Tuesday, September 22, 2015

Horsepower Versus Torque: What’s the Difference?

Jaguar F-Type R Coupe. Image courtesy of Jaguar Land Rover.
Unless you are a big car enthusiast or an engineer, you likely have no idea what the difference is between a vehicle’s horsepower and torque ratings. Sure, you see them listed all the time with a car’s specifications, and you know bigger numbers are better, but just what is the difference between the two ratings?

A simple explanation is that horsepower measures the amount of power produced by your engine, while torque measures the amount of twisting force produced by the engine. Torque is the feeling of power when a car first launches off the line, which is what most buyers think of when they wonder how powerful a car is. In contrast, horsepower is the ability of the car to sustain that initial surge of power. People think they are buying horsepower, when in fact the torque is what they are feeling.

To be more precise, horsepower is a measurement of the engine’s ability to move a certain amount of mass. Specifically, one unit of horsepower represents the force needed to move 550 pounds a distance of one foot in one second, or 33,000 pounds the same distance in a minute’s time.

Torque is produced by the engine, transferred to a fly wheel which in turn transfers that twisting power to the transmission. The transmission in turn transfers that power to the drive shaft and then the axle, allowing the car’s wheels to turn.

When buying a vehicle to tow anything, whether it’s a boat or another vehicle that is stuck in the snow, the important figure to pay attention to is the engine’s peak torque output.  A high torque output at a low RPM provides plenty of pulling power when the vehicle first starts rolling forward.

In city driving, most people drive on torque since there is a lot of stop-and-go traffic. On the highway horsepower becomes much more important, since your car’s engine needs to ability to sustain the speed at which you are traveling. 

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