Originally Posted by socaltony
"Wide range"??? I have a double and 9 speed rear.
The way you figure your max. chain wrap requirement is:
large chainring minus small chainring plus largest cog minus smallest cog.
Example: 53t -39t +27t-12t=29t.
Shimano short cage "road" rear derailleurs have a max. chainwrap capacity of 29t, so for this scenario a short cage would work fine no matter what chainring/cog combo you use.
I expect a short cage rear derailleur will work fine for your nine speed double unless you're using a very wide ratio "mountain" cassette.