Tread (2) of a radial tire for a heavy vehicle. The tire alternatingly rolls in laden and unladen states on ascent and descent, respectively. Tread (2) has total width WT and comprises first median portion (21) having median width Wc, where 0.2WT≤Wc≤0.5WT. Tread (2) axially delimited by second and third lateral portions (22, 23) that have respective lateral widths (WS2, WS3) at least equal to 25% and at most equal to 40% of total width WT. Angle A51 of leading face (51) of every element in relief (31) of first median portion (21) is strictly less than angle A61 of trailing face (61) of said element in relief (31). Angle (A52, A53) of leading face (52, 53) of every element in relief (32, 33) of each of second and third lateral portions (22, 23) is strictly greater than angle (A62, A63) of trailing face (62, 63) of said element in relief (32, 33).