Originally Posted by
chaadster
Thanks for the clarification. What I was meaning to address was the OP's concern that the Powertap was not informed of the circumference size; the hub does not do calculations, rather *transmits* only hub rotations for calculation at the head unit into speed/distance based on circumference info there. That's correct, no?
Yes, that's correct. There's no way of informing the Powertap about the circumference.
Originally Posted by
chaadster
Again, thanks for the clarification. I thought a Garmin would reconcile GPS distance with circumference value,
It's not clear what "reconconciling" would mean.
(If you don't have a circumference specified, the unit will use GPS to determine it.)
Originally Posted by
chaadster
but I guess it just gives precedence to a paired S/C sensor (which requires circumference value) when available.
Yes, it does the simple thing. If the wheel circumference is accurate, the distance using that (and wheel rotations) is going to be more accurate.
Originally Posted by
chaadster
Could the OP's wheel size setting have switched from Custom to Auto (after the wheel build) causing the discrepancies?
Maybe.