Engineers at HD discovered that the design of the brake caliper and rotor combined with the fork dimensions created what they called, a "Negative Turbulence Coefficient" of -3Ap to -7Ap. This phenomena usually occurred on deceleration between 75mph and 68 mph. The result was destabilization of the airflow behind the front wheel causing "Steering oscillation" (wobble)......The flared fender creates a positive pressure behind the front wheel to offset this condition..........Disclaimer: the aforementioned paragraph is complete BS and the poster admits to being a little drunk...lol
It was designed so to eliminate the engine heat, the high speed wabble, the 5th gear whine, the abnormal tire wear, and fix the wind buffeting on my '07 Roady. However, because of the angle of the flare it has increased the above and also caused my HK radio to go on the blink. Damn those fenders!