long/med/short rear deraillers?

[Slave2Gus]

OK, this is a total newbie question but...what is the purpose and application of long vs medium vs short deraillers? Rear casette size? Crankset? Thanks in advance for the education.

[slowgoing]

the size accomodates (takes up) the extra play in the chain between the big/big and small/small combinations of the crank/cassette. The difference in this delta is much bigger for a triple using small granny and a large cassette (29 tooth on campy) than a double using a small cassette. In other words, a chain that would work on a triple with a large cassette must be big enough to accomodate the 53/29 combination, but the der. must take up the play when the chain is in the 30/13 combination. That's a big chain length difference and requires a big rear der. to make the chain tight. The difference is much smaller in a double where the chain must accomodate the 53/25 or 23 combination on the large side, but der. must only take up enough slack to make the chain tight on the small combination of 39/12. Much smaller delta on the double with a small cassette.

[Serotta PETE]

Size (length) of rear derailler cage determines if it is regular, mid, or long. Purpose of length of cage is to have "take up" for chain if you are running casettes that have a large difference between small cassette cog and large one. (example 12/29). As well as if you are running a triple crank in front.

= Shimano has a regular and a long cage. Reqular for up to 27 tooth cog in back. The long cage is for the use of a triple.


Campy allows a 29 tooth in back and they offer a medium cage to handle that (although many use the regular cage and just do not put chain in large ring in front and 29 tooth in back.) Long cage is for triple,


Hope this is of some assistance. Typically a triple has long cage and a double has regular cage - for "production" off the shelve bikes.

PETE

[hypnos]

The longer the derailleur, the more chain it can wrap. They are rated for certain ranges in tooth difference.

(big ring + largest cog) - (small ring + smallest cog)

From the Campagnolo web site:

Short cage derailleur for combining a double/compact crankset with a 13-26 sprocket set or smaller.
Medium cage derailleur for combining a double/compact crankset with a 13-29 sprocket set or smaller or triple crankset with a 13-26 sprocket set or smaller.
Long cage derailleur for combining a triple crankset with a 13-29 sprocket set or smaller.

[Birddog]

I'm currently running with Record 10, 12/28 Miche cassette on a short cage der. It works ok (not great) even when cross chained.

Birddog

[Slave2Gus]

I am wiser than before!

[hybridbellbaske]

I run a 13/29 with a Chorus 10 short cage rear derailleur without any problems- so the "rules" may not be absolute.