Inside bias is a form of track bias where horses racing on or near the rail (inside paths) are consistently running overfaster or more efficient part of the surface than horses in the middle or outside lanes, so inside trips and inside posts are advantaged beyond what you'd expect from the normal ground‑saving effect. In practice, you see inside paths winning disproportionately, while horses forced to race wide underperform relative to their apparent ability.

Synonyms:
rail bias, golden rail, gold rail, live rail, live inside, good rail