A tire comprising a tread portion provided with a plurality of circumferential grooves extending continuously in a tire circumferential direction, a plurality of lateral grooves extending in a tire axial direction, and a plurality of first blocks, wherein each of the first blocks is provide with at least one first sipe which extends zigzag in a cross section perpendicular to the length direction thereof, and extends zigzag in a cross section parallel with the ground contacting top surface of the first block, each of the first sipes is provided with at least one tie bar which is locally raised outward in a tire radial direction from the sipe bottom, and terminated without reaching the ground contacting top surface of the first block so that the first sipe is partially divided in the length direction of the sipe by the above-said at least one tie bar into at least a first portion and a second portion, in each of the first sipes, the sipe bottom of the first portion communicates with a first wide portion having a groove width larger than the sipe width of the first portion, and the sipe bottom of the second portion communicates with a second wide portion having a groove width larger than the sipe width of the second portion, the above-said first wide portion comprises, in its cross section, an outer portion in the tire radial direction formed by a pair of first arcuate groove wall portions each convex toward a center line of the first sipe so that the groove width continuously increases from the sipe bottom toward the inner side in the tire radial direction, and an inner portion in the tire radial direction formed by a pair of second arcuate groove wall portions each convex toward the opposite side to the center line of the first sipe so that the groove width continuously decreases inward in the tire radial direction to the bottom of the first wide portion, and the first wide portion and the second wide portion do not communicate with each other, characterized in that a curvature radius of the first arcuate groove wall portion is larger than a curvature radius of the second arcuate groove wall portion, wherein the curvature radius is not more than 5.0 times the curvature radius. a plurality of circumferential grooves extending continuously in a tire circumferential direction, a plurality of lateral grooves extending in a tire axial direction, and a plurality of first blocks, wherein each of the first blocks is provide with at least one first sipe which extends zigzag in a cross section perpendicular to the length direction thereof, and extends zigzag in a cross section parallel with the ground contacting top surface of the first block, each of the first sipes is provided with at least one tie bar which is locally raised outward in a tire radial direction from the sipe bottom, and terminated without reaching the ground contacting top surface of the first block so that the first sipe is partially divided in the length direction of the sipe by the above-said at least one tie bar into at least a first portion and a second portion, in each of the first sipes, the sipe bottom of the first portion communicates with a first wide portion having a groove width larger than the sipe width of the first portion, and the sipe bottom of the second portion communicates with a second wide portion having a groove width larger than the sipe width of the second portion, the above-said first wide portion comprises, in its cross section, each of the first blocks is provide with at least one first sipe which extends zigzag in a cross section perpendicular to the length direction thereof, and extends zigzag in a cross section parallel with the ground contacting top surface of the first block, each of the first sipes is provided with at least one tie bar which is locally raised outward in a tire radial direction from the sipe bottom, and terminated without reaching the ground contacting top surface of the first block so that the first sipe is partially divided in the length direction of the sipe by the above-said at least one tie bar into at least a first portion and a second portion, in each of the first sipes, the sipe bottom of the first portion communicates with a first wide portion having a groove width larger than the sipe width of the first portion, and the sipe bottom of the second portion communicates with a second wide portion having a groove width larger than the sipe width of the second portion, the above-said first wide portion comprises, in its cross section, an outer portion in the tire radial direction formed by a pair of first arcuate groove wall portions each convex toward a center line of the first sipe so that the groove width continuously increases from the sipe bottom toward the inner side in the tire radial direction, and an inner portion in the tire radial direction formed by a pair of second arcuate groove wall portions each convex toward the opposite side to the center line of the first sipe so that the groove width continuously decreases inward in the tire radial direction to the bottom of the first wide portion, and the first wide portion and the second wide portion do not communicate with each other, characterized in that a curvature radius of the first arcuate groove wall portion is larger than a curvature radius of the second arcuate groove wall portion, wherein the curvature radius is not more than 5.0 times the curvature radius.