This past week Yours Truly was stuck at an airport for 7 hours. That’s a long time, so long that in fact I broke down and paid way too much for food, water, and magazines. One mag caught my eye, the January 2012 issue of American Iron Magazine. A lowered Fat Bob, clean and cool lured me over from the candy bars, giving me bad ideas about one day building a bad ass air cooled twin.
Not long after scanning the periodical for cool builds and babes, I stumbled upon an article asking the identified tech writer about what BHP means and how dyno readings work.
Call me crazy but I enjoy it when riders want to understand what’s going on underneath them and what exactly to call that instant snap of GO when you grab a handful of throttle. Let’s find out how “Tom” of American Iron Magazine chose to answer the question:
“…Serious types use words like twist and torsion to define torque, but I think of it as the force that gets my motorcycle moving when I grab a handful of throttle, with horsepower the force that makes it move faster and faster if I don’t back off...” –American Iron Magazine, Jan 2012 pg.87
I read this a few times and felt let down. So much so that I decided to pull out the dusty College Physics book and dig in to help the readers have a deeper understanding.
Let’s start with an illustration: A door. Where is the force that you apply to that door the most effective? Close to the hinges? The middle? The very opposite edge of the hinges?
This may seem to be an elementary image but this was just to get your gears turning. The force (F) that you apply (in a perpendicular direction to the outward direction of the door) x the actual distance from your applied force to the hinge of the door yields torque. Eureka!
Unlike the definition of Power, knowing a torque is useless unless the distance from the pivot point is noted. Power on the other hand is in simple terms: energy given in a defined time interval. In physics classes, we used the classic SI unit of Newton-meters. Here in the Good ‘ol USA we use ft/lbs. Meters and feet being the constant measurement of distance from the pivot point.
These forces as “Tom” mentioned are what deliver those (hopefully) instant changes in acceleration. Think of torque as the leverage that wants you lift you off the ground as you let out the clutch or when you need that extra grunt to pass grandma on the outside corner on your favorite back road! I decided to keep this entry short and sweet, aiming only to get the concept of torque in your heads without doing any numbers crunching. If there is anything to take away from this it would be: torque = leverage; HP = force. Think about that next time you go canyon carving.
P.S. If you ever read this Tom, please take note I didn’t use the words “Twist” or “torsion.”