Originally Posted by
SalsaShark
This happens on one of my bikes, and seems to be caused by the flexing of the frame and fork when applying excess power.
I have the Canyon Ultimate CF SL 8.0 Di2 as well, and there is no brake rub standing, and I regularly put in 700-800W on hill sprints out of the saddle. (And, no, that's not even beer league peak power.)
However, I also make a point not to excessively rock the bike; it might only lean 5-10˚ back and forth, and I pay attention to riding in a straight line. This avoids side loading wheels, hubs, tires, frame, etc, and keeps the sidewalls off the pavement and away from debris. It also makes me ride in a straight line, which is the shortest path between two points, so I cover less distance while more energy is put into propelling me forward as opposed lean angle induced losses. (As a result, it'll feel a little harder. The same reason riding out of the saddle on a trainer feels harder.) And, yes, it requires pulling hard on the bars.