Dave Barrett said:
BTW, I think this is really a height issue. I'm 5' 7" and use the BMW lower seat. If I stand up a bit, there is a reduction in under-chin turbulence. I'm also considering changing the seat height every time it rains....
Dave (and others with the same problem):
You're spot on and I commented on this a few weeks ago after some wind-testing results from our biomechanics lab at work. Many riders suffering from buffeting/turbulence waste a lot of money trying to buy a taller screen. The people who suffer most are shorter riders with the seat in the low position. The turbulence is created largely round the sides of the lower part of the screen (putting the screen in its most upright position makes it worse) and the airflow is further disturbed by the brake/clutch cylinders, mirrors, and handguards.
If you're short and have the seat set low you get this turbulent air hitting you smack on the chin. Because of my height I don't feel it at all because it hits me across my chest at armpit level.
All screens will create turbulence. There are only three solutions:
(1) remove the screen - more wind pressure but no turbulence and buffeting;
(2) fit a screen wide enough to deflect the air further and move the turbulence behind the rider (but it now effects the pillion) - you might also experience a feeling of being pulled slightly forwards which can become tiring after a while;
(3) fill the space behind the screen with air at an equal or greater pressure to remove the partial vacuum.
Solution 1 is very effective up to about 80mph when it becomes tiring just like it does on all naked bikes.
Solution 2 possibly works for the some of the extra wide Cee Baileys screens which use the Adventure mounts, but it doesn't work for the Wunderlich because the Wunderlich extra width is not at the base where it needs to be. In fact the shape of the Wunderlich possibly exaggerates the amount of turbulence if you're short. Yet it's probably the best solution for somebody about 6' to 6'2".
Solution 3 works for the MRA because of its dual nature - air flows through the screen. One of the best screens ever on any sports bike was the standard screen on the Honda CBR1000 which was one of the first to feature holes/ducts at the base of the screen to produce a wall of air behind the screen and a venturi effect. IMHO what would be better is a screen based on the MRA but without the adjustability (which I think can make it flimsy and unstable according to some reports), just one-piece moulded on the same principle and maybe as wide as the Adventure screen using Adventure mounts.
All of this is specific to each rider as well, their height, seat position, body position, arm length, back curvature. You really have to try before you buy. So, somebody will rave about the Wunderlich screen. Another member will go out and buy one and claim it doesn't solve the problem.
I'm not a physicist so more knowledgable members out there will correct me if my basic fluid mechanics is wrong, but I work with and talk to professional biomechanists every day (mostly concerning airflow around golf balls and cyclists and so on) and it amazes me why bike/screen makers can't apply simple mechanics to develop screens that work instead of relying on the car-windscreen school of design.
Let us know how your MRA copes with the rain!