What Do Horsepower and Torque Mean?

December 8th, 2012 by

Mazda CX7 EngineEach vehicle, large and small, will list both a horsepower and a torque rating. A common misconception is that engine size equates to power, but this isn’t necessarily true. A turbocharged 2.0L could easily go head-to-head with a V6. Regardless, if you’re interested in an efficient subcompact or a tough SUV, knowing how horsepower and torque affect performance is an important part of a vehicle decision process.

Torque

Torque is force rotating around an axis. In terms of the engine, it’s the force created by the spinning crankshaft. Torque is measured in lb-ft, meaning that, if you placed a one foot lever on the crankshaft, the amount of force it would exert at the opposite end of that lever is your torque rating.

Horsepower

Horsepower is a rating of engine power. The term was coined by engineer James Watt in the late 18th century in an effort to quantify power output from an engine. He figured that one horse could move a load of 33,000 lbs over one foot in one minute. Thus, 1 HP is rated as 33,000 ft-lbs/minute.

You can see the direct relation between torque and horsepower here in the units. Since torque is measured much more easily than horsepower, engineers use an equation to derive an engine’s horsepower output from its torque. Torque power is multiplied by RPM and divided by 5,252 to reach horsepower. The factor 5,252 is figured by dividing the 33,000 lbs by 2?, or one revolution.

What They Mean For Your Car

You don’t need to wrap your head fully around the math to understand what torque and power do for your vehicle. Many beefier vehicles like pickups and tractors have higher torque ratings at lower RPMs. They won’t have the higher horsepower that smaller, more performance oriented vehicles do, put they’re built to haul, not race. If you add weight, performance doesn’t suffer as much as if you added it to say, a MX-5 Miata.

More horsepower means that you can accelerate more quickly and reach a higher top speed. Because all modern vehicles that are powered by fossil fuels use a gear system though, a similar effect can be generated by using high torque and low RPM and low torque at higher RPMs. Horsepower often matters more in higher performance vehicles, where drivers are using the full range of RPMs.

Posted in Mazda Features