Difference between Power and Torque

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   One of the attached file shows a bike specification, in which you may see a red box marked under torque and power. Why Max power and Max torque has to be mentioned separately even though we know that power is dependent on torque? Here’s the answer:-



There has been a common formula that is used for finding power of engine:-
              Power = 2 x N x Ʈ /60000,
                                                  Where  Ʈ  = Torque produced (units in Nm), N= speed of the engine (units in rpm), Power produced (units in watts divide by 746 to get hp or ps)

      This relation holds well till the point of intersection of curves for torque and power, since until that point both torque and power kept on increasing together. After this point, the torque decreases but power keeps on increasing until a certain limit since power is also dependent on speed also and then power starts decreasing.

                                 

      Torque of the engine determines the load taking capacity of the engine and power determines the acceleration of the engine. The reason for the torque to increase and decrease after certain limit is that torque is the twisting moment or rotational force for the shaft to the flywheel (in this case). When it attains its max rotational force, it means engine is kept at maximum load, beyond which the engine will stop working. This is why the engine of bikes or cars moving at 3rd or 4th gear stops when it is riding uphill and it is always advised to drop the gear to 1st, due to which it can take maximum load.

      The speed of cars and bikes are varied by achieving variation in torque and power. For example, if we compare the sports car and truck, the sports car will be having lower torque and higher power compared to truck. Truck is built for taking heavy loads while sports car are built for achieving higher speeds. This can be properly explained by taking another example of bodybuilder and sprinter. When a bodybuilder is being told to run for 100m, he wouldn’t be able to achieve the speed of sprinter but if both are running 100m with 10kg weights, the cases may be different, which mainly depends on power and stamina.

      Finally, the parameters of power and torque are mainly specified for comparison of engines of any vehicle (not the vehicle by itself) based on speed and load carrying capacity.

  •       To increase load carrying capacity of any vehicle, the torque needs to be                       increased.

  •       To increase speed of a vehicle, the power needs to be increased.

     This case is common not only in vehicles but also in compressors or any machine run by engines.

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