Gross Torque Vs. Horsepower in a Lawn Mower

Lawnmower manufacturers traditionally explain the performance of their products through horsepower. However, in the 21st century, torque appears more and more commonly in place of horsepower ratings to describe lawnmower performance. This change occurred thanks to a lawsuit that alleged the falsification of horsepower ratings on the part of lawnmower manufacturers at the expense of consumers. Understanding the difference between these ratings requires an understanding of what they describe and how that relates to mowers.

Horsepower measures the power of engines on a scale based on the power of a horse. It was devised originally to describe the power of steam engines, and a single horsepower equals the amount of force required to perform 33,000 foot-pounds of work in one minute, as a strong horse can. In the 21st century, horsepower describes the amount of work an engine can do in terms of driving an object forward, from a lawnmower to an automobile.

Torque refers to power created by circular motion, described in foot-pounds. For instance, if you use a foot-long wrench for a job and apply 15 pounds of force to the wrench, you exert a torque of 15 foot-pounds. If you apply the same force to a two-foot-long wrench, you exert a total of 30 foot-pounds (15 pounds x 2 feet) of force. Gross torque describes the overall force generated by an engine as it rotates.

Gross torque and horsepower ultimately measure different things. Horsepower ratings describe the power of an engine, while gross torque ratings describe the force it creates. For instance, two engines with the same torque may operate at different speeds because they exert different levels of power, despite generating the same force. Two engines with the same horsepower, on the other hand, generate the exact same amount of power, but may exert different levels of force.

Horsepower ultimately measures how quickly an engine operates. A five-horsepower lawnmower, for instance, moves at higher speeds than a two-horsepower lawnmower. Torque, on the other hand, indicates the strength of a machine. A lawnmower with a torque rating of 10 foot-pounds ostensibly generates twice as much force as one with a torque rating of five foot-pounds, meaning the blades on the mower with more force, more effectively cutting grass. A lawnmower with high horsepower and torque ratings exhibits power and force.