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New Chain + Cassette, Slippage when in small front and mid-to-small rear
I have an ultegra 10-speed setup, dual-front. I just replaced the chain and cassette(11-25), and it appears that my chain is too long to achieve suitable chain tension when on the small front ring, and on any ring below about the middle of the cassette, yet when on both large rings, I can't see that there is enough capacity in the chain to be able to remove an extra link without problems (derailleur is already being pulled fairly far forward). This problem manifests itself with my chain slipping around the cassette whenever I am on the small front ring and on the smaller half of the cassette. I don't remember this being an issue prior to replacing the chain and cassette.

Am I mistaken to belive I should be able to use the full extent (or at least most of the gears) of the cassette when on the small front gear? I know this is bad technique, but in principle I would have thought the chain shouldn't slip. Is it due to the small "capacity" of the derailleur?

Removing an extra link appears out of the question as the chain is already tight when on both large sprockets.

Thanks in advance for any tips!
- What was the setup before (also 11-25?)
- If it was related to the chain length you would have had slippage before

So two likely things remain:
- setup: check and realign / dial in the dérailleur.
- wear on the chain rings, I guess you spent most of the time on the smaller one in the front (or the material is softer and wears more easily, materials for big / little chain rings do differ). Then you need to replace the culprit (at least the small chain ring), though a worn big chain ring will wear your chain more rapidly.

Do you still have the old chain? How badly was it worn? (Check video on this site regarding "measuring chain wear").

Oh, and you shouldn't ride the large-large combo (nor the small-small one)
Hi Joe,
Thanks for the quick reply.

The chain is only slipping through the rear cassette, sorry I should have made that clear... so I don't think the state of the chainrings is an issue (not that they are in bad shape anyway).

The setup is good as far as I can tell, on the large chainring all gears index sweet and smooth.

Old chain was stretched and had suffered a bent link due to coming off the front chainring (but that's a different story, I hadn't setup the front mech correctly; it was too high on the seat-tube allowing the chain to slip off easily), fixed now.

When the bike is upside down, and on the small-small gear, the chain is sagging and the mech is fully contracted... could it be that the spring on the mech is too soft? I've tried adjusting the mech d(?) adjuster to try to bring the mech arm back to increase chain tension, but this doesn't seem to go far enough to make a difference.

I probably just need to pull a link out tbh... I just don't want to do that only to find out the chain is too short on large-large!

Oh and yup, I know small-small, large-large gears are bad Smile
Check Alex's tutorial for calculating chain length. By chance, when you calculated the length, did you feed it through the pulleys? Hopefully not.

You can get a appropriate master link to fit your chain - this will allow you to easily remove the chain during transportation and maintenance. You'll have to pop out a pin and maybe a link. About $5-10 or so at a LBS.

The other thing you can do is to lay the old chain side by side the new chain, and use the same amount of links.
Re-check the setup of the rear dérailleur...
Also: If the chain had a bent link, did you encounter problems with the dérailleur being pulled or bent by the chain? Can you check the alignment of the dérailleur hanger?
Regarding the spring: A soft spring will "just" make adjustment impossible. How old is the bike? If it is not older than 10 years or so, I guess you should be ok.
Regarding chain wear: How bad was the chain wear? Can you check that (again)?
Well, surprise surprise, I was being a muppet. My chain was indeed too short (rubbing against the deraillure on small-small). Removing one link has fixed the issue.
Sorry for wasting your time people! Thanks for the replies.
(01-12-2012, 11:58 AM)reform Wrote:  Well, surprise surprise, I was being a muppet. My chain was indeed too short (rubbing against the deraillure on small-small). Removing one link has fixed the issue.
Sorry for wasting your time people! Thanks for the replies.

Congrats! Hope that works out. On these forums most of us are hear for you. Smile

By chance, how did you determine it was one link long? I assume you meant long instead of short.

Have you tried to adjust the rear derailleur cable? If the cable is relatively new, it will have stretched slightly coming out of adjustment. If you tighten the cable with the chain in the outer cog, it should put the derailleur in alignment with the cogs that have been skipping. Hope that helps. It did for me.

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