Use a board to build a ramp that is about 1.5m long, and set it at an angle of 30 degrees to the floor, with a clear, bare floor in front of it for the cars to run on. Mark a finishing line across the floor approximately 3m in front of the bottom of the ramp. Measure the exact distance between the top of the ramp and the finishing line.
To race a car, place it at the top of the ramp, and then let it go. Use a stop watch to record the start time, and the finish time, when the back of the car crosses the finishing line.