a gear arrangement in which the axis of the drive pinion gear is located below the radial center line of the crown gear it drives. it’s often used in truck differential carrier gearing because its spiral bevel gear geometry allows the absorption of driving torque to be spread over a greater number of teeth, meaning that it is both tougher and quieter.
this occurs when differential action allows one drive wheel on a slippery surface to spin while the other remains stationary and receives no driving torque. On tandem drive trucks (because of the additional differential action between the drive axles) it is possible to turn a spinning wheel at 4x its normal speed. this can take out the inter-axle differential or carrier differential. it is a driver abuse failure of differential carriers.