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Understanding Horsepower and Torque Cars

By Justin Reimlinger
On May 10, 2017

To me, being “in the know” versus out is all dependent on my understanding of what someone is talking about.

When friends or mechanics talk to me, they use strange words like planetary gears, spool rears, modular motors, overhead cam and overhead valve, or even something as simple as “stancing”, which is what morons do to cars to make them look cool, yet reduce their safety and tire life, and I find myself constantly translating words for my girlfriend because, though I am speaking English, the car world has its own language and set of rules, just like computers or sports. Believe it or not, there are many technical words you know that form the basis for understanding everything I just mentioned. I’d like to begin with two: horsepower and torque. Both a measure of your cars performance but two very different beasts. Ask a typical car guy (or gal) about what these are and you’ll quickly realize not many car enthusiasts even know what these mean.

Horsepower is equal to 745.7 watts, or 32,580 ft.-lbs/ minute. Long story short, James Watt measured a horse attached to a mine pump and found it pulled with 180 lbs of force and made almost 2.4 trips per minute. He then calculated its speed (~181 feet per minute) and multiplied that by the force the horse pulled (181x180). That equals to 32,580 ft.-lbs./ minute and that figure was eventually rounded up to 33,000 ft.-lbs./ minute. That number is defined as one horsepower (hp), or the amount of mechanical energy it takes to lift 33,000 lbs. one foot in one minute.

Torque in short is twisting force. It’s measured in units of force multiplied by distance from the axis of rotation. If you have a one-foot-long wrench on a tire nut and you exert a force of 10 pounds on the end of it, then you apply a torque of 10 pound-feet (10 lb-ft). If the wrench were two feet long, the same force would apply a torque of 20 lb-ft. The measurement for torque in the U.S. is pound-foot (lb-ft). Torque is what lifts your front tires off the ground and horsepower keeps them there.

Many people today look at performance cars and think “more horsepower, more speed!” and generally that’s true, but not always. Among other things weight is a huge factor. It’s the reason a CBR1000rr sport bike can go 200 plus mph with 175 hp and the new SI Civic can’t even hit 135 with 205 hp. The second factor that goes into your car is the gearing, represented by your transmission and final drive ratio, or sprocket on a motorcycle. Most vehicles today come equipped with a six, seven, or eight speed transmission.

The numbers represent the gears in the transmission, and if you’ve ever paid attention to your vehicle while driving, you can count the gears in the transmission as the car shifts, generally highlighted by a little jerk or nudge through the first few gears. The gears get progressively smaller as the vehicle shifts through them. For instance, first gear might be 2.5:1 while the last might be .86:1. These are called gear ratios, and they always go from numerically higher to numerically lower. The gear ratio is the ratio of the number of teeth on the output gear to the number of teeth on the input gear. The larger ones when you first start out (first and second gear) are designed to produce more torque so your vehicle will accelerate faster when you push the gas.

The last gears are generally designed for highways speeds, where the transmission doesn’t need to manipulate the engines torque because the vehicle is already in motion, so it shifts to overdrive gears, designed to drop the rpm’s (engine speed, measured by rotations per minute-the tachometer on your dash represents this) while achieving relatively great fuel economy.

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