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I'm going to the Alps soon and thought that it is a good idea to change my cassette from 11-30 to a 11-32 (with a fresh chain).

I started with replacing the chain, so I used like 3 different 'chain length calculators' and it came out for my setup (52-36 front, 11-32 rear, 410 mm length) I would need 108 chain links, so this is what I did. Interestingly, my old chain has the same length (though the calculator says 107 would be the best for 11-30 cassette).

Now with the old cassette it works smooth, but after I replaced the cassette, on the biggest cog (32) it jumps there fast, but while I am pedaling I notice some kind of jumping between the derailleur and the cassette. I tried to adjust the L-screw a bit but to be honest (and I am quite noob in maintaining this part) I didn't see much of a difference. And I also don't see the logic, why would I need to change the L-screw, the cassette cog positions are the same..

Some pictures: enter image description here enter image description here

and while the front is on big ring as well: enter image description here

Any advice is appreciated,

Mat

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    Are you able to post a picture of your transmission while the chain is on the largest cog and largest chainring? Does your chain jump on the largest cog when using only the largest chaining, only the smaller or both?
    – olliebulle
    May 6, 2023 at 20:39
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    Side comment: is this a short cage (RD-R8000-SS) rear derailleur? It does look like that, although scale can be hard to judge in photos. 32t max cog is technically out of spec for that RD.
    – Weiwen Ng
    May 7, 2023 at 16:54
  • @WeiwenNg I think so (I tried to read it but couldn't get the last part... It was not changed from the stock bike). Does it have any disadvantages then to use it with 11-32, should I stay with the 11-30?
    – Mat
    May 7, 2023 at 20:17
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    Shimano RDs can frequently be run a bit outside their specs. You definitely need to adjust the B-tension screw, as others said. If you can't get it far enough away from the big cog, then you can't use that RD.
    – Weiwen Ng
    May 7, 2023 at 21:44
  • While technically out of spec, I've run a 32T on an R8000 deraileur just fine for a few thousand km. That's not a issue.
    – calofr
    May 8, 2023 at 8:34

2 Answers 2

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I didn't understand why you replaced the chain as the old one had already required number of links but anyway you may need to adjust (release a little bit) your b-tension screw on the rear derailleur in order to pull the pulley a little bit upwards so that it won't touch to the biggest cog on the cassette.

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    This. All other adjustments should be able to stay the same, it's just the b-tension that would need to be adjusted so the guide pulley doesn't touch the 32T cog.
    – shox
    May 7, 2023 at 18:22
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    If I had a properly fitted chain for a 30 tooth rear cassette, then it might not be long enough for a 32t. So changing the chain is a reasonable idea for length. And also, the chain and cassette tend to wear at the same time, so keeping them together makes sense for re-use later. However, based on new photo, the old chain was over-length already and would have fitted the new cassette (wear and potential skipping aside)
    – Criggie
    May 7, 2023 at 19:38
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You probably don't want to fiddle too much with the L limit screw. When putting in big efforts in low gears, your bike will flex and can throw the chain off the inside of the cassette causing damage.

  • Set the Low Limit screw such that the chain just gets to the largest cog, and no more.

First thing to do is look up your rear derailleur's model number and see what it's rated at for a low gear. Many derailleurs will still work a little beyond their rated maximums, but some won't. And if your's has a low max of 28T or 25T then 30 was pushing it and 32T is right-out.

A photo of your chain from the right-hand side, with the gears set to Big-Big will help us diagnose further.

In this gear, the derailleur cage should be heading toward horizontal but not completely stretched flat. The top jockey wheel should be close-to but not hitting the teeth on the cassette.

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    I updated the description with some photos. Every 4-5th chain link has this very little jump. I would say that the derailleur should work with this cassette, since they both are ultegra.
    – Mat
    May 7, 2023 at 16:06
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    @Mat if that first photo is in big-big then you have too many links in the chain. I'd expect to see the derailleur's cage kicked forward much more. Its hard to know but your B-tension screw looks to need tightening as well, because the top jockey wheel is very close to the largest cog. However that may resolve itself if you shorten the chain by a set of links.
    – Criggie
    May 7, 2023 at 19:36
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    Actually, won't the B-tension screw will need tightening (to move the pulleys away from the cogs) regardless of chain length? Also, that does look to me like it might be a short cage R8k RD, technically rated to 30t max cog, but may be OK with 32t.
    – Weiwen Ng
    May 7, 2023 at 19:59
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    @Criggie I'm sorry, I overlooked the big-big part, just uploaded a third photo that shows in that state.
    – Mat
    May 7, 2023 at 20:07
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    @Mat Oh yeah that looks perfect for chain length. OK that's not your issue at all.
    – Criggie
    May 7, 2023 at 21:36

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