Horsepower vs Torque – What’s the difference?


Whenever we see advertisements of cars or trucks on televisions, we mostly see words like horsepower or torque. While some of us know the terms individually, majority don’t. Conventionally one says the bigger the numbers the better. But does anyone really know what they are or how they are related? Well, let’s find out!

Also Read: 4-Stroke vs 2-Stroke engine – All you need to know!

Horsepower:

As the term suggests, horsepower was first coined by James Watt in the 18th century, which literally means the number of horses needed to pull a car (steam engine in that time). In layman words, if 5 horses are required to pull a car, thus the power would be 5 horsepower (or HP). It is a term that is used to quantify the work an engine undergoes. That is in terms of horses, the amount of work a horse can do per minute. One horsepower is the equivalent amount of work that it takes to move 33,000 pounds for a distance of one foot in one minute. For cars, HP is a constant supply of power. It is that high end power which does not initiate or start a car but, when it reaches up to speed, it keeps it there. A greater HP means higher acceleration and a smoother ride. It has been standardized to be 550ft-lb/sec or 745watts. In cars, horsepower is still the preferred mode of measuring the power output of an engine, but cars have a specialized method of measurement and the result is in brake horsepower. It is taken by measuring how much power an engine can put out without all the other intervening mechanisms like the alternator, generator, gearbox, and other devices that are needed in the car. It is usually measured with the aid of a dynamometer, a device that is used to determine an engines performance. HP is usually measured in ft-lb/sec, however, the electrical equivalent of one horsepower is 746 watts in the International System of Units (SI), and the heat equivalent is 2,545 BTU (British Thermal Units) per hour.HP

Torque:

Torque is another term used by car enthusiasts to define the output of their car. Torque is basically the force required to rotate an object. Or, in car terms, the force exerted on the ground to get the vehicle off and running. As previously stated, it is not HP but torque that initiates the car and gives it the necessary power to move from rest. Hence it can be defined as the low RPM power of the machine, as opposed to horsepower. The unit newton meter is properly denoted N-m and is used to measure torque in system international (SI). The SI unit for energy or work is the joule. It is dimensionally equivalent to a force of one newton acting over a distance of one meter, but it is not used for torque.Torque

Difference between Horsepower and Torque:

Many of you have probably ridden dirt bikes or street bikes, and probably know that 2-stroke dirt bikes are really fast as long as they are in the “power band”. When they are below the power band though, they perform really inefficiently, especially if there is a rider on the back. A 4-stroke bike will make much more torque and won’t be as inefficient on hills of steep roads and the power comes-on smooth and at a much lower RPM than a 2-stroke bike. Think of the 2-stroke bike as a high horsepower bike, and the big 4-stroke bike as a high torque bike, and that is pretty much the difference between horsepower and torque.

In racing where there is an accident, remember – Horsepower is how fast the car hits the wall. Torque is how far it moves that wall. If a 300 pound race bike crashes into the wall at 100 mph, horsepower got it to hit the wall at that speed, and the wall probably won’t move much. Hit the same wall with a 75,000 pound truck traveling at just half that speed, and the wall will get knocked down and pushed off the race course a few hundred feet. This is because of its higher torque.

Horsepower-vs-Torque

Happy motoring!


Notable Replies

  1. Very good description... !

  2. Rugal says:

    No, bro. No HP = No Torque. Some horsepower is always required to get a torque and only then will a car move off. To get any speed at all, you need some HP. HP creates torque. How much is another question for another day.

    Torque, as you've stated is the turning effect of force. It cannot be defined as the low RPM power of a machine though.

    Actually, both HP and power are in the form of a wave. Dependent on the engine RPM. So at idle, they'll be low, moving up as the RPM increases. At a certain point, they'll be at maximum and then taper off again.

    Slightly misleading but nonetheless popular description of horsepower and torque. Horsepower and torque are interdependent but have nothing to do with moving the wall anywhere.

    If you hit a wall, how far you'll take it with you or how far the wall moves out of the way are actually dependent on the mass of the object hitting the wall and the speed at the point of impact. In other words, momentum. That 10 ton truck will obliterate the wall at 60 kmph while a 100 pound motorcycle at the same speed won't do anything besides a few deep scratches on the wall.

    So that old racing cliche might be good for an explanation but it really doesn't cut mustard, if you know what I mean.

  3. Seeing it at an abstarct level without going into miniature details;
    Petrol Engine=Horse Power=Ghora
    Deisel Engine=Torque=Hathi
    It depends upon application k kahan hathi chahiye aur kahan ghora.

    Horse Power(Petrol) is something for Bebay bachey and Torque(Diesel) is something for Bamban bachey.

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