Originally Posted by
Athens80
Starting with the concept that average speed equals distance divided by time -- which of those two factors is different on the iPhone versus the Cateye? Does the Cateye show you've traveled a greater distance, or does it show you covered the same distance at greater speed (... or both)? Or, a related question, how different are the average speed reports? The Cateye would register small side to side (even slight weaving/wobbling) motions that would not register as forward motion on a GPS track, wouldn't it? Leading to the question ... what's the case that the iPhone GPS distance is more accurate than the Cateye distance, in terms of forward motion?
Actually the Cat Eye would the more accurate device for measuring the distance because every wiggle or swerve is real distance you have traveled. The GPS won't pick that up. While the difference will be small unless you are weaving all over the road, it is still distance you did travel. The Garmin Edge 500 can be set to auto stop the ride timer so it does not continue counting when you come to a stop so it won't be throwing your average speed off.