A spherical plain bearing, said bearing comprising: an outer ring having a first peripheral edge, an opposing second peripheral edge, and a spherical concave bearing surface extending between said first peripheral edge and said second peripheral edge; an inner ring having a bore located therein and a spherical convex bearing surface, said spherical convex bearing surface being located in interfacial sliding engagement with said spherical concave bearing surface; a lubrication groove (225b, 225a, 230) in at least one of the spherical convex bearing surface and the spherical concave bearing surface, the lubrication groove (225b, 225a, 230) comprising a contoured shape defined by a concave central portion conforming substantially to a circular arc defined by a first radius of curvature a first center point of which is on a line that is perpendicular to at least one of the spherical convex bearing surface and the spherical concave bearing surface, the center point being offset from at least one of the spherical convex bearing surface and the spherical concave bearing surface, the lubrication groove (225b, 225a, 230) being further defined by convex side portions (RS 1, RS 2) conforming substantially to circular arcs defined by a second radius of curvature (R 1 and R 2) with second center points (PS 1 and PS 2) on lines (LW 1 and LW 2) that extend perpendicular to at least one of the spherical convex bearing surface and the spherical concave bearing surface, the concave central portion having the first radius of curvature and the convex side portions having the second radius of curvature (R 1 and R 2), characterized in that the second radius of curvature (R 1 and R 2) is at least 0.7 times the first radius of curvature; and wherein the lubrication groove (225b, 225a, 230) allows for periodic flushing of a lubricant when additional lubricant is introduced into the lubrication groove (225b, 225a, 230) under pressure. an outer ring having a first peripheral edge, an opposing second peripheral edge, and a spherical concave bearing surface extending between said first peripheral edge and said second peripheral edge; an inner ring having a bore located therein and a spherical convex bearing surface, said spherical convex bearing surface being located in interfacial sliding engagement with said spherical concave bearing surface; a lubrication groove (225b, 225a, 230) in at least one of the spherical convex bearing surface and the spherical concave bearing surface, the lubrication groove (225b, 225a, 230) comprising a contoured shape defined by a concave central portion conforming substantially to a circular arc defined by a first radius of curvature a first center point of which is on a line that is perpendicular to at least one of the spherical convex bearing surface and the spherical concave bearing surface, the center point being offset from at least one of the spherical convex bearing surface and the spherical concave bearing surface, the lubrication groove (225b, 225a, 230) being further defined by convex side portions (RS 1, RS 2) conforming substantially to circular arcs defined by a second radius of curvature (R 1 and R 2) with second center points (PS 1 and PS 2) on lines (LW 1 and LW 2) that extend perpendicular to at least one of the spherical convex bearing surface and the spherical concave bearing surface, the concave central portion having the first radius of curvature and the convex side portions having the second radius of curvature (R 1 and R 2), characterized in that the second radius of curvature (R 1 and R 2) is at least 0.7 times the first radius of curvature; and wherein the lubrication groove (225b, 225a, 230) allows for periodic flushing of a lubricant when additional lubricant is introduced into the lubrication groove (225b, 225a, 230) under pressure.