What is the difference between power and torque?

What is the difference between power and torque? Which one makes your car accelerate quicker?

Stephen Scott (Dublin)

May 2010 Filed under: science

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Expert answer

Hi Scott,

There is no easy answer to that one! Power and torque are directly linked. Power is the rate at which work is done, where the work is the torque figure.

Think of torque as 'twist' (the tendency of a given force to rotate an object about its axis in school book terms) and it begins to make a little more sense. The force in this case is that exerted on the car's pistons. This is created by the explosion of air and fuel, which increases the pressure in the cylinder. The pistons then move down and turn the crankshaft, which transfers drive to whatever transmission is fitted and eventually the wheels.

So basically it's the torque that causes acceleration.

Many people simplify all this to say that the maximum power figure has a bearing on the car's top speed, while the torque figure is a better representation of its acceleration.

Just to confuse things, there are loads of different units for power and torque in use. These include:

Power: bhp, hp, PS, kW

Torque: Nm, lb.ft

Hope that helps!

Shane O' Donoghue - Complete Car Adviser
@Shane_O_D