[Mark McM]

So, take a look spoke loading from the disc brake:

Torque loads (as from pedaling or hub brakes) are distributed nearly equally among all the spokes. So with a large number of spokes, the stresses from torque loads will be much smaller than the stresses from radial (weight bearing) loads, which are distributed over a smaller number of spokes. But with a smaller number of spokes, stresses on individual spokes increase. But there are several mitigating factors at work on this particular wheel:

1) Stresses from torques are inversely proportional to flange size. Since rotor-side flange on this wheel is oversized, that will help reduce spoke stress.

2) Spoke stresses from torque also decrease with spoke angle. The rotor-side spokes on this wheel are laced in a 2x pattern which results in a 72 degree spoke angle, which isn't far from tangential (and also greater than the 67.5 degree spoke angle in the popular 32 spokes 3x pattern).

Personally, I wouldn't have a problem with this 20 spoke disc brake wheel. Spoke stresses from disc brakes are small and infrequent enough to begin with, and this particular wheel doesn't increase them by much.