Most commercials you’ll see online or on TV for trucks show a large and powerful truck hauling some even bigger over rough terrain. They boast about the impressive amount of torque and horsepower the truck has and how it can tow a house if that’s what you need it to do. Of course, when it comes to the numbers, bigger is always better. What do those numbers mean, though? What’s the difference between horsepower and torque?
What is Horsepower?
Simply put, horsepower is the amount of power an engine produces. One horsepower is the power needed to move 550 lbs. one foot in one second, or it’s the power needed to move 33,000 lbs. one foot in one minute.
In physics, power is the rate of doing work. The horsepower an engine produces is measurable using a dynamometer. A dynamometer puts a load on the engine, usually in the form of brakes preventing the wheels from turning and measures the twisting force the engine crankshaft puts against the load.
There are two recognized standards for determining horsepower: net and gross. Gross horsepower removes most loads from the engine before testing, including emission controls. Net horsepower is found by testing a stock vehicle, like what you'd find in a showroom. But ultimately, what the dynamometer is really measures is torque.
What is Torque?
Torque is a rotating force that may or may not result in motion. In practical applications, torque is the amount of force multiplied by the length of the lever from which it acts; T= r x F. If you use a one-foot long wrench to apply 10 lbs. of force to a bolt, you’re making 1-pound feet of torque. In any vehicle, torque is measured at various engine speeds or revolutions per minute (RPMs). The RPMs are recorded and used in the formula to calculate torque.
As mentioned, torque is creatable without moving an object. However, when torque does move an object, it then becomes work. That is what most people think of when thinking about torque—work. The more torque an engine has, the greater its potential for work.
What’s the Difference?
Horsepower and torque are closely related when discussing engines. Because it’s easier to calculate, torque is used to figure the horsepower of an engine. Horsepower = (RPM) x T / 5252. Torque is the base number for doing work, the potential amount of work, and horsepower is the rate of doing that work.
For example, a race car and tractor may have the same size engine and produce the same horsepower. In the racecar, the torque is for reaching top speed through gearing; there’s not a lot of work needed to push the car, so less work is accomplished, leaving more power for speed.
But in the tractor, that horsepower is for doing work through the gearing. It can’t reach high speeds, but it can push and pull massive amounts of weight. Torque and horsepower can’t exist without each other, but they stand for different aspects of making a truck work.