Jockey wheels - Page 4

carlfogel@comcast.net (Carl Fogel) wrote in message
news:<8bbde8fc.0309161442.6709ee6b@posting.google.com>...
> jobst.brandt@stanfordalumni.org wrote in message
> news:<fXv9b.21944$dk4.682918@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?
>
> > >> 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.brandt@stanfordalumni.org
>
> 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.

Thanks to Dan Daniel, Andrew Muzi, and GWhite for their explanations 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.

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 +-----------------------------------------------+
| Who has deceived thee as often as thyself? | -- Benjamin Franklin |
+-----------------------------------------------+ 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 <CaptBike@sheldonbrown.com> wrote in message
news:<3F6A3956.4090807@sheldonbrown.com>...
> 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 +-----------------------------------------------+
>

Alas, I not only missed or misunderstood some postings, but am 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?

Evan Kirshenbaum <kirshenbaum@hpl.hp.com> wrote:

> Ray Heindl <rheindl@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 (remove the X to reply)

"A Muzi" <am@yellowjersey.org> wrote:

> 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.

--
Ray Heindl (remove the X to reply)

On Thu, 18 Sep 2003 16:16:16 GMT, jobst.brandt@stanfordalumni.org 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.

Rick Onanian <spamsink@cox.net> wrote in message newsprvnsa7w2w8gzvw@news.east.cox.net...
> On 17 Sep 2003 09:59:16 -0700, Evan Kirshenbaum <kirshenbaum@hpl.hp.com> 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

In the Parliamentary system of government, they're introducing Private Member's Bills all the time.
(Not sure about that apostrophe, though.)

Cheers, Sage

On Thu, 18 Sep 2003 22:32:30 -0000, Ray Heindl <rheindl@nccwx.net> wrote:

>Evan Kirshenbaum <kirshenbaum@hpl.hp.com> wrote:
>
>> Ray Heindl <rheindl@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.

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

hayesstw@yahoo.com (Steve Hayes) wrote:

> 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.

--
Ray Heindl (remove the X to reply)

hayesstw@yahoo.com (Steve Hayes) wrote in message news:<3f6ab78e.18431379@news.saix.net>...
>
> 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.

The original thread on jockey wheels or idler pulleys drifted off 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.

On Fri, 19 Sep 2003 20:47:36 -0000, Ray Heindl <rheindl@nccwx.net> wrote:

>hayesstw@yahoo.com (Steve Hayes) wrote:
>
>> 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.

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.

--
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

On Thu, 18 Sep 2003 07:15:36 GMT, jobst.brandt@stanfordalumni.org wrote:

>Dan Daniel writes:
>
>>>>> 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.brandt@stanfordalumni.org

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.