Tiagra front rerailleur problem

glasgowbhoy
glasgowbhoy Posts: 1,341
edited January 2011 in Workshop
When chaniging through the gear on the big rinf when I get to the 25 ring (biggest) on the back the front derailleur kicks the chain into the smalll chain ring.
Can I make an adjustment to fix this ?

Comments

  • keef66
    keef66 Posts: 13,123
    Your bike is trying to tell you not to use the 25t sprocket from the big ring!

    You could try and prevent it by increasing the cable tension a bit, but that would likely make the chain rub on the inside or the cage.

    Might also be worth checking that the derailleur cage is absolutely parallel to the chainrings rather than twisted sideways.
  • I take it that this is a Double chainset? If so then you should be able to use the 25 sprocket with the large ring. I would try unscrewing the "H" screw on the FD a quarter turn at a time and see if this cures the problem. If the "H" adjustment is just a bit on the tight side, then the chain's deflection to the largest sprocket may be enough to pull the chain over to the small ring.
  • glasgowbhoy
    glasgowbhoy Posts: 1,341
    cheers, will play around with the H screw see if it helps.
  • boblo
    boblo Posts: 360
    edited January 2011
    Errr, you don't wanna be using big/big or small/small combos. The world will end you'll fall down a worm hole to a place where errant cyclists who torture their chains are detained.

    Big/big and small/small puts too much zig (or is it zag) in your chain and may cause premature wear. Schoolboy error. :-)
  • boblo wrote:
    Errr, you don't wanna be using big/big or small/small combos. The world wil end you'll fall down a worm hole to a place where errant cyclists who torture their chains are detained.

    Big/big and small/small puts too much zig (or is it zag) in your chain and may cause premature wear. Schoolboy error. :-)

    to illustrate, at the end of the video, they show why this is bad :P

    http://www.youtube.com/watch?v=_05Eic7KgcA
  • John.T
    John.T Posts: 3,698
    I take it that this is a Double chainset? If so then you should be able to use the 25 sprocket with the large ring. I would try unscrewing the "H" screw on the FD a quarter turn at a time and see if this cures the problem. If the "H" adjustment is just a bit on the tight side, then the chain's deflection to the largest sprocket may be enough to pull the chain over to the small ring.
    You have lost me. :roll:
  • boblo
    boblo Posts: 360
    He's saying adjust the front der out a bit to stop the chain rubbing it when fully deflected.

    However, even on doubles, you should not use big/big or small/small combos if you want your transmission to last.
  • gethmetal
    gethmetal Posts: 208
    I don't buy the 'accelerated wear' business. It may be true if you womble around on the big ring/smallest sprocket all the time, but I reckon it's fine for short periods.

    Also, where is the Andy Schleck gear-changing video on youtube? :wink:
  • boblo
    boblo Posts: 360
    edited January 2011
    gethmetal wrote:
    I don't buy the 'accelerated wear' business.

    No but I bet you buy lots of cassettes and chains. :-)

    BTW, big ring/small sprocket is an approved combination ;-)
  • John.T
    John.T Posts: 3,698
    The H screw has nothing to do with this. It's only purpose is to stop the chain from going over the big ring on up-changes. The actual position of the cage is governed by the cable setting (ie, tension).
    Likewise the L screw is only to stop the chain from dropping off the inside of the small ring when changing down. It is not there to keep the chain on when running out of line.
    The chain should not come off when running big/big and the most likely reasons are bad chain line (especially if the frame has short chain stays) or worn rings or chain. If the cage was too far towards the inner ring it would be rubbing very badly on the smaller sprockets.
    As others have said, you should not be using this gear. It is not unknown to fold a big ring this way (if your name is Thor Hushovd).
  • gethmetal
    gethmetal Posts: 208
    boblo wrote:
    gethmetal wrote:
    I don't buy the 'accelerated wear' business.

    No but I bet you buy lots of cassettes and chains. :-)

    BTW, big ring/small sprocket is an approved combination ;-)

    Hahaha, you got me there :wink:

    But you know what I meant. And no, I don't. I got 5000 miles out of my last setup with half of my regular riding on sand/unsurfaced gravel bikepaths. Regular cleaning and Mobil1 motor oil seems to work for me.
  • 1stGenRex wrote:
    boblo wrote:
    Errr, you don't wanna be using big/big or small/small combos. The world wil end you'll fall down a worm hole to a place where errant cyclists who torture their chains are detained.

    Big/big and small/small puts too much zig (or is it zag) in your chain and may cause premature wear. Schoolboy error. :-)

    to illustrate, at the end of the video, they show why this is bad :P

    http://www.youtube.com/watch?v=_05Eic7KgcA

    The video shows a Triple chainset and use of the large ring and the largest sprocket should be avoided in this case. The OP would appear to have a Double and from my experience any wear using this combination would be minimal.
  • It would be useful to know if the BB has been changed at any time. It seems to be a Double chainset, so unless the BB has been mis-sized I think it unlikely that the chainline could be so far out as to cause the chain to go from big ring to small on changing at the back. Unless you know what changes have been made then one can only speculate.
  • John.T
    John.T Posts: 3,698
    It would be useful to know if the BB has been changed at any time. It seems to be a Double chainset, so unless the BB has been mis-sized I think it unlikely that the chainline could be so far out as to cause the chain to go from big ring to small on changing at the back. Unless you know what changes have been made then one can only speculate.
    Too true. This one really needs looking at 'hands on'.
  • glasgowbhoy
    glasgowbhoy Posts: 1,341
    It would be useful to know if the BB has been changed at any time. It seems to be a Double chainset, so unless the BB has been mis-sized I think it unlikely that the chainline could be so far out as to cause the chain to go from big ring to small on changing at the back. Unless you know what changes have been made then one can only speculate.

    No, no change of BB.
    I'm going to take it in to the LBS and will get back to you with the outcome. Cheers for the input.