[QueNota]

K well im receiving my bike soon, just purchased a FSR Stumpjumper
and i need help on choosing what size REAR derailer i should go with. I'm looking into a SRAM X-0 , i know the size depends on the sprockets but im not sure how many sprockets go with long derailer/medium derailer
Please if anyone has time to fill me in with a brief explanation, feel free

 

[ultraNoob]

I'd say go with a medium, so you're good for whatever comes your way.