2x 9 conversion problems

coblck
coblck Posts: 217
edited May 2012 in MTB workshop & tech
Hi have hit a snag converting to 2 x9, all parts are new so no worries about worn parts, bought new blackspire 38-26t front rings and new xt gs mech with knc chain and xt cassette, all went fine except when i select small ring at front and back ( i know its a gear that will not be used) the chain seems to jump at the front ring like symptons you get with worn teeth or chain all other gears fine. I know its not a gear that i will use but it says to me there is a problem somewhere. I followed guide to the letter as well on else were on this web site.

Any ideas.
Giant tcr pro ultegra
Cannondale CAADX GRX 812
Voodoo Marasa 2011

Comments

  • nicklouse
    nicklouse Posts: 50,675
    Sounds like the chain is being lifted by the outer ring.

    But as you will never use that combo it ain't an issue.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • coblck
    coblck Posts: 217
    cheers nick it does look and sound like that, so in your opinion should not cause a problem long term on anything else.
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011
  • tofu21
    tofu21 Posts: 359
    I have the same problem on my road bike.

    I'm not sure how advisable it would be but could you put another spacer drive side on your BB to help straighten the chain line?
  • steelie600
    steelie600 Posts: 519
    Ive thought about this option, bit confusing all the different bb lengths. Is there anywhere with crank specs etc so the correct spacing could be worked out?
    Idiot ^^^^^^^^^

    Ralph
  • nicklouse
    nicklouse Posts: 50,675
    steelie600 wrote:
    Ive thought about this option, bit confusing all the different bb lengths. Is there anywhere with crank specs etc so the correct spacing could be worked out?
    Yes but as there are 1000s of combinations it all depends what you want and ave, but generally just use what you have.

    But a you know from your other post nothing is actually easy if you do not av the required Infos. And the you ay need chain ring spacers if different rings are used.

    So when you have the Infos start a new thread.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • coblck
    coblck Posts: 217
    I did add 2mm spacer to drive side of my hope bb but just the same, i have found out that the blackspire chainrings are slightly thicker. Being a novice i didn't know you can get chainring spacers, will have go Google that to see were i can find them. But as nicks advice (who has never let me down) its s combo a will not use but my concern is that there was a problem i hadn't encountered before.
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011
  • nicklouse
    nicklouse Posts: 50,675
    BUT you don't need any chain ring spacers as your rings are correctly spaced.

    For your set up it is basically the granny and the other ring are too different in size so you will get chain contact when in the granny and the small. Just look down and you will see on the angle of the chain it will be intersecting the big chain ring. Or damn close to.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • coblck
    coblck Posts: 217
    Ok Nick cheers should i remove the extra drive side bb spacer i added. Also nick do i need to adjust height of front mech as not as crisp a shift as before.
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011
  • nicklouse
    nicklouse Posts: 50,675
    As you have changed the ring sizes yes.

    What is your chain line now?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • coblck
    coblck Posts: 217
    Not sure in chain line now , how do i measure that is it centre of seat tube to middle ring ?
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011
  • mrmonkfinger
    mrmonkfinger Posts: 1,452
    coblck wrote:
    is it centre of seat tube to middle ring ?

    yes
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  • coblck
    coblck Posts: 217
    48mm
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011
  • The Rookie
    The Rookie Posts: 27,812
    Stnd is 47.5mm, so your spot on.... I just checked my 2x9 (36/22) and it looks like it would do the same.....
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • coblck
    coblck Posts: 217
    hi just to confirm i measures chainline from centre of seat tube to in between 26t ring and 38t ring is that right, i added spacer on drive side bb to see if that would help in the chain being lifted which in didnt, so should i remove the spacer again or leave it. Chain line 48mm
    Giant tcr pro ultegra
    Cannondale CAADX GRX 812
    Voodoo Marasa 2011

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