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I am struggling to diagnose the cause of an intermittent side to side wobble of the cogs on a rear wheel. Here's what I know:

  • Periodically (maybe every 10-15 minutes) during a ride, I experience slippage between gears not associated with shifting. A glance at the rear cassette while continuing to pedal reveals the cause: the rear cogs are all wobbling side to side, a few mm each way.
  • The wobble is in sync with the rotation of the cogs: slow pedaling = slow wobble, fast pedaling = fast wobble, no pedaling = no wobble.
  • If I stop pedaling, coast, and then resume pedaling, the wobble goes away. I can't say for certain whether the inverse is true: that the wobble always starts after coasting, by the time I notice it, I can't be sure exactly when it started. Nor can I say for certain that it goes away every time after I coast--I just know that by coasting (even briefly) and then pedaling, I can eliminate the wobble (for a while).
  • With the wheel off the bike, I have not been able to reproduce the wobble. There does not appear to be any plan in the hub or the cassette. I have checked that the cassette is securely tightened to the freehub and it is. There is not noticeable play in either the freehub or the cassette.
  • With the wheel on the bike and the bike in a stand, I haven't been able to reproduce the wobble either. I have tried moving the pedals slowly while watching the rear cassette, stopping the pedals, and re-starting and ran out of patience before seeing the wobble.
  • I do not believe the whole wheel is wobbling. This is tough to know for sure since I have only witnessed the behavior on the bike, but to my distracted on-the-bike eye, the wheel is rim is rolling true while the cogs wobble.
  • The hub is a Velocity Road Rear Hub, the cassette is a SRAM PG-970 9 Speed

What are the most likely causes of this behavior? What additional diagnostic or troubleshooting steps would you recommend?

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    My guess is that some of the ratchet pawls in the freehub are sticking and so the force on the cassette is not evenly transferred to the hub. This might also imply problems with the hub bearings.
    – Daniel R Hicks
    Commented Jul 18, 2015 at 19:45
  • Remove the cassette and check the rotor for play.
    – Carel
    Commented Jul 19, 2015 at 8:19
  • Just to add another possible cause in addition to what Dan and Carel mentioned above - remove the cassette and check that the cassette is not digging into the hub spindle with obvious damage on the hub spindle. I had such a problem and spoke with others who had similar problems - the overall consensus was that cheap aluminum hub spindles are to blame and this problem can be minimized by tightening the sprocket to 50 or 60 Nm instead of the recommended 40 Nm. I never had this problem until I got a new hub, so the "cheap aluminum hub" rings true.
    – Craig Hicks
    Commented Aug 3, 2015 at 20:48
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    @Carel - rotor?
    – Batman
    Commented Sep 2, 2015 at 19:59
  • Is the cassette properly fastened (40Nm)?
    – Michael
    Commented Sep 2, 2015 at 20:15

2 Answers 2

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Check:

  • Freehub body: no play radially? laterally? Try to reproduce it when lightly apply the brake (with barrel adjuster) and hand-pedal while the bike on stand. does it still wobble?
  • Cassette spacing: remove the cassette and see if there is any irregularities in the spacer.
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Yup. Time for a rear hub overhaul. Easy and fun job. Not too expensive. It'll be like a new wheel when you are done. Just replace and re-grease the bearings.

Another guaranteed fix is just tp replace the entire rear wheel assembly with a new one. No more problems.... It just depends on how much money you want to spend. Personally, I would try overhauling the hub first, then if that doesn't work, scrap the rear wheel and replace it. Of course, I would cannablize the spokes and save them for future replacements....

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    Welcome to Bicycles SE. We're looking for answers with more detail. Please consider expanding your answer to explain why you believe that the bearings are causing the problem that the OP describes and why a rear hub overhaul is likely to fix the problem. A short, one-line answer like this is likely to get downvoted, flagged for moderator intervention, and possibly deleted.
    – jimchristie ♦
    Commented Sep 28, 2015 at 11:10
  • The OP stated he did not believe the whole wheel was wobbling, which makes it unlikely that overhauling bearings would have any effect.
    – Christopher Hunter
    Commented Mar 2, 2018 at 18:58

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