GPS Recording Accuracy cycling/running

Question

Hi,
Have been having this issue with iPhone 5 where it doesn't seem to be recording cycling or running activities as accurately as my old iPhone 4 did (or even a Samsung android!) - I have tried using runkeeper and several other fitness tracking apps with same results.
The same route of roughly 6 miles will vary in recorded length by anything between 5.84 to 6.04 miles. My bike computer records this consistently at 5.91miles, but the iPhone seems to do what it likes!
Apple have already replaced the handset once after running through all the usual troubleshooting ideas (wi-fi on, location services etc), and this one is slightly better, but still far from perfect - or even consistent.
Any help or advice much appreciated.

Answer 1

As well as Aspergerguy's suggestion related to possible loss of signal there is the following.
The nav system can only work out distance travelled by periodically accepting a fix from the GPS and calculating the distance between each such fix and summing them. The frequency it does this will depend on both the frequency of position update in the GPS itself and of the nav application (in this case your sports application).
The more accurately the nav system does this the longer the distance travelled will become - for example, if you are going around a curve and imagine each of the periodic fixes used to measure the distance being dots on the curve and the distance measured between each pair of dots is a straight line, then the closer together the dots the longer the route will be measured as.
So, from that, my first inclination would be that all else being equal the nav system that measures the travelled route as being the longest is likely to be the most accurate one. It would also seem to me that loss of signal would also result in a shorter rather than longer route.
I would suggest that off an accurate topographic map select two points along a long straight road and measure the distance on the map and then travelling it with the phone and seeing what the nav system on the phone measures it at. If you are indeed a spud that is all at sea :-) then some main harbours have an accurate measured mile in them between shore beacons for setting up vessel's logs and so that could be used.