New chain falling off

Smee707 Posts: 22
edited June 2019 in The workshop
Hi guys

I recently purchased a new rear wheel, an 8 speed casette and an 8 speed chain. However, when trying to switch to the largest rear sprocket the chain falls off the casette.

I think the rear derailleur is pushing it too far but this is the first time I've done any sort of bike maintenance so would be grateful for some help.

The wheels I purchased are

I was also advised to purchase an additional spacer (to the one that came with the wheel) but I can't put both spacers on at the same time, as I can't lock the casette down with both on.

Is the casette not on properly? I'm also concerned I dont have the right chain length but not sure how to check.



  • slowbike
    slowbike Posts: 8,498
    You need to first check the cassette is on properly - it should be tight and you shouldn't be able to wiggle any of the rings.
    Then - assuming that is done, you need to put the wheel on and re-index and do the limit screws on the rear mech. Plenty of videos on how to do that online.
  • gbsahne001
    gbsahne001 Posts: 1,973
    sounds like you purchased an 11 speed hub, which comes with a spacer to adapt it to an 8/9/10 cassette. 1 spacer should be all you need and as SB suggests, reindex the rear mech.

    Chain length is usually easy to judge, move the chain to the large ring on front and back; the rear mech should be angled towards the front rings but not excessively. Then put it small ring to small ring, the rear mech should now be angled away and up from the front rings but still have tension on it.

    Selection of videos to choose from

    rear indexing
    Correct chain length