The first step in sorting out the buffeting is determining the source. I can’t speak for everyone but my experience is that any windscreen is going to create a pocket of negative pressure downstream. If you’re in that pocket you’re in the eye of the storm and life is good. If that pocket is in front of you then the task is to get it to expand to include you. You can try moving the GIVI to one of the other two positions on the cowling - the highest position isn’t always the best. Once you’ve found the position that creates the least amount of buffeting you can try moving the airflow by adjusting the front auxiliary screen up or down. When you find the best spot for that with the least buffeting then you can try other things. Since you already have mirror extensions I’m going to move on to my next step in diagnosing to problem. Before I do, I will say some people have gotten varying levels of relief by swapping out the Suzuki mirrors for some more aerodynamic aftermarket versions. I can’t speak to those results because in my case I didn’t need to.
In trying to determine the source of buffeting, I went for a cruise on the freeway and moved my cupped hand around it front of me. By doing that at various speeds up to 100+mph I determined that almost all the buffeting wind was coming up from the front wheel/suspension area and around both sides of the fairing. Now, in the interest of full disclosure my bike is a 2014 V-Strom dl1000 Adventure with factory crash bars. On my bars I have mounted a pair of GIVI Bar Bags that are about 5 liters each. Also I am 6’2” and 235lbs. with a 35” inseam. I mention that because, while I think the PROCESS is as applicable to your bike as mine, the RESULTS may be quite different.
Having said that, my approach to dealing with this turbulent air coming up from the front was to fabricate a pair of wind deflectors which I attached to the fairing on either side of the tank using the existing screws. I fabricated them from Lexan sheet that I bought at Home Depot using a handheld jigsaw and a heat gun to create the bends. I’ll attach pictures below. I posted a pretty thorough pictorial on the V2 section of this forum a couple years back. You may be able to search around and find it, but I couldn’t begin to tell you how.
The results were impressive - only mild buffeting remained at speeds over 100+ and I could easily channel cooling air to my body just by lifting my elbows. At any rate, here are a few shots of the finished deflectors and details of how they’re mounted.
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I hope this helps and you get your buffeting issues resolved. If you’re not able to craft your own you might try to find some online. I have heard of people buying the ones BMW makes for the GS and adapting them to the Strom. Good luck and good riding!