The word for the gain in a race acquired by taking the inside track
Solution 1:
Chris had to over come the inside advantage gained by Sara as he passed her on the turn.
Solution 2:
I might go with "geodesic gain" where geodesic means "of, relating to, or denoting the shortest possible line between two points on a sphere or other curved surface" (here)
- "Chris had to overcome the geodesic gain accrued by Sara on the turn."