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BHP And Torque

BHP and Torque play an integral role in the automotive market. The numbers are emphasized as ways of illustrating what an automobile can do. In reality, the numbers play a more complex role than most consumers realize.

When reading about a car’s specifications, the most popular statistic that we are often presented with is BHP or Brake Horsepower. This is a measure of how much power the car’s engine can actually generate. Another, but less known statistic is torque, which is a measure of how much turning force can be generated at the crankshaft. Torque is actually a physical quantity that can be measured while BHP is a derived quantity that is the product of torque and RPM. All the physics talk is a bit difficult to relate to the real world and how does it actually affect a vehicle’s performance, so let’s understand.

Basics

Horse Power

The term horsepower was first used on engines by James Watt, a British inventor, who was associated with steam engines. James Watt used the term to measure steam engine power to the power from a horse. Horsepower is the rate at which work can be done (over a given distance).

Torque

Torque is nothing more than a measurement of twisting, or rotational, force. The easiest way to think of this is to imagine a long shaft — like a car’s axle — and imagine it’s in a room suspended in midair. Hanging on the bottom of one end is a rope with a weight attached — a very heavy weight.

 

The Common Mistake

The mistake most people make when engaging in this debate is considering horsepower and torque independently. Almost everyone argues as if they are separate, unrelated values. They aren’t.

Horsepower = (Torque x RPMs) / 5252

 

BHP vs Torque

Torque is a more important value than BHP when you are considering acceleration. Take for example, a forklift that has a lot of torque at low RPMs. It may be quick to accelerate but it reaches its top speed pretty quickly as it is pretty low. Although it may not be able run very fast, it is able to accelerate huge loads without any problems. If you strap the same amount of weight on your car, you may find out that getting the vehicle running is a bit of a problem.

On the other hand, an F1 race car is the best example to illustrate how BHP relates more closely to speed than torque. An F1 race car generates a lot of BHP when it is already moving at high speeds. Although it does not produce a lot of torque, the huge RPMs compensate in producing the high BHP. If you’ve noticed, F1 race cars are not really that snappy when starting from rest and they can take a while before they are able to reach top speed. That is because they have very little torque at low RPMs.

A street car is the perfect marriage between torque and BHP. It has enough torque to quickly accelerate moderate loads while still having enough BHP at high RPMs to provide high speed driving. Although the engine does all the work, it is the gears that would determine whether your vehicle is aimed towards providing a lot of torque or a lot of BHP.

Summary:

  1. Torque is a measurable quantity while BHP is simply calculated from torque and RPM
  2. Torque is much easier to relate to acceleration and force compared to BHP
  3. BHP is much easier to relate to speed compared to torque

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