Michael Press writes:

I recently read that Barnett's Bicycle Manual recommends a certain
spoke orientation for wheels with disc hubs. They state that the
major disc brake manufacturers don't specifically require this
orientation, but they recommend it. They also note that the
orientation is what their wheelbuilding instructions follow.

I recently had a wheelset built up for disc brakes (700c wheels, if
it makes a difference), and the spoke orientation appears to not
follow Barnett's recommendations, if I understand them correctly.

Is it common to follow these recommendations? What's the likely
outcome for wheels with reversed orientation - going out of true?
broken spokes? Spokes pulling through the rim? Nuclear war?

No, and no. Spoke orientation is an old bugaboo, similar to ankling,
that also has no merit.

Here's the blurb from chapter 37 about disc brakes:

"The recommended cross patterns are limited to 3x and4x.
Deceleration can occur much more rapidly than acceleration, so
consequently the torsional loads from deceleration are much higher
than those generated during acceleration. The recommended cross
patterns are required to transfer the higher torsional loads that
hub-mounted brakes can generate during rapid deceleration.

That is also untrue and has not been analyzed by these folks or they
wouldn't say these things. There is an analysis of this in "the
Bicycle Wheel" that shows what the spoke loads would be for the torque
needed to climb a vertical wall, if that were possible. This was done
mainly so that relative forces could be compared, they all being the
weight of rider and bicycle. The forces are small compared to those
that just rolling along on the flat causes the load bearing spokes to
go through.

"Although Hayes makes no recommendation regarding lacing patterns,
other manufacturers require that the left-side head-out spokes
radiate clockwise from the hub and that the right-side head-in
spokes radiate counterclockwise from the hub. These are the same
directions that result from following the wheel-lacing instructions
in this manual. The vernacular terms for these patterns are that
the 'pulling' spokes are "head out" and the "pushing" spokes are
'head in'. An alternate term to 'pulling' is 'trailing' and an
alternate term to 'pushing'" is 'leading'."

Yes, its all hocus-pocus. I don't understand why people should
believe this stuff when there no reasons are given why this should be
beneficial and no explanation of how great the forces are.

Jobst Brandt