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Discussion Starter #1
Ok... I've been looking through my large stack of Motorcycle magizines... and compairing numbers and what not... hey... I'm bored :twofinger anyways... my question is this...

WHAT IS THE DIFFRENCE BETWEEN HP AND TORQUE? when I sat down and thought about it... the explination I used to define HP was sounded more like Torque... :confused:

oh... just fyi my definition of HP was how much force the engine could produce to turn wheels or what ever it's intended job is...

thanks in advance :cheers
 

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Seat of the pant's definitions:
Torque = how hard a jolt you will feel when you crank it at low speeds. A bike with a lot of torque won't even notice you're there. A high torque bike will burn rubber, get you across the intersection and maybe up to 50 PDQ. A big cruiser will accelerate well at lower speeds, but will not be able to keep the acceleration going at higher speeds.

Power = the ability to continue to haul ass at higher speeds. A powerfull bike keep stretching your arms and flattening your eyeballs as you go from 80 to 120 mph.

Definitions from physics: (see cole's notes at end).

Power is how much energy is used (work is done) per unit time. The energy is converted to kinetic energy in a bike Ek =1/2 *m*V^2. As you can see a change from 10 to 20 mph involves less energy being used than a change from 110 to 120 mph. So you need more power to change by 10 mph at the higher speed.

Torque sort of a twisting force; it is force x distance away from the axis of rotation. Think of a wrench. You can get the same twist by pushing with 10 lbs at 2 feet from the not/bolt, as you can by putting 20 lbs at 1 foot.

Torque is what provides the force where the rubber meets the road.

Force x distance down the road is the work done, which neglecting losses due to friction equals the energy used (converted to Ek).

Energy per unit time is power which is Force x distance down the road /time
which is equal to force at the wheel times velocity.

Coles notes:
peak torque varies as force at the wheel = how hard you can stretch your arms at about 30 mph.
Peak power varies as force at the wheel x speed = how easily you can loose followers at over the ton speeds.

torque = ability to accelerate.
power = ability to accelerate at high speeds.
 

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Discussion Starter #3
Ghost Rider said:
Coles notes:
peak torque varies as force at the wheel = how hard you can stretch your arms at about 30 mph.
Peak power varies as force at the wheel x speed = how easily you can loose followers at over the ton speeds.

torque = ability to accelerate.
power = ability to accelerate at high speeds.
Ok... so given what you've said... at what point durring acceleration does it stop being torque and start being power? :confused:
 

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Torque is a measure of twisting force. Horsepower is a strictly measure of total work the engine can perform in a given period of time. The two values are related.

In motorcycle terms, torque represents acceleration. Horsepower represents top speed potential. Specifically, the thump in the ass you feel as you roll on the throttle. Engine design and tuning determines a lot of this. It is possible to build a high-torque, low horsepower engine (a single cylinder engine is a good example). The bike will accelerate and feel very peppy at low speeds but won't have a high top speed. Contrast this to a sportbike inline four engine that produces high horsepower, moderate torque. The bike will accelerate slowly compared to the single at low rpms but as the speed and rpms increase, the sportbike engine will begin to take off. V-twins and V-fours make different tradeoffs in this area to achieve different performance goals.

Bottom line, a cruiser and a sportbike may each produce the same torque figures but the cruiser may have half the horsepower of the sportbike. Off the line, the cruiser will probably hand the sportbike its ass as it reaches its peak torque point quicker and lower in the rpms than the sportbike. Thus it takes off faster. As the sportbike winds up and hits its torque point high in the rpms, it will begin to take off. Since horsepower is a function of rpms, even with the cruiser at peak torque, the lower redline of the V-twin engine will limit how fast the bike will be able to go. By comparison, the sportbike will just be hitting its stride, blow past the cruiser and still be accelerating as the cruiser tops out.

Not a pure explanation but hopefully close to a real world one.
 

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Ebbs15 said:
Ok... so given what you've said... at what point durring acceleration does it stop being torque and start being power? :confused:
I'm not an engineeer so don't hold me to this.

As I understand it, peak torque tends to occur before peak power. My FZR600 is an example. Peak torque is at 8500rpm. Peak horsepower is at 10,500rpm. As you pass the peak torque threshold, your torque will either remain steady at the maximum or begin to fall off. At this point, you are starting to transition towards peak power. To answer your question, any rpms beyond the peak torque point is moving towards power since you have already maxed out the amount of force the rubber is putting into the road.

In ideal engines, peak torque and peak power occur at the same point. On motorcycles, V4 engines tend towards this ideal. Inline fours tend to reach peak torque before peak power. So these bikes have a trade-off. Acceleration vs. top speed. V-twins hit peak torque low in rpms and horsepower much higher up. The gap is much wider than the one typically seen in an inline four. Thus, V-twins get up and go in a hurry with little effort but lose steam as by the time they reach peak power, their torque has usually fallen way off. Simply watching the amount of time a cruiser takes getting to high speed will confirm thus. Mind you, you have to playing in the 70mph+ range to really get a feel for the differences.
 

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Here's the simple answer: Torque is a real measurement of work. Horsepower is a mathematical formula applied to torque. HP was created to market early steam engines to actual horse users. It was meant to be more usable comparison to the work performed by actual horses. And it was crafted to look attractive. Hence the random multiplication factor 5250 in the formula.

HP exists to this day only because it is generally a higher number than torque, continuing to be a marketing tool. It is useful only for comparison to a like machine in where it occurs and how much it is. However even in calculated HP, Torque is doing the work.
 

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good explanations
 

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The relationship between HP and torque is simple:

HP = (Torque * RPM) / 5250

Based on the formula, as the engine's RPMs are increased, the HP generated increases. The limits of HP are set by friction, both within the engine and external (wind, rolling resistance, etc).

You can also increase your horsepower by increasing the torque applied to a/the driven hub. Two routine ways to do this: 1 - alter the drivetrain and/or 2 - alter the internals of the engine.

Torque is (force x distance from axis of rotation). As someone noted above, if you push on the free end of a 2' long wrench with 10 lbs. of force, you are applying a 20 ft-lb moment to the axis of rotation (the bolt/nut/whatever). Considering this, it is possible to increase your bike's "seat of the pants" torque by increasing the size of the rear sprocket. Doing so increases the distance thru which the force (the drive chain pulling on the sprocket) is applied, thereby increasing torque generated about the hub of the rear wheel.

One way to increase the amount of real torque that the engine produces (measured at the crank, not at the rear wheel) is by altering the stroke of the piston. To keep it short, the longer the con rod the greater the torque generated. Consider a stroker Harley; the con rod is repositioned further from the crank shaft's axis of rotation, thereby increasing the "distance" part of the T=f*d, thereby increasing torque and, consequently, HP. It's not that easy in real life; some other things have to change as well, but that's the bottom line.

If I missed something or misstated something, somebody please let me know -
 

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Ebbs15 said:
Ok... so given what you've said... at what point durring acceleration does it stop being torque and start being power? :confused:
Both torque and horsepower are always there. Take a look at the dyno curves in any sportbike mag. The torque curve and the HP curve are both plotted against engine rpm. For any rpm you have a value for torque and a value for HP.

It's the torque that pushes you down the road, but if you want to push your bike at a higher speed (say you're moving along at 9000 rpm in top gear) you will need to have enough HP. You can use the above-mentioned equation to see what I mean:

HP = (Torque * RPM) / 5250

becomes

Torque = 5250 * HP / RPM. (works for foot-pounds and horsepower)

As you can see, unless you have a high-enough HP, you won't have enough torque to move you down the road at higher speeds.

Long story short, if you want to whip up to 30 mph in an eye-blink, get torque, if you want to go from 80 to 150 in a hurry get Horsepower, if you want it all get an in-line-4 litre bike.
 

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----
Hence the random multiplication factor 5250 in the formula.

HP exists to this day only because it is generally a higher number than torque, continuing to be a marketing tool. It is useful only for comparison to a like machine in where it occurs and how much it is. However even in calculated HP, Torque is doing the work.
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Incorrect.

Torque is the twisting force of 1 foot pound placed on a 1 foot bar. It is not 'work'. Work requires movement, which is where the horsepower formula comes into play. 5250 (The actual number is 5252) is a mathematical standard applied to the formula used to calculate Horsepower. Horsepower is work that is produced that maintains movement. One horsepower is defined as producing 33,000 foot lbs of work in 1 minute. An engine will continue to make Horsepower as long as RPM increases faster than Torque is falling.

Basically, horsepower is torque measure over time. As you can see it is more than a marketing tool. It is a very real formula used to measure, and create a target for bike performance building.
 

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You want an easy explanation???


Torque is a twisting pressure - Movement isn't necessarily involved. Put a wrench on a frozen bolt and try to loosen it. You are applying a torque to the bolt. But unless it actually moves, then you haven't actually accomplished any work.

Horsepower is Torque applied over time/distance. In Other Words - HP is a measure of the amount of work the motor is capable of doing.


The reason for the 5252 constant is because of some old dude: I think his name was James Watt (yes, *that* "watt" - The electricity dude). He needed a way to sell his motors, and explain to his customers why one is better than the other. So he took a horse, tied it to a pulley, and made the animal lift buckets of rocks until he figured out what the animal could do.

He could then say that an electric motor (because that's what he sold) that was capable of moving as much as that nameless nag equalled one horsepower. Later on, that same measure was applied to gasoline engines.


Now, the 5252 number is merely a constant to describe the relationship between Torque (expressed in lbs/ft) and horsepower as a function of RPM. This way you can do the math to figure out one if you knew the other.

Scott :)
 

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Discussion Starter #16
Scotteq said:
Now, the 5252 number is merely a constant to describe the relationship between Torque (expressed in lbs/ft) and horsepower as a function of RPM. This way you can do the math to figure out one if you knew the other.

Scott :)
Ok.... but what about like the new pickups that make like 400+ ftlb's of torque but produce only 300 hp?... yet a WRX STI will make 300 hp and only 300 ft lb's of torque... :confused: I"m confused again :lol
 

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Ebbs15 said:
Ok.... but what about like the new pickups that make like 400+ ftlb's of torque but produce only 300 hp?... yet a WRX STI will make 300 hp and only 300 ft lb's of torque... :confused: I"m confused again :lol

Because the engine either doesn't rev to/past 5200 RPM, or doesn't make as much torque up high as it does down low...

Presuming the TQ curve is flat, which they usually aren't very...

For the WRX:
300 multiplied by 5252RPM, divided by 5252 = 300 Right!?!?


For the Truck:
400 * 3939RPM/5252 = 300


Does that help???

Scott :)
 

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Man I learned some good stuff, my definitions of both were short and didn't have a full explanation....
 
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