I’m in the process of switching from an 11-25 to 11-32 rear cassette. The upgrade has involved replacing the cassette, rear derailleur (short to medium cage) and fitting a new chain.

I can cleanly shift through all rear gears on the small front cog, however on the large cog I’m unable to shift to the lowest few gears. Towards these lowest gears the rear derailleur looks to be under a lot of tension, the upper jockey wheel is not engaged and things get jammed up:

rear derailleur

I believe I’ve sized the chain too short but I’m looking for confirmation as I thought I used the largest front/rear without derailleur + 2 links when sizing.

If I have sized things incorrectly can I just pick up a few more link pins and add some links back? Anybody able to offer suggestions on how many additional links to add?

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    I don't think you would need lower gears (larger rear sprockets engaged) with the largest chainring in the front engaged, crosschaining is one of the reasons. Before we say "the chain is too short" can you, please, post a picture with the smallest chainring in the front and one of the smallest in the back? Can the derailleur still tension the chain then? You don't want a slack chain in the first place. – Mike Sep 13 at 7:10
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    It’s possible that when you were sizing the chain, it slipped off the chainring just a few links at the six o’clock position, hence ending up shorter than expected – Swifty Sep 13 at 9:04
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    That chain is way too short IMO. A slack chain when crosschained in small/small won't cause a snapped-off derailleur or a bent axle like you're risking with that chain. – Andrew Henle Sep 13 at 11:26
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    @Criggie It worse than that, I ran a short chain once thinking (just don't shift up there), ended up tearing off the derailleur and destroying a wheel as the derailleur got pulled into the spokes when the derailleur hanger got twisted/broke. Too short of a chain can be disastrous – Rider_X Sep 13 at 16:48
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    @Mike Cross-chaining isn't the end of the world with a correctly-sized chain. Sure, it's not the most efficient way to run the chain but there are plenty of situations where it makes more sense to cross-chain for a little while than change onto the small chain-ring. Riding a bike where the chain is so short that cross-chaining will cause immediate physical damage "because you'd never cross-chain" is just dumb. – David Richerby Sep 14 at 11:02

Yep, chain too short.

Yes, you can add some extra links in. The chain is new so you wont have links with different amounts of wear.

What I would suggest is splicing the left over links into the chain first. Then you will have a chain a few links shorter then original unshortened chain. Then size, re-cut and join it.

UPDATE: I was reminded by a comment that you cannot push out the link pin used to join the chain. You have to break the chain in a different place and push out a regular pin. Therefore, when you splice a section of links in you will have three link pins in the chain (the one you first joined the chain with and one on ether end of the spliced in section). This is very important. The link pins are of a slightly greater diameter than the regular pins and widen the hole through the outer plates when pushed in. A link pin installed where a link pin was pushed out will be substantially weaker.

I prefer Park Tool's recommended method to size the chain because it is far easier to perform (and safer). All you do is size the chain on the largest sprockets without threading the chain through the derailleur (because the chain would be pulled straight through the cage anyway). Without tension on the chain it's easier to hold in in place and mark the appropriate link.

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    I'm a bit puzzled by "Yes, you can add some extra links in." That doesn't seem to be safely possible anymore with the prevalence of bushingless, press-fit chains where the chain is designed so the rivet being squished into the chamfered link is actually a structural feature. – Gabriel C. Sep 13 at 18:36
  • @GabrielC. One has to use a special chain joining pin (OP refers to these as 'link pins'). New chains come with one or two of them and one can buy extras. They are of slightly greater diameter than the regular pins and can be used to join chain links. However, this reminds me that one cannot remove a joining pin and then re-join the chain at that link - Thanks. I'll update answer with that info. – Argenti Apparatus Sep 13 at 18:54
  • Isn't that only Shimano chains? SRAM uses their powerlinks and I'm pretty sure 10-speed and up chains won't hold if spliced with a Shimano pin. – Gabriel C. Sep 13 at 19:12
  • @GabrielC. Shimano uses the link pins on their chains. I've never had a SRAM chain and use missing link link on KMC. All Shimano chains can be spliced with a link pin because you have to do exactly that when shortening and joining the chain when you first fit it. – Argenti Apparatus Sep 13 at 20:11
  • Yes, I miswrote. I'm aware of how Shimano chains are set-up. I meant that you couldn't use a Shimano pin on a SRAM chain (or KMC either). Maybe amend the answer specifying the splicing applies to Shimano chains only while other brands use different linking techniques? *edit: the only reference in the question is in the tags and from the picture. Someone might skip these cues and think it applies to all chains. – Gabriel C. Sep 13 at 20:34

The RD should be in this position with the chain on the largest ring and on the largest sprocket. See this document from Shimano for the correct chain-length on a 28+ teeth combination (page 10) http://si.shimano.com/pdfs/dm/DM-CN0001-06-ENG.pdf

Your chain is definitively too short. This has nothing to do with cross-chaining. But with a chain this short, accidental cross-chaining might result in the destruction of the RD.

This video shows three different methods to find the correct chain-length.

No need to be cross-chained like that with multiple chainwheels and my experience has been that only an SGS caged derailleur with handle 30+ sprocket teeth reliably. Try moving B-tension screw clockwise to give the guide pulley more room. It's troubling when you've followed the directions for chainsizing correctly and then it seems too short in practice. I've seen set-ups on mountain bikes where the derailleur cage is laid out pretty much horizontal on the big-big (XT shadow on Cannondales) and the shifting is quite fine.

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  • If the cage on this long cage RD is pulled straight like this on the third to last cog the chain is definitely too short. Turning the B-screw won't be of any help. It will even put more strain on the cage and jockey wheels axles. – Carel Sep 14 at 9:46

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