<div class="section abstract"><div class="htmlview paragraph">Spherical involute surface topography for straight bevel gears including surface coordinates and normals are calculated. The significance of calculation of normal to the surface is mainly because it is needed for ease-off construction, tooth contact analysis and CMM measurement. The calculated surface and normals are then used to establish ease-off topography and the so-called surface of roll angle. The resultant surface of roll angle is used to allocate potential contact lines and contact ratio. The developed approach is applied to an example automotive differential straight bevel gear to calculate tooth surface, ease-off topography and surface of roll angle.</div></div>