Rear Derailleur Sizes- What's the formula?

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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.

Mark wrote:
> 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 wrote:
> 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 http://www.campagnolo.com/groupsets.php?gid=3&cid=1

~PB

On 8 Apr 2004 08:18:08 -0700, apoman60612@yahoo.com (Mark) wrote:

>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.

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 <vecchio51@aol.com> wrote in message
news:20040409091319.25504.00000052@mb-m04.aol.com...
> 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
> http://www.vecchios.com
> "Ruote convenzionali costruite eccezionalmente bene"

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
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

On 09 Apr 2004 13:13:19 GMT, vecchio51@aol.com (Qui si parla
Campagnolo ) wrote:
>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

Rick-<< .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. >><BR><BR>

Yep, there are a lot of combos that the manufacturers say won't work, but do.
Sometimes ya just gotta try them. I put a 12-32 8s cogset onto a 8s DA setup
once for a hill climb race. It worked.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"