Rear derailleur question

cframe

Why do some rear derailleurs have a long cage on them and some have a shorter one?

What are the benefits/drawbacks of each style?

redddraggon

For rear derailers, the capacity relates to the amount of chain slack the derailer can take up, and is equal to the front range (22 in the example above) plus the rear range. Thus, if you have a 52/42/30 crank set, and a 12-28 (16 tooth difference) cluster, the total capacity required would theoretically be 38 teeth (22 front difference + 16 rear difference).

The long caged mech can take up more slack and has a higher capacity. A short arm mech has a smaller capacity.

sloboy

Shorter ones are supposed to give a snappier change.

So a short cage gives crisp changing over a narrow range. If you want a wider range, you fit a derailleur with a longer cage.

cframe

Ah cool, cheers for clearing that up guys

Would I be right in assuming that most compact chainsets could use a short cage rear mech then?

willbevan

You can use a short cage with a compact(i have, and a stupidly large 12-28 cassette with a short cage sora, didn't work amazingly but did work)...

Depends on the difference between the chainrings, and the difference on the back cassette.

http://sheldonbrown.com/gloss_ca-g.html#capacity

The specs for a mech are usually conservative in my opinion..

Blonde

I agree with the above that it is more to do with which gears you have and the spacing between the gears (a combination of chain set and cassette) rather than just the number of teeth on the chain rings. I use a triple chain set with a 12-23 cassette so use a long cage mech. The gear changes should be slick no matter which you go for - it's down to the indexing adjustment and to some extent the quality of the mech.

cframe

Cheers guys