No size M is fine

 Sweet. Seems to be Shimano saying you can only go to 36T on the Medium cage, how's this worked?

 Adjust B allmost full in works smooth no struggle at all. Chain does come off in 40 when I back pedal so I'm going to remove BB spacer off the drive side over to none drive side .that should solve that . Just had email back from HOPE stating you will need aleast a M mech

 I had no prob with a 11/40 and a Zee

www.pinkbike.com/video/351634

YMMV

 On what bike ?

 cannondale prophet, single pivot, has some chain growth, been spot on.

 That's short travel tho ant it ? My bike is 160 travel ...see my othe pics to see just why the ZEE don't work. It's cost me a little over £100 for the ring and new casset . But I'm puting the ZEE mech on a winter hardtail basher )

 yeah it only 140, but chain growth depends a lot on the suspension design as well as travel. It is on the limit of what the zee can do on mine, thought i might need to get a med cage XT but its been good as gold out on the trails

i made my own out of an old chainring as there was no 40t available at the time and I am running 9 speed as well

 Good stuff )