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  1. #1
    mtbr member
    Join Date
    Oct 2007

    2x9 Drivetrain Questions

    Hi Folks,

    In the quest for the lowest Q-Factor possible, I've gone to a 2x9 drivetrain. A few questions for the pros out there:

    1. The crank is an old Ritchey/Sugino 94BCD 5-arm and I found a 108mm Phil Wood BB that seems to fit about perfectly. How much clearance do I need on my chainstays? I've got 3-4mm on either side with everything mounted up. Is that enough? I've got a 110mm UN-73 if necessary, but the Phil is much nicer.

    2. The "tabs" on the Ritchey crank are too high to let the chain fully engage the teeth of the 29t chainring. I'm guessing I just need to fire up the Dremel. There is plenty of material on the spider arms such that some judicious removal shouldn't cause any trouble. Am I missing anything?

    3. I'm using an XT 77X front derailler right now. Will shifting improve with the new 2x9 specific SLX front? Its rated for 36t front and I'll be using either a 42t or 44t.

    Many Thanks!!!

  2. #2
    mtbr member
    Join Date
    Nov 2008
    1- If I read you correctly, 3-4 mm clearance between the crank arms and chainstays is plenty, unless you bend a crank. Double check that both chainrings also clear.

    2- I've never seen a crank with tabs so high beyond the BCD that they limit the chainring size. It's usually, if not always the chainring bolts themselves that determine the minimum size chainring. Check that the BCD of the 29t matches the cranks.

    3- double fronts are more forgiving of front shifters since the difference largest to smallest is generally less than with a triple. In your case which shifter works best is more a matter of how well the curvature of the cage is matched to the chainrings, and the ability to set the height properly.

    The key to solving any problem is to understand and address the underlying cause.

  3. #3
    Custom Bike Builder
    Reputation: xpatenaude's Avatar
    Join Date
    Apr 2009
    3-4 mm is close. I would watch for flexing when you pedal.

  4. #4
    mtbr member
    Join Date
    May 2007
    Good work, getting the Q factor that close!

    Its like the narrow Q factor will be SRAMS big "revelation" next year and be offered as an "upgrade" to the 2x9 platform FSA purposely screwed up with the wrong BB pipe length then sold for 2 years already.

    My KFL 2x9 arms are close to 10 mm from the chainstays. Not a stupid mistake either. . .

    I practiced on big girls when I was younger so I'm bowlegged anyway.

    FB is correct:

    "The key to solving any problem is to understand and address the underlying cause".

    Let us know how that Phil BB works out

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