I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of
the chain falls /outside/ of the fourth teeth after the initial tooth insertion.
Hello all,
I have been having issues with my chain falling off the large ring for a while, and I am wondering what could be wrong with my transmission.
First, to make things clear, it is /not/ an issue of derailer high
limit. It does happen when I shift from middle to large chainring, but
after the derailer pushed the chain off the middle ring : at that time
the derailer cage is not even touching the chain anymore.
My transmission is a 3|u9 Shimano MTB; the middle chainring is a 36 teeth FC-M590 and the largest chainring is an 48 teeth FC-M590. The chain is a Whippermann Connex 908. The chain is new; the chainrings are not but the issue kept happening after I last replaced them.
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of
the chain falls /outside/ of the fourth teeth after the initial tooth insertion.
The concerned teeth do not seem to be bent, and as I mentionned, the
issue did persist after a replacement of the largest chainring. It does disappear when the chain gets older though, which suggests me it could
have to do with chain flexibility. After all, during the shift, the
chain it temporarily held in a diagonal position.
Did anyone already encounter such an issue? Any idea that could help
prevent it? Or something I could do to better diagnose it?
Chain off the outside, yes?
First, check the front changer height.
Should have 1~2mm between cage and chainring at the closest
point. No more.
If still, look straight down at the front changer when in
high gear. Is the outer plate parallel to the chainring?
Tanguy Ortolo, 2026-01-29 16:09+0100:
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of
the chain falls /outside/ of the fourth teeth after the initial tooth
insertion.
Here are pictures. Chain starts to engage outside of one tooth: >http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-03-666.jpg
At that moment, the derailer cage is /not/ touching the chain, and--
therefore not pushing it too far.
One quarter of turn later, chain is now visibly derailed. The way the
chain engaged and fell off is completely visible: >http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-36-424.jpg
On Thu, 29 Jan 2026 15:43:35 -0000 (UTC), Tanguy Ortolo
<tanguy@ortolo.eu> wrote:
Tanguy Ortolo, 2026-01-29 16:09+0100:
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of >>> the chain falls /outside/ of the fourth teeth after the initial tooth
insertion.
Here are pictures. Chain starts to engage outside of one tooth: >>http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-03-666.jpg
It's difficult to see any detail in the photo. Black on black in the
dark doesn't work well. I suggest that you turn OFF the flash and use
some better lighting that does NOT cast shadows (i.e. multiple sources
or diffusers).
This is what your Fairphone photo after some image enhancement using >Irfanview to increase contrast and brightness: ><https://www.learnbydestroying.com/jeffl/crud/RBT/bike_chain_falls_off.jpg> >It looks like the tooth is on the wrong side of the inner plates. My >guess(tm) is a bent sprocket tooth or bad chain line.
At that moment, the derailer cage is /not/ touching the chain, and >>therefore not pushing it too far.
One quarter of turn later, chain is now visibly derailed. The way the
chain engaged and fell off is completely visible: >>http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-36-424.jpg
Tanguy Ortolo, 2026-01-29 16:09+0100:It is a little difficult to interpret those pictures but it looks like either the front derailleur is not paralell to the chain rings or the outer limit screw is not tight enough.
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of the chain falls /outside/ of the fourth teeth after the initial tooth insertion.
Here are pictures. Chain starts to engage outside of one tooth: http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-03-666.jpg
At that moment, the derailer cage is /not/ touching the chain, and
therefore not pushing it too far.
One quarter of turn later, chain is now visibly derailed. The way the
chain engaged and fell off is completely visible: http://tanguy.ortolo.eu/tmp/2026-01-29-16-21-36-424.jpg
It's difficult to see any detail in the photo. Black on black in the
dark doesn't work well. I suggest that you turn OFF the flash and use
some better lighting that does NOT cast shadows (i.e. multiple sources
or diffusers).
This is what your Fairphone photo after some image enhancement using Irfanview to increase contrast and brightness: <https://www.learnbydestroying.com/jeffl/crud/RBT/bike_chain_falls_off.jpg> It looks like the tooth is on the wrong side of the inner plates.
Myg uess(tm) is a bent sprocket tooth or bad chain line.
First, check the front changer height.
Should have 1~2mm between cage and chainring at the closest
point. No more.
If still, look straight down at the front changer when in
high gear. Is the outer plate parallel to the chainring?
On 1/29/2026 9:09 AM, Tanguy Ortolo wrote:
Hello all,
I have been having issues with my chain falling off the large ring for a
while, and I am wondering what could be wrong with my transmission.
First, to make things clear, it is /not/ an issue of derailer high
limit. It does happen when I shift from middle to large chainring, but
after the derailer pushed the chain off the middle ring : at that time
the derailer cage is not even touching the chain anymore.
My transmission is a 3|u9 Shimano MTB; the middle chainring is a 36 teeth
FC-M590 and the largest chainring is an 48 teeth FC-M590. The chain is a
Whippermann Connex 908. The chain is new; the chainrings are not but the
issue kept happening after I last replaced them.
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner plate of
the chain falls /outside/ of the fourth teeth after the initial tooth
insertion.
The concerned teeth do not seem to be bent, and as I mentionned, the
issue did persist after a replacement of the largest chainring. It does
disappear when the chain gets older though, which suggests me it could
have to do with chain flexibility. After all, during the shift, the
chain it temporarily held in a diagonal position.
Did anyone already encounter such an issue? Any idea that could help
prevent it? Or something I could do to better diagnose it?
Chain off the outside, yes?
First, check the front changer height.
Should have 1~2mm between cage and chainring at the closest point. No more.
If still, look straight down at the front changer when in high gear. Is
the outer plate parallel to the chainring?
Those are most probable but could be several other issues.
On 1/29/2026 11:20 AM, AMuzi wrote:
On 1/29/2026 9:09 AM, Tanguy Ortolo wrote:
Hello all,
I have been having issues with my chain falling off the
large ring for a
while, and I am wondering what could be wrong with my
transmission.
First, to make things clear, it is /not/ an issue of
derailer high
limit. It does happen when I shift from middle to large
chainring, but
after the derailer pushed the chain off the middle ring :
at that time
the derailer cage is not even touching the chain anymore.
My transmission is a 3|u9 Shimano MTB; the middle
chainring is a 36 teeth
FC-M590 and the largest chainring is an 48 teeth FC-M590.
The chain is a
Whippermann Connex 908. The chain is new; the chainrings
are not but the
issue kept happening after I last replaced them.
I reproduced the issue on a stand. When I shift from
middle to large
ring, the chain is properly pushed out of the middle ring
(but again,
not enough as to cause an immediate fall off), catched
and raised by
some helper pin on the inside face of the large ring, and
it inserts
into one of its teeth. But about one time our of four, an
inner plate of
the chain falls /outside/ of the fourth teeth after the
initial tooth
insertion.
The concerned teeth do not seem to be bent, and as I
mentionned, the
issue did persist after a replacement of the largest
chainring. It does
disappear when the chain gets older though, which
suggests me it could
have to do with chain flexibility. After all, during the
shift, the
chain it temporarily held in a diagonal position.
Did anyone already encounter such an issue? Any idea that
could help
prevent it? Or something I could do to better diagnose it?
Chain off the outside, yes?
First, check the front changer height.
Should have 1~2mm between cage and chainring at the
closest point. No more.
If still, look straight down at the front changer when in
high gear. Is the outer plate parallel to the chainring?
Those are most probable but could be several other issues.
I was thinking derailleur parallel issue....
Another point to consider is the rear cog selection. If the
crank is too far inboard (aka "chain line") and the shift is
made while on a smaller cog it can kick off the big ring. Of
course, he would be getting a lot of grinding/catching on
the big ring ramps while in the middle ring at that point as
well.
On 1/30/2026 4:20 AM, zen cycle wrote:
On 1/29/2026 11:20 AM, AMuzi wrote:
On 1/29/2026 9:09 AM, Tanguy Ortolo wrote:
Hello all,
I have been having issues with my chain falling off the large ring
for a
while, and I am wondering what could be wrong with my transmission.
First, to make things clear, it is /not/ an issue of derailer high
limit. It does happen when I shift from middle to large chainring, but >>>> after the derailer pushed the chain off the middle ring : at that time >>>> the derailer cage is not even touching the chain anymore.
My transmission is a 3|u9 Shimano MTB; the middle chainring is a 36
teeth
FC-M590 and the largest chainring is an 48 teeth FC-M590. The chain
is a
Whippermann Connex 908. The chain is new; the chainrings are not but
the
issue kept happening after I last replaced them.
I reproduced the issue on a stand. When I shift from middle to large
ring, the chain is properly pushed out of the middle ring (but again,
not enough as to cause an immediate fall off), catched and raised by
some helper pin on the inside face of the large ring, and it inserts
into one of its teeth. But about one time our of four, an inner
plate of
the chain falls /outside/ of the fourth teeth after the initial tooth
insertion.
The concerned teeth do not seem to be bent, and as I mentionned, the
issue did persist after a replacement of the largest chainring. It does >>>> disappear when the chain gets older though, which suggests me it could >>>> have to do with chain flexibility. After all, during the shift, the
chain it temporarily held in a diagonal position.
Did anyone already encounter such an issue? Any idea that could help
prevent it? Or something I could do to better diagnose it?
Chain off the outside, yes?
First, check the front changer height.
Should have 1~2mm between cage and chainring at the closest point. No
more.
If still, look straight down at the front changer when in high gear.
Is the outer plate parallel to the chainring?
Those are most probable but could be several other issues.
I was thinking derailleur parallel issue....
Another point to consider is the rear cog selection. If the crank is
too far inboard (aka "chain line") and the shift is made while on a
smaller cog it can kick off the big ring. Of course, he would be
getting a lot of grinding/catching on the big ring ramps while in the
middle ring at that point as well.
Possible but the images don't show scuffing on the inner faces of the chainring that a poor chainline (crank too inboard) usually exhibits.
Thank you all for the advice, I made progress with this issue. Progress
I would never have made if I only relied on what I can find on the Web.
:-)
After checking, the derailer was clearly much too high. And possibly
slightly unparallel. I put it at the correct height, and very parallel
to the chainrings, and it does make shifting far easier. Faster, in
fact: the chain is shifted immediately instead of rCLhesitatingrCY. I still experience derailments out of the large ring, much less than before.
I have not measured the chain line, but I am pretty sure it is correct,
since I never modified it since I bought the bike, and it was fine at
that time. I mean, I never replaced the crankset, and while I did
replace the rear wheel, it is similar enough to the original one : a
wheel with an hyperglide freehub suitable for a 9 cogs cassette.
Also, the issue occurs even on the middle cog (the exact middle one: 5th
out of 9). It would take a very very bad chain line to cause derailment
out of the largest chainring while on the middle cog, would it not?
I am also pretty sure this is not caused by the derailer pushing the
chain too far, because if I release a bit of cable, I can no longer
shift from small to middle chainring. And hardly shift from middle to
large chainring.
I need to take better pictures, but this will have to wait a couple of
days since I need a bike stand, and I only have one at my office. Stay
tuned!
Great, you made it better.
Besides height, worn or older design front changers benefit
from a small bend to the front of the inside cage; slightly
out and up. With a more positive push at the leading edge
of the chain during a shift, the chain lands more solidly on
a tooth rather than wandering off the outside.
AMuzi, 2026-01-31 16:20+0100:
Great, you made it better.
More than better in fact: it now works perfectly. It was still very
slightly out of parallelism with the chainrings, and I have just fixed
it. I am now unable to reproduce the issue, and therefore, I cannot take
new, better pictures of it. :-)
Besides height, worn or older design front changers benefit
from a small bend to the front of the inside cage; slightly
out and up. With a more positive push at the leading edge
of the chain during a shift, the chain lands more solidly on
a tooth rather than wandering off the outside.
That does not seem to be necessary in my case.
Thank you all for the advice, this is an issue I would never have been
able to solve by just searching the Web.
On 2/3/2026 7:32 AM, Tanguy Ortolo wrote:
AMuzi, 2026-01-31 16:20+0100:
Great, you made it better.
More than better in fact: it now works perfectly. It was still very slightly out of parallelism with the chainrings, and I have just fixed
it. I am now unable to reproduce the issue, and therefore, I cannot take new, better pictures of it. :-)
Besides height, worn or older design front changers benefit
from a small bend to the front of the inside cage; slightly
out and up. With a more positive push at the leading edge
of the chain during a shift, the chain lands more solidly on
a tooth rather than wandering off the outside.
That does not seem to be necessary in my case.
Thank you all for the advice, this is an issue I would never have been
able to solve by just searching the Web.
There are no secrets regarding front changer setup:Those compressed "tinyurl"'s don;t work on my newa reader.
https://tinyurl.com/ms3wevrv
https://tinyurl.com/mshjces8
On Tue Feb 3 08:04:34 2026 AMuzi wrote:
On 2/3/2026 7:32 AM, Tanguy Ortolo wrote:
AMuzi, 2026-01-31 16:20+0100:
Great, you made it better.
More than better in fact: it now works perfectly. It was still very
slightly out of parallelism with the chainrings, and I have just fixed
it. I am now unable to reproduce the issue, and therefore, I cannot take >>> new, better pictures of it. :-)
Besides height, worn or older design front changers benefit
from a small bend to the front of the inside cage; slightly
out and up. With a more positive push at the leading edge
of the chain during a shift, the chain lands more solidly on
a tooth rather than wandering off the outside.
That does not seem to be necessary in my case.
Thank you all for the advice, this is an issue I would never have been
able to solve by just searching the Web.
There are no secrets regarding front changer setup:
https://tinyurl.com/ms3wevrv
https://tinyurl.com/mshjces8
Those compressed "tinyurl"'s don;t work on my newa reader.
On 2/3/2026 7:01 PM, cyclintom wrote:
On Tue Feb 3 08:04:34 2026 AMuzi-a wrote:
On 2/3/2026 7:32 AM, Tanguy Ortolo wrote:
AMuzi, 2026-01-31 16:20+0100:
Great, you made it better.
More than better in fact: it now works perfectly. It was still very
slightly out of parallelism with the chainrings, and I have just fixed >>>> it. I am now unable to reproduce the issue, and therefore, I cannot
take
new, better pictures of it. :-)
Besides height, worn or older design front changers benefit
from a small bend to the front of the inside cage; slightly
out and up.-a With a more positive push at the leading edge
of the chain during a shift, the chain lands more solidly on
a tooth rather than wandering off the outside.
That does not seem to be necessary in my case.
Thank you all for the advice, this is an issue I would never have been >>>> able to solve by just searching the Web.
There are no secrets regarding front changer setup:
https://tinyurl.com/ms3wevrv
https://tinyurl.com/mshjces8
Those compressed "tinyurl"'s don;t work on my newa reader.
They both redirect in Thunderbird.
long versions:
https://grupetaciclista.com/wp-content/ uploads/2021/12/1640600496_839_Guia-de-instalacion-del-desviador- delantero-GRX-FD-RX815-Ultegra.png
https://external-content.duckduckgo.com/iu/? u=https%3A%2F%2Fwww.parktool.com%2Fassets%2Fimg%2Frepairhelp%2Fft_der_8.jpg&f=1&nofb=1&ipt=aa07240bdebe32055f9798f2cbe9de9d364ca8080910fdc04f3cb2e40377c965
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