When it is necessary to transmit quietly and smoothly a
large torque through a right angle at high velocities, spiral bevel gears can be
used. Spiral bevel gears have teeth cut in a helix spiral form on the surface of
a cone. They are quieter running than straight bevel gears and have a longer
life. Spiral bevel gears are used in motorcar rear axle gearboxes. An example of
spiral bevel gears are shown below.