A heavy duty pneumatic tire comprising: a tread portion comprising a central region (Cr) having a 10% width of a tread width (TW) centered on a tire equator (C), the central region (Cr) being provided with at least one circumferentially and continuously extending zigzag central main groove having 40 to 50 zigzag pitches; the at least one central main groove comprising a bottom and a pair of groove walls ; each groove wall comprising a bottom side steep sloped portion and a top side gentle sloped portion ; the steep sloped portion comprising a height (Hs) of from 10% to 35% of a groove depth (D1) of the central main groove from the bottom and an angle (α1) of from 0 to 10 degrees with respect to a tire normal line of a tread ground-contact surface ; the gentle sloped portion extending from the steep sloped portion toward the tread ground-contact surface with an angle (α2) greater than that of the steep sloped portion ; the central main groove having a groove width (Ws) of from 4.0 to 12.0 mm measured between top edges of the steep sloped portions ; and each groove wall comprising internal corners protruding toward a groove centerline of the central main groove and external corners protruding in an opposite direction to the centerline , the angle of the gentle sloped portions decreasing in a range of from 15 to 25 degrees from the internal corners toward the external corners , wherein the difference between a maximum angle (α2a, α2c) of one of the internal corners and the minimum angle (α2b, α2d) of one of the external corners is in a range of from 15 to 25 degrees, and wherein the maximum angle (α2a, α2c) of said internal corner is greater than or equal to 15 degrees and less than or equal to 35 degrees, characterized in that the minimum angle (α2b, α2d) of said external corner is greater than or equal to 1 degree and less than or equal to 10 degrees. a tread portion comprising a central region (Cr) having a 10% width of a tread width (TW) centered on a tire equator (C), the central region (Cr) being provided with at least one circumferentially and continuously extending zigzag central main groove having 40 to 50 zigzag pitches; the at least one central main groove comprising a bottom and a pair of groove walls ; each groove wall comprising a bottom side steep sloped portion and a top side gentle sloped portion ; the steep sloped portion comprising a height (Hs) of from 10% to 35% of a groove depth (D1) of the central main groove from the bottom and an angle (α1) of from 0 to 10 degrees with respect to a tire normal line of a tread ground-contact surface ; the gentle sloped portion extending from the steep sloped portion toward the tread ground-contact surface with an angle (α2) greater than that of the steep sloped portion ; the central main groove having a groove width (Ws) of from 4.0 to 12.0 mm measured between top edges of the steep sloped portions ; and each groove wall comprising internal corners protruding toward a groove centerline of the central main groove and external corners protruding in an opposite direction to the centerline , the angle of the gentle sloped portions decreasing in a range of from 15 to 25 degrees from the internal corners toward the external corners , wherein the difference between a maximum angle (α2a, α2c) of one of the internal corners and the minimum angle (α2b, α2d) of one of the external corners is in a range of from 15 to 25 degrees, and wherein the maximum angle (α2a, α2c) of said internal corner is greater than or equal to 15 degrees and less than or equal to 35 degrees, characterized in that the minimum angle (α2b, α2d) of said external corner is greater than or equal to 1 degree and less than or equal to 10 degrees. <EOS>