Monday, January 15, 2018

What is Torque and How Is It Different from Horsepower?

Let us now talk about Torque, the single terminology that separates engineers and physicists from the rest of the human race. Some people have heard about it, others read about it, and the vast majority of people simply don’t care about it. To be fair, torque is not actually that important to the point where you have to actually choose between knowing what it is and dying. Spending money on books about torque and time to read them all will not give any considerable change to your life either. It is just like knowing that the Earth is round, rotating on an imaginary axis, and orbiting the solar system center mass; will knowing those facts change your life? It probably will not.

The principal of torque can be seen in various objects or activities in everyday situations such as opening a bottle cap, hinged doors, playing seesaws, wrenches, as well as bolts and nuts. Despite the common applications, it is highly unlikely that you are aware of it. No one counts how many pound-feet of torque are necessary to open a lemonade bottle or the basement doors. It also does not help that your plumber never explained to you about the torque he generated while he was in the toilet – to loosen the rusty bolt and nut form the drain pipe, of course.

Torque is most prominently used in automobile and associated with cars or vehicles in general, measured in either Nm (Newton meter) or lb-ft (pound feet). Among the common examples, the single biggest chance that torque is mentioned during a conversation between two people during lunch break is when they talk about cars. By the time one of them mentions it, they realize that they cannot afford the cars they talked about and so they go back to work. While torque is not as popular as horsepower or turbocharger and supercharger, it actually is one thing that makes them all work. You can think of horsepower as lamps, turbocharger as TV, and supercharger as a computer, but torque is the electricity puts them to function.

While all average car enthusiasts realize that torque and horsepower play major roles in determining performance, many (if not most) of them do not exactly how those things work. Some probably have good ideas in their heads, but they don’t know how to tell it properly; in other words, they just pretend to understand.


Simplest definition of torque is engine rotational force, which gives no comprehensible meaning to the average mind. Remember that any car starts the acceleration and reaches whatever top speed allowed by road signs from zero. Your car does not start at 60 miles per hour or any speed for that matter; it starts from zero, and this is what torque is for. The initial energy that moves your car forward originates from the engine combustion chamber; fuels and oxygen are delivered to the chamber where they collide and explode. Forces generated from the explosion move a group of pistons connected to the crankshaft. The rotating crankshaft is where torque develops. Once the crankshaft rotates, the energy is forwarded to multiple components including flywheel and transmission before it actually reaches the wheels.

What is Torque and How Is It Different from Horsepower
 If you look hard enough there is torque somewhere in there, maybe
Vehicle specification sheet often lists the maximum torque at certain engine revolution speed or RPM, for example your car has 250 pound feet of torque at between 2,000rpm and 5,000rpm. Besides the obvious possibility of poor performance, the stated number also indicates peak torque it can generate. In general, a car is more responsive when it can produce higher torque at lower rev range.

Remember that torque number simply tells you how much rotating force is at work inside the engine. Higher rotating force generally means faster acceleration, but it depends on how much the car weighs as well. You can also say that torque is the force required to move the entire car. Imagine a plumber’s wrench that clamps to a rusty toilet pipe; assuming the wrench is about 1.5 feet long and he needs to apply 100 pounds of torque to start loosening the pipe, the total amount of torque he generates is 150 pound-feet (100 pounds x 1.5 feet). Double the torque and the plumber probably will twist the rusty pipe as if it is nothing and burst some damp ugliness all of a sudden into the air. Apply that analogy to a car, and you get the idea of how torque works.


Another way to put it, torque is the potential energy of a car used for rotating the wheels – and potential is what it’s all about. Torque is the base number of work for moving the car, whereas horsepower is the rate at which the car is doing the work. Our understanding of horsepower is a little bit ancient. James Watt and Mathew Boulton standardized horsepower as the amount of power required to perform 33,000 foot-pounds (not to be confused with pound feet) of work in one minute in 1783.

  • Foot-pound (ft/lb): the traditional English unit of work indicating the amount of work possibly done by one pound of force for one foot distance.
  • Pound-feet (lb-ft): the traditional English unit of torque that indicates the tendency or potential energy of a force to generate rotation.

James Watt used an actual brewery horse to measure that. Now whether or not the fact that the horse was working in a brewery played a role in the number is anybody’s guess. Maybe a winery horse was more relaxed and therefore it generated less power, for example. Centuries later we still use the same equation to measure the horsepower of supercars.

What is Torque and How Is It Different from Horsepower
Use one more wrench and it is just going to be a waste of torque
If torque starts a car movement from a point of standstill, horsepower is what keeps it moving to maintain speed. You want torque to get the car start moving quickly such as in the start line of a race or more realistically in a parking lot because you don’t want to rev-up the engine only to move the car as far as 15 feet. On the other hand when the vehicle is going, you want low torque and more horsepower. Of course it is not that simple because you also have to calculate downforce, too. Lack of downforce and more torque leads to excessive wheel-spin which does not always translate to how fast the car is going. Sure the wheel is rotating unbelievably fast, but the wheels have to grab and stick to the road and generate traction for movement, so it helps if you are slightly overweight.