Same suburban loop four times a week, half of it under mature trees and one section between two blocks of flats. The watch has read anywhere from 5.18 to 5.42km on that loop this month and my paces look better than they are. I care because I am pacing a half marathon off these numbers in September. Is there a way to find out which is lying before race day?
The mapping tool is not automatically the honest one either. If you drew the route by clicking along the centre of the path, you measured a line nobody runs, and every corner you cut or curve you swing wide on is real distance the map never counted. Two of my local loops measure short on the map for that reason alone.
Also worth saying that a certified race course is measured along the shortest legal line, so on race day everyone runs at least that far and most of us run more. My watch has read long on every half I have done, sometimes by 200m.
Stop pacing off distance and pace off effort and time. For the September race, run your long efforts by feel and heart rate, then on race day use the kilometre markers on the course rather than the watch buzzing at its own idea of a kilometre. Every runner I know who blew up in a half did it chasing a watch that was quietly 3 percent optimistic.
Go to a running track and do four laps in lane one, which is 1600m, then look at what the watch says. That is the only cheap ground truth you will get, and it takes twelve minutes. If it reads 1.63 there, your loop is fine and the map is what is wrong.
Three percent in clean sky is more than drift, that is the watch smoothing your arm swing into extra distance. Wear it slightly tighter and a centimetre further up the wrist and retest, it moved mine by about half of that.
Did this on Saturday. Four laps read 1.66km, so the watch is running about 3 percent long even in the open.
Turn off any wrist-based distance calibration that has learned from months of bad data, then rebuild it with two or three runs in clear sky. On most watches that is a reset buried in the phone app rather than on the watch itself. Mine was consistently long until I wiped that history.
@two_hills_up · 3w ago
Trees and tall buildings are exactly where satellite positions get noisy, and the watch fills the gaps by guessing, and its guesses are almost always long rather than short. The variation you are seeing across the same loop, roughly a quarter of a kilometre spread, is completely normal for that environment. What is not normal is trusting it for pacing.
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