Shimano says 35-55nm.
http://bike.shimano.com/media/techdo...9830672281.pdf
I can guarantee you they will stay on with less. 35-55nm is pretty tight. Tighten them nice and firm and you'll be fine.
__________________
You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.