Originally Posted by
wphamilton
Not true IMO. The speed sensor is the same hardware as a wired bike computer, and you're probably thinking that it's only used for measuring instantaneous speed and the GPS is used for overall distance.
The wired bike computer properly calibrated is much more accurate (in the case that the GPS ignores the wheel sensor for distance) because of the numerous sources of error of the GPS. Primarily among them, the transient variance of measured position (5 meter accuracy) by the GPS means that it only approximates the actual path travelled.
1) Rollout calibrations for a GPS-based computer can actually be a bit better than a wired computer, because the rollout measurement can be performed automatically at the beginning of every ride over a much longer distance.
2) 5m is the typical
absolute accuracy of a GPS-based bike computer, but you don't need high absolute accuracy for distance measurement, just high precision. (Accuracy and precision here are used in the strict metrological sense.)
3) Wired computers will measure distance better at short distances than a GPS-based computer, if the GPS computer is not used with a speed sensor. The distance error of a wired computer accumulates (linearly) as the distance increases, however, giving a GPS-based computer the advantage at long distances because GPS positional errors do not accumulate linearly.
4) If a GPS-based computer is used with a speed sensor, there's no reason it couldn't measure distance as well as a wired computer at short distances, but I don't know if they use speed sensor data when they calculate distance.