What's the difference between torque and horsepower?

The Relationship Between Torque and Horsepower

Torque and horsepower play an integral role in the automotive market. The numbers are emphasized as ways of illustrating what a car or truck can do. In reality, the numbers play a more complex role than most consumers realize. More importantly, how the numbers function in the real world of driving and hauling is defined by how a vehicle's design allows the two concepts to work together.

Remember, torque is the base number for work, and power is the rate of doing more work. The gear system, for instance, can affect how work within the engine occurs: A pickup truck can have a low gear to channel more amount of torque into a specific application, like towing very heavy loads. However, if the same gearing is used on Saturn SL1 versus a RAM 1500, the RAM will always be able to tow more because of the difference in horsepower produced. The more horsepower produced, the more torque potential there is from the engine.

But that's just what it is -- potential. Torque potential is translated to real-world applications through the vehicle's transmission and axles, specifically the axle differentials. The way these units are geared determines how the horsepower is translated to torque.

To understand this, think of the difference between a race car and a tractor. The race car develops an enormous amount of horsepower, but the torque is used for speed through gearing. There's not a lot of work needed, in a relative sense, to push a race car forward, so less work is accomplished, leaving more power for speed.

A tractor, on the other hand, may have the same size engine producing the same amount of horsepower. That horsepower is harnessed for doing work through gearing. The tractor can't reach high speeds, but it can pull and push huge amounts of weight.

Next time you see a vehicle advertised on television, think about what it means when they talk about horsepower and torque. There's a relationship between the two -- they can't exist without each other, but they stand for very different aspects of making a car or truck work.

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  • Chamberlin, Ken; Chrysler Master Technician; personal interview; Dec. 7, 2011
  • Halderman, James D., Chase D. Mitchell Jr.; "Automotive Engines: Theory and Servicing;" Pearson Prentice Hall, 2005; pgs. 55-58
  • Landry, Greg; Chrysler Engine Performance Specialist; personal interview; Dec. 7, 2011