2 x 10 rear setup

[thunderfox87]

I have a sram XO crank with a 42 and 22 with a MRP two speed tensor then in the rear I have a 12 to 36 cassette. I am trying to figure out if I should get a medium or long cage. I know that a medium is meant for a 2x10 setup but just wondering if i should get a long because of the size of the rings. 

[aramid]

I have a sram XO crank with a 42 and 22 with a MRP two speed tensor then in the rear I have a 12 to 36 cassette. I am trying to figure out if I should get a medium or long cage. I know that a medium is meant for a 2x10 setup but just wondering if i should get a long because of the size of the rings. 

you need long cage

[Hop Head]

Agreed.  I just went through that last year in converting my bike from 3x9 to 2x10.  I have a 12-36 cassette and 24-36 chain rings and was just barely able to get by with a medium cage.  Without getting into the calculations, you definitely want a long cage with those gears.

[thunderfox87]

What if the front was a 38 22 and rear 36 12, Would I be able to get by with a medium?

[Hop Head]

You still need long.  You're not anywhere close to a medium.  See this link on how to calculate derailleur capacity.

http://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/when-use-long-cage-vs-short-cage-derailleur-205890.html