Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: andyoxon on 14 January, 2022, 08:32:46 pm
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Really seized up. Fortunately I was able to detect the jam and didn't 'crunch it'. Any thoughts on why, based on the pics.
I was changing up (from small 24t chain ring) I think. Chain is pretty oily - haven't checked for stiff links yet.
I undid the rear QR to try and push the wheel forward to release the chain but no cigar. In the end I completely slackened off the front mech clamp and managed to release the chain.
The chain goes from cassette to middle chain ring, around and jammed up the inside of the front mech (I think) & kinks back to the rear mech.
edit.
(https://live.staticflickr.com/65535/51821270875_10f3286fdd_z.jpg) (https://flic.kr/p/2mXgypv)PXL_20220114_1 (https://flic.kr/p/2mXgypv) by a oxon (https://www.flickr.com/photos/145942400@N06/), on Flickr
(https://live.staticflickr.com/65535/51820552841_1a5798b46b_z.jpg) (https://flic.kr/p/2mXcSXB)PXL_20220114_2 (https://flic.kr/p/2mXcSXB) by a oxon (https://www.flickr.com/photos/145942400@N06/), on Flickr
(https://live.staticflickr.com/65535/51819604492_2cf9987b34_z.jpg) (https://flic.kr/p/2mX823L)PXL_20220114_3 (https://flic.kr/p/2mX823L) by a oxon (https://www.flickr.com/photos/145942400@N06/), on Flickr
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Generally it's due to accumulated gunk, coupled with a dry chain. Assuming no bent links, give it all a good clean and then lube.
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Thanks Adam. Will to check chain.
I've had this once before 6 mths ago (chain 2mths old). I'm wondering if the wide range triple (50-39-24) has anything to do with it. Generally works really well - but thinking there may be a rare cross chaining event or something that triggers it.
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Also caused by worn hooked teeth on the granny ring. It was so bad on early 90s MTBs, before everyone changed to steel granny rings, that we had monstrosities like the Alpinestars Cro-Mega.
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Also caused by worn hooked teeth on the granny ring. It was so bad on early 90s MTBs, before everyone changed to steel granny rings, that we had monstrosities like the Alpinestars Cro-Mega.
Blow me down! Suzy had one of those (or a version of it) and I never knew why it was configured that way.
Every day, as they say…
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They're retro-cool now, and you never have to break the chain to clean it! I don't think they were very stiff at the back, though.
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Didn't find any stiff links, & chain has had a good clean & lube. Chain ring teeth are fine - cleaned off gunk, & re-adjusted the front mech. Will probably try a 26t (steel granny) instead of 24t.
So still a bit of a mystery.
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Did you take any pictures of the bottom run of the chain where the actual chain suck took place?
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Only other pic is this one, sorry it's a bit oof.
(https://live.staticflickr.com/65535/51822557563_503f082937_z.jpg) (https://flic.kr/p/2mXo9TM)PXL_20220114_4 (https://flic.kr/p/2mXo9TM) by a oxon (https://www.flickr.com/photos/145942400@N06/), on Flickr
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How long is your chain? Does your wide-ish triple mean that you leave a link or more in the chain to accommodate a big:big combination? It won’t cause suck, but it might enable it if there is a bit too much slack in it in some combinations.
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Thanks will have a look. I think I sized with small-small through the derailleur, until the der arm just flexes down + allowing for missing/quick link use.
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Thanks will have a look. I think I sized with small-small through the derailleur, until the der arm just flexes down + allowing for missing/quick link use.
Shimano advocates big-big without going through the derailleur. It works for me using triples on my bikes.
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Thanks. Will probably check big-big chain length, when I install slightly bigger small chain ring.
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I used to use "jockey wheels in a vertical line with front big and rear small". These days, I use an online chain length calculator. It seems to give the same result.
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I used to use "jockey wheels in a vertical line with front big and rear small". These days, I use an online chain length calculator. It seems to give the same result.
Could check this too - without removing chain.
Possible cause. I was running a GoPro at the time, with shifters visible. I would have been on small front chain ring & probable mid-ish cassette sprocket, starting from lights up hill, but then possibly made the error of cross-chaining to smallest rear sprocket (photo) as road flattened, before I then tried to shift up to middle 39t chain - possibly even overshifted to large. Technically I'm outside the 105 FD-5703 22t range, but the front mech copes very well, with no clicking or noise even with major cross chain - noises which are useful sometimes as a warning...
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I know it’s not the same, but if you have a stand you could try to replicate that.
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Thanks. Have now tried this. Bike on stand small to small, changed up to middle - no issues at all. tried a few times, different cadences, works.
But, in small to small the rear mech upper section contacts the chain, so I need to lose a link. I'll be swapping small c/r 24 to 26, so that may lift the RD off the chain. As it is, 2nd smallest sprocket i.e. 11>12 gives space between chain & RD.
On small to big, the lower jockey wh is slightly backward of upper wheel.
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Thanks. Have now tried this. Bike on stand small to small, changed up to middle - no issues at all. tried a few times, different cadences, works.
But, in small to small the rear mech upper section contacts the chain, so I need to lose a link. I'll be swapping small c/r 24 to 26, so that may lift the RD off the chain. As it is, 2nd smallest sprocket i.e. 11>12 gives space between chain & RD.
On small to big, the lower jockey wh is slightly backward of upper wheel.
Be cautious shortening a chain.
The critical factor in determining chain length is that it *must* be long enough to accommodate big-big; otherwise you are into frame-wrecking territory.
Conventional wisdom is to wrap it round big-big without threading through the rear mech, find the shortest it can be made up in this configuration, then add one complete link (eg a half-link inner plus a quick-link outer, same thing.)
Any shorter is dangerous.
Any longer is un-necessary and you might run out of stroke on the rear mech to take up slack.
ETA based on Paul's comment: If the chain length required for safe big-big is too long for the rear mech to take up the slack in small-small, then you have over-reached the spec of the rear mech by quite a large margin. Shimano are quite conservative in their spec, and will accept a bit of tolerance abuse, but in the case I am describing, you need a longer arm mech.
Any other method of sizing the chain is not good enough if it cannot guarantee big-big safely.
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Agreed. People can make decisions about their own bikes, obviously, but what you say is very sensible.
But I think a problem might arise if the spread of gears is too great for the RD to handle effectively, and there’s too much slop when using smaller rings and sprockets.
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Thanks.
Top two pics are big-big - showing slack take up by rear mech. Bottom L: Small - Small. Bottom R: Small - Big
(https://live.staticflickr.com/65535/51828030016_77bbf4db71_z.jpg) (https://flic.kr/p/2mXScEq)collage (https://flic.kr/p/2mXScEq) by a oxon (https://www.flickr.com/photos/145942400@N06/), on Flickr
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I'd probably ride that. But I think the (perhaps necessary) chain length is creating enough slack in the small/small (or smaller/smaller) combos to allow chain suck to happen when it does. But if you want to keep that spread of gears it might be best to leave the chain as long as it is, and try to avoid small/small.
And then there's the cause, whatever that is. Hooked teeth on a ring (as someone has already suggested) or some other aspect that is catching the chain when shifting as you did. Are the rings correctly aligned? They may have ramps/pins that require specific alignment. I don't know, but maybe if they aren't aligned, it might affect the shift. I can see a tab on the granny that I think is used to indicate positioning.
But maybe the best bet is just to try to avoid going from smallest sprocket/granny to smallest sprocket/middle or even large ring? I have bikes that just don't like those big shifts.
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Make sure all of the bolts on all of the chainrings are sufficiently tightened.
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I'd never bother about small/small. It's not a ratio I'd need or want to use. It's not dangerous like big/big with a too short chain, if you change into it by mistake the main effect is chain noise to prompt you to change to something more useful.
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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.
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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.
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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.
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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.
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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.
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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.
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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. ;D