FYI. I bought a Madstad adjustable F800GT windshield and fitted it to my 93 K1100RS. The mount brackets need to be bent (I used a sheet metal brake) to match the flat(ish) K1100RS windshield, but it otherwise fits well and is easy to install (if you're brave enough to mount it to the stock plastic windshield). I used an english wheel to fabricate a replacement stock windshield out of .080" aluminum to ease my mind.
In the low position (height and angle) it easily pushes most air to the top of my helmet. Tilting it up and looking through the windshield will block everything. It also functions as a laminar lip to greatly reduce buffeting (stock windshield and flap is terrible for this, IMO).
I do plan on trimming 2" off the top so that I actually have a use for the 2" of adjustment in the madstad bracket.
