I'd guess short.
My Long cage X7 is 4" between jockey wheel bolts.
My medium cage X7 is 3" between jockey wheel bolts.
Hope this helps from SRAM's webpage. Different rear D designs may vary a little bit, just not too much:
10 speed only
Material Aluminum alloy links and forged B-knuckle, High Strength Grilon® P-knuckle, sealed cartridge bearing upper pulley, Aluminum long/medium cage/composit short cage
Weight 204 grams (medium cage)
Outer Cage 6061-D-Stamp , Composite
Compatibility Exact Actuation 10 speed
Inner Cage 6061-D-Stamp , Composite
Cage Sizes 55mm, 75mm, 99mm
Max Tooth 36 tooth compatible
Technology Highlight(s) Exact Actuation
Hope that helps.....
Thats for a 10 speed. Mine is a 9 speed which is why im trying to figure out. Thanks.
Do you measure center to center?
Originally Posted by Slash5
It won't vary that much because 9 and 10 spd RDs are very similar save indexing. If you measure you should come up with something near the values listed above. And I'd guess short cage as well, FWIW.
Im thinking its short cage too but the person I bought it from says its a medium. I know they will help out if its a mistake but I dont want to go back and try to get this resolved if its a medium cage in fact. It just looks too small to me to be a medium. I weighed it and its 202 Grams.Do you measure the cage from the outside or inside?
Just a rough measurement with a tape measure, bolt to bolt - does 1/4" matter?
Originally Posted by cman8
Found this on the web:
"X-9 10-speed rear derailleur on their website - they are listed as 55mm, 75mm, and 99mm for the short, medium, and long versions."