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  1. #1
    mtbr member
    Join Date
    Mar 2014

    XX1 chainring clearance workaround - side effects?

    I've been building a new bike from a used MootoX YBB frame over the past few weeks. The XX1 group arrived so I started to install the components. The frame has a 68mm wide BB shell, so as instructed I installed the GPX BB with one 2.5mm spacer on each side. It turns out the 34t chainring I ordered is too large for the frame. It starts touching the seatstay before tightening the crank arm completely. The crank arms (168Q) have plenty of clearance.

    Sram's specs for 32t rings show it as being 4mm smaller in radius. That should fit the frame without interference, so downsizing the ring is one option.

    Out of curiousity, I shifted both spacers to the drive-side and reinstalled the crank. In this configuration, the 34t ring clears the chainstay with just over 1mm to spare. Enough clearance as far as I've read.

    My question is this: what, if any, negative effects will mounting the BB 2.5mm to the right have? I'm concerned that the XX1 derailleur/cassette are so fine-tuned that the offset will cause chainline/shifting issues and extra wear. Or less likely, that the offset enough to affect my pedal stroke, e.g. cause knee pain?

    I appreciate any input.

  2. #2
    mtbr member
    Reputation: Epic_Dude's Avatar
    Join Date
    May 2010
    I would expect if the rear derailleur still shifts correctly with the spacers on the right side, then you should be good to go. Yes, you have effectively moved the chain line outward, however, depending on which rear cog you are in ,the chain will be biased to one side or the other with respect to the chain ring so I would not expect there to be more wear than usual on the smaller cogs. However, the chain will have a bit more angle when using the larger cogs, but it would be difficult to say for sure it you would get more wear in the taller gear ratios.

    I suppose it would be worth a call to SRAM CS to see if they could give you more information on this.

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