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What Torque Really Is Explained

What you think you know about torque is wrong. And we’re here to fix it.

Everyone knows about horsepower, the archaic term referencing a horse to denote how much power a steam engine has. Replace “steam engine” with a gasoline (or nowadays, hybrid or all-electric) and replace “horse” with nothing and you’ve got a general idea of how powerful your engine is.

Torque is a little different. It still measures the output from the engine, but in a very specific, very scientific way.

Torque, according to Wikipedia, is “rotational force”. In mathematical terms, if it’s the force multiplied by the rotational distance. Torque, when applied to engines, measures the force applied to the crankshaft, which provides an output in lb-ft —pounds for the force, and ft for the radius of the crankshaft.

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But while a mathematical answer does a great job of telling us what torque is, it does a terrible job of telling us what torque does.

via greasengasoline.com

Torque is usually given at the same time as horsepower to describe the performance of the engine, and there’s an old proverb that tries to explain the difference: "Horsepower is how fast you hit the wall, torque is how far you drag the wall with you."

This proverb is wrong. Horsepower is a good measure of how fast you hit the wall, but torque is more like how much horsepower you have per turn of the crankshaft just before you hit the wall.

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To understand what torque does you have to understand the relationship between torque and horsepower. Horsepower is just torque multiplied by the engine RPM - the harder the engine is working along with more torque means you have more horsepower. But torque can be manipulated by gearing, so you can easily inflate or deflate the torque values depending on how the car is constructed.

A vehicle is usually geared in one of two ways: high torque at lower RPM, or high torque at higher RPM. Higher torque at lower RPM means you have a lot more horsepower at lower RPM, which makes it easier to tow things from a standstill. That’s usually how trucks are geared.

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High torque at higher RPM means more power while you’re already underway, which usually results in higher top speed. This is how sports cars are geared.

Complicating matters further is how manufacturers will only give you peak torque or horsepower, but those values actually change wildly over an engines RPM. Even worse, a CVT can change gearing continuously to ideally match the torque to RPM to create the most efficient power.

All this is to say that torque doesn’t really mean much until the torque number is particularly large on a pickup, in which case the torque value you see is peak torque and is usually at low RPMs, making it extremely good at towing. Otherwise, you see peak torque somewhere in the middle range of RPMs and doesn’t mean much.

If that didn’t make sense, check out this video from Engineering Explained. Jason Fenske does a pretty good job of explaining torque via the example of a Honda S2000 and Ford F250 Diesel.

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