Originally Posted by
rsiesta
Since speed over time is what distance is I can see how this would make my route appear shorter then it really is, which is what I have
observed. Has anyone else experience this or have any suggestion on how to resolve it?
You don't say what the distance the GPS gives nor how you determined the distance was really 1 mile.
You are using a phone, which can do funny things with the GPS readings. Some of them use GPS locations directly. The iPhone may or may not use direct GPS locations. I use GPS on an iPhone (for other purposes) and it's accurate enough.
GPS devices determine location and time. They get total distance by adding the distances between each of the points (measured every second or so). They determine speed from the change in distance divided by the change in time.
At the speeds cyclists go at, GPS not very good for determining instantaneous speeds.
As long as the circumference is accurate, a wheel rotation counter is very accurate for distance and speed. GPS is still accurate for distance. The wheel sensor is better able to measure the extra distance of the bicycle moving back and forth. The wheel sensor takes (roughly) 3 measurements every second and the GPS is generally about 1 every second. GPS can have reception issues if one is in a "concrete canyon" or under heavy tree cover.
There is nothing about cul-de-sacs that would make GPS measurements less accurate.