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 ; 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 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 relative to the inner raceway , D inr is the diameter of the inner raceway , and β is the contact angle between a tangent line (T) through a contact point (C p ) between the first end surfaces of the plurality of rollers and the inner guide surface 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 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 ; 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 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 relative to the inner raceway , D inr is the diameter of the inner raceway , and β is the contact angle between a tangent line (T) through a contact point (C p ) between the first end surfaces of the plurality of rollers and the inner guide surface 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 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 . <EOS>