@_Ray_C I’m finding the same thing. I just changed my trainer tire from a Vittoria to a Continental which seems to have much lower rolling resistance. Pressure at 110 psi, 2.25 turns on the SNAP’s knob for both tires. Spindown time increased from 15.2 seconds (Vittoria) to 21.5 seconds (Continental).
According to Wahoo, this should not matter.
According to my legs and lungs, it sure does!
I’d guess that with the longer spindown time the SNAP is under reporting power by ~30 watts.
Wondering if you, or someone else with a SNAP 17 and a crank/pedal/hub power meter could do a comparison and post the results. Adjust the wheel tension to give a spindown time of about 15 seconds, perform a spindown using the Wahoo app, then ride at ~250 watts and compare the readings of the SNAP and the external meter. Then adjust the wheel tension to give a spindown time of about 22 seconds and repeat the test.
I’d really like to see the results!