Wheel horsepower (WHP) is the amount of horsepower that a vehicle actually makes on the ground. It is measured at the wheels and refers to the actual power available for the acceleration of the car minus the power loss in the drivetrain and all types of parasitic losses including power draining by the alternator, fans, pumps, muffled exhaust, and some other accessories. In contrast, engine horsepower is the amount of power produced by the motor measured at its flywheel. This horsepower number is what car manufacturers will advertise that a vehicle has. The power made by the engine is influenced by the transmission, drivetrain, vehicle weight, tire and wheel size, gear, and other external variables such as weather, altitude, and what type of dyno the vehicle is on. All of these variables play a factor into the WHP number.