Drag of a sealed ceramic jockey wheel

[Zog The Undeniable]

The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
bushings and tight-fitting rubber seals. Even after cleaning and
lubrication, there is quite a substantial drag from the seals. Is this
likely to be significant in use, e.g. comparable to the 5W drag of a
good hub generator? I assume the drag increases linearly with chain
speed.

Maybe it's a trade off between efficiency and longevity, given that XT
stuff is expected to spend much of its life caked in mud?

 

[Jim]

On Tue, 14 Mar 2006 19:26:33 +0000, Zog The Undeniable
<[email protected]> wrote:

>The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
>bushings and tight-fitting rubber seals. Even after cleaning and
>lubrication, there is quite a substantial drag from the seals. Is this
>likely to be significant in use, e.g. comparable to the 5W drag of a
>good hub generator? I assume the drag increases linearly with chain
>speed.

Spin it and see if it heats up. Not precise, but it gives you an
idea.

>Maybe it's a trade off between efficiency and longevity, given that XT
>stuff is expected to spend much of its life caked in mud?

 

[john]

Jim wrote:
> On Tue, 14 Mar 2006 19:26:33 +0000, Zog The Undeniable
> <[email protected]> wrote:
>
> >The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
> >bushings and tight-fitting rubber seals. Even after cleaning and
> >lubrication, there is quite a substantial drag from the seals. Is this
> >likely to be significant in use, e.g. comparable to the 5W drag of a
> >good hub generator? I assume the drag increases linearly with chain
> >speed.
>
> Spin it and see if it heats up. Not precise, but it gives you an
> idea.
>
> >Maybe it's a trade off between efficiency and longevity, given that XT
> >stuff is expected to spend much of its life caked in mud?

I've usually been amazed how little friction a clean & greased one has,
for such a simple design. I remember reading back in the 80's in "Bike
Tech" (or some such title, IIRC it was published once a quarter) where
the friction of a sealed bearing jockey wheel was measured to be
greater than the cheap big S unit. I'm absolutely certain that I read
it some where back then because it ran so contrary to what I believed,
that it stuck w/ me. To this day I have no idea, which creates less
drag

John

 

[john]

Jim wrote:
> On Tue, 14 Mar 2006 19:26:33 +0000, Zog The Undeniable
> <[email protected]> wrote:
>
> >The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
> >bushings and tight-fitting rubber seals. Even after cleaning and
> >lubrication, there is quite a substantial drag from the seals. Is this
> >likely to be significant in use, e.g. comparable to the 5W drag of a
> >good hub generator? I assume the drag increases linearly with chain
> >speed.
>
> Spin it and see if it heats up. Not precise, but it gives you an
> idea.
>
> >Maybe it's a trade off between efficiency and longevity, given that XT
> >stuff is expected to spend much of its life caked in mud?

I've usually been amazed how little friction a clean & greased one has,
for such a simple design. I remember reading back in the 80's in "Bike
Tech" (or some such title, IIRC it was published once a quarter) where
the friction of a sealed bearing jockey wheel was measured to be
greater than the cheap big S unit. I'm absolutely certain that I read
it some where back then because it ran so contrary to what I believed,
that it stuck w/ me. To this day I have no idea, which creates less
drag

John

 

[Phil, Squid-in-Training]

Zog The Undeniable wrote:
> The top pulley aka "jockey wheel" of my Shimano XT rear mech has
> ceramic bushings and tight-fitting rubber seals. Even after cleaning
> and lubrication, there is quite a substantial drag from the seals.

Maybe the polar bears are out hunting and the seals are scared to go on
land...

--
Phil, Squid-in-Training

 

[Qui si parla Campagnolo]

Zog The Undeniable wrote:
> The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
> bushings and tight-fitting rubber seals. Even after cleaning and
> lubrication, there is quite a substantial drag from the seals. Is this
> likely to be significant in use, e.g. comparable to the 5W drag of a
> good hub generator? I assume the drag increases linearly with chain
> speed.
>
> Maybe it's a trade off between efficiency and longevity, given that XT
> stuff is expected to spend much of its life caked in mud?

Take the seals and toss them and grease into the ceramic parts. The
seals make for a lot of drag, some times it will even unscrew the top
pulley bolt.

 

[Qui si parla Campagnolo]

Qui si parla Campagnolo wrote:
> Zog The Undeniable wrote:
> > The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
> > bushings and tight-fitting rubber seals. Even after cleaning and
> > lubrication, there is quite a substantial drag from the seals. Is this
> > likely to be significant in use, e.g. comparable to the 5W drag of a
> > good hub generator? I assume the drag increases linearly with chain
> > speed.
> >
> > Maybe it's a trade off between efficiency and longevity, given that XT
> > stuff is expected to spend much of its life caked in mud?
>
> Take the seals and toss them and grease into the ceramic parts. The
> seals make for a lot of drag, some times it will even unscrew the top
> pulley bolt.

I should mention that tech tip came from Wayne Stetina, in about 1994,
when he visited Morgul Bismark and I asked about another 7410 top
pulley that fell off when riding.

 

[Helmut Springer]

Qui si parla Campagnolo <[email protected]> wrote:
> The seals make for a lot of drag, some times it will even unscrew
> the top pulley bolt.

How poorly does one have to fasten the bolt to have unscrewed like
that? Rhetorical question, the drag is negligible, even after
riding a winter through salt and ice...

--
MfG/Best regards
helmut springer

 

[Qui si parla Campagnolo]

Helmut Springer wrote:
> Qui si parla Campagnolo <[email protected]> wrote:
> > The seals make for a lot of drag, some times it will even unscrew
> > the top pulley bolt.
>
> How poorly does one have to fasten the bolt to have unscrewed like
> that? Rhetorical question, the drag is negligible, even after
> riding a winter through salt and ice...
>
> --
> MfG/Best regards
> helmut springer

Anecdotal experience only. In the early 90s, saw about 4 DA 7410 top
pulleys come unscrewed, talked to Wayne, removed the rubber seals, saw
no more on the ones we worked on....The ones that fell off were on new,
never taken apart rear derailleurs.

 

[Werehatrack]

On Tue, 14 Mar 2006 19:26:33 +0000, Zog The Undeniable
<[email protected]> wrote:

>The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
>bushings and tight-fitting rubber seals. Even after cleaning and
>lubrication, there is quite a substantial drag from the seals. Is this
>likely to be significant in use, e.g. comparable to the 5W drag of a
>good hub generator? I assume the drag increases linearly with chain
>speed.

Have you been noticing any drag when you've ridden it? What seems
like a lot of drag as you're sitting there fiddling with it may not be
significant in actual use. I'd ride it a few miles and see if it gets
warm; no heat means no significant amount of energy lost to friction
at that spot. If it was eating one watt, you'd feel the temp
difference.

>Maybe it's a trade off between efficiency and longevity, given that XT
>stuff is expected to spend much of its life caked in mud?

Could be. Another poster noted that the drag can be eliminated by
ditching the seals. If you're using this for what amounts to street
riding, I don't see a problem with that tactic.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Jay Beattie]

Qui si parla Campagnolo wrote:
> Helmut Springer wrote:
> > Qui si parla Campagnolo <[email protected]> wrote:
> > > The seals make for a lot of drag, some times it will even unscrew
> > > the top pulley bolt.
> >
> > How poorly does one have to fasten the bolt to have unscrewed like
> > that? Rhetorical question, the drag is negligible, even after
> > riding a winter through salt and ice...
> >
> > --
> > MfG/Best regards
> > helmut springer
>
> Anecdotal experience only. In the early 90s, saw about 4 DA 7410 top
> pulleys come unscrewed, talked to Wayne, removed the rubber seals, saw
> no more on the ones we worked on....The ones that fell off were on new,
> never taken apart rear derailleurs.

This may only indicate that the installation torque was low. Never
know. Did the problem reoccur in any derailleur where you just
tightened the top pulley? -- Jay Beattie.

 

[john]

Peter wrote

>Anecdotal experience only. In the early 90s, saw about 4 DA 7410 top
>pulleys come unscrewed, talked to Wayne, removed the rubber seals, saw
>no more on the ones we worked on....The ones that fell off were on new,
>never taken apart rear derailleurs.

Am I the only one who uses Loctite in situations like this, where for
one reason or another it is impossible to apply enough torque to keep
the connection tight? In this case, lack of thread depth. This is just
the sort of situation that it's made for.

John

 

[Lou Holtman]

"john" <[email protected]> wrote in message
news:[email protected]...
> Peter wrote
>
> >Anecdotal experience only. In the early 90s, saw about 4 DA 7410 top
> >pulleys come unscrewed, talked to Wayne, removed the rubber seals, saw
> >no more on the ones we worked on....The ones that fell off were on new,
> >never taken apart rear derailleurs.
>
> Am I the only one who uses Loctite in situations like this, where for
> one reason or another it is impossible to apply enough torque to keep
> the connection tight? In this case, lack of thread depth. This is just
> the sort of situation that it's made for.


No you are not the only one. I use loctite 243. When you disassemble a new
one you see that they use loctite in the factory. I still throw away the
rubber seals though.

Lou

 

[Zog The Undeniable]

Werehatrack wrote:

> On Tue, 14 Mar 2006 19:26:33 +0000, Zog The Undeniable
> <[email protected]> wrote:
>
>
>>The top pulley aka "jockey wheel" of my Shimano XT rear mech has ceramic
>>bushings and tight-fitting rubber seals. Even after cleaning and
>>lubrication, there is quite a substantial drag from the seals. Is this
>>likely to be significant in use, e.g. comparable to the 5W drag of a
>>good hub generator? I assume the drag increases linearly with chain
>>speed.
>
>
> Have you been noticing any drag when you've ridden it? What seems
> like a lot of drag as you're sitting there fiddling with it may not be
> significant in actual use. I'd ride it a few miles and see if it gets
> warm; no heat means no significant amount of energy lost to friction
> at that spot. If it was eating one watt, you'd feel the temp
> difference.

Possible, but in the airflow a few watts of heat is likely to be
dissipated quite quickly.
>
>>Maybe it's a trade off between efficiency and longevity, given that XT
>>stuff is expected to spend much of its life caked in mud?
>
>
> Could be. Another poster noted that the drag can be eliminated by
> ditching the seals. If you're using this for what amounts to street
> riding, I don't see a problem with that tactic.

I may well do that. The ceramic bushes are supposed to be harder than
most grit that's likely to get in there, and they are grooved to trap it
anyway.

 

[john]

>Maybe the polar bears are out hunting and the seals are scared to go on
>land...

What with global warming an all, the polar are so dang hungry that
they'll eat rubber seals.

John