Torque and Horsepower: What's the Difference?

We all know that torque is what slams you into the seat and that horsepower is what carries you at 100 MPH (or at least we're told), but when it comes down to it, how many of us actually understand what torque is and what horsepower is?

Curve of Horsepower and Torque Vs. RPM Source

Think of it this way: both have definitions that can come from your physics text books that can be easily applied to your favorite automotive hobby.

A Car's Wheel on a Dynomometer Roller Source

There is a specific equation relating the two via RPM value, but more simply put, power is defined as "the rate at which energy is transferred, used, or transformed."  Basically, the more horsepower you have, the higher the rate at which you transfer rotational energy from your wheel and tire to kinetic energy, moving your car forward.

This Honda S2000 produces about 125 horsepower per liter, but very little torque in comparison-- very good for road racing in stock form but not fun for the drag strip where force is an important part in getting down the drag strip in a short amount of time.  Source

Torque, however, is defined as "the tendency of a force to rotate an object about an axis, fulcrum, or pivot."  In other words, the more torque your car has, the more ability your car has to twist the wheels.  If you have a lot of torque, but little horsepower, like in a diesel car, you'll be able to turn the wheels with great force, but the rate of energy transfer from your wheels' rotational movement to your car's forward movement will not be as great.

Jetta TDi's are well known for their high mileage due to the amount of work they extract out of the fuel they run off of and they are also known to produce more torque than horsepower (nearly double for this model).  Source

I hope this helps you to familiarize yourself with the differences between horsepower and torque.  This writeup is only intended to help you acquaint yourself with the concepts rather than understand the mathematical relation.  But still, it should make you sound a little more knowledgeable if the topic ever comes up.  ;)

Until next time, Lexi.Laron signing off.