Hard to say for sure but, most likely, the air is coming around the bottom of the shield, hitting the tank, and then your head. Easiest way to see is go for a ride. At about 50 mph, put your hand on your knee, palm down. Then slowly raise your hand to your chest, keeping your palm facing out. If you feel a difference in the helmet buffetting and the wind pushes your hand to your chest, you definitely need lowers.