Horsepower vs Torque

[scooter trash]

I have been asked several times:
What is the difference between Horsepower and Torque?

I have two answers to that question.

1. The Technical Definition:

Q: What is Horsepower?

Horsepower is defined as work done over time. The exact definition of one horsepower is 33,000 lb.ft./minute. Put another way, if you were to lift 33,000 pounds one foot over a period of one minute, you would have been working at the rate of one horsepower. In this case, you'd have expended one horsepower-minute of energy.

Q:     What is torque?

A:     Torque is a physical vector quantity characteristic for an object in rotational motion around a certain given axis.  By definition torque (tau2.gif (826 bytes)) is the cross product between the vector of position (r) of the point where a force is applied (from an origin considered to be on the axis of rotation) and the applied force (F)  (tau2.gif (826 bytes) = r x F).   According to the definition of the cross (or vector) product, the magnitude of the torque is equal to the magnitude of r times the magnitude of F multiplied by sine of the angle (phi2.gif (845 bytes)) between r and F (tau2.gif (826 bytes) = r F sin phi2.gif (845 bytes)).  In this expression for magnitude of the torque, the product (r sin phi2.gif (845 bytes)) is equal to the magnitude of the distance (d) between the axis of rotation and the "line of action" of the force (F) (r sin phi2.gif (845 bytes) = d).  This distance (d) is called "arm of the force."  Now, the torque can be expressed as tau2.gif (826 bytes) = Fd (torque is equal to force multiplied by the arm of the force.)  Intuitively, torque can be interpreted as "force with a twist" since it results in rotation of the object on which the force is applied.



2.  The Easy Definition:

Horsepower is the speed at which you hit the wall and torque is the distance you push the wall after you hit.


Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*."

Next week class, we will discuss how modern industry uses radioisotopes in a variety of ways to improve productivity.

       

[2005B12S]

Torque is big pistons booming at relatively low rpm pushing you by the seat of the pants down the road.

RPM is the high pitched scream of small pistons at a relatively high rpm  pulling you down the road.

Machines that use torque to full advantage are the TL1000, RC51, just about any 2v Ducati, yada yada

Machines that use rpm to full advantage are the GSXR750, GSXR1000 and practically any inline 4 600cc sport bike.

The Bandit 1200 falls right in the middle. Nice even blend of the two, it doesn't grunt like a TL1000 or scream like a GSXR, what it does is fill the big void between the two compramises.

This is why it is so popular with the older "been around the block" kind of riders as they recognise it for what it is.

[Farre]

i always remember it simply, like
Torque is the fun factor, 'feeling' the acceleration.
HP is in the figures, more hp means higher top speed (simply put, of course)

[zaphoid42]

If you know the torque-speed curve of the motor, the horspower-speed curve of the motor is also a known.  They are one and the same.

In SI units, power is the rate of torque.  In English units its complicated, but do-able.

I am on my third Molsen XXX.  Those dam canadians are to blame for everything.

Why is my nose numb?

[Silverstreak]

No moving the wall isn't torque, it's inertia. Torque is what happens in your guts when you hit an oil slick at a red light.

[GaryB12VA]

When I was in Colorado a couple of weeks ago, we took the Cog Railway to the top of Pikes Peak

http://www.cograilway.com/

During the ascent up Pike Peak they explained that the trains were driven by 4 diesel engines each producing about 350 hp, and 1,500 lb. ft. of torque. There were places where the train was going up a 25% grade at the amazing speed of 10 mph.

[Bob Holland]

Torque is measured by a dyno, Horsepower is calculated from torque and rpms. At 5252 rpms, HP and torque are always the same. Below 5252, torque is always higher, above 5252 rpms, HP is higher.
Torque times: RPMs divided by: 5252 = horsepower

[jfudo]

My favorite explanation:  Torque is how hard the engine can pull.  Horsepower is how fast and far it pulls.

A 1 hp, 1,000 lb torque engine will accelerat to 1mph very quickly, and keep pulling at that pace no matter what gets in its way.

A 1lb torque, 1,000 horsepower engine will slowly accelerate to a very high speed, and lose a lot of speed up hills or against wind.

Numbers examples only.

[Bob Holland]

A engine making 1 lb of torque, would have to turn 520,000 rpms to make 1000 horsepower

[snofrog]

A engine making 1 lb of torque, would have to turn 520,000 rpms to make 1000 horsepower

if it is a yammy tach(ala r-6) then it would be concievable to turn those rpm`s  

[jfudo]

A engine making 1 lb of torque, would have to turn 520,000 rpms to make 1000 horsepower

That's pretty interesting, but I think your math was wrong, you would be turning 5,200,000 RPMs.  That just crazy.   That would be one short stroke motor.

[Bob Holland]

1 torque x 5252 rpms divided by (5252) = 1 hp
1 torque x 52,520 rpms divided by (5252) = 10 hp
1 torque x 525,200 rpms divided by (5252) = 100 hp
1 torque x 5,252,000 rpms divided by (5252) = 1000 hp
Your Right

[Andrew1157]

Power sells bikes
Torque wins snarl ups at traffic lights

[jfudo]

Torque gets you into trouble, hp gets you out of it. :suzmoto:

Wait, that comment probably should've been on the Starboyz FTP website.  

[Brit-400]

Had a good comparison of this last night. Me and a friend went for a ride, he's just got a Ducati monster 600. Not as much power, more torque. In a straight drag race, my b-4 was quicker. Not by a whole lot, but i could pass him if i wanted on a good straight.But, in the real world, if you were on a twisty road and wanted to just roll on and off the throttle, he would kill my bandit completely - i really had to work the revs to keep with him.

I think torquey bikes make better road bikes.