What causes chain suck?

[msl819]

On an otherwise new and clean drivetrain one of my bikes experienced chain suck. It wasn't a dropped chain to the inside of the small ring but the chain pulled up from the bottom and wedged itself between the chainstay and big ring for a split second. Obviously would like to not have this happen again and would like to take the necessary precaution(s) to do so.

[fbhidy]

Check for a stiff link in the chain, then check your derailleur hanger alignment, both can contribute to this type of chain suck. Remember stiff links can happen with incorrectly assembling new chains as well as worn/dirty old chains.

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[regularguy412]

Worn chainring(s). And the occasional bad timing of a bump in the road during shifting.

Mike in AR:beer:

[mtechnica]

Mine has done it several times and chipped up my carbon, but the chain rings were quite old and I just replaced them to see if it will help. Before that I added a chain catcher which made it 90% better but it did it again a couple weeks ago.

[oldpotatoe]

On an otherwise new and clean drivetrain one of my bikes experienced chain suck. It wasn't a dropped chain to the inside of the small ring but the chain pulled up from the bottom and wedged itself between the chainstay and big ring for a split second. Obviously would like to not have this happen again and would like to take the necessary precaution(s) to do so.

Stiff link, front der adjust, odd chain line. Mostly worn rings that get hooked and don't let go of the chain cleanly. But I'd look at the chain, since clean and new.

[wallymann]

What causes chain suck?

can also be a dirty/unlubed chain, behaves similar to a tight link -- a pivot or multiple pivots do not swing freely especially under lateral shifting load but no linear driving tension.

when shifting big-to-small the affected link doesnt fully release and straighten when leaving the lower side of the chainring, so the chain keeps curving around to get jammed up into the chainstay.

[nickrenfro]

Even if it's new - it may not be properly lubricated. That could be an easy fix.

[Vientomas]

The waxy covering on some new chains is very sticky and makes the chain kind of stiff. I suspect that has caused me to experience chain suck in the past with a new chain. I remove the waxy covering from new chains now and make sure the links move freely before installing.

[rustychisel]

The waxy covering on some new chains is very sticky and makes the chain kind of stiff. I suspect that has caused me to experience chain suck in the past with a new chain. I remove the waxy covering from new chains now and make sure the links move freely before installing.

Very true. Put that together with worn chainrings and you do, indeed, have a recipe for error.