From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Jockey wheel mix-up
Date: 18 Jun 2001 15:34:26 GMT

Andrew Bradley writes:

> I have mixed up my DA jockeys.  One has built-in side-to-side
> "float", the other is "fixed".  Also, the "fixed" one has an arrow
> on it, seemingly indicating the direction it should turn (perhaps
> due to the chamfers on it), the other doesn't.

The wobbly one goes nearest the sprockets.  It does the shifting.

> What is the theory behind these jockey wheels?

The wobble allows the derailleur to move to an adjacent gear position
without the chain moving.  This was first introduces when down tube
shift levers were still the mainstay.  Many riders could not pedal and
reach down to shift at the same time.  This way they could coast and
shift, the change taking place when they again pedaled.  I'm not
convinced that the feature has any merit anymore now that people can
shift with both hands on the bars but then who knows what their shift
routines are.

> Wait a minute, I've sussed it.  Assuming the arrow indicates
> direction of turn, then if this is to be visible from the
> drive-train side there can only be one solution - the "floating"
> jockey nearest the freewheel.

I doubt that the arrow has anything to do with how it must rotate but
rather that it indicates where it belongs.

Jobst Brandt    <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Jockey wheel mix-up
Date: 18 Jun 2001 21:44:25 GMT

Ray Heindl writes:

> Interesting.  All these years I've assumed the float was to allow for
> imperfect alignment between the pulley and the cog in indexed shift
> systems, since indexing doesn't allow fine-tuning to get rid of the
> noise.  Is there really enough float for the derailleur to shift a
> whole cog?

Oh but no.  All modern derailleurs have a fine tune thimble where the
cable housing bears on the mechanism.  After tightening the cable
anchor, the precise position is achieved by this adjustment.

Jobst Brandt    <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Jockey wheel mix-up
Date: 19 Jun 2001 20:54:00 GMT

Ray Heindl writes:

>> All modern derailleurs have a fine tune thimble where the cable
>> housing bears on the mechanism.  After tightening the cable anchor,
>> the precise position is achieved by this adjustment.

> Yes, but that assumes that the shift spacing of the derailleur,
> complete with backlash, slop, etc., is equal to the cog spacing,
> which seems difficult to guarantee.  The floating jockey wheel
> allows for some variation on all the cogs, since the derailleur
> position is fine- tuned for only one cog.

Gear spacing does not change with backlash because that is a constant
offset.  The reason Click-shift didn't work is that it had the detents
in the derailleur rather than in the lever where relative position is
constant and overshift can be controlled.  All that aside, you must
not have ridden other derailleurs that work well or you would be aware
that the wobbly wheel is completely unnecessary.  I have Sun Tour,
Shimano, and Campagnolo derailleurs that worked excellently without
this gimmick that, like profiled and synchronized sprockets, are aimed
at people unclear on the concept, people who cannot reasonably shift a
derailleur on a bicycle from the 1960's.

> Still, the can't-shift-while-pedaling explanation seems equally
> reasonable.  What happens if you shift without pedaling on an
> old-style derailleur without the float?

The derailleur won't move fully into gear if its a sprocket that's
close to the upper derailleur idler and with friction shift levers,
it's a hopeless exercise.  Pre-shifting is something people tried with
little success before the wobbly wheel came along.  I notice that most
riders today have no concept of light pedaling while shifting.  Many
ride as car drivers with automatic transmissions, not letting up on
the gas as one must for shifting a manual transmissions.

> It would take a lot of experience to do this with non-index
> shifting, though, which may be why the float came in with the
> indexing.

That may be, but it appears to me that these features came along
incrementally, each time still not guaranteeing flawless shifts under
all conditions with no special skills.  First the index for people who
could not imagine discrete gears being selected by feel, then the
wobbly wheel to make pre-shifting possible, then side cut gears with
chain ramps to carry the chain when shifting under load, then
synchronized sprockets to prevent chain skip when shifting under load.

All this helped bring on continual shifting for the slightest undulation
in the road and the use of gears to start from a traffic light ala
Peterbilt Truck with xx gears.

To bad that these folks don't get the gist of Lance's great utterance:
"It's not about the bicycle (it's the rider)."

Jobst Brandt    <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Why did it take so long?
Date: 29 Sep 2000 01:58:03 GMT

William Meredith writes:

> It seem the our current level of cycling technology took one hell of
> a long time to come about and I been wondering why we did not have
> the many gears high tech bikes in the 1920's instead needing to wait
> until the ten gear bikes came on the market in the late 70's or so.
> Sorry if I am wrong about the date of the 10 speed bikes coming into
> the market place but it was well after my childhood in the 50's-60's
> at least.

You can find similar mental blocks in industry and technology in
general.  Take for instance a center jointed bucket loader or earth
scraper.  The center jointed tractor was around since the late 1930's
but did not get wide spread use until 1960 and later.  Le Tourneau
built Tournapul scrapers in Sunnyvale CA while others built scrapers
with a 4-wheel tractor.  Today there are only center jointed tractors
for these tasks.

Until Campagnolo introduced the parallelogram derailleur, the devices
built typically by the French (Simplex and Huret) were unreliable,
subject to jamming in the rain and cumbersome enough to have push-pull
cables that forced the motion in both directions.  Not that Campagnolo
invented anything but he was astute man who recognized a good design
when he saw it and put it in reliable production.  That was the
beginning and it was at about 1955.  Some historians can get the exact
date.  That there were not more gears was twofold.  Only racers
(professional was the only kind) used these multi-speed gears and they
rode on dirt roads until the late 1060's.  Chains wore out fast enough
to convince people that narrower chains were not reliable so closer
spacing wasn't either as was a crookeder chain line.  The standard
7-speed had a poorer chainline than today's 10-speed cluster.

> Is there anything on our current bikes that the technology of the 20's
> could not had come up with, but for the high tech component frames?

Better steel in the sprockets and chains and better freewheel ratchets
due to better materials and machining.  The market had to be there for
applying high tech methods to a sport that is contested among the
untouchables of society.  I think that social fact is most often
overlooked by the American public.  Who do you think those nameless
riders in the pack are?  Many would have a hard time holding any job
but sweeper.  Today that is a bit better but they are still grunts
with low pay and don't inspire high tech firms to make hardware.  It's
the .com folks who drive that market and the professional racers are
needed to advertise the stuff.

Jobst Brandt      <jbrandt@hpl.hp.com>