Past Articles Archive

Horsepower and Torque. What horsepower means is this: From the early industrial days, the experience has shown that a single horse could do 33,000 foot-pounds of work every minute. Imagine a horse raising coal or water out of a coal mine. A horse exerting himself as a 1 horsepower can raise 330 pounds of coal 100 feet in one minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. You can make up whatever combination of feet and pounds you like. As long as the product (multiplication) is 33,000 foot-pounds in one minute, you have a one horsepower.

In modern terms a one horsepower is equivalent to 746 watts of power. Your home toaster could be rated as a 2 horsepower powerhouse with no wheels and handlebars attached. Riding a motorcycle, often you are being asked "how many horsepower is this engine ?", you could find the answer by looking at the motorcycle specification. 50 HP ? 90 HP ? Those are the kinds of figures. But if you were riding a horse and were asked the same question "how many horsepower is this horse ?" you might answer "1". But it's not true. In a motorcycle performance terms the actual horsepower of a horse is actually many times that. It depends on the engine RPM and it's gearing. The measurement of the vehicle horsepower is done at a point where the rubber meets the road.

What is torque; Your wife wants to open a marmalade jar. She can't do it so she asks the warrior-man to do it for her. The warrior-man has big muscles, plenty of horsepower, and a long forearm, good for a torque. He grabs the jar, twists it's lid with ease, the lid pops open. What has happened ? In a technical terms a warrior-man has applied to the jar's lid a lot of torque. We can now define a torque as a twisting power. If you would be a physics nerd then most likely you would attach to the lid a horizontally protruding 1 foot stick and proceeded to hang weights at it's end. Once the jar's lid pops open, you inform your wife that it only took 30 pounds of weight hanging at the stick's end to do the job. With a little effort and a motivation she could have done it herself. The nerd has, hence, applied a 30 foot pounds of torque. Torque is defined as: Torque = Force x Moment Arm Force and horsepower are cousins. Some other useful relationships: (horsepower x 5250) / RPM = Foot-Pounds (Foot-pounds x RPM) / 5250 = Horsepower Torque, Horsepower, and Drive-trains.

Don't confuse torque with horsepower. While it is true from the above relationship engine running at 1750 base RPM will deliver about 3 foot-pounds of torque per horsepower, this is only true if it is running at that base RPM. Conversely a 1 hp engine running at 1/2 RPM (875 RPM) while delivering a 3 foot-pounds of torque will need only 1/2 hp of input power. Carrying this relationship to the extreme, say dropping the RPM to 1, a 3 foot-pounds of torque will be delivered with almost no horsepower. But this is only a mathematical equation, after all we have traveled to the moon and the outer space. Our science cannot be that wrong. In practice our engine will be belching maximum horsepower anyway in this case a 1 HP. So, (1hp x 5250)/1rpm = 5250 Foot-Pounds of torque. Not bad ... ha?. Let's increase RPM to 5250, hence, (1hp x 5250)/5250rpm = 1 Foot-Pound of torque. What a hell is going on ?! It appears as the torque is inversely proportional to the speed (RPM). Opening the jar's lid took place at zero RPM, this is when the torque is most effective. Ok ? ... But when I ride, say, at 5250 RPM developing only a 1 Foot-Pound of torque and cracking the throttle I still have plenty of torque ... surely more than 1 Foot-Pound ... what's going on ?!. Now we are jumping from an arithmetic into a differential equations and what's worse potentially into the calculus arena of mathematical delights. Believe me, you don't want to go there, let the Smart-Car owners do this one.

But being practical as we bikers are ... just imagine that riding (or as you aren't accelerating cruising) at 5250 RPM. This is your new ground-zero situation where you can pretend that you are not moving. Hard to pretend ? ... take a digital picture of yourself ... you see, during the picture tiny fraction of time you weren't moving where everything is in focus. Any new acceleration will be counted from this point-on as your uncontrollable throttling dictates and adds new horsepower to the equation, hence, the new calculated acceleration will be for the RPM above the cruising one. You can than add this new torque value to the cruising torque for the total torque generated at that point in time. "Piece-of-cake" we bikers eat such concepts for a breakfast.

It is true that the torque is needed for acceleration (from a stationary or a slow moving status) while the Horsepower is mainly needed to maintain the speed, overcoming the friction and dealing with aerodynamics. For a safety reasons when crossing an intersection I would, however, appreciate some horsepower combined with a lot and lot of torque. Torque can be a life saver giving an escape ability sometimes badly in need. This lead's us to other motorcycle related topics such acceleration, balanced and unbalanced forces, centripetal force, energy, force, friction, g, gravitational force, inertia, kinetic energy, mass, momentum, Newton's First Law of Motion, Newton's Second Law of Motion, Newton's Third Law of Motion, period, potential energy, speed, velocity, weight, weightlessness, and aerodynamics ... oh ... forget it ... the physics of a motorcycle riding puts me into a semi-comatose state anyway........ Eagle

Harley sound: The exhaust sound is created by the piston firing. A single piston engine will generate a firing sound every second revolution. A two piston "boxer" configuration will generate a firing sound on every revolution. Both engines will generate a similar and a balanced sounds like: pop .. pop .. pop .. pop .. nothing spectacular. The interesting thing happens on the big twins "V" engines. Basically, taking a two opposing pistons "boxer" configuration and closing them from opposing 180 deg to smaller angle will generate a firing sounds that are no longer uniform.

Harley unique sound has originated on a "V" 45 degree engine. Because of such a close angle, both pistons are connected at the same point on the crankshaft. Both appear to move up and down almost simultaneously. The firing sound is still originating from firing of each piston on every second revolution. But now the firing sequence is like this: First piston fires on first 360 degrees. Second piston fires on next 315 degrees (that is 360 deg - 45 deg "V" angle = 315 deg). Then there is a one revolution + gap of 405-deg without a firing (that is 360 deg + 45 deg = 405 deg). Then the firing cycle repeats as per above sequence and so on. If I could simulate this sound with my lips, it would be like this: pop .. pop ....... pop .. pop ...... pop .. pop

Tuning this sound through virtually straight exhaust pipes give this unique Harley signature combined with a lot of engine vibration ... falling-off parts etc...thanks goodness for the rubber engine mounts. Wow ... the V12 Merlin sound as a major marine engine. Miss Supertest World's Fastest ... Breaks Unlimited Record At Picton. Bob, did you participate in these races and if so in what capacity ? As for the Einstein's theories many of them have been disputed by the scientific community. The quantum theory is changing the thinking. However, some of his basic theories are still valid, like a relativity theory........ Eagle

Biker's Vocabulary