Originally Posted by
GeoMan
Garmin thought of this with the Edge series of their GPS enhanced training computers. The cadence/speed sensor option on the Edge 305 (Edge 305 + CAD or the Edge 305 Bundle) enhances accuracy by filling in data missed by the GPS. The Edge 305 also uses a barometric altimeter.
I have the Edge 305 with the cadence/speed sensor and HRM. When I have the cadence/speed sensor working properly, the speed seems very accurate compared with my bike computer (a cheap one I still have mounted). A few weeks ago, I had a problem with the cadence/speed sensor, and the first thing I notice was inaccurate speeds when under heavy tree cover. Once I adjusted the speed magnet to where it was reading again, the accuracy is MUCH improved again. I guess the speed sensor fills in data when GPS coverage is poor, thus improving accuracy somewhat.