What is Torque?
Horsepower. Torque. Pound-feet. Foot-pounds. Lb-ft. Your car or truck‘s maintenance specifications are full of confusing jargon. But understanding torque is key to understanding engine output and the capabilities of your car or truck. Luckily, torque and the lb-ft label are relatively simple to understand. So here is my twist on torque.
What is torque?
Torque is a measure of rotational/twisting force. You can also think of it as leverage. Imagine the amount of force you must exert on the lid of a sealed pickle jar to pop it open. That amount could be measured as torque–according to J.D. Power.
You can increase the amount of twisting force you exert by increasing the length of the lever you use to twist. It’s easier to break a rusty bolt free with a long wrench than with a short wrench. The long wrench gives you more torque.
Why is this? Because the long wrench twists the bolt more slowly: As you must move the end of the wrench twice as far, you exert twice as much energy on that rusty bolt. This is principal is also known as leverage.
You can also think of leverage like turning a small circle with a large circle. You are acting on the large circle–the end of that long wrench. But you are impacting a much smaller circle–the bolt at the other end of that wrench. Therefore, you double your impact.
If this large circle/small circle metaphor sounds familiar, it is probably because gears work in the exact same way. The various gears in a bicycle–or a transmission–use the same principle of leverage as that long wrench.
What is lb-ft?
The label pound-feet, also often abbreviated to lb-ft, is a measurement of torque. It includes a distance and a force because it is essentially a measurement of leverage. One lb-ft is one pound of force amplified through one foot of leverage.
When an engine’s output is described in torque, it means the amount of energy it can exert a certain distance away from its crankshaft. This is why we always see torque written as both an amount of force and a measure of distance. In the U.S., torque is usually written as pound-feet (or lb-ft). This is a measurement of force over a given distance.
Journalists and advertisers in the automotive industry almost always use the lb-ft interchangeably with foot-pound (ft-lb)–according to Donut Media on Youtube. But physicists do differentiate between the two. In fact, my colleagues explained that a ft-lb is technically the amount of force it will take to move a one-pound object one foot in this extended torque explainer article. But if you are reading or talking about cars, you don’t have to differentiate between the two measurements.
You can see torque demonstrated for yourself in the video below:
What is the difference between torque and horsepower?
Torque and horsepower are both measurements of force. But while torque measures force over distance, horsepower measures force over time–or how quickly an engine can create force. One ft-lb of torque is a pound of force amplified by a foot of leverage, and one horsepower is torque over time.
Torque is a useful unit for measuring engine performance because engines create rotational force. A car or truck with a longer stroke (piston travel) will make more leverage at its crankshaft. Likewise, a vehicle with more displacement in its engine cylinders will make more torque. This torque allows the vehicle to accelerate more quickly, even while pulling a heavy load.
To calculate horsepower, on the other hand, you need to factor in the speed at which an engine is turning. Therefore, you measure an engine’s torque and how many revolutions it is completing every minute (RPM). Then you multiply the torque by the RPM. This formula gives you torque over time–but not horsepower.
Our modern measure of horsepower is actually based on an old measurement: the force it supposedly took one work pony to lift 330 pounds of coal 100 feet up a mineshaft in exactly one minute. Obviously, this number was more important to people back in the 1700s, and simply acts as an agreed-upon constant today.
So to get horsepower, you take the result of Torque times RPM and divide it by 5,252. That’s because it would have taken that old work pony 52.52 revolutions of a pulley to drag that bucket of coal out of the mine in one minute. As a result, one lb-ft of torque at 5,252 RPM is exactly one horsepower.
Is the number 5,252 intrinsically important? Not really. All that truly matters is that every automaker uses this same constant. Then, we can agree to all label the result “horsepower.”
What does horsepower tell us? How quickly an engine can do work. An engine with a higher redline is going to make more peak horsepower. The RPM at which it reaches peak horsepower is the sweet spot for acceleration.
Horsepower is a very important number for calculating how a vehicle will perform. While torque tells us how hard an engine will pull from a standstill, horsepower better indicates how fast an engine could accelerate from, say, 50 MPH to 150 MPH.
Next, find out why diesel engines make more torque or learn more about the difference between horsepower and torque in the video below: