Why is the Garmin 705 different than the PowerTap?
Numerous differences exist between the PowerTap and the Edge 705 in regards to how data is measured and displayed. To ensure the least difference, you should verify the wheel diameter is correctly entered into the both devices and that both devices handle ride stops, pauses and resumption the same way. Garmin typically measures distance (and speed, depending on setup options) based on GPS data and does not use the auto-pause feature by default. The PowerTap measures 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 zero’s, while the PowerTap does not by default, but there is a setting to change this. Garmin does offer a POD that allows the 705 to read speed and distance using a similar approach to the PowerTap. The Garmin tends to apply more smoothing to the power data, which can cause discrepencies with the PowerTap in maximum power output values.
