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Shifting Gears

What does horsepower really mean? (VIDEO)

by Andy Greaser | Dec 17, 2024

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Horsepower is a strange measurement, isn’t it? Think about it. When was the last time you used a horse for any kind of work or travel?

Like candlepower, the original horsepower attempted to express the output of a newer technology in comparison to its predecessor. Today, horsepower is one of the most common metrics we use to quantify vehicle performance, yet most of us in the auto repair industry have no experience with real horses at all. And even if we did, how would we meaningfully measure the work potential of a horse? How might that measurement of power translate to mechanical devices?

Thankfully, a clever guy named James Watt did the math for us over 240 years ago while developing steam engines that would kickstart the Industrial Revolution. This old Chevrolet video from 1937 does a fine job of explaining Watt’s journey to the earliest version of the horsepower measurement we know today. (The informational part of this video starts about two minutes in.)

Later advancements in power measurement made Watt’s horsepower obsolete with new variations like metric horsepower and imperial (mechanical) horsepower, but it is fitting that the International System of Units (SI) uses the watt as its standard for the same type of power measurement today.

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