What happens when a car or truck tires hits a rock on the highway? When the rock impacts the road, it is the tire that is accelerated, and it travels against the traffic. If a car or truck does not accelerate, the tire will not exert enough force to fling the rock. The rock may have a high velocity and may hit the windshield of a car behind it, but the car does not accelerate to that speed.
A truck with large wheels has large wheels, and they have to install mud flaps. But mud flaps are not always effective at stopping rocks, so be wary of trucks with worn mud flaps. Even a brand-new mud flap cannot guarantee that it will stop every rock that lands on the road. Moreover, if a rock is thrown from the truck, it can still hit cars in the opposite lane.