
    (but not more tense than that)
    (make sure you route it correctly - I have mine so its clamped at the furthest point from the pivot)
    4) sue barrel adjuster to apply correct cable tension for it to shift to middle ring and to be in correct position when on middle ring

    setting up front mech without a barrel adjusters can be a nightmare.
     
  7. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Well, hit a few problems.

    When the chain drops between the middle and inner it invariably jams. Looking at the Shimano I've taken off it has an entirely different profile to the Stronglight. Not tooth profile but it's not flat if you look down the ring in profile. Instead it has shaped hoods which both recess the chainring bolts more and also seem to act as a guide when dropping to or climbing from the inner. The stronglight on the other hand is flat. So when the chain drops between inner and middle it goes past the bolt heads which are not flush and jams.

    So, unless someone can tell me different, I figure I can't use a Stronglight middle because the Tiagra chainset is designed only to work with the tiagra middle chainring. This doesn't matter on the inner and outer but the middle is a different story. The question is why do that. So I guess this now means I have to buy a new chainset if I want to change the middle ring, which I do. Anyone advise?

    I also discovered that I have an Octalink or Isis crankset which I had no clue about until I came to take it off. I need a new crank extractor now. That's the trouble with out of date knowledge.

    Well cheesed off now.
     
  8. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Stuck the Shimano middle back on. All working perfectly now but just not what I want.
     
  9. Monst

    Monst New Member

    Location:
    The boonies
    Take it the Tiagra is 9spd and maybe the stronglight is a replacement for a 10 spd? Only a 10spd is slightly narrower.
     
  10. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Thanks Monst, no not the issue but I think I have identified it.

    The Stronglight middle ring is not 'ramped' in any way as the Shimano is. As far as I can ascertain the only ramped comaptible middle is made by TA. I'm trying to find out more before I order a TA middle ring.

    Also, having put back the 42 middle and left on the 46 outer I discovered that there isn't enough of a tooth gap difference between the two. So setting up the shifter to clear the outer by a few mm results in the inner guide rubbing the middle 42 when the chain is on the outer as there is not enough height to clear it. There would be if the middle was 38 as I'd planned. So now I've had to put back the 49 outer.

    Still I'm getting there slowly. There's going to be a few chainrings on e-bay soon.
     
  11. Tynan

    Tynan Veteran

    Location:
    e4
    idiot savant says you can't mix and match stuff willy nilly
     
  12. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
  13. monnet

    monnet Über Member

    I think, if I understand right, you need to make sure that the middle ring is triple compatible. ie: it should have chain carriers on the inner side (four little rivets placed in pairs at opposite sides of the chain wheel. Without the carriers there is nothing to stop the chain dropping when you shift gear. As most inner chain rings are designed for use with doubles this is probably something to check out.

    It's also worth remembering that the chainwheels all have to line up (though this is less important with the inner ring). This is indicated by little arrows on TA rings (and shimano, I think Stronglight have a similar symbol). Usually the arrows should all be lined up under the crank arm.
     
  14. Monnet is right. You've installed a 'double inner' rather than a 'triple middle.
     
  15. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Thanks guys, you've confirmed what I've found out and didn't know previously. Also found out about the lining up as well.

    From what I've read, the shifting won't be as fast as normal under pressure as the Shimano UD profile originals, however with the chainrings correctly fitted it won't be far out.

    So only one chainring for e-bay then.