If you look at a tire from the rear, you'll notice that the tire isn't quite a cylinder. It has edges that are slightly beveled. Sometimes this effect is clearly apparent, but other times, as in many car tires, it's hard to see.
I can understand the use on motorcycles, since they are typically angled on turns, but cars are, in general, not designed to take corners on two wheels.
Why do cars have beveled tires?