A roller bearing defining a bearing axis and a radial plane oriented parallel with the bearing axis, the roller bearing comprising: an inner ring including an inner raceway and an inner flange extending from the inner raceway, the inner flange including an inner guide surface (48, 48'); and a plurality of rollers in rolling engagement with the inner raceway about the bearing axis, each roller including a first end surface in engagement with the inner guide surface (48, 48') of the inner flange as the plurality of rollers move relative to the inner ring; wherein the first end surfaces of each roller define a curvature (R rol2) such that a ratio of a first principal effective curvature radius (R x) in a plane perpendicular to the radial plane and a second principal effective curvature radius (R y) in the radial plane is no less than 3.0; wherein the first principal effective curvature radius (R x) at a contact area between the inner flange and the first end surfaces of the plurality of rollers is defined as: R x = D rol − 2 h cnt D inr + 2 h cnt 2 D rol + D inr sin ⁢ β and wherein D rol is the diameter of the plurality of rollers, h cnt is the height of contact between the plurality of rollers and the inner guide surface (48, 48') relative to the inner raceway, D inr is the diameter of the inner raceway, and β is the contact angle between a tangent line through a contact point (C p) between the first end surfaces of the plurality of rollers and the inner guide surface (48, 48') and a line perpendicular to the bearing axis; and wherein the second principal effective curvature radius (R y) is defined as: R y = R rib 2 ⋅ R rol 2 R rib 2 + R rol 2 and wherein R rib2 is a curvature radius of the inner guide surface (48, 48') within the radial plane, and R rol2 is a curvature radius of the first end surfaces of the plurality of rollers near the contact point (C p) within the radial plane. an inner ring including an inner raceway and an inner flange extending from the inner raceway, the inner flange including an inner guide surface (48, 48'); and a plurality of rollers in rolling engagement with the inner raceway about the bearing axis, each roller including a first end surface in engagement with the inner guide surface (48, 48') of the inner flange as the plurality of rollers move relative to the inner ring; wherein the first end surfaces of each roller define a curvature (R rol2) such that a ratio of a first principal effective curvature radius (R x) in a plane perpendicular to the radial plane and a second principal effective curvature radius (R y) in the radial plane is no less than 3.0; wherein the first principal effective curvature radius (R x) at a contact area between the inner flange and the first end surfaces of the plurality of rollers is defined as: R x = D rol − 2 h cnt D inr + 2 h cnt 2 D rol + D inr sin ⁢ β and wherein D rol is the diameter of the plurality of rollers, h cnt is the height of contact between the plurality of rollers and the inner guide surface (48, 48') relative to the inner raceway, D inr is the diameter of the inner raceway, and β is the contact angle between a tangent line through a contact point (C p) between the first end surfaces of the plurality of rollers and the inner guide surface (48, 48') and a line perpendicular to the bearing axis; and wherein the second principal effective curvature radius (R y) is defined as: R y = R rib 2 ⋅ R rol 2 R rib 2 + R rol 2 and wherein R rib2 is a curvature radius of the inner guide surface (48, 48') within the radial plane, and R rol2 is a curvature radius of the first end surfaces of the plurality of rollers near the contact point (C p) within the radial plane.