Anyone who has bought a car or seen adverts should have heard the terms horsepower and torque. They are mentioned in almost every advertisement especially when bigger cars are involved like bakkies, SUVs, vans and trucks. The adverts always talk about the impressive horsepower and torque but what exactly does that mean? What is the difference between horsepower and torque?
Put simply, the power that an engine produces is called horsepower which is defined as “the rate of doing work”. Digging a little deeper into mathematical terms – one horsepower is the required power to move 250 kg (550 lbs) one foot in one second or to move 15 000 kg (33 000 lbs) one foot in one minute.
Torque is a rotating force produced by an engine’s crankshaft and more torque results in a greater ability to perform work. Torque is the equivalent of linear force and can be defined as “the rate of change of angular momentum of an object”. It is the twisting force that may or may not result in rotation.
How Do You Measure Horsepower?
A vehicle’s engine horsepower is measured with a dynamometer which places a load on the engine and measures the twisting force of the engine crankshaft against the load. What this really means is that the dynamometer is measuring the torque output of the engine. Torque is measured at various engine speeds or RPM (revolutions per minute). Horsepower is measured by entering the above-mentioned two numbers into a formula which is ‘torque times RPM divided by 5,252’.
The two standards for determining horsepower, according to the Society of Automotive Engineers, are net and gross. With gross horsepower, they remove most loads from the engine before testing, including emission controls. Net horsepower, on the other hand, is what you would find by testing the same type of vehicle on a showroom floor. It is also the figure used in all manufacturer advertising and literature.
How To Measure Torque
The formula for torque involves measuring the lever arm at a perpendicular distance from the axis of rotation to the line of the force (rotational inertia x rotational acceleration). For example, if you use a two-foot-long wrench and apply 20 pounds of force to a lug, you are essentially generating 40 pound-feet of torque.
As mentioned earlier, torque can also be generated without moving an object but as soon as it does, it becomes “work”. Many people would refer to this is as the towing ability and the more torque a car produces, the more potential it has.
The Vital Connection Between Horsepower And Torque
While horsepower and torque both impact a vehicle’s speed, there are differences which also involve vehicle design and purpose. It goes without saying that torque and horsepower both play an essential role in the automotive market. Remember, the more horsepower the engine produces, the more torque-potential it has to offer.
Considering that torque is the base number for “work” and power is the rate of doing more work more effectively, gear systems can affect how well the engine performs. The way we translate the “potential” torque of a vehicle into real-world applications is through the axle differentials and transmissions.
A simple way to explain this is by comparing the numbers between a performance car and a delivery truck. The performance car may have loads of horsepower but the torque is used for speed through gear changes. Considering it doesn’t require too much “work” to push a fast car faster, more of the power is used for speed.
The truck may have a similar engine size producing the same horsepower which is also used for doing work through gearing. However, while the truck can still reach decent speeds, it is not designed or built for performance but rather to transport huge amounts of weight. Here, the torque power is used for pulling heavy cargo instead of speed.
In conclusion, horsepower and torque cannot exist without one another and are equally important to make an engine work. The choice ultimately lies in what you need the vehicle for. While torque is essential for every engine, the amount of horsepower separates the great engines from the good ones.
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