According to the British Columbia Driving Commercial Vehicles Manual, torque is the ability of the engine to move the vehicle, and horsepower is used to develop speed. At any given speed, the engine develops both torque and horsepower. Peak torque is found at a lower engine speed than peak horsepower. The vehicle should be operated between the engine’s peak torque and peak horsepower. This range is referred to as the normal operating rpm range of the engine.