ASK THE MXPERTS: SEMANTICS & THE SUBJECT OF POUND-FEET OR FOOT-POUNDS?
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.