Originally Posted by
Papa Zook
Trikes are not posi-traction, which is pretty much used only in race cars or mud trucks. Cars and trikes both use what is called an open differential, meaning that both wheels get the same amount of torque. The open differential allows each wheel to rotate at different speeds because in turns it allows each wheel to turn freely.
Going straight, both wheels move at the same speed, but in turns, the outer wheel is always turning faster than the inner wheel, if not it would want to bind and hinder turning. The reason it sometime seems that only one wheel is turning on open differentials, is that if either tire loses traction, that wheel is getting all the torgue and will spin faster when it breaks loose. Think path of least resistance.
Here is an oldie but a goodie video showing how differentials work.