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I re-installed new tires for the first time yesterday. Now I'm having problems with my rear derailleur. The chain keeps popping off the derailleur guide pulley when I pedal forward. I can re-seat it easily but it just keeps popping off. Pics (and a video) below.

Disclaimer: this is a piece of crap bike that I got for free so thats why it looks like garbage. Also I am new to bike repair so I almost certainly did multiple things wrong 🙃

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  • Hard to see - you might be able to search for a bike-cooperative in your area who can help with problems like this. Also, to test the idea of chain tension, does it pop off when the chain is in big chainring at the front and big cogs at the rear ?
    – Criggie ♦
    May 23, 2020 at 21:42
  • Bike co ops near me are all closed because of Covid. Is there a better angle that would be more helpful? I tried moving the chain to the big cogs at the rear but I'm not sure I did it right because it pulls away from the guide pulley at an angle. imgur.com/a/XiVVB86
    – ale19
    May 23, 2020 at 21:54
  • That looks like the derailleur just isn't over far enough. IE, its not pulling enough inner cable ?
    – Criggie ♦
    May 23, 2020 at 22:10
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    Oh well i feel like a dumbass. To answer your earlier question...when it's on the bigger cogs and I pedal, it doesn't pop off the G-pulley derailleur anymore but it wont stay on the big cog in the front derailleur. It slips to the lower cog. youtu.be/AgSw5XCQfXw
    – ale19
    May 23, 2020 at 22:30
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    Perhaps the upper limit adjustment is allowing the derailleur cage to move too far outboard. The jockey wheels may also be worn allowing the chain to slide off.
    – Argenti Apparatus
    May 24, 2020 at 0:41

1 Answer 1

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I think the chain is not tensioned enough. Since you did not change the chain, or the crank, just the tires, the wheel position seems to me to be the culprit.

From the last picture it looks like the axle was farther behind (see paint chipped ... or at least I am seeing it, maybe it is an artifact?)

So, release the nut, slide the wheel more to the back in the guides and then close the nuts. Setting the gear in the small rings (back and front) should help you pushing the wheel back.

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  • Probably the wheel won't go any further back, due to the way the derailer hanger mounts on the other side. It's also possible that the hanger is bent, fairly common for a bike of this state.
    – Daniel R Hicks
    May 23, 2020 at 21:03
  • Yeah it really doesn't want to slide back anymore. The chain is already in the smallest gear. I cant tell if the hanger is bent, but if it is, what can I do? Is there a way to un bend it?
    – ale19
    May 23, 2020 at 21:42
  • Here's what the bike hanger looks like. Doesn't look bent to me? imgur.com/24c7abf4-128d-4b31-92b5-e5f23b20e6f4
    – ale19
    May 23, 2020 at 21:48
  • @ale19 - Can't see your image, but to check for a bent hanger you swivel the derailer back and forth and see if it seems to be staying parallel to the wheel.
    – Daniel R Hicks
    May 24, 2020 at 1:00

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