[suicideneil]

Simplest way to explain is a demonstration- grab a wheel, then hit the throttle; the opposite wheel will spin twice as fast as it 'unloads' (same theory with a center diff). Its all to do with the internal gearing of a diff and its design to split power/ allow one wheel to turn faster or slower when turning a corner. Thicker diff fluid will tame then effect, which can help or hinder steering performance depending on the track etc.