Either term could be used when describing an engine’s torque without being incorrect, but one is actually correct

The post ASK THE MXPERTS: SEMANTICS & THE SUBJECT OF POUND-FEET OR FOOT-POUNDS? appeared first on Motocross Action Magazine.

]]>**There are two different kinds of torque.**

**Dear MXperts,**

**Come on MXA, which is it? Foot-pounds or pound-feet? I notice that you seem to use the two terms interchangeably from one bike test to the next when talking about torque. Which one is it?**

We admit to jumping back and forth on the subject of torque measurement, but that is because either term is acceptable, but not necessarily correct in all situations. Let us explain.

**Pound-foot (lb.-ft.)** is a unit of torque and is a measurement that is created by 1 pound of force acting on a 1-foot lever. The formula for torque in tightening a nut would be: torque equals force times radius (with radius being the length of the wrench).

**Foot-pound (ft.-lb.)** is a measurement of work. Work is the measurement of force over a given distance. Thus, 1 foot-pound is the energy required to lift a 1-pound object 1 foot of vertical distance. When James Watt determined that a horse could lift 550 pounds at a rate of 1 foot per second, he declared it 1 horsepower.

**Here is where it gets confusing, but in many ways enlightening.** It is a given that the correct unit of measurement when tightening a nut is the pound-foot (lb.-ft.). Logically, you would then assume that the correct unit of measurement for an engine’s torque would be foot-pounds (ft.-lb.). But, if you perused the owner’s manuals of all the motorcycle brands, you would find that some refer to it as foot-pounds and some pound-foot (or pound-feet). Truly, they are as confused as everyone else, and this acceptance in common literature makes it obvious that either term could be used when describing an engine’s torque without being incorrect; in truth, all the reader really cares about is the number in front of the definer.

However, in all matters technical, the true source of accuracy is the Society of Automotive Engineers (SAE). The SAE lists the “pound-foot” as the official unit of measure for engine torque. Since the abbreviation for foot is the same as for feet, a lb.-ft. could easily be referred to as pound-feet.

The post ASK THE MXPERTS: SEMANTICS & THE SUBJECT OF POUND-FEET OR FOOT-POUNDS? appeared first on Motocross Action Magazine.

]]>Perhaps in the future, scientists may find a more precise measurement of motorcycle power, but whether they choose kilowatts, cheval-vapeur or joules, it won’t matter if the public doesn't go along

The post ASK THE MXPERTS: HI HO, SILVER, AWAY—WHAT DOES HORSEPOWER ACTUALLY MEASURE? appeared first on Motocross Action Magazine.

]]>**The spinning wheel tells no lies—just not the whole story.
**

**HI HO, SILVER, AWAY**

**Dear MXA,**

**What does horsepower measure, and what does a horse have to do with it?**

*Every motorcycle racer wants a measurement that explains how powerful his bike is. Horsepower is an easy reference number that everyone can relate to. Perhaps in the future, scientists will come up with a more precise measurement of how fast a motorcycle engine is, but whether they choose kilowatts, cheval-vapeur or joules, it won’t matter if you can’t get the public to go along. Horsepower has a long tradition, and it will not go gentle into that good night. People won’t want to change from 50 horsepower to 37,285 watts.*

*We mention watts because horsepower as a measure of power was coined by James Watts, who wanted to market his industrial steam engines to replace horses in 1782. Watts determined that a horse could turn a standard 12-foot radius grain mill wheel 144 times in an hour (or 2.4 times per minute). He then extrapolated a horse’s effort to the performance of his steam engine to be able to rate it by “horse power.”*

*The ultimate calculation was that 1 horsepower was equal to 550 foot-pounds per second (or, in simpler terms, that a horse could raise 550 pounds of weight 1 foot in one second). These numbers could be converted easily to other units of measurement. Thus, one horsepower also equals 33,000 foot-pounds per second, 745 watts, 0.645 kilowatts or 745 joule per second.*

*The point isn’t about what unit of power we use but whether that unit can be used in science and industry as a reliable measurement of how powerful a machine is. It is a given that 1 horsepower equals 550 foot-pounds per second. The importance of the “per second” part of the equation is that it changes horsepower from a measurement to a calculation. The time factor means that you don’t actually measure horsepower, you measure the force exerted over a distance during the duration of a given time. The resulting number is called horsepower, but the force that is being measured is torque.*

**How do you apply all of this?** Motorcycle tuners use a dynamometer to determine the power an engine produces. They do this by applying a load to the engine output shaft by means of a water brake, a generator, an eddy-current absorber or any other controllable device capable of absorbing power. The dynamometer control system causes the absorber to exactly match the amount of torque the engine is producing at that instant, then measures that torque and the rpm of the engine shaft. From those two measurements, it calculates observed power. What the dynamometer is really doing, however, is measuring the torque output of the engine. In a vehicle, torque is measured at various engine speeds, or revolutions per minute (rpm). These two numbers are fed into a formula—torque times rpm divided by 5252—to arrive at horsepower.

*What is more important, torque or horsepower? Most motorcycle companies advertise the horsepower and torque that their engines produce. It seems, as usual, the bigger the numbers, the better. Torque is the base number for work, and horsepower is the rate of doing more work. Thus, one can’t exist, or even have meaning, without the other.*

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