It is the force of rotating action about the crankshaft axis at any given instant of time. It is given by,
Where 'T' is the engine torque (nm), 'F' is the force applied to the crank and 'r' is the effective crank radius (m). As the value of 'r' varies during the power stroke the torque on the power stroke is continually varying. Moreover there is no torque delivered during the three idle strokes. Therefore the engine manufactures always quote the average value of torque throughout the engine cycle. Engine torque goes through the vehicle transmission system, to the road wheels and is responsible for rotation of the latter and hence for pulling of the vehicle.