Originally Posted by
JohnDThompson
3x ought to be fine. Depending on the hub flange diameter, 4x might be difficult with 650B diameter rims.
+1 I'm with John on this.
You know 3X will NOT cause ANY kind of problem.
4X has that element of doubt. (as small as it may be)
I'm in the same boat as you. I haven't built enough wheels to experience the little nuances that might bite ya re: larger hub diameters/small dia. rims.
I don't see any reason that 4X would be "enough better", if at all, over 3X. Especially if you are going to fatter tires which will absorb a lot of peak impacts.
3X would probably save the weight of a spoke or so vs 4X.
Build it right and you won't have a problem.