86 on the speedo or actual GPS speed? As we know speedo is not accurate and reads 5-7 knots slow.
The resonate frequency of the fenders occurs at a much lower speed and once above 57 the fenders no longer flap, they sail.
BY the way, 14 degrees f today and Ol flappy fenders starts right up and once cockpit is heated, rolls right on out.


~ HB
1966 Chevrolet K-10 | Ghost: formerly Flappy Fenders | In the Stovebolt Gallery
1962 Chevrolet C10
1962 Suburban