Chainsuck?

[andyoxon]

Thanks all.

From the first photo, the granny ring looks *ver* small.
What's the total difference the rear mech is being asked to take up?
(Big chainring - Small chainring) + (Big sprocket - small sprocket)

Could be you are asking too much of the rear mech to take up all that, but you'd need to look at the actual numbers.

An excessively slack chain in small-small would be the consequence of this, and that *might* be playing a part in the issue.

Max range of 105 FD is "22t".  FC is 50-39-24, but I'll be changing it to 26t, so range will = 24t.   Suppose I could always stick the 30t back on.  Last time had chainsuck on this bike was June, on the way to Porthgwarra, so have probably done ~2500km on it since then.  RD is a M591 9spd MTB Deore long cage with 11-32 10sp cassette - seems to work very well, & should be able to cope with small chain ring (?)  Small- small not something I ever intend to use - though, that grass thing...    Have had long grass tangled in it before.

[zigzag]

when the granny ring is so small, the middle ring gets in the way when cross-chained. it then tries to grab the chain with it’s pins and ramps. no big deal if this happens on the top part, but on the bottom part you get chainsuck. it’s usually a combination of events, as the chain on the bottom is moving away from the chainring and is not optimised to hook onto it, but sometimes it can happen. shouldn’t be using small-small on a triple, especially when it’s out of spec.

[mrcharly-YHT]

Can I suggest another potential issue?

Slightly gunky freehub and loose chain, you are pedalling fast, pause pedalling slightly for the shift, freehub doesn't completely stop and 'throws' some chain forward, creating a slack ripple in the chain. As front derailleur comes across, this slack ripple hits derailleur, some going under and jamming against chainrings.

Solutions would be to ensure freehub is freewheeling easily, and increase chain tension. Either shorten chain or check that rear derailleur is working freely.

[andyoxon]

Thanks both.  Testing on small-small change up was OK on bike stand, but guessing that may not replicate on-road 'real life'.  Have a 105 50-39-26 +11-34 on another steel bike, but never had an issue.  Anyway will see how I get on with the 26t here I guess, but may go to 28t.


UPDATE:  26t small ring now installed.  On small-small, there is now a finger's width gap between rear mech arm & chain.

[MartinC]

I'd never bother about small/small. It's not a ratio I'd need or want to use.

The only real use for small:small is raising the derailleur cage of a small-wheeled bike away from recently cut grass.

Everyone's entitled to their own definition of real.