The windshield is a real nuisance.
The problem is that - at least for taller riders (I am 1.87 m tall) - the helmet is exactly in the area of the air vortex zone caused by the edge of the windshield. Consequence: unbearable noise.
MOTORRAD writes in issue 11/2000 about the BMW series windshield of the R1100GS in an article about spoiler discs:
"relatively small and far forward mounted cockpit fairing, nevertheless noticeable relief of the upper body, for drivers over 1.65 m the helmet is in the turbulent area, therefore restless and noisy; free inflow only for two-meter giants.
Unfortunately, the problem is also present with the R1150GS. BMW apparently builds its motorcycles in such a way that the majority of riders only get suboptimal wind protection. (I dare to doubt that there are GS riders with a height of 1.65 m at most).
Since there are also hardly any usable alternative windscreens, I decided to find my own solution. And this is "shorten the windshield". By driving tests (getting up during the ride) I found out that for my height the windshield would have to be shortened by about 16 cm.
Then I opened the yellow pages and looked under plastics processing. I called the companies. The problem manifested itself that not all companies were able to cut curved plastic parts. But some can. I marked the cutting height and delivered the windshield. After about one week I got it back shortened and with a professionally machined edge (not noticeable difference to the original).
Now is silence. The vortex zone hits me at neck and upper shoulder. The windshield is still quite neat. Even vmax is still possible without the head falling off immediately. I can only recommend this operation.