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Stupid question about my rear derailleur

Old 03-01-22, 06:49 AM
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Stupid question about my rear derailleur

I currently have a 2x10 setup with shimano deore.
i know that i must use the larger cog while on the rear the chain is near the smallest ,at the same time on other bikes i can use the combination of the smallest front cog and smallest rear cog even if is not correct. In that case i can still pedaling whitout noticing that the cogs combinations is not right , on my bike the chain seems working in a strange way amd sometimes jump (in the worst case scenario if i try to climb with the wrong combinations the chain keep jumping and the bike is not pedalable at all).
I noticed that the derailleur seems in a wrong positions , compared to other bikes with the same setup.

This is the derailleur on my bike , notice that the chain is touching himself at the point of the bigger pulley.


this other image has been taked from a random website , as you can see the derailleur is almost on the same position but the chain seems to be in a better positions.




Do you think i must adjust my derailleur (maybe adding more tension to the hanger's bolt forcing it to keep the chain more in tension) or i must shorten the chain a bit?
(or i there is another solution please write it down)

Sorry for my bad eng
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Old 03-01-22, 06:55 AM
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There are no stupid questions and sorry for my lack of Italian, but I'm pretty sure your chain is too long. No doubt more experienced voices will chime in soon.

Here's a good chain length video
https://www.parktool.com/blog/repair...-length-sizing
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Old 03-01-22, 07:27 AM
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Agree with @BTinNYC that the chain appears to be too long for that specific gear combination. But the large sprocket on the cassette is pretty big, so shortening the chain may cause problems in the large-large gear combination. If that's the case, a longer derailleur cage to wrap more chain may help. Failing that, I'd leave the chain as is and just avoid the small-small combination, because too short chain risks damaging the derailleur, while too long chain is just annoying.
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Old 03-01-22, 07:34 AM
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One more thing: it is best to use the smallest cogs as little as possible because they wear out the fastest. Using the big or middle ring in front with the middle cogs in back gives the same gear ratios as using the small ring in front with the smaller cogs and is best for long wear.
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Old 03-01-22, 08:31 AM
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When in the small/small crossover combo the chin can snag on the chain pick up tabs that are on the large chainring. It's possible that one bike has just enough chain/large ring clearance to not catch on these shift tabs but another bike might not have that clearance and thus the chain will be trying to shift onto the large ring, sort of but without enough help (via the ft der being shifted). Andy
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Old 03-01-22, 08:48 AM
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Check your B screw. I'm guessing your B gap is off also.
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Old 03-01-22, 09:03 AM
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Your chain might be too long. However you also need to put it in the big/big combo and see what that looks like. If your rear DR cage is stretched extended or articulated to it's max with no more travel left, that will be an issue if you shorten the chain.

edit: changed stretched to extended or articulated. I knew someone would probably pounce on that saying you can't stretch a DR cage!

Last edited by Iride01; 03-01-22 at 09:06 AM.
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Old 03-01-22, 10:44 AM
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Originally Posted by Iride01 View Post

edit: changed stretched to extended or articulated. I knew someone would probably pounce on that saying you can't stretch a DR cage!
I’m reasonably certain he’d object to saying anything other than a rubber band can be “stretched”
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Old 03-01-22, 10:46 AM
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Post a pic with the chain in the largest chainring and largest cog (big-big).

John
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Old 03-04-22, 08:48 AM
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Update: i adjusted the B-screw and removed 3 links from the chain (based on the parktool explaination video) now seems pretty good.

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Old 03-04-22, 01:10 PM
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You should shift into the large-large combination and confirm that the rear derailleur can accommodate this. If the chain's too short, it will bind and stop the pedals. If the rider does this while riding, they may tear the derailleur and/or hanger off! (As me how I know! OK, I'll tell you. I set up my mountain bike with a short cage derailleur way back when to "be cool." I knew not to shift into large-large. Just a quirk of my bike. But when I let my uncle ride my bike, I didn't remember to tell him this and he had no idea about avoiding large-large, so he did it. And I had a two-piece derailleur thereafter!)
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Old 03-04-22, 01:41 PM
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+1 on making sure large/large works.

we all say "oh I know it doesn't work, but I will never use it" which is good until you slam into that position without thinking..... which can result in a bunch of things including sudden deceleration (another ask my how i know )
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Old 03-04-22, 02:31 PM
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Originally Posted by squirtdad View Post
+1 on making sure large/large works.

we all say "oh I know it doesn't work, but I will never use it" which is good until you slam into that position without thinking..... which can result in a bunch of things including sudden deceleration (another ask my how i know )
Originally Posted by LV2TNDM View Post
You should shift into the large-large combination and confirm that the rear derailleur can accommodate this. If the chain's too short, it will bind and stop the pedals. If the rider does this while riding, they may tear the derailleur and/or hanger off! (As me how I know! OK, I'll tell you. I set up my mountain bike with a short cage derailleur way back when to "be cool." I knew not to shift into large-large. Just a quirk of my bike. But when I let my uncle ride my bike, I didn't remember to tell him this and he had no idea about avoiding large-large, so he did it. And I had a two-piece derailleur thereafter!)
Already tested and everything seems to work correctly. But is better to test it out during a ride session.
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Old 03-05-22, 11:22 AM
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Originally Posted by Trakhak View Post
One more thing: it is best to use the smallest cogs as little as possible because they wear out the fastest. Using the big or middle ring in front with the middle cogs in back gives the same gear ratios as using the small ring in front with the smaller cogs and is best for long wear.
On the flip side they're the easiest to find and replace individually.
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