Bike is a Cannondale Topstone Ultegra RX2. Rear hub is a Formula RXC-400, 12x142 centerlock.

I got a flat rear tire on a ride and swapped the tube. When I retightened the thru axle I noticed that there was definitely some play in the rear wheel, even when the axle was fully tightened. Seems like the hub is slightly loose or something. I can provide pictures of the hub body etc if needed. I'm not quite sure how to fix this problem.

Removing the wheel at home and inspecting the cassette, it feels very slightly loose with some horizontal play. I guess I need a lockring to tighten it?

Images available here: https://imgur.com/a/xflq8qL

  • Likely it's not the cassette that is loose, but the whole hub on the axle, which means you have play in the bearings. How to fix that (or even if it can be fixed) is dependant on the design of the hub. – Argenti Apparatus Aug 8 '20 at 0:38
  • @Argenti Apparatus It actually looks more like the freehub has a bit of play. If you watch the video closely, it's easiest to see the movement by watching the largest cog, and that is enough play that you would see the end of the axle shimmy very clearly if it were as loose as the large cog. – bradly Aug 8 '20 at 2:12
  • @fantods wiggle it again and compare the slack in the cassette to that of the axle itself. You may just need to adjust the freehub. – bradly Aug 8 '20 at 2:16
  • Yeah I think it was actually an issue with the thru axle not threading properly on the non-drive side. I think a bit of play in the cassette is normal, you certainly don't want it overtight. I removed and then reinstalled the rear axle, making sure to keep both sides of the chainstay tight and flush and the wiggle disappeared. Thanks for your help with this Argenti and Brad. – fantods Aug 9 '20 at 20:10

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