Chain Drop


The frequency of dropped and jammed chains in this season’s pro races has become silly (never mind frustrating for the riders). But why is it happening? In four decades of racing/riding it never once happened to me - and I think there’s a clue in that time-line. Obviously I wasn’t using newly fashionable bike technology - and still resist it (even the minor accessory of a chain catcher). So
what exactly is the problem?

On Stage 3 of the current Tour de France I heard Nico Roche (co-commentator on the NZ broadcast) refer interestingly to the ‘long chain’ phenomenon - and that sounds plausible given close-up shots of chains bouncing around wildly between the cassette and the chain-rings. He went on to speculate that this may be a function of the now standard wide range cassettes (10/11 to 30/32) and chainrings (54/38). Obviously, at an extreme, using, say, a 10 sprocket with a 38 chainring is effectively going to lengthen the chain.

Maybe that’s the answer, but I suspect there’s more to it, and would like to hear others’ opinions.
My own intuitions include also the still imperfect technology of electronic shifting (eg riders kicking the derailleur mechs to ‘re-boot’ them), and the limitations of the single-position of the rear dropouts, especially thru-axles for disc-brakes (and are the latter also complicit in chain-drop I wonder?)

Chain adjustment used to be mechanically more satisfying and effective. First, with long-slot drop-outs, the wheel could be secured at the right point of chain tension (using the trackies’ trick of, er, a finger). Second, the stop-screws on both front and rear derailleurs could be adjusted precisely and thread-sealed to prevent chain overshift.

The old technology had elegant solutions for the competent home mechanic, without the assistance and expense of your LBS.


I’ve wondered about this too. I think the current situation is caused in part by riders running the new Di2 front mech with the previous generation of chain rings and cranks (which are in very short supply). There is apparently a difference in width. There was also a firmware update issued shortly after the new Di2 launched to address the issue of FD overshift (the cause(s) of which are beyond me).

We have known for a while that AXS has had significant issues in this area (causes and solutions debated as nauseam here and elsewhere.

EPS is so rare I can’t comment.

So electronic is possibly a factor, and longer chains may play a role too.

All this said, chain drop was pretty rare on the old Di2, and it’s possible on any mechanical system. While I suspect tech plays a part, these riders are really pushing the systems very hard and the nature of bunch riding means they may well hit more bumps.

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I think there was another thread on this topic talking about 12 speed and dropped chains and the consensus was mixing older 11 speed front mechs/chainrings and new 12 speed stuff. I did do some digging to see if maybe chain stays had gotten shorter but if anything they’re longer these days which explains why we’re seeing chain drop and not chain suck like you see on a lot of TT bikes.

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I have suffered from chain drop for about a decade. Frustratingly annoying is as polite as it can be framed.
It occurs predominately on one bike. I run Campagnolo mechanical on all the bikes. On the bike in question, have run compact 34-50, mid-compact 36-52 and regular 39-53 chainring setups. Have experimented with subtle changes over the period; FD limit stops adjustments, chain-catchers, OEM chainrings versus after market, chain length & chain tension (via RD ‘B’ screws, cursing & arm waving too.
Current theory is the speed of the FD change. i.e. the tension and it’s counter, (damping)friction on the FD spring action. Could be impacted by lever action, cable and sheath friction even cable routing. Feel like I need to bolt on a sticky 1980’s FD to test this one…


Damn, if even cursing and arm waving doesn’t help… :wink:

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I was going to reply to Mintaerobar’s first comment on my original post that EPS was too rare to warrant a comment on chain drop. But Shane_G leaves me a bit rattled. Like him I’ve ALWAYS
used Camapagnolo mechanical (at least since I could afford to!), but with none of his problems.

It’ll be interesting during the Tour to check any cases of chain drop on the only three World Tour
teams now using Campagnolo: UAE, AG2R Citroen, and Cofidis .

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I’ve run Campag mechanical predominantly for a number of years with very few issues. I’ve found the new 12sp a little fiddly to set up (the tolerances are very tight), and the maximum smoothness cables make a real difference, but overall it’s been great and I can only remember one instance of chain drop in >10,000km. 11sp Chorus before that was bomb proof, though I did find it was fussy about chains, and played much nicer with Campag stuff than KMC (perhaps no surprise),

There have been some instances in the peloton of EPS rear derailleurs ‘freezing’ in the last year or so; Ewan blamed losing a sprint on not being able to access his 11t cog iirc.

Given my new bike will have EPS, I’m hoping it’s not a widespread problem!

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Doesn’t that bike have some shorter chainstay than what campagnolo recommends?

I don’t really understand why thru axles would cause drops. MTB has been using for years with no issues on 1x setups.

AXS/Di2 has also been fine on MTB. Road is a different story (I can personally attest). But electronic wouldn’t be a cause

Manual limit screws don’t seem to be any better or worse than an micro adjust and are more easily to vibrate out of position.

So I have no answer for you, but I think some ideas are less plausible.

Anecdotally, I never dropped chains with di2 11 speed and have not dropped any yet with Rival 1x12 AXS or 2x12 Red AXS (w/ chain catcher).

I did drop a chain 3x with force AXS. 2x inside, 1x outside.

The only thought here was that with older (long-slot) rear dropouts is that chain tension can be adjusted by moving the wheel backwards or forwards. You can’t do this with thru-axles, or single-point rear dropouts. It’s why most track machines retain long-slot rear-facing dropouts. Cheers

I was going to say “Short Chainstays” and you beat me to it. The long(er) chainstays allowed…well, more chain and a more subtle curve of the chain from chainring to cogset. Shorter stays make this angle more acute and more prone to pop off.

Some years ago I had chain drop issue on a Cervelo P3 (before the P3C, long ago). I was able to use the shifter to be a bit more subtle on shifts in certain scenarios and have a bit more control. The electronics as great as they are have no idea what subtle means.

To answer someone who said they do not have the issue on MTN…well, in general you also do not have a Front Der. or two chainrings.

That is not why track bikes have a horizontal drop out, it is there to take up the slack of the chain that may be new, maybe a bit stretched…it would be almost impossible to get a chain the proper length for a track bike if it had a thru-axle and did not have a means to take out or allow for chain length.

I had this issue with an Orbea Ordu TT bike a few years back, horrible chain suck. Tried everything I had in the junk bin, different chains, different cranks, different chain lengths, different cassettes. Ended up kvetching to a friend of mine who was an amateur frame builder at the time and he calmly said nothing and then pulled up the minimum chainstay length specs from that bible Shimano publishes and mine were significantly shorter. Positive was it made me start my TTs in the 39t and then shift up to the 53 and also flick down to the 39 at turn arounds which was much faster than inevitably trying to grind out speed in a 53 from 0mph and increasing my VI/NP on the first part and halfway point of the race.

Never dropped a chain on that bike again.

You seem to be disagreeing with my point about chain tension adjustment with track dropouts, but I don’t see why. The principal reason for regular track chain re-tensioning is not a new or stretched chain but to accommodate different size chainrings (or even sprockets) for types of race.