If you are in the market to buy a new car, it is imperative to realize both torque and horsepower are playing a big role in your new car’s performance. Most car deals you see advertise the impressive amount of horsepower the engine provides, but tend to ignore torque. It seems, as usual, the bigger the numbers, the better, but be warned that having too much of either can be a bad thing.
Don’t always look for the highest numbers in the specs, but work backwards after figuring out your needs as a new driver, as simply having a high horsepower is not the key to good performance. So, what do all these numbers mean, and how are the two concepts related? Let’s find out.
What You Need to Know About Horsepower
In mathematical terms, horsepower is a measurement for power, abbreviated as “hp.” James Watt invented this unit after observing that a horse could lift at a rate of about 550 foot-pounds per second for about an 8-hour shift. From this definition you can see that the components of horsepower are force, distance and time. Distance and time are self-explanatory, but force, specifically a twisting force, is where torque comes into the picture.
In essence, many vehicles are designed to have higher horsepower, but depending on the torque, you may not be able to take advantage of the added horsepower until you are at a very high RPM. Hence, you can have a very powerful engine on your new car, but it could take a long time to rev up to that horsepower.
What You Need to Know About Torque
Torque is the twisting, rotational force generated by an engine; this force is transferred through the drive system into the wheels. Torque is what pushes you back in the seat when you step on the accelerator. It is simply a measurement of twisting or rotational force. The easiest way to think of this is to imagine a long shaft suspended in midair, such as a car’s axle. Hanging on the bottom of one end is a rope with a significantly heavy weight attached to it.
Now imagine someone trying to twist the shaft using their hands so as to lift the weight. Think of them as essentially trying to act like a wrench. The amount of force they are able to generate to lift the weight in this manner is the torque that they’re able to produce. A common unit for measurement of torque is the foot-pound. As the name suggests, a foot-pound is the rotational force generated by hanging a one-pound weight at the end of a 1-foot wrench.
The Relationship Between Torque and Horsepower
The mistake most people make when debating this topic is considering horsepower and torque independently. Almost everyone argues as if they are separate, unrelated values when in fact they are intricately related. Horsepower is determined from torque because torque is easier to measure. In a vehicle, torque is measured at various engine speeds, or revolutions per minute (RPM). These two numbers are fed into a formula:
Horsepower = (Torque x RPM) / 5,252
In other words, at 5,252 RPM, your car’s engine will have the exact same horsepower and torque.
To better see how torque and horsepower interact, imagine a 2014 Ram 1500 truck at the base of a steep hill. As the driver begins to press on the throttle, the engine’s RPM increases, resulting in a force being transmitted from the crankshaft to each wheel, and the Ram 1500 begins to climb upward. The twisting force going to each wheel as the vehicle moves up the hill is torque. Let’s say the engine is at 4,000 rpm, the gear ratio is four, and the vehicle is creating 200 pound-feet of torque. Using the following formula, we can calculate horsepower:
Take the torque of 200 multiplied by a shaft speed of 1,000 (4,000 rpm divided by a gear ratio of four) for a total of 200,000. Divide 200,000 by 5,252 and you get 38.1 horsepower, which is what the engine is producing as the truck ascends up the hill.
The Key Differences Between Torque and Horsepower
To simplify things, think of torque as responsible for acceleration and horsepower for top speed. Torque is the measured power or output of an engine, horsepower is a number obtained through a calculation based on the torque, as seen in the formula above. Torque is what gets you to the speed you want quickly; horsepower is what keeps you there.
An engine might have plenty of horsepower, but hardly any torque. Think of a ship’s engine: it has the strength to move thousands of tons of steel, but it takes a very long time to get up to speed. In other words, it has very little torque. On the other extreme, a car can have so much torque that its tires are unable to get a grip, simply spinning in place.
Next time you take a car for a test drive, think about what it means when they talk about horsepower and torque. There’s a relationship between the two. They can’t exist without each other, but they stand for very different performance aspects.
