The big difference between circuit racing and rallying on tarmac, as that the circuit racer knows the track intimately, where as the rally driver doesn't. Apparently having the car sideways makes it easier to adjust the car mid corner. Also I remember hearing about the optimum slip angle. If the car starts sliding greater than this, then you start to wash off speed. If you look at F1 prior to wings, they basically four wheel drifted around every corner, as it was the fastest way to drive those cars. Mind you, they didn't quite have the same amount of grip that cars do these days.

