A car speed governor, or speed limiter, is a device that sets and limits a car's top speed. When a car that is fitted with a speed governor reaches a preset top speed, the device begins to curtail combustion and limits the supply of fuel and air to the engine.
A speed governor helps to ensure vehicle stability and keep the speed of the car below the speed rating of the tires for safety purposes. Most cars sold in the United States are fitted with electronic speed governors. A governor has electronic sensors that determine how fast the car is moving and relays this information to the engine's computer, which controls all engine functions.