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Recently I noticed I'm getting a bit of noise and vibration through the drivetrain if I backpedal on the largest sprocket at a reasonable speed.

There is enough vibration that when I'm stopped at lights getting into position the whole bike vibrates.

I looked at the chain while the bike was on the stand and it looks like the lower segment is jumping up and down while the bike is on the stand back-pedalling unless it's really slow.

It looks to me like the top jockey wheel might be putting pressure on the largest sprocket.

The chain is at basically 0 wear, and has been running fine for a while.

Recently I changed lubricant from a paraffin wax + paraffin oil 1:1 blend to 100% paraffin wax.

Apart from the noise & vibration the bike seems to be running fine.

If you're interested in the sound & behaviour here's a short video:

You can hear the vibration when the back-pedal speed increases

Is this something that requires maintenance to correct or should I not worry?

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Your video shows that the problem resides in the position of the derailleur. The RD is much too close to the cassette. The jockey wheel almost touches the large sprocket.

Use the B-screw to move the upper jockey wheel further away from the sprockets.

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  • Thanks, that took care of the rumbling! I had to push the b-screw in almost the whole way: there's probably about 1cm left protruding. I notice there seems to be a fair bit of rotation on the derailleur when changing cranking direction. Should I have a look at anything else in the area that might need adjustment? The derailleur feels solidly fixed to the hanger - I couldn't comfortably tighten the bolt any further at least. – Scottmeup Aug 10 '19 at 4:49
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    As a general rule: If a system works well, don't change anything. (aka Never change a winning team!) – Carel Aug 10 '19 at 11:47
  • Sounds like a good rule! I was worrying the movement might mean wear or a loose component. Thanks @Carel :) – Scottmeup Aug 10 '19 at 20:50
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I note from your video that you have a Tiagra derailleur with the GS (medium but longest available) cage, but your largest sprocket appears to be huge. I can't get the video to pause at a spot that allows me a clear, still shot to try and count the number of teeth, but is it over 34 teeth? (My initial impression is that it's a 42t monster).

Shimano specs indicate that the newest Tiagra (the RD-4700 GS) can handle a max sprocket size of 34t when combined with a front double. Total capacity being 41t. Even given the overly conservative limits decreed by Shimano for their offerings, if the large sprocket is over 36t, that's pushing the envelope.

Don't get me wrong, this is not an admonishment, but I'd like to know what's up front and more details about the sprocket. Also to hear you still have a whole centimeter of B-screw left amazes me as well since I find my set ups of compatible components that include a 32t+ low sprocket get all but 2 or 3 threads of the B-screw. On some bikes, I've stopped winding it in because it looked like the end was in danger of sliding off the hanger.

At any rate, the B-screw adjustment was the right one to make. My information--and curiosity-- may not be expressed in the proper format or place, but I'd like to hear more about what you have going there.

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    Watched the video a few more times and compared with the way my bike's 11-34t looks. Idk maybe it's the phenomenon of "video adds 10 pounds" but OP's cassette looks grande. – Jeff Aug 11 '19 at 0:26
  • I think @Jeff could be on to something :) The largest sprocket is 34t. The camera might be potato tier... – Scottmeup Aug 14 '19 at 12:17

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