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?

Perhaps I should consult "The Dancing Chain"!

AW

Alan Walker 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?

> Perhaps I should consult "The Dancing Chain"!

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.brandt@stanfordalumni.org

On 15 Sep 2003 17:07:00 -0700, walker@netcon.net.au (Alan Walker) wrote:

>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?
>
>Perhaps I should consult "The Dancing Chain"!
>
>AW

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.

On 15 Sep 2003 17:07:00 -0700, walker@netcon.net.au (Alan Walker) wrote:

>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?
>
>Perhaps I should consult "The Dancing Chain"!

The top one is sometimes referred to as the derailleur pulley and I think the bottom one is
the jocky.

Alan Walker wrote:
>
>>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

Alan Walker wrote:
>
>>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.

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 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

walker@netcon.net.au (Alan Walker) wrote:

> 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)

On Tue, 16 Sep 2003 23:16:44 -0000, Ray Heindl <rheindl@nccwx.net> 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?

Lots of things sound cool lately. Learning C++, teacher introduced the "destructor", and I was
rather impressed with that term.

--
Rick Onanian

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.

Actually, the top pully is properly called the jockey wheel, because it "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

Rick Onanian wrote:
> 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 <spamsink@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".

--
Peter Moylan Peter.Moylan@newcastle.edu.au http://eepjm.newcastle.edu.au (OS/2 and eCS information
and software)

On Tue, 16 Sep 2003 18:23:38 -0700, Skitt <skitt99@comcast.net> 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?

--
Rick Onanian

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.
--
Skitt (in Hayward, California) www.geocities.com/opus731/