Originally Posted by e(ho0n3
Have you ever seen a drag race? When the light turns green and the drag racer accelerates, you can see that the wheels aquire an elliptical shape. But I guess this occurs because the wheels are slipping.
Ah... now I think I see what you are talking about. For the car to accelerate, frictional force must be exerted on the tire (and, vice versa, on the road). There is no way to do this without some distortion of the tire. (Good observation.)
But I don't think that has anything to do with the picture in your book, which I'm sure just shows a wheel rolling without slipping. Once it's up to speed, no further frictional force is needed (ideal case, of course). The top is probably blurred just to give you the feel that it's moving with respect to the ground (and the observer), while the bottom is unblurred because it's not moving. Makes sense to me.