I have had the good fortune to drive, ride and fly cars, motorcycles, airplanes and boats. It was always fun to see big numbers on the speedo and then came radar and gps. It quickly became apparent that what the speedo said, the radar said and the gps said didn't always agree. In general speedometers tend to be optimistic. On all of the Jap bikes I have owned they are wildly off. Using a certified police radar gun I found the bike's speedo was 10 to 20 mph over what the radar said. Some cars could be off the same amount, but generally it was 5 to 10 mph different. In the airplanes I have flown indicated airspeed only reads the same as ground speed if you are at sea level and there is no wind. I have seen a 50 knot head wind and tail wind. So flying at 135 knots indicated going with the wind I had a 185 knot ground speed then I turned the airplane around into the wind I had a 85 knot ground speed. Flying 100 miles down wind only took little more than 30 minutes. The return flight home took more than an hour to go the same distance.
BUT buzzing some friends house 10 feet over their roof at 200 mph was funnn,
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