Originally Posted by
icemanbb
I experienced a case this past summer where my GPS unit (Garmin GPSmap 60CSx) registered 48mph for a segment. I know that I was nowhere near 48mph on that segment (or any segment for that matter). I was in downtown Pittsburgh at the time and think that the buildings caused the unit to become temporarily confused (switching satellites combinted with ± 20' error). I agree with the poster that said that a "more" traditional cyclocomputer (properly calibrated) would give a more accurate measure of speed.
My 60CSx clocked my cycling speed at 248mph at one point. In fairness I had just emerged from a long tunnel. Otherwise I'd have to say I can only imagine how humiliated the likes of Contador and Schleck will be next year when they are roundly thrashed in the Tour de France by a fat guy on a mountain bike...