Originally Posted by
tomato coupe
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.
This is about accurately measuring the circumference. That is, whether GPS is more accurate for measuring circumference is a different question from whether it's more accurate for distance.(Obviously, the wired computer needs an accurate circumference.)
Originally Posted by
tomato coupe
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.
It's not really a "speed sensor". It's a wheel rotation sensor. A wired computer also counts wheel rotations (it's the same thing as a "speed sensor"). It's not clear how you think having both ("GPS-based computer is used with a speed sensor") makes GPS better.
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One issue with GPS is loss of signal.
https://support.garmin.com/en-US/?fa...623Z535geTx2e9
The wheel rotation counter is taking measurements 3 times a second. The GPS is typically only taking measurements once every second.
That means the counter has a higher resolution than GPS (which has a straight line between each one second measurement).
The GPS measurement has an error of 10 feet or more. The wheel counter has error on the order of centimeters. This really matters for accurate "instantaneous" speed.
If you have an accurate circumference, the distance based on wheel rotations will be very accurate. There's no reason to expect that GPS (at the low speed of bicycles) would be better.