Jockey wheels
Alan Walker
They are normally called "jockey wheels" in the bicycle world. In my
experience, wheels performing a similar function in other types of
machinery are usually called "idler wheels" or "tension wheels".
Am I correct about the usage in general engineering? If so, why a
different term for the bicycle industry? Is the term "jockey wheel"
used in other industries?
Perhaps I should consult "The Dancing Chain"!
AW
jobst....@stanfordalumni.org
Not to worry. In bicycling, many terms are odd and even mis-applied.
This is probably beyond repair because people love their jargon and
don't relinquish it freely. Take rims, for instance. There are rims
with eyelets, ones with sockets and eyelets and plain drilled rims.
Just the same, we hear of "double eyelets" a design hard to visualize.
Rear wheels don't have a left and right side, but rather "drive-side"
and "non-drive-side".
Jobst Brandt
jobst....@stanfordalumni.org
Dan Daniel
wrote:
I always thought that the upper wheel (nearest the cogs or whatever
the correct term may be) is the jockey or guide wheel/pulley, and the
lower wheel is the tension wheel/pulley. I assumed that this is some
play on 'jockeying for position' or steering/guiding the chain to the
correct position.
Paul Kopit
wrote:
>Bicycle derailleurs have two small wheels on the chain tension cage.
The top one is sometimes referred to as the derailleur pulley and I
think the bottom one is the jocky.
Sheldon Brown
>
>>Bicycle derailleurs have two small wheels on the chain tension cage.
>>They are normally called "jockey wheels" in the bicycle world. In my
>>experience, wheels performing a similar function in other types of
>>machinery are usually called "idler wheels" or "tension wheels".
>>
>>Am I correct about the usage in general engineering? If so, why a
>>different term for the bicycle industry? Is the term "jockey wheel"
>>used in other industries?
Paul Kopit wrote:
> The top one is sometimes referred to as the derailleur pulley and I
> think the bottom one is the jocky.
I've always understood the term "jockey pulley" to refer to the upper
pulley.
The lower is called the "tension pulley."
Sheldon "Cyclexicographer" Brown
+-----------------------------------------------------+
| Life is the art of drawing sufficient conclusions |
| from insufficient premises. --Samuel Butler |
+-----------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
Sheldon Brown
>
>>Bicycle derailleurs have two small wheels on the chain tension cage.
>>They are normally called "jockey wheels" in the bicycle world. In my
>>experience, wheels performing a similar function in other types of
>>machinery are usually called "idler wheels" or "tension wheels".
>>
>>Am I correct about the usage in general engineering? If so, why a
>>different term for the bicycle industry? Is the term "jockey wheel"
>>used in other industries?
Paul Kopit wrote:
> The top one is sometimes referred to as the derailleur pulley and I
> think the bottom one is the jocky.
I've always understood the term "jockey pulley" to refer to the upper
pulley. This is because it "jockeys" or guides the chain from sprocket
to sprocket. It isn't used in other industries because derailers are
not used in other industries.
jobst....@stanfordalumni.org
>>> Bicycle derailleurs have two small wheels on the chain tension
>>> cage. They are normally called "jockey wheels" in the bicycle
>>> world. In my experience, wheels performing a similar function in
>>> other types of machinery are usually called "idler wheels" or
>>> "tension wheels".
>>> Am I correct about the usage in general engineering? If so, why a
>>> different term for the bicycle industry? Is the term "jockey
>>> wheel" used in other industries?
>> The top one is sometimes referred to as the derailleur pulley and I
>> think the bottom one is the jockey.
> I've always understood the term "jockey pulley" to refer to the
> upper pulley.
> The lower is called the "tension pulley."
I don't use the term for either wheel because it is undefined. I find
it used to refer to either of the two idler wheels. Idler is in
contrast to drive sprockets, since some early derailleurs used
sprockets for these wheels. In many derailleurs they are identical
parts as they were in all the early ones by Campagnolo, Huret, Simplex
and others.
Avoid vague jargon (AVJ)!
Jobst Brandt
jobst....@stanfordalumni.org
Carl Fogel
Is there any mechanical difference between the two pulleys? That is,
might one be expected to handle a different load?
I'm curious because I recently replaced a badly worn pair on a Schwinn
LeTour by robbing parts from spare LeTours that I bought for that
purpose and for visiting friends to ride.
To my surprise, the upper and lower 10-tooth plastic pulleys are
different parts. One is stamped on both sides "SHIMANO NARROW" and
has a noticeably narrower profile. The other is stamped "SHIMANO
CENTERON G-PULLEY NARROW" and
has a thicker shoulder extending to the base of the worn plastic
teeth.
Below are crude illustrations of the upper halves of each pulley with
a tooth on top. Only the tooth is worn, not the other parts.
| _|_
/ \ | |
/ \ | |
/ \ / \
| | | |
------------ -----------
narrow g-pulley
Obviously, Shimano thought that there was some functional difference.
The only thing that I can think of is that the lower pulley where the
chain arrives from the front gears might be blockier and thicker
without causing any trouble, but the pulley where the chain exits to
the rear cogs might somehow profit from being narrower to allow the
chain to flex sideways without wearing the pulley?
Regrettably, I paid no attention when removing the pulleys on three
different LeTours, so I don't know which pulley was upper or lower.
Ray Heindl
> Bicycle derailleurs have two small wheels on the chain tension cage.
> They are normally called "jockey wheels" in the bicycle world. In my
> experience, wheels performing a similar function in other types of
> machinery are usually called "idler wheels" or "tension wheels".
>
> Am I correct about the usage in general engineering? If so, why a
> different term for the bicycle industry? Is the term "jockey wheel"
> used in other industries?
They're apparently also used on trailers -- the small wheel attached to
the front of a trailer to allow it to be moved around by hand. See
<http://www.winterhoff.de/html/wheels.html> for a picture.
Google hits for "jockey wheels" seem to be about evenly divided between
bicycles and trailers.
There's also a linear accelerator in the Netherlands that has them,
though it's not clear what their function is.
<http://www.radiotherapie.nl/linaceng/linacfaq/>
--
Ray Heindl
(remove the X to reply)
Rick Onanian
> There's also a linear accelerator in the Netherlands that has them,
> though it's not clear what their function is.
> <http://www.radiotherapie.nl/linaceng/linacfaq/>
I don't know what a linear accelerator is, but it sure
sounds cool. What is it?
Lots of things sound cool lately. Learning C++, teacher
introduced the "destructor", and I was rather impressed
with that term.
--
Rick Onanian
Chris Zacho The Wheelman
"jockeys" the chain from one cog to the next.
The lower is usually called the tension wheel (or some similar name).
May you have the wind at your back.
And a really low gear for the hills!
Chris
Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner
Skitt
> Ray Heindl wrote:
>> There's also a linear accelerator in the Netherlands that has them,
>> though it's not clear what their function is.
>> <http://www.radiotherapie.nl/linaceng/linacfaq/>
>
> I don't know what a linear accelerator is, but it sure
> sounds cool. What is it?
Type the phrase into the box provided by MWCD10 at
www.m-w.com and you'll find out.
--
Skitt (in Hayward, California)
www.geocities.com/opus731/
Rick Onanian
>> I don't know what a linear accelerator is, but it sure
>> sounds cool. What is it?
>
> Type the phrase into the box provided by MWCD10 at
> www.m-w.com and you'll find out.
So, it's a particle accelerator that doesn't go in
circles? How long does a linear accelerator have to
be in order to be useful?
--
Rick Onanian
Skitt
> Skitt wrote:
>>> I don't know what a linear accelerator is, but it sure
>>> sounds cool. What is it?
>>
>> Type the phrase into the box provided by MWCD10 at
>> www.m-w.com and you'll find out.
>
> So, it's a particle accelerator that doesn't go in
> circles? How long does a linear accelerator have to
> be in order to be useful?
Gosh, I wouldn't know. The one at Stanford is two miles long.
Peter Moylan
>Lots of things sound cool lately. Learning C++, teacher
>introduced the "destructor", and I was rather impressed
>with that term.
If you're learning C++, you'll be even more impressed once you
get to the definition of "friend".
--
Peter Moylan Peter....@newcastle.edu.au
http://eepjm.newcastle.edu.au (OS/2 and eCS information and software)
jobst....@stanfordalumni.org
>>> I've always understood the term "jockey pulley" to refer to the
>>> upper pulley.
>>> The lower is called the "tension pulley."
>> I don't use the term for either wheel because it is undefined. I
>> find it used to refer to either of the two idler wheels. Idler is
>> in contrast to drive sprockets, since some early derailleurs used
>> sprockets for these wheels. In many derailleurs they are identical
>> parts as they were in all the early ones by Campagnolo, Huret,
>> Simplex and others.
>> Avoid vague jargon (AVJ)!
> Is there any mechanical difference between the two pulleys? That is,
> might one be expected to handle a different load?
It depends on the included angle between entry and exit of the chain,
and its tension. Since tension is the same, only the angle between
the two chain lines has a differentiating effect. That would be
T * sin A = idler load.
> I'm curious because I recently replaced a badly worn pair on a Schwinn
> LeTour by robbing parts from spare LeTours that I bought for that
> purpose and for visiting friends to ride.
The wear has more to do with side loads and chain pitch. A worn chain
widens the round recesses in the idler.
> To my surprise, the upper and lower 10-tooth plastic pulleys are
> different parts. One is stamped on both sides "SHIMANO NARROW" and
> has a noticeably narrower profile. The other is stamped "SHIMANO
> CENTERON G-PULLEY NARROW" and has a thicker shoulder extending to
> the base of the worn plastic teeth.
I am not familiar with these parts. I can't say what that is about.
> Below are crude illustrations of the upper halves of each pulley
> with a tooth on top. Only the tooth is worn, not the other parts.
> | _|_
> / \ | |
> / \ | |
> / \ / \
> | | | |
> ------------ -----------
> narrow g-pulley
> Obviously, Shimano thought that there was some functional
> difference. The only thing that I can think of is that the lower
> pulley where the chain arrives from the front gears might be
> blockier and thicker without causing any trouble, but the pulley
> where the chain exits to the rear cogs might somehow profit from
> being narrower to allow the chain to flex sideways without wearing
> the pulley?
> Regrettably, I paid no attention when removing the pulleys on three
> different LeTours, so I don't know which pulley was upper or lower.
I don't think it makes any difference, knowing how fast these things
wear. The old wobbly pulley was designed to help people pre-shift
before starting to pedal, they bing unable to pedal and shift at the
same time. That was before brake/shift levers.
Jobst Brandt
jobst....@stanfordalumni.org
A Muzi
> >
> >>Bicycle derailleurs have two small wheels on the chain tension cage.
> >>They are normally called "jockey wheels" in the bicycle world. In my
> >>experience, wheels performing a similar function in other types of
> >>machinery are usually called "idler wheels" or "tension wheels".
> >>
> >>Am I correct about the usage in general engineering? If so, why a
> >>different term for the bicycle industry? Is the term "jockey wheel"
> >>used in other industries?
>
> Paul Kopit wrote:
>
> > The top one is sometimes referred to as the derailleur pulley and I
> > think the bottom one is the jocky.
"Sheldon Brown" <Capt...@sheldonbrown.com> wrote in message
news:3F668371...@sheldonbrown.com...
> I've always understood the term "jockey pulley" to refer to the upper
> pulley. This is because it "jockeys" or guides the chain from sprocket
> to sprocket. It isn't used in other industries because derailers are
> not used in other industries.
>
> The lower is called the "tension pulley."
>
> Sheldon "Cyclexicographer" Brown
Hmmm. I find "upper" and "lower" pulley sufficient.
Do you really say "jockey pulley" when writing service with a
non-afficionado?
--
Andrew Muzi, who also likes "crank bearing assembly" instead of "BB"
www.yellowjersey.org
Open every day since 1 April, 1971
Dan Daniel
wrote:
>
>Below are crude illustrations of the upper halves of each pulley with
>a tooth on top. Only the tooth is worn, not the other parts.
>
> | _|_
> / \ | |
> / \ | |
> / \ / \
> | | | |
>------------ -----------
>
> narrow g-pulley
>
>Obviously, Shimano thought that there was some functional difference.
>The only thing that I can think of is that the lower pulley where the
>chain arrives from the front gears might be blockier and thicker
>without causing any trouble, but the pulley where the chain exits to
>the rear cogs might somehow profit from being narrower to allow the
>chain to flex sideways without wearing the pulley?
>
>Regrettably, I paid no attention when removing the pulleys on three
>different LeTours, so I don't know which pulley was upper or lower.
The 'G-Pulley' is for the upper/jockey and the other is for the
lower/tension. That is Shimano's system and designation.
I haven't looked for a while, but the 'G-pulley' used to have a
certain amount of 'float,' lateral movement. This was either to help
with shifting, or to allow a small amount of slop in alignment of the
derailleur. Maybe someone else knows the technical reason.
I never swapped the two on older derailleurs to see if their position
made any difference in shifting or noise. And I do not know if newer
shifting/indexing makes this difference moot.
Rick Onanian
wrote:
> Rick Onanian <spam...@cox.net> wrote:
>> Lots of things sound cool lately. Learning C++, teacher
>> introduced the "destructor", and I was rather impressed
>> with that term.
>
> If you're learning C++, you'll be even more impressed once you
> get to the definition of "friend".
I got that the same day, but it wasn't nearly as exciting.
I'd have more fun as a Destructor than a Friend. ;)
--
Rick "The Friendly Destructor" Onanian
Evan Kirshenbaum
> On 17 Sep 2003 03:10:32 GMT, Peter Moylan
> <pe...@seagoon.newcastle.edu.au> wrote:
>
> > Rick Onanian <spam...@cox.net> wrote:
> >> Lots of things sound cool lately. Learning C++, teacher
> >> introduced the "destructor", and I was rather impressed with that
> >> term.
> >
> > If you're learning C++, you'll be even more impressed once you get
> > to the definition of "friend".
>
> I got that the same day, but it wasn't nearly as exciting.
Not even the fact that a friend has full access to your private
member?
--
Evan Kirshenbaum +------------------------------------
HP Laboratories |Ye knowe ek, that in forme of speche
1501 Page Mill Road, 1U, MS 1141 | is chaunge
Palo Alto, CA 94304 |Withinne a thousand yer, and wordes
| tho
kirsh...@hpl.hp.com |That hadden prys now wonder nyce and
(650)857-7572 | straunge
|Us thenketh hem, and yet they spake
http://www.kirshenbaum.net/ | hem so
| Chaucer
jobst....@stanfordalumni.org
>> Below are crude illustrations of the upper halves of each pulley
>> with a tooth on top. Only the tooth is worn, not the other parts.
>> | _|_
>> / \ | |
>> / \ | |
>> / \ / \
>> | | | |
>> ------------ -----------
>> narrow g-pulley
>> Obviously, Shimano thought that there was some functional
>> difference. The only thing that I can think of is that the lower
>> pulley where the chain arrives from the front gears might be
>> blockier and thicker without causing any trouble, but the pulley
>> where the chain exits to the rear cogs might somehow profit from
>> being narrower to allow the chain to flex sideways without wearing
>> the pulley?
>> Regrettably, I paid no attention when removing the pulleys on three
>> different LeTours, so I don't know which pulley was upper or lower.
> The 'G-Pulley' is for the upper/jockey and the other is for the
> lower/tension. That is Shimano's system and designation.
These designations don't come out of Shimano engineering but rather
from their USA contacts who are no more savant than the average
wreck.bike contributor, many of whom prefer bicycle jargon to plain
English. The more bicycle jargon the more exclusive the club.
> I haven't looked for a while, but the 'G-pulley' used to have a
> certain amount of 'float,' lateral movement. This was either to
> help with shifting, or to allow a small amount of slop in alignment
> of the derailleur. Maybe someone else knows the technical reason.
As I mentioned, this arose back in the days before integrated brake
and shift mechanisms. It allowed riders to pre-shift while not
pedaling. Many riders cannot pedal without both hands on the bars.
Jobst Brandt
jobst....@stanfordalumni.org
John Varela
> How long does a linear accelerator have to
> be in order to be useful?
Long enought that when they build it they have to worry about the curvature of
the Earth.
--
John Varela
Tom Nakashima
-tom
"John Varela" <jav...@earthlink.net> wrote in message
news:ZKRm3c4Ddl7U-p...@dialup-171.75.32.152.Dial1.Washington1.Level3.net...
Rick Onanian
wrote:
>> I got that the same day, but it wasn't nearly as exciting.
>
> Not even the fact that a friend has full access to your private
> member?
Okay, I'll concede that point, but I already have
someone who has full access to my private member; OTOH,
I have yet to build anything called a destructor.
So, let's destroy something already! It's inappropriate
to access private members here anyway.
--
Rick "Maybe We Should Destroy This Thread" Onanian
Ray Heindl
> Rick Onanian wrote:
>> Skitt wrote:
>
>>>> I don't know what a linear accelerator is, but it sure
>>>> sounds cool. What is it?
>>>
>>> Type the phrase into the box provided by MWCD10 at
>>> www.m-w.com and you'll find out.
>>
>> So, it's a particle accelerator that doesn't go in
>> circles? How long does a linear accelerator have to
>> be in order to be useful?
>
> Gosh, I wouldn't know. The one at Stanford is two miles long.
The one in the Netherlands is used for medical purposes, so they
probably don't need TeV energy levels -- they want to cure people, not
annihilate them. I suspect it's a bit less than 2 miles long.
Skitt
The MIT Bates linear accelerator is only 160 meters long.
Evan Kirshenbaum
> The one in the Netherlands
Which one is that? NIKHEF talks about running experiments at CERN,
SLAC, FermiLab, and CERN, but doesn't mention using one in their own
back yard.
> is used for medical purposes, so they probably don't need TeV energy
> levels -- they want to cure people, not annihilate them. I suspect
> it's a bit less than 2 miles long.
Well, sure. They'd do it in kilometers.
--
Evan Kirshenbaum +------------------------------------
HP Laboratories |It is a popular delusion that the
1501 Page Mill Road, 1U, MS 1141 |government wastes vast amounts of
Palo Alto, CA 94304 |money through inefficiency and sloth.
|Enormous effort and elaborate
kirsh...@hpl.hp.com |planning are required to waste this
(650)857-7572 |much money
| P.J. O'Rourke
http://www.kirshenbaum.net/
g.daniels
so sez the labeling.I took their word for it. like they spent the
dough on it right? i'm very pleaed with boat trailer bearing grease
applied frequently which is a sufficient conclusion based on
suffiecient experience that this lube is sufficiently necessary for
the reasonabley prudent rider who isn't droolingover a set of sealed
bearing aluminum wheels which are as Hegel once said empirically
unproven firsthand.
sage
Alan Walker <wal...@netcon.net.au> wrote in message
news:5cb9c6e4.03091...@posting.google.com...
> Bicycle derailleurs have two small wheels on the chain tension cage.
> They are normally called "jockey wheels" in the bicycle world. In my
> experience, wheels performing a similar function in other types of
> machinery are usually called "idler wheels" or "tension wheels".
>
> Am I correct about the usage in general engineering? If so, why a
> different term for the bicycle industry? Is the term "jockey wheel"
> used in other industries?
>
>
How about: They are called jockey wheels because that's what they do -- move
and jockey the chain over to the next gear wheel, up or down, when the lever
on the handlbars is moved?
As for other industries, I don't know.
Cheers, Sage
Dave Lehnen
> Carl Fogel writes:
<snip>
>>Is there any mechanical difference between the two pulleys? That is,
>>might one be expected to handle a different load?
>
>
> It depends on the included angle between entry and exit of the chain,
> and its tension. Since tension is the same, only the angle between
> the two chain lines has a differentiating effect. That would be
> T * sin A = idler load.
>
2T * cos (A/2) = idler load, if A is the included angle between
chains, and (180 deg. - A) is the chain wrap angle. Load is zero
for the case of 0 deg. chain wrap and 2T for 180 deg. of wrap.
Dave Lehnen
gwhite
Carl Fogel wrote:
>
> To my surprise, the upper and lower 10-tooth plastic pulleys are
> different parts. One is stamped on both sides "SHIMANO NARROW" and
> has a noticeably narrower profile. The other is stamped "SHIMANO
> CENTERON G-PULLEY NARROW" and
> has a thicker shoulder extending to the base of the worn plastic
> teeth.
The CENTERON is the slop pulley and is the upper one (the guide pulley).
It has slop so any inaccuracy of the indexing can be slopped out and the
chain won't make much noise against the cogs.
I'm really sorry about the sloppy vague jargon. Wait, no I'm not.
Dan Daniel
wrote:
>Dan Daniel writes:
>
>>> Below are crude illustrations of the upper halves of each pulley
>>> with a tooth on top. Only the tooth is worn, not the other parts.
>
>>> | _|_
>>> / \ | |
>>> / \ | |
>>> / \ / \
>>> | | | |
>>> ------------ -----------
>
>>> narrow g-pulley
>
>>> Obviously, Shimano thought that there was some functional
>>> difference. The only thing that I can think of is that the lower
>>> pulley where the chain arrives from the front gears might be
>>> blockier and thicker without causing any trouble, but the pulley
>>> where the chain exits to the rear cogs might somehow profit from
>>> being narrower to allow the chain to flex sideways without wearing
>>> the pulley?
>
>>> Regrettably, I paid no attention when removing the pulleys on three
>>> different LeTours, so I don't know which pulley was upper or lower.
>
>> The 'G-Pulley' is for the upper/jockey and the other is for the
>> lower/tension. That is Shimano's system and designation.
>
>These designations don't come out of Shimano engineering but rather
>from their USA contacts who are no more savant than the average
>wreck.bike contributor, many of whom prefer bicycle jargon to plain
>English. The more bicycle jargon the more exclusive the club.
>
So all the exploded views of derailleurs put out by Shimano that use
these terms are pure marketing and have no basis in any engineering?
That's a strange company, that goes to all the trouble to make such
diagrams, lets the US marketing people design and install two
different pulley designs, and lets the same people do all the labeling
in order to make themselves part of some exclusive jargon club.
So tell me, what *is* the source for the designations in the Shimano
diagrams, and on what do you base this assertion of yours?
Peter Moylan
Even though a friend is defined as someone who is allowed to see
your private parts?
With the help of a friend, you can be a constructor.
A Muzi
> >
> >>> Below are crude illustrations of the upper halves of each pulley
> >>> with a tooth on top. Only the tooth is worn, not the other parts.
> >
> >>> | _|_
> >>> / \ | |
> >>> / \ | |
> >>> / \ / \
> >>> | | | |
> >>> ------------ -----------
> >
> >>> narrow g-pulley
> >
> >>> Obviously, Shimano thought that there was some functional
> >>> difference. The only thing that I can think of is that the lower
> >>> pulley where the chain arrives from the front gears might be
> >>> blockier and thicker without causing any trouble, but the pulley
> >>> where the chain exits to the rear cogs might somehow profit from
> >>> being narrower to allow the chain to flex sideways without wearing
> >>> the pulley?
> >
> >>> Regrettably, I paid no attention when removing the pulleys on three
> >>> different LeTours, so I don't know which pulley was upper or lower.
> >
> >> The 'G-Pulley' is for the upper/jockey and the other is for the
> >> lower/tension. That is Shimano's system and designation.
> On Wed, 17 Sep 2003 17:18:09 GMT, jobst....@stanfordalumni.org
> >These designations don't come out of Shimano engineering but rather
> >from their USA contacts who are no more savant than the average
> >wreck.bike contributor, many of whom prefer bicycle jargon to plain
> >English. The more bicycle jargon the more exclusive the club.
"Dan Daniel" <dda...@pacbell.net> wrote in message
news:h29imvsi85ah3hrbm...@4ax.com...
> So all the exploded views of derailleurs put out by Shimano that use
> these terms are pure marketing and have no basis in any engineering?
> That's a strange company, that goes to all the trouble to make such
> diagrams, lets the US marketing people design and install two
> different pulley designs, and lets the same people do all the labeling
> in order to make themselves part of some exclusive jargon club.
>
> So tell me, what *is* the source for the designations in the Shimano
> diagrams, and on what do you base this assertion of yours?
I'm sorry to report that Jobst is mistaken. Those are two different
features, introduced at about the same time. He mixed them in his post.
Shimano at one time included a stiff spring in the anchor assembly of the
rear derailleur such that one might preselect a gear at the shifter. The
derailleur would complete that shift once the pedals moved again. That was
on the "L" series in the early eighties.
The "Centeron" idler and the similar design found on almost all modern
changers automatically centers the chain under a cog within a millimeter
or so and makes shifting smoother than it would otherwisw be. Helps
friction shifting too!
So, back to your question-- Put the one with sideplay in top. Campagnolo
handily labels theirs "upper" and "lower" in plain English.
--
Andrew Muzi
jobst....@stanfordalumni.org
>>>> Regrettably, I paid no attention when removing the pulleys on
>>>> three different LeTours, so I don't know which pulley was upper
>>>> or lower.
>>> The 'G-Pulley' is for the upper/jockey and the other is for the
>>> lower/tension. That is Shimano's system and designation.
>> These designations don't come out of Shimano engineering but rather
>> from their USA contacts who are no more savant than the average
>> wreck.bike contributor, many of whom prefer bicycle jargon to plain
>> English. The more bicycle jargon the more exclusive the club.
> So all the exploded views of derailleurs put out by Shimano that use
> these terms are pure marketing and have no basis in any engineering?
> That's a strange company, that goes to all the trouble to make such
> diagrams, lets the US marketing people design and install two
> different pulley designs, and lets the same people do all the
> labeling in order to make themselves part of some exclusive jargon
> club.
There is nothing strange about that. They have the option to do their
own translation that usually sounds like a foreign type of English or
they can rely on the bicycle "experts" in the USA, or worse, from the
land of bicycle jargon, England. As an example, my first job at
Porsche KG was to translate their 356 Shop manual into technically
correct English after it had previously been translated in Germany.
They were aware of the problem because they often got comments from
the US dealers.
I'm sure you have gotten instruction manuals for foreign made goods
that were difficult to decipher. The proper way to write them is to
get a well versed native to translate it. In that regard, finding
technically versed people in the bicycle business is difficult,
although many are willing to offer their services.
> So tell me, what *is* the source for the designations in the Shimano
> diagrams, and on what do you base this assertion of yours?
I base that on Campagnolo and Japanese camera manuals that I have
read. When I see Shimano literature with colloquialisms I detect an
American bicyclist's translations.
Jobst Brandt
jobst....@stanfordalumni.org
Paul Kopit
<dcle...@worldnet.att.net> wrote:
>> It depends on the included angle between entry and exit of the chain,
>> and its tension. Since tension is the same, only the angle between
>> the two chain lines has a differentiating effect. That would be
>> T * sin A = idler load.
>>
><snip>
>
>2T * cos (A/2) = idler load, if A is the included angle between
>chains, and (180 deg. - A) is the chain wrap angle. Load is zero
>for the case of 0 deg. chain wrap and 2T for 180 deg. of wrap.
>
>Dave Le
Pardon my inability to fully understand. I have a cassette with a 19t
cog. It is actually the 19,21 together on a Record Ti. cassette.
The 19t cog only skips on occasion with the 39t ring and never with
the 53. If the chainring were 42 or 34 might the cog not slip?
Sheldon Brown
> ...I have a cassette with a 19t
> cog. It is actually the 19,21 together on a Record Ti. cassette.
> The 19t cog only skips on occasion with the 39t ring and never with
> the 53. If the chainring were 42 or 34 might the cog not slip?
Your 19 sprocket is probably worn out. Worn-out sprockets tend to skip,
but only when the chain tension reaches a certain level. The more worn
out the sprocket, the lower the tension level required to cause skipping.
Chain tension is inversely proportional to the chainring size, so for
the same amount of foot force, the chain tension is 36% higher when
you're on your 39.
Given common realities of gear usage, you also probably pedal harder
when you're in the 39/19 than in the 53/19, so it's not surprising that
you only notice the skipping in the former combination. If you continue
riding without replacing the worn parts, the problem will gradually get
worse.
Sheldon "Time For A New Cassette And Chain" Brown
+---------------------------------------------------------+
| I don't like spinach, and I'm glad I don't, because |
| if I liked it I'd eat it, and I just hate it. |
| --Clarence Darrow |
+---------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
Donald Gillies
owned by some company (maybe shimano or suntour?) Or was it just a
design feature that was quickly copied once competitors figured out
its purpose ??
- Don
"A Muzi" <a...@yellowjersey.org> writes:
>> >Dan Daniel writes:
>> >>> Below are crude illustrations of the upper halves of each pulley
>> >>> with a tooth on top. Only the tooth is worn, not the other parts.
>> >
>> >>> | _|_
>> >>> / \ | |
>> >>> / \ | |
>> >>> / \ / \
>> >>> | | | |
>> >>> ------------ -----------
>> >
>> >>> narrow g-pulley
>I'm sorry to report that Jobst is mistaken. Those are two different
jobst....@stanfordalumni.org
>> It depends on the included angle between entry and exit of the
>> chain, and its tension. Since tension is the same, only the angle
>> between the two chain lines has a differentiating effect. That
>> would be: 2T * cos (A/2) = idler load, if A is the included angle
>> between chains, and (180 deg. - A) is the chain wrap angle. Load is
>> zero for the case of 0 deg. chain wrap and 2T for 180 deg. of wrap.
> Pardon my inability to fully understand. I have a cassette with a
> 19t cog. It is actually the 19,21 together on a Record
> Ti. cassette. The 19t cog only skips on occasion with the 39t ring
> and never with the 53. If the chainring were 42 or 34 might the cog
> not slip?
This has nothing to do with sprockets, only the with the load on the
idler wheels of a derailleur.
Chains do not "slip" they being digital devices, they skip a whole
tooth or more. Slip is a frictional analog process. Chain skip is
caused by sprocket wear from an elongated (worn) chain that rides
higher on the tooth than a chain in correct pitch will. When a new
chain is subsequently used, it rides in the wear marks made by the
longer pitch chain making the sprocket, in effect, have too large a
pitch, one that the new chain will not engage under load. It is on
the engagement (incoming) end that the chain fails to engage the
sprocket and subsequently skips over to drop into the next engagement.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> ...I have a cassette with a 19t cog. It is actually the 19,21
>> together on a Record Ti. cassette. The 19t cog only skips on
>> occasion with the 39t ring and never with the 53. If the chainring
>> were 42 or 34 might the cog not slip?
Don't use Titanium sprockets.
> Your 19 sprocket is probably worn out. Worn-out sprockets tend to
> skip, but only when the chain tension reaches a certain level. The
> more worn out the sprocket, the lower the tension level required to
> cause skipping.
> Chain tension is inversely proportional to the chainring size, so
> for the same amount of foot force, the chain tension is 36% higher
> when you're on your 39.
> Given common realities of gear usage, you also probably pedal harder
> when you're in the 39/19 than in the 53/19, so it's not surprising
> that you only notice the skipping in the former combination. If you
> continue riding without replacing the worn parts, the problem will
> gradually get worse.
But no. The chain will wear, it's pitch getting longer, and it will
begin to fit the larger pitch diameter of the worn sprocket. However,
I wouldn't put up with the skipping in the meanwhile.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> I'm sorry to report that Jobst is mistaken. Those are two different
> features, introduced at about the same time. He mixed them in his
> post.
> Shimano at one time included a stiff spring in the anchor assembly
> of the rear derailleur such that one might preselect a gear at the
> shifter. The derailleur would complete that shift once the pedals
> moved again. That was on the "L" series in the early eighties.
I disagree. The wobbly wheel allows the derailleur to move to the
next gear position before the chain makes the move. This allows not
only the original concept of pre-shifting for non pedalers, but it
allows quicker shifts in which the indexed lever is moved quickly to
the desired gear position, regardless of chain speed. It's origins
came from the desire to shift while not pedaling but benefits remain
for shifting in general.
> The "Centeron" idler and the similar design found on almost all
> modern changers automatically centers the chain under a cog within a
> millimeter or so and makes shifting smoother than it would otherwise
> be. Helps friction shifting too!
Wait a minute. Does it benefit shifting or silent running once in
gear? These refinements miss my enthusiasm. Unless stalled on a
steep bump, my chain speed is enough to make shifting go as fast as I
can move the lever. The wobbly wheel cannot make up for derailleur
misalignment because if it were out of correct position, shifting
in one or the other direction would be unreliable... for all gears.
> So, back to your question-- Put the one with side play in top.
> Campagnolo handily labels theirs "upper" and "lower" in plain
> English.
Yes, just like 'left' and 'right' sides of the wheel or bicycle rather
than 'drive-side' and 'non-drive-side'.
Jobst Brandt
jobst....@stanfordalumni.org
Sheldon Brown
> Shimano at one time included a stiff spring in the anchor assembly of the
> rear derailleur such that one might preselect a gear at the shifter. The
> derailleur would complete that shift once the pedals moved again. That was
> on the "L" series in the early eighties.
This was a great feature, which Shimano has unfortunately abandoned, but
it considerably predates the "L" series.
The overload spring was featured on the Lark and Eagle derailers of the
1970s (These inexpensive units were heavy, but nearly indestructible,
and shifted notably better than anything else available in the '70s.)
This feature was actually introduced, I believe, for the benefit of
children's wheelie bikes with "stick shift" shifters. The main purpose
was to prevent cable breakage when a clueless adolescent yanked on the
shift lever while stopped.
The really clever thing about this was how Shimano was able to implement
it without actually adding an additional spring...it used the "dead" end
of the spring that moved the derailer parallelogram.
Sheldon "Can't Figure Why They Discontinued This Feature" Brown
+---------------------------------------------------------------------+
| A man of character finds a special attractiveness in difficulty, |
| since it is only by coming to grips with difficulty |
| that he can realize his potentialities. -- Charles DeGaulle |
+---------------------------------------------------------------------+
Sheldon Brown
Carl Fogel wrote:
I wrote:
>>>I've always understood the term "jockey pulley" to refer to the
>>>upper pulley.
>>
>>>The lower is called the "tension pulley."
Andy Muzi wrote:
>
> Hmmm. I find "upper" and "lower" pulley sufficient.
>
> Do you really say "jockey pulley" when writing service with a
> non-afficionado?
Certainly not, but the O.P. asked what the term meant.
Jobst Brandt wrote:
>>I don't use the term for either wheel because it is undefined. I find
>>it used to refer to either of the two idler wheels. Idler is in
>>contrast to drive sprockets, since some early derailleurs used
>>sprockets for these wheels. In many derailleurs they are identical
>>parts as they were in all the early ones by Campagnolo, Huret, Simplex
>>and others.
Carl Fogel wrote:
> Is there any mechanical difference between the two pulleys? That is,
> might one be expected to handle a different load?
>
> I'm curious because I recently replaced a badly worn pair on a Schwinn
> LeTour by robbing parts from spare LeTours that I bought for that
> purpose and for visiting friends to ride.
>
> To my surprise, the upper and lower 10-tooth plastic pulleys are
> different parts. One is stamped on both sides "SHIMANO NARROW" and
> has a noticeably narrower profile. The other is stamped "SHIMANO
> CENTERON G-PULLEY NARROW" and
> has a thicker shoulder extending to the base of the worn plastic
> teeth.
>
> Below are crude illustrations of the upper halves of each pulley with
> a tooth on top. Only the tooth is worn, not the other parts.
>
> | _|_
> / \ | |
> / \ | |
> / \ / \
> | | | |
> ------------ -----------
>
> narrow g-pulley
>
> Obviously, Shimano thought that there was some functional difference.
> The only thing that I can think of is that the lower pulley where the
> chain arrives from the front gears might be blockier and thicker
> without causing any trouble, but the pulley where the chain exits to
> the rear cogs might somehow profit from being narrower to allow the
> chain to flex sideways without wearing the pulley?
>
> Regrettably, I paid no attention when removing the pulleys on three
> different LeTours, so I don't know which pulley was upper or lower.
Nice ASCII art! The blockier pulley is the upper (jockey) pulley. The
fatter "teeth" control the chain better because they're a snugger fit
into the chain, so the chain doesn't slop back and forth on them.
The pointy pulley is the lower (tension) pulley. The teeth are narrow
and pointed so that they'll engage the chain smoothly even when the
chain is approaching the derailer at an angle due to different gear
positions.
I believe SunTour was the first to use this profile difference.
The old Benelux derailers used a more sprocket-like upper pulley, and a
round, toothless bottom pulley, presumably for the same reason. I've
actually used old Benelux pulleys on modern Shimano derailers with good
results...they have adjustable ball bearings, and I've never found
Shimano's "Centeron" slop in the upper pulley to be of any great utility
in a properly adjusted system.
Jobst:
> I'm sure you have gotten instruction manuals for foreign made goods
> that were difficult to decipher. The proper way to write them is to
> get a well versed native to translate it. In that regard, finding
> technically versed people in the bicycle business is difficult,
> although many are willing to offer their services.
As to the origin of the usage "jockey" and "tension" pulleys, you can't
hang that on Shimano. I don't recall exactly where I first encountered
these terms, but I belive it would have been with the instructions for
the first derailer I ever bought, a British Benelux Mark VIII, circa 1959.
I've heard that the translation problem with Japanese companies is
complicated by a concern lest their in-house translators lose "face".
This results in such solecisms as calling brake calipers "arches" as
well as clumsy locutions like "crank arm."
Sheldon "Pulleys" Brown
+---------------------------------------------------+
| Even if you do learn to speak correct English, |
| whom are you going to speak it to? |
| --Clarence Darrow |
+---------------------------------------------------+
Carl Fogel
> jobst....@stanfordalumni.org wrote in message news:<fXv9b.21944$dk4.6...@typhoon.sonic.net>...
> > Sheldon Brown writes:
> >
> > >>> Bicycle derailleurs have two small wheels on the chain tension
> > >>> cage. They are normally called "jockey wheels" in the bicycle
> > >>> world. In my experience, wheels performing a similar function in
> > >>> other types of machinery are usually called "idler wheels" or
> > >>> "tension wheels".
>
> > >>> Am I correct about the usage in general engineering? If so, why a
> > >>> different term for the bicycle industry? Is the term "jockey
> > >>> wheel" used in other industries?
>
> > >> think the bottom one is the jockey.
>
> > > I've always understood the term "jockey pulley" to refer to the
> > > upper pulley.
> >
>
> > > The lower is called the "tension pulley."
> >
> > it used to refer to either of the two idler wheels. Idler is in
> > contrast to drive sprockets, since some early derailleurs used
> > sprockets for these wheels. In many derailleurs they are identical
> > parts as they were in all the early ones by Campagnolo, Huret, Simplex
> > and others.
> >
> >
> > Jobst Brandt
> > jobst....@stanfordalumni.org
about my differently shaped Shimano idler pulleys.
It sounds as if the thick-shouldered "Centeron" pulley is meant to be
the lower idler pulley and is designed to accept the chain returning
from the front chain-ring and keep the lower run of chain taut, hence
the term tension pulley. Side-play is not important between this
pulley
and the front chain-ring, which I belatedly noticed has the same
square-shouldered shape.
The narrow sloping-shoulder plastic pulley is designed to be the upper
idler pulley and serves a different function, namely guiding or
jockeying
the chain from side to side over the rear gear cluster. Its thinner
shoulder allows more slop or side-play as it drags the chain back and
forth, reducing
the need for perfect alignment between the rear derailleur and each
cog.
How well this design works is another matter, but Andrew Muzi points
out
that Campagnolo also uses differently shaped idler gears and marks
them
upper and lower.
When I looked at my bike, I found that the toast has once again landed
butter-side down--my idler gears need to be swapped. When I put the
narrow-sloping-shoulder-jockey pulley in the upper position, next to
the
rear cogs, and the thick-shoulder-tension pulley in the lower
position,
closest to the front chain-ring, I may find that my shifting improves.
Paul Kopit
wrote:
>
>> Given common realities of gear usage, you also probably pedal harder
>> when you're in the 39/19 than in the 53/19, so it's not surprising
>> that you only notice the skipping in the former combination. If you
>> continue riding without replacing the worn parts, the problem will
>> gradually get worse.
>
>But no. The chain will wear, it's pitch getting longer, and it will
>begin to fit the larger pitch diameter of the worn sprocket. However,
>I wouldn't put up with the skipping in the meanwhile.
I must confess, the Record 10sp cassette was a gift from someone that
knows I collect cogs. Only the 19 is bad enough to skip. I'm not a
weight weenie and the titanium doesn't make a difference to me. But,
I have yet to wear out a Ti cog on either a DA or 9sp Record cassette.
I usually kill a 17 first. My cassettes don't get to skipping. They
just begin to get sluggish shifts.
Ray Heindl
> Ray Heindl <rhe...@nccwx.net> writes:
>
>> The one in the Netherlands
>
> Which one is that? NIKHEF talks about running experiments at CERN,
> SLAC, FermiLab, and CERN, but doesn't mention using one in their own
> back yard.
It's a commercial product put out by a company called Elekta, formerly
made by Philips, I think. It's strictly a medical product, used for
radiotherapy (which doesn't mean listening to Joyce Brothers on NPR).
It makes X-rays at 6 and 25 MeV, and electron beams at 4 to 22 MeV.
>> is used for medical purposes, so they probably don't need TeV energy
>> levels -- they want to cure people, not annihilate them. I suspect
>> it's a bit less than 2 miles long.
>
> Well, sure. They'd do it in kilometers.
I checked their web site but couldn't find any dimensions or pictures.
Ray Heindl
> The "Centeron" idler and the similar design found on almost all
> modern changers automatically centers the chain under a cog
> within a millimeter or so and makes shifting smoother than it
> would otherwisw be. Helps friction shifting too!
Did the Centeron come out with the first indexing systems? The first
time I saw one I asked the LBS owner about it, and he said they were
necessary with indexed shifting because you couldn't guarantee that the
derailleur would line up with the cog exactly.
Sheldon Brown
>>Below are crude illustrations of the upper halves of each pulley with
>>a tooth on top. Only the tooth is worn, not the other parts.
>>
>> | _|_
>> / \ | |
>> / \ | |
>> / \ / \
>> | | | |
>>------------ -----------
>>
>> narrow g-pulley
>>
>>Obviously, Shimano thought that there was some functional difference.
>>The only thing that I can think of is that the lower pulley where the
>>chain arrives from the front gears might be blockier and thicker
>>without causing any trouble, but the pulley where the chain exits to
>>the rear cogs might somehow profit from being narrower to allow the
>>chain to flex sideways without wearing the pulley?
On the contrary, the "g-pulley" is the upper, the pointy one is the
lower. This is explained in a separate posting of mine from earlier
today, so I won't belabor the point.
Sheldon "Upside Down" Brown
+-----------------------------------------------+
| Who has deceived thee as often as thyself? |
| -- Benjamin Franklin |
+-----------------------------------------------+
Chalo
> Rear wheels don't have a left and right side, but rather "drive-side"
> and "non-drive-side".
That usage is hard to fault, since whether the drive is on the right
or on the left depends on the viewer's vantage point. You can
arbitrarily designate one "correct" frame of reference, but others may
not, and that can lead to confusion.
Consider that these so-called "jargon" terms arise for a reason, to
dispel misunderstanding. I have a left arm and my bike has a crank,
but when I say "left crank arm" I am understood, object though you
may.
Chalo Colina
Carl Fogel
> Quoth Carl Fogel:
>
> >>Below are crude illustrations of the upper halves of each pulley with
> >>a tooth on top. Only the tooth is worn, not the other parts.
> >>
> >> | _|_
> >> / \ | |
> >> / \ | |
> >> / \ / \
> >> | | | |
> >>------------ -----------
> >>
> >> narrow g-pulley
> >>
> >>Obviously, Shimano thought that there was some functional difference.
> >>The only thing that I can think of is that the lower pulley where the
> >>chain arrives from the front gears might be blockier and thicker
> >>without causing any trouble, but the pulley where the chain exits to
> >>the rear cogs might somehow profit from being narrower to allow the
> >>chain to flex sideways without wearing the pulley?
>
> On the contrary, the "g-pulley" is the upper, the pointy one is the
> lower. This is explained in a separate posting of mine from earlier
> today, so I won't belabor the point.
>
> Sheldon "Upside Down" Brown
> +-----------------------------------------------+
>
still puzzled. I'm not arguing, just baffled.
Why is the wide pulley meant to be used as the upper pulley?
Doesn't a narrow pulley allow more chain side-play and slop?
If so, shouldn't it be used as the upper pulley?
That is, doesn't the chain angle bend sideways far more as it
is dragged sideways across the rear gears at close quarters by
the upper jockey-pulley than it bends when it arrives at the
lower tension-pulley after the long lower run from the front
chain-ring?
Perhaps I'm mistaken about the narrow pulley being the sloppy one?
Or perhaps I'm wrong about the upper pulley needing more slop? That
is, perhaps what matters is the angle at which the chain engages
the pulley, not the angle at which it exits?
If the entry angle of the chain is what matters, then using the
sloppy narrow pulley as the lower pulley would make sense. The
bouncing lower chain run would enter at a slight angle from at
least one of the front chain-rings, while its entry angle onto
the upper pulley would never vary.
Am I coming close to your understanding of the matter, or just
missing your point again?
jobst....@stanfordalumni.org
>> Rear wheels don't have a left and right side, but rather
>> "drive-side" and "non-drive-side".
> That usage is hard to fault, since whether the drive is on the right
> or on the left depends on the viewer's vantage point. You can
> arbitrarily designate one "correct" frame of reference, but others
> may not, and that can lead to confusion.
I had no idea you could not tell left from right depending on which
way you face. That's extraordinary. I suppose when you face someone
his left and right change to right and left in contrast to when
standing behind him.
> Consider that these so-called "jargon" terms arise for a reason, to
> dispel misunderstanding. I have a left arm and my bike has a crank,
> but when I say "left crank arm" I am understood, object though you
> may.
Not at all. Jargon is like the secret handshake of the initiated.
The less others understand the more important the discourse. What
ever you do, don't ask what is meant by such talk or you'll fall into
the trap of ridicule. How could you!
Jobst Brandt
jobst....@stanfordalumni.org
sage
Rick Onanian <spam...@cox.net> wrote in message
news:oprvnsa7...@news.east.cox.net...
> On 17 Sep 2003 09:59:16 -0700, Evan Kirshenbaum <kirsh...@hpl.hp.com>
> wrote:
> >> I got that the same day, but it wasn't nearly as exciting.
> >
> > member?
>
> Okay, I'll concede that point, but I already have
> someone who has full access to my private member; OTOH,
> I have yet to build anything called a destructor.
>
> So, let's destroy something already! It's inappropriate
> to access private members here anyway.
>
> --
> Rick "Maybe We Should Destroy This Thread" Onanian
In the Parliamentary system of government, they're introducing Private
Member's Bills all the time. (Not sure about that apostrophe, though.)
Cheers, Sage
Steve Hayes
I'm lost...
What does this have to do with the jockey wheels?
This is the first post I have seen on jockey wheels, or rather alleged to be
about jockey wheels, but really about something quite incomprehensible.
--
Steve Hayes from Tshwane, South Africa
http://www.geocities.com/Athens/7734/stevesig.htm
E-mail - see web page, or parse: shayes at dunelm full stop org full stop uk
Ray Heindl
> I'm lost...
>
>
> What does this have to do with the jockey wheels?
>
> This is the first post I have seen on jockey wheels, or rather
> alleged to be about jockey wheels, but really about something
> quite incomprehensible.
Several exchanges back I pointed out that the linear accelerator in
question uses jockey wheels, though I don't know what for. It pretty
much went downhill from there, as usual.
Carl Fogel
>
> What does this have to do with the jockey wheels?
>
> This is the first post I have seen on jockey wheels, or rather alleged to be
> about jockey wheels, but really about something quite incomprehensible.
into an unrelated discussion about linear accelerators.
If you search for "jockey" and "fogel" you should find the original
thread, which began with a question about what to call the two idler
pulleys on the derailleur.
Most posters suggest the upper pulley is the jockey pulley drags or
jockeys the chain across the rear gear cluster, while the lower pulley
is the tension pulley that keeps the lower chain run taut.
I asked why my two idler pulleys were obviously different and that led
to posts that are continuing. Sheldon Brown has explained which pulley
is meant to go where, but I'm still puzzled.
Steve Hayes
For some reason I never saw the original exchanges, and the first posting I
saw with the subject line "jockey wheels" didn't mention them at all.
Dan Daniel
wrote:
Yes, translations can be hard and lead to jargon, but I am not
convinced that Porsche manuals and camera manuals provides any 'proof'
that Shimano's use of 'guide pulley' and mine and other people's use
of 'jockey pulley' is an example of insider jargon. I've encountered
both of those terms for thirty years, in books, manuals, discussions,
etc. If Shimano had used a term like 'system integrated positional
transfer roller' then I would agree, but using terms that have existed
in the bicycle world for decades makes sense.
So I am still confused as to why having two different names for the
two different pulleys seems to bother you. Do they perform different
functions? I'd say yes. So distinguishing one from the other is good
engineering, I think, not bad translation or marketing/insider jargon.
Does the second/upper/whatever you'd like to call it pulley exist in
other mechanisms? If so, is it called a tension pulley? Upper pulley?
'That other thingy'? Pulley number 2?
Until I encountered the Shimano 'guide pulley' and 'tension pulley' as
two different designs, the distinction was purely functional and made
no difference when I rebuilt other derailleurs. Maybe the engineering
is bad or flawed, but the distinction is real. And having different
names for parts that are not the same is a good thing in my
experience.