* Speed of the car: A faster car will impart more energy to the rock.
* Size and weight of the rock: A larger, heavier rock will travel farther.
* Angle of impact: The angle at which the rock hits the tire or undercarriage affects its trajectory.
* Type of tire and road surface: The interaction between the tire, rock, and road influences the launch.
* The height the rock is thrown from: If the rock gets caught in the wheel well and thrown from higher up it could travel further than one simply bouncing off the tire.
A rock could be thrown a few feet, or, in extreme cases with a very large rock, a very fast car and the right conditions, potentially dozens of yards. However, this is highly unpredictable and dangerous. It's not something you should ever try to test.
