Downshifting by itself; what causes it?

-----BEGIN PGP SIGNED MESSAGE-----

In article said:

I got a new chain put on my Bianchi Veloce 9 speed road bike (2001 model)
at the start of the summer. Several times, when going up a tough hill in
the second chain ring, the bike will shift itself onto the third chain ring.
Now, I could understand this (maybe) if the chain was on the big chain ring
in front and the big cog in back, but this shifting happens when on the
middle chain ring in front and the big one in back.

_ It's going from the middle to the small? Does the front
derailler move at all? If the front derailler is moving you
should check out this page

http://sheldonbrown.com/autoshift.html

Generally, autoshifting happens on the rear derailler, but
it could happen on the front as well.

Quoted message said:

I am lucky that it hasn't happened while I was out of the saddle, but I
would like to know what causes it and what I should do to fix the problem.

_ Did you get a different brand of chain? Did you recently put a
bigger cog on the rear cluster? What might be happening is that your new
chain has slightly different side plates and the ramps on the
middle chainring are engaging the side plates and down shifting
as they are designed to do. Basically the ramps on the middle
chainring are designed to down shift the chain if the side
plates of the chain engage the ramps. If the derailler is not
moving then something is causing this to happen.

_ You might also check the chainline of your crankset, it may be
farther out for some reason. I would suggest avoiding the
middle/big and using a gear with the same ratio on the small
chainring as a temporary work around until you find the real
cause. This might be a better gear to use anyway.

_ Booker C. Bense

-----BEGIN PGP SIGNATURE-----
Version: 2.6.2

iQCVAwUBQYJxK2TWTAjn5N/lAQGdhgQAjkSY5odOInI05E8Xjt/TEaPVp+Mw0Slm
q54oW2JZ4hAH+rcCvaaIok2zraGmGBJx7HDRAPmdjgcorPlS8GUMI9ri8z8eWsXW
CWfxmSTnKgoB6P9OpixGDjnSiwm1vZJdP9mSHC9Mc7qTkrBZskaI1c0Qa4TNETcM
0Wkiqwf24s0=
=uKvt
-----END PGP SIGNATURE-----

:
: _ It's going from the middle to the small? Does the front
: derailler move at all?

No, the front derailleur stays the same; it starts making that scraping
sound after the chain goes to the granny gear in the back.

: _ Did you get a different brand of chain?

Yes, the brand of chain is different. It had a KMC chain and now it has a Z
chain. Z9000? Something like that.

Did you recently put a
: bigger cog on the rear cluster?

No, no changes on the rear or front rings.

What might be happening is that your new
: chain has slightly different side plates and the ramps on the
: middle chainring are engaging the side plates and down shifting
: as they are designed to do. Basically the ramps on the middle
: chainring are designed to down shift the chain if the side
: plates of the chain engage the ramps. If the derailler is not
: moving then something is causing this to happen.

It doesn't happen every time, with every hill. Just about 1/3 of the time.

:
: _ You might also check the chainline of your crankset, it may be
: farther out for some reason. I would suggest avoiding the
: middle/big and using a gear with the same ratio on the small
: chainring as a temporary work around until you find the real
: cause. This might be a better gear to use anyway.
:
: _ Booker C. Bense
:
thanks

Are your rear clogs worn? The cause may be your chain slipping. There may
be only one or two clogs showing wear so you may be able to notice wear by
comparing them to each other. If you needed a new chain then one would
think it may be time to change the clogs too.

"Pat" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

:
: _ It's going from the middle to the small? Does the front
: derailler move at all?

No, the front derailleur stays the same; it starts making that scraping
sound after the chain goes to the granny gear in the back.

: _ Did you get a different brand of chain?

Yes, the brand of chain is different. It had a KMC chain and now it has a

Z

Quoted message said:

chain. Z9000? Something like that.

Did you recently put a
: bigger cog on the rear cluster?

No, no changes on the rear or front rings.

What might be happening is that your new
: chain has slightly different side plates and the ramps on the
: middle chainring are engaging the side plates and down shifting
: as they are designed to do. Basically the ramps on the middle
: chainring are designed to down shift the chain if the side
: plates of the chain engage the ramps. If the derailler is not
: moving then something is causing this to happen.

It doesn't happen every time, with every hill. Just about 1/3 of the

time.

Quoted message said:

:
: _ You might also check the chainline of your crankset, it may be
: farther out for some reason. I would suggest avoiding the
: middle/big and using a gear with the same ratio on the small
: chainring as a temporary work around until you find the real
: cause. This might be a better gear to use anyway.
:
: _ Booker C. Bense
:
thanks

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.784 / Virus Database: 530 - Release Date: 10/27/04

: >
: > Yes, the brand of chain is different. It had a KMC chain and now it has
a Z
: > chain. Z9000? Something like that....
:
: The Z9000 is a KMC chain. See:
:: Tom Sherman

Okay, I just went and looked. It is a chain by SRAM.

Pat in TX
:

DT said:

Are your rear clogs worn? The cause may be your chain slipping. There may
be only one or two clogs showing wear so you may be able to notice wear by
comparing them to each other. If you needed a new chain then one would
think it may be time to change the clogs too.

Is this a Dutch bicycle? 😉

--
Tom Sherman

Pat said:

: _ Did you get a different brand of chain?

Yes, the brand of chain is different. It had a KMC chain and now it has a Z
chain. Z9000? Something like that....

The Z9000 is a KMC chain. See:
<http://home.earthlink.net/~kmcchain/english/9speed.html>.

--
Tom Sherman

i notice that many hi end bikes i meet along the way are
underlubed-for example, closing the grips gives a ratcheting
sensation, this on a $2000 up bike(s) whereas my 20 year old $800
rebuild steel GT works smoothly all over with a little
wax?teflon/boatgrease/and FL-CC now Valvo.
BUT! the cables sometimes bind and shift the derays when the temp goes
down causing too much friction and suck where i lubed the cables.
there i went to cleanliness and no lube: at the bar leadoff cable
sections.
and quality housing.
no more self shifting.

oh yeah: when i clean and lube the minor points on a tri weakly basis,
turning the bike upside down and on end gravity being what it is
, I loosen the shifters and brake cables, and then drip a few drops
wax/teflon? onto the exposed cable(after brushing or wiping clean off
course) then work back und forth.
i assume this does not lube the entire cable(but who knows?) just the
scraping end segments at the frame stops. This is a positive step
forward from your problem which I experienced as expletive deleted
with florida's 8-14 summer fall winter cycles.
this maintenence is on a cable outside the frame antiquo.

Pat said:

I got a new chain put on my Bianchi Veloce 9 speed road bike (2001 model)
at the start of the summer. Several times, when going up a tough hill in
the second chain ring, the bike will shift itself onto the third chain ring.
Now, I could understand this (maybe) if the chain was on the big chain ring
in front and the big cog in back, but this shifting happens when on the
middle chain ring in front and the big one in back.

Depending on the chainline and der adjustment, that might be enough to
cause it to want to walk over. Chances are good that you've got some
chainring wear on the middle sprocket, though.

Quoted message said:

I am lucky that it hasn't happened while I was out of the saddle, but I
would like to know what causes it and what I should do to fix the problem.

Check the front der cable adjustment, and if it's on target, then look
really hard at the condition of the middle chainring. I suspect
that's the one you use most, and I have a funny feeling that it's
probably worn.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.