Originally Posted by
mrodgers
Well then, I actually now use Runtastic: Road Bike app for recording my ride, though the GPS doesn't seem as accurate as my cheap $20 cycle computer. Googlemaps gives me exactly 6 miles to the other side of the tunnel on the rails to trails I ride which matches the bike computer and Runtastic gives me only 5.5 miles. Then again, I guess the GPS doesn't work real well in the tunnel. Also the bike computer calculates time and average speed riding where Runtastic calculates any stopped time as well so the elapsed time and average speed is wrong from actual riding. I think My Tracks will actually give you moving time/average and overall time/average.
Cycling computers measure distance by counting wheel rotations and multiplying that count by the wheel circumference.
If you are using the correct/actual wheel measurement, the cycling computer (regardless of cost) will generally be more accurate than GPS.
The GPS isn't precise enough to measure all the "weaving" that you do. And it only works when it can get a signal. If you are moving in a straight line, signal loss won't matter but, if you are on a curve, the GPS will "cut the corner" and show a shorter distance than actual.