Rear Derailleur Sizes- What's the formula?

Quoted post said:

Originally posted by Mark
Hi Folks, Please forgive me if this question has recently
been posed to you all.

I'm not too confused about Front Derailleur types, as I do
understand you basically don't use a "double front"
Derailleur with a "triple Chainring" set.

But I am confused about what properly determines what size
Rear Derailleur Cages should be used in any given instance?
(Short-Medium-Long)

How would I know what size Derailleur Cage I need if I went
with a 9 Speed Campy Chorus, or 9 Speed Campy Centaur group
on a road bike? Is it the Cassette Size that determines what
size cage to use? Or?

Forgive me for my lack of knowledge on this subject, but I
would like to learn what determines the proper selection of
cage size. TIA Mark
D.

The total amount of chain wrap-up required is what determines what cage length you should use. The wrap-up is the difference between biggest and smallest chainrings plus the difference between biggest and smallest rear cogs. For example, if you run a 39x53 double up front with a 12-27 cassette, you would need a chain wrap-up capability of (53-39)+(27-12) or 29 links.

Mark said:

How would I know what size Derailleur Cage I need if I
went with a 9 Speed Campy Chorus, or 9 Speed Campy Centaur
group on a road bike? Is it the Cassette Size that
determines what size cage to use? Or?

It's the combination of cassette and chainrings.

See campagnolo.comgroupsets.phpOpen ↗

~PB

(Mark) said:

How would I know what size Derailleur Cage I need if I went
with a 9 Speed Campy Chorus, or 9 Speed Campy Centaur group
on a road bike? Is it the Cassette Size that determines
what size cage to use? Or?

The chain needs to be of a length so that the largest ring
and cog can be engaged and ridden. That given, the rear
derailleur must be long enough to not drag on the bottom of
the rear derailleur when in the small/small combination.
Additionally, the top derailleur pulley should not hit the
largest cog when in the small ring and largest cog.

YOu can't just look at gear sizes to find out what length
chain is needed. The length of the chainstay is also a
determinent.

No formula.

apoman-<< How would I know what size Derailleur Cage I need
if I went with a 9 Speed Campy Chorus, or 9 Speed Campy
Centaur group on a road bike? >><BR><BR>

Here's what they recommend altho it's not as strict as
they imply.

Double crank-cogs to 13-26-short Double crank-13-28-medium
cage TYriple crank-cogs to 13-26-medium cage triple crank-13-28-
long cage.

BUT you can use a short cage with a double and 13-28 and you
can use a long cage with any setup-

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali
costruite eccezionalmente bene"

To add to Peter's comment about the universality of app. for
long cage, the old tale of slower shifting with long cage is
truly old. Mountain bikers shift as quickly as anyone. this
is especially true in the small/small extremes as the
tension on the long cage is higher in those combos. Tom

--
Bruni Bicycles
"Where art meets science"
brunibicycles.com
410.426.3420
Qui si parla Campagnolo <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

apoman-<< How would I know what size Derailleur Cage I need if I went with

a 9

Quoted message said:

Speed Campy Chorus, or 9 Speed Campy Centaur group on a road bike?

Quoted message said:

<BR><BR>

Here's what they recommend altho it's not as strict as they imply.

Double crank-cogs to 13-26-short
Double crank-13-28-medium cage
TYriple crank-cogs to 13-26-medium cage
triple crank-13-28-long cage.

BUT you can use a short cage with a double and 13-28 and you can use a

long

Quoted message said:

cage with any setup-

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
vecchios.comvecchios.comOpen ↗
"Ruote convenzionali costruite eccezionalmente bene"

On 09 Apr 2004 13:13:19 GMT, [email hidden] (Qui si parla

Campagnolo ) said:

BUT you can use a short cage with a double and 13-28 and
you can use a long cage with any setup-

...and I can use a short cage Shimano 105 with a triple (30-42-
52) and 11-27 cassette. No droop. The derailer is pretty
wound up in small-small and pretty stretched in big-big, but
nothing will break if I accidentally use either combo.
--
Rick Onanian