|3iker

Just wondering what's the difference in terms of RD operations b/t a short cage and long cage. Is cage the word... I am referring to the arm-like thingy that holds the jockey wheels.
And is it worth upgrading a Sora RD to a Tiagra RD? Worth the time and effort?

Al1943

The operation is generally the same provided you stay with Shimano and stay away from pre-9-speed Dura-Ace.
The purpose of a long cage is to wrap more chain, avoiding slack. Usually needed for a triple crankset drivetrain.
A Tiagra RD would be a slight improvement but probably not worth an upgrade. Most derailleur problems can be corrected with adjustments.
Rear derailleurs are usually one of the more dependable trouble-free components and often get blamed for problems related to adjustments, dirty shifters, or excess friction in the cable housings.

Al

bluenote157

from my understanding.. a shorter cage will allow for quicker shifts???
but yes, the long cage will help accommodate the difference and take up the slack from say 53t chainring to a 30t... or something like that.

FBinNY 

I always suggest using the shortest cage RD that'll meet your chain take up needs. There's a marginal performance advantage, better ground clearance, usually slightly higher chain tension and a few grams of saved weight.

But in total the differences aren't enough to compromise gear (chainring/cassette) selection, or to spend dough replacing a functional RD. So, if you're replacing anyway, get the shortest cage that'll work, otherwise save your dough for something else.

|3iker

Thanks guys for the explanation!