Speed measurements with a Garmin GPS-12

One of the more frivolous uses of a GPS reciever is to measure personal speed records, which I have done for various sports listed below.
Estimating accuracy is tricky, because most of the errors in the GPS position measurement vary slowly with time and so cancel out in speed calculations. Perhaps the best measure is the velocity indicated at rest, which is usually less than 2kph. Positions are measured once per second, and the maximum speed indicated is the average over this time, which means that lurching forward could give a misleading velocity for that interval. Averaging over 3 seconds is a better indication of true top speed, but I've only been able to do that for those runs where I have access to the tracking log. The third column is the peak speed translated to mph.

Mark Harris 21-Feb-2000

Sport Peak speed 3-sec average Peak mph
Slalom skis 123 kph 115 kph 76 mph
Telemark skis 71 kph 67 kph 44 mph
Sea kayak (surfing) 21 kph   13 mph
Windsurfing 41 kph 35 kph 25 mph
Skate sailing 42 kph   25 mph
Kite skiing 38 kph   23 mph
Kite skating 40 kph   24 mph
Ice yacht 38 kph   23 mph
Ice surfing 26 kph   15 mph

GPS page

(MRH homepage)