Why does the Garmin GPS show a longer distance than the actual course distance of the last race I ran? There are two possible explanations, but likely only one is most likely the case. The first is, due to a race-day placement issue – a cone, turn or otherwise – was incorrectly executed. But the second and more likely explanation is that you ran longer than the official course distance.

Let’s look at a simple two-turn case. In the below scenario, the actual course distance is officially measured 30cm (11.8110236 inches) from the curb. The total course should also have a .1% error factor (added to it to ensure it’s never short).

Now imagine the typical case where a few thousand (or tens of thousands) of runners are running the course, where will you likely end up running? Probably the red line instead of the tangent (black line). Weaving and swerving around runners.

So how much extra does this one measly turn add? This weaving and swerving can add 100’ or more to your run. Multiply this by 10, 20 or 50 turns… hmm.

So, the point being if you are off by a little bit, it’s probably not because the course is mis-measured, it’s more than likely you simply ran a little bit extra. NEXT TIME RUN THE TANGENTS.