A trailing shoe in a drum brake is pivoted at the end of the shoe facing in the same direction as the rotation of the drum. So on the right-hand side of a car travelling forwards, a shoe facing the front of the car would be trailing if it was pivoted at the top.
A trailing shoe is constantly being forced away from the drum and so offers considerably less braking force than a leading shoe.
A trailing shoe becomes a leading shoe when travelling in reverse.
