12spd XTR skipping with oval?- Mtbr.com
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  1. #1
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    12spd XTR skipping with oval?

    Just put an oval (blackspire) onto a pair of m9100 12 speed XTR cranks, going back to matching XTR derailleur + cassette. Bike rode just fine before, but now in the middle of the cassette, it will jump gears and skip around under load as the oval cycles. Top and bottom of range seem to be OK. If the bike wasn't running perfect ahead of time I'd suspect a bent hanger but since the only thing I swapped was the oval - wth is going? Do I need to adjust or rebuild the clutch? The drivetrain has about 1k miles on it so far.

    Thanks

  2. #2
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    Is the blackspire chainring designed for hyperglide+?

    Sent from my LIO-N29 using Tapatalk

  3. #3
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    Supposedly yes. Although I still haven't ascertained exactly what hyperglide does or means exactly.

  4. #4
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    Well I had assumed it was well tuned from the previous owner since it shifted pretty well with the round ring but it looks like the b screw was way out of adjustment. Got that dialed in and reset cable tension and it seems to be better. Some upshifts seem to bind depending on the position of the oval and the chain is rubbing the end of bash guard when in the granny however. Closer, better, but not quite there yet.

  5. #5
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    Quote Originally Posted by B. Rock View Post
    Well I had assumed it was well tuned from the previous owner since it shifted pretty well with the round ring but it looks like the b screw was way out of adjustment. Got that dialed in and reset cable tension and it seems to be better. Some upshifts seem to bind depending on the position of the oval and the chain is rubbing the end of bash guard when in the granny however. Closer, better, but not quite there yet.
    Oh, a secondhand bike?

    Yeah, all bets are off on adjustments/service.

    IME, 12spd drivetrains like things to be adjusted "just so" and require a decent amount of precision during the setup to get them there. Once set, I've found Shimano's 12spd, at least, to be pretty reliable in holding that adjustment.

  6. #6
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    Could also be clutch adjustment. The oval makes the derailleur cage move a little bit, so you may need to turn it out an eighth turn or so.

  7. #7
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    I was wondering about the clutch. I'll give that a go, thanks.

    And yeah - second hand but came from one of the guys at a bike manufacturer so I thought it would have been pretty dialed.

  8. #8
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    Make sure the clutch is lubed appropriately per Shimano's instructions. I recall hearing some made it out dry. Is the chainline the same as the original chainring?

  9. #9
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    Yeah, both 52mm chainline.

    After I started from scratch and retuned the whole thing, it seems to be way better. Guess I just got lucky that it was working with the round ring being so far out of tune but it's much more sensitive with the oval. Good to know.

  10. #10
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    I put an Absolute Black oval on my XTR 12 for my last endurance race (34T round to 32T oval) with a new chain. No difference in drivetrain performance.

    THough I think I am going back to the round and only using the oval for longer endurance events. Maybe a 34T oval is more ideal.

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