Originally Posted by
CoogansBluff
My Garmin sometimes doesn't begin measuring average speed and grade of hill until I'm about a half mile into the ride. Elapsed time and time of day still show.
I replaced the battery on the part that attaches to the wheel, but I'm not certain it was a brand new batter (it was out of the package) so it might not be a new one. But seems that if it were the battery that nothing would show.
Without knowing which Garmin you have this can't be 100% but in general if a Garmin can't talk to the speed sensor that should be there, it will just use GPS instead. If the battery is completely dead, it would still give you a speed based on satellites.
I'd probably change the battery just to see if that's it. If not, check if the magnet and sensor are aligned, maybe something moved a little.