Why is the data different between Garmin and PowerTap CPU?
Numerous differences exist between PowerTap and Garmin computers in regards to how data is displayed. To ensure the least difference, you should verify the wheel diameter is correctly entered into both devices and that both devices handle ride stops, pauses, and resumption the same way. Garmin computers typically measures distance (and speed, depending on setup options) based on GPS data, and does not use the auto-pause feature by default. PowerTap computers measure speed based on wheel speed and distance based on the number of wheel rotations and uses an auto-pause by default. Garmin calculates average power output without zeros, while PowerTap does not by default, but there is a setting to change this (on both Garmin and PowerTap computers). Garmin does offer a POD that allows the 705 to read speed and distance using a similar approach to the PowerTap. Garmin computers tend to apply more smoothing to the power data, which can cause discrepancies when compared to PowerTap computers.
