see guys, i think u all are mistaken. We dont consider in what direction the car is going, but in which direction the wheel is turning. for the car to go forwards, the wheel must roll clockwise. so for the car to go east, wheel must roll in the clockwise direction. Now consider a very small part of the wheel which is touching the ground. to wheel to roll in clockwise direction , that small part must slide backward, and that must continously happen in order for wheel to turn clockwise and car to go in east direction. And u know, friction is b/w the surface in contact, i.e the rolling part of the wheel, not with the car. so friction should oppose the backward-going part of the wheel, and thus in the ame direction with the motion of the car. if friction were to be in west, the car would never go in east direction, because the wheel would'nt have any force to oppose, to make it go in that direction, and thus the car would never be able to go towards the east direction!