What is Torque and Horsepower?

[Sungfooo]

Can someone please answer this question in the MOST BASIC form. What is Horsepower and Torque? And how do both of them affect Speed , acceleration , rpms , or whatever else they affect.

I've been looking around and every forum i've come across , people just explain it using scientific mumbo jumbo that I cannot understand.

like seriously try to explain it like you would to a 10 year old girl , then maybe I'd understand.

thankyouuuuuuuu

[Samer]

The best way to know if you understand some scientific quantity is by looking at the units.

Torque is simply a force applied at a particular distance (or radius). So if you apply a force of one pound-force at a radius of one foot, that would be one pound-force foot (or foot-pound) of torque.

Power is how much energy is produced in a given time period. Horsepower just happens to be the unit people use for cars or bikes. A Watt is another example of a unit of power. They both measure the exact same thing. So your 50 Watt light bulb is consuming electrical energy at 50 joules per second. An engine produces energy at a certain rate, more power means more energy for the same unit of time. If it is an engine on a bike, that power would translate to more acceleration and a higher top speed.

There is a lot more but that is a starting point. Hope it helps a little.

[Christofeser]

emmmmm I'll try simple it as much as possible.

Torque's are usually to do with levers. As you know, the longer the lever the less effort needed to turn something. e.g. using longer spanners to turn harder things... the torque (or "turning force") is the result of how much force YOU put on the spanner, and the length of the spanner itself. If you put in the same amount of force, but a longer spanner, obviously you have a larger turning force and THEREFORE more torque. The equation is "force x distance". How it relates to bike's I don't know - read the previous poster's explanation for that... something about time - but it's Christmas and I'm far too drunk for that.

Horsepower however is merely the amount of power it produces divided by the power of a horse, to see how many horses it would take to produce that much power.
(I am joking, as I said, I've just got back from the pub!)

[Samer]

One more thing, the relationship between power, torque and RPM is simple:

Power = Torque * RPM

Obviously you need to be careful with units for this to work properly. In SI units:

Power [Watts] = Torque [N*m] * Omega [rad/s]

[Alex]

For definitions, wikipedia does a pretty good job on both Torque and Power. But I'll give it a shot, as it applies to our bikes. Torque is a measure of instantaneous force. Basically, how much force can that motor apply to turn that sprocket, immediately and instantaneously. Not how quickly it can turn it, not how many times it can turn it, but how much force it can apply while attempting to turn it.

Horsepower (or watt, or any of the other measures of Power), is how much work can be done turning that sprocket over a certain time period. One horsepower is the amount of work to lift 550 lbs, 1 foot higher, in one second. If you do it in 2 seconds that's 1/2 a hp, if you do it in 1/2 a second, it's 2 hp.

You can't have horsepower without torque, and you can't have torque without horsepower (well, you can if the sprocket isn't turning at all, but you can't measure it as easily ). They are joined at the hip. The more torque an engine makes at a certain RPM, the more HP it makes. The less torque, the less hp. But, since hp = tq * rpm (divided by a constant), an engine does in fact double its HP if it doubles its RPM, as long as it can produce the exact same torque at both of those engine rpms.

When people say an engine has alot of torque, that generally means that you don't have to rev the crap out of it for it to make enough hp to move the bike smartly. Say something like a ZRX1200, or even the new Z1000. 100 - 110 peak hp at the rear wheel, and 80ish ft/lbs of torque, while still down low in the revband. Compare that to a bike that has the same hp but isn't very torquey, like a GSX-R600. Same 100 - 110 peak hp at the rear wheel, but only 40ish ft/lbs of torque. To make that same hp, the motor has to spin almost twice as fast to make that same amount of hp.

[00NissanNinja]

Samer you are an engineer aren't you?
Yeah Samer explained it pretty well in a simple fashion.

[Samer]

Originally Posted by 00NissanNinja

Samer you are an engineer aren't you?
Yeah Samer explained it pretty well in a simple fashion.

Good guess. Yes, I'm a Mechanical Engineer. Specifically, I'm an aerodynamic designer for gas turbine engines. Maybe I'll be designing one for a bike one day

[Sungfooo]

Originally Posted by Alex

When people say an engine has alot of torque, that generally means that you don't have to rev the crap out of it for it to make enough hp to move the bike smartly. Say something like a ZRX1200, or even the new Z1000. 100 - 110 peak hp at the rear wheel, and 80ish ft/lbs of torque, while still down low in the revband. Compare that to a bike that has the same hp but isn't very torquey, like a GSX-R600. Same 100 - 110 peak hp at the rear wheel, but only 40ish ft/lbs of torque. To make that same hp, the motor has to spin almost twice as fast to make that same amount of hp.

haha thankyou alex .. that last paragraph was what i was looking for

[00NissanNinja]

Originally Posted by Samer

Good guess. Yes, I'm a Mechanical Engineer. Specifically, I'm an aerodynamic designer for gas turbine engines. Maybe I'll be designing one for a bike one day

I am also a Mechanical Engineer. I remember my thermodynamics teacher always tried to get us interested in gas turbine engines and energy production cycles.

[JMcDonald]

HP is the engine's ability to create thrust. Thrust is both what you feel whn you twist the throttle, and is the force that accelerates you and the bike. Even the instantaneous acceleration qhen you cracked the throttle is ultimately determined by the power generated by the engine at that RPM. I think the direct relationship between HP and final ratios is often hard to connect. Maximum possible instantaneous acceleraton is at peak HP.


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[sombo]

The best explanation that was ever given to me by an automotive teacher was thus:

Torque = the amount of work an engine can do.

Horsepower = how fast the motor can do that work.


Torque is applied first, it's the part responsible for acceleration off the line. Once you get moving fast enough, then horsepower takes over to bring you to the top speed of the gear.

[00NissanNinja]

Originally Posted by sombo

Torque is applied first, it's the part responsible for acceleration off the line. Once you get moving fast enough, then horsepower takes over to bring you to the top speed of the gear.

I like that definition. If you think about if you see some of the new electric cars they have tons of torque right from the beginning of the rpm range, but then they don't have much horsepower. This results in quick acceleration but a low top speed since there isn't enough power to overcome things like aerodynamic drag.

[JMcDonald]

Torque is a force, and is not equal to work.

And again, acceleraton is determined by thrust, which is determined by power. The power is indeed a derivative of torque, but torque itself is not what determines the acceleraton of the vehicle at any given instant. The mechanical ratio and the current power output are the only factors in the amount of thrust generated to accelerate a body.

Say you have two identical vehicles going 50mph. One engine is at 6000rpm and is capable of producing 40 units of torque, while the other engine is at 12000rpm and is capable of producing 20 units of torque. They are both generating the same power, and their drive ratios are such that they are both doing the same speeds at this power output, so they accelerate the same. If you look at a dyno graph, peak acceleration at a given vehicle velocity will occur when engine power is highest for that given output (vehicle) speed.

In its very basic form, power is the determining factor in the amount of acceleration a vehicle can undergo at a given vehicle velocity.
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[Alex]

Originally Posted by sombo

Torque is applied first, it's the part responsible for acceleration off the line. Once you get moving fast enough, then horsepower takes over to bring you to the top speed of the gear.

It's statements like these that make this more confusing than it needs to be. Even immediately off of the line, a motor is producing torque, and therefore horsepower. And when the vehicle is moving quite fast, it is still producing torque throughout. One cannot happen without the other.

That doesn't mean there isn't a nugget of truth in there, but what it really means is that an engine with quite a bit of torque (larger-displacement, forced induction, etc.) can pull a vehicle off of the line quicker when it is still low in its rev range. While a vehicle with much less torque, will be much weaker while down low in its rev range, and won't feel particularly strong until it is revving quite high to make its power.

But once either engine is in its sweet spot, and making close to its maximum power, it will have the ability to continue to accelerate the vehicle at about the same rate as any other vehicle with the same maximum power.

[Ichiro]

My completely NON scientific way of describing the 'feel' of torque. Using the same vehicle and how torque feels:
High torque would feel like taking off from a complete stop in first gear.
Lower torque would feel like taking off from a complete stop in third gear
No torque would feel like taking off from a complete stop in Neutral.
Does that make any sense?

[JMcDonald]

And to add to what Alex said, the reason a vehicle with low torque values would not accelerate as quickly at low revs is because it is not making much power either (low tq * low revs = low power). But still, acceleraton at any instant and at a given velocity is only a direct function of engine power at that velocity.
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[Samer]

Originally Posted by JMcDonald

Torque is a force, and is not equal to work.

Don't mean to nit pick but this statement is false. Not my opinion, that is a fact. Again, I'm just trying to make sure people are not misinformed.

I can easily prove to you that torque is not a force. The unit of torque in SI units is Newton*meter. Force is measured in Newtons, hence Torque is not a force. It is force times radius. The units speak volumes, and they are the first step in understanding a physical quantity.

[JMcDonald]

Ichiro, what you are describing is actually thrust (which is a function of engine power and drive ratio), not torque itself. You dont actually feel torque, you feel thrust.

It is a difficult concept to understand, especially when we've all been saturated with statements like "horsepower sells cars, torque wins races" since we opened our first gearhead magazines, despite that statement practically being at the polar opposite to the truth.
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[JMcDonald]

It is a different unit of measurement. When measuring angular force (torque), the unit is always a combination of a force and a distance. This is so we can differentiate between 10lbs of force at the end of a 1ft wrench (10lb-ft) and the same force at the end of a 2ft wrench (20lb-ft).
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[Alex]

Thrust isn't a proper measure of work, force, or power, in this context. It's something that a few enthusiast magazines use to get the point across that effective torque at the rear wheel is different depending on the overall gear ratio from the engine back to the wheel.

It's not that rider (or driver) is feeling thrust instead of torque, or power instead of thrust, or any of the above. The rider is feeling the engine propel them forward. That can be measured instantaneously as torque (as long as the gear ratio is taken into account), or over time as power.

[JMcDonald]

Thrust is a meaningful term for a linear force as the final result of the power of some engine through all the mechanical advantages used to propel some body forward. It can be applied to everything from rockets and their nozzles, to motorcycle engines and their mechanical ratios.

Indeed, separating it into instantaneous engine torque, and only conditionally adding in the present mechanical advantages of the drivetrain allows one to more easily connect torque to acceleration. But, the overall picture is that the linear force the tire applies to the pavement to accelerate the bike is the thrust generated by the power as it works through mechanical advantages. To perhaps more easily compare it, consider this. If you select gears to keep the revs near peak HP you will always accelerate faster than when keeping the revs near peak torque.
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[sombo]

Actually alex, mine is simple and easy to understand. It's yours that makes it more complicated then it needs to be. He asked for the simplest, most basic, easy to understand, non-scientific explanation to it all. That's just what I did, then you went and made it all complicated again. What you said is correct, but it makes it complicated. Think basic, think easy, think like a child (or an airhead your choice of which would be harder).

Think of how you would explain it to a 5 year old. Then post that and get back to me.

Also, remember alex, this is how an AUTOMOTIVE TEACHER explained it to us in a class.


If you want to get technical:

horsepower
1806, from horse + power, established by Watt as the power needed to lift 33,000 pounds one foot in one minute, which is actually about 1.5 times the power of a strong horse.

torque
1.
Mechanics. something that produces or tends to produce torsion or rotation; the moment of a force or system of forces tending to cause rotation.
2.
Machinery. the measured ability of a rotating element, as of a gear or shaft, to overcome turning resistance.

[Alex]

I hear you, but simplifying anything to the point of no longer being correct isn't helping anyone. Just because it can't be explained clearly to a 5 year old doesn't mean that we should make up a definition that a 5 year old can understand, does it?

[Alex]

/moved to General (link left here in tech for a week as well)

[sombo]

First off, I didn't make the definition. A professional automotive teacher did. Also it's not simplified to being incorrect. You are still trying to make it more complicated then it really is, that's all it is.

[JMcDonald]

Good point Alex.

And i think your way of thinking about it--looking it as taking the torque value and multiplying it by the mechanical advantage (final ratio)--is a simpler way to accurately understand it. The power curve, however, is the simplest way to say "keep the revs around peak HP for the best acceleration.

Good discussion .
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[FrugalNinja250]

(Torque x RPM) divided by 5252 = horsepower. So, if you want more power, you need either more torque or more RPM, or both. Engines that can keep producing torque when going to higher RPMs tend to make more horsepower.

Units: Torque, lbs/ft.

[JMcDonald]

I was trying to drive home the point that it is the power, and not the value of the torque, that generates the thrust to accelerate the bike.
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[00NissanNinja]

I wouldn't say that sombo is completely wrong although I wouldn't say torque is applied first then horsepower carries you to top speed. I would say initially torque is helping the machine accelerate (higher torque down low in the revs means better acceleration) while horsepower helps the machine reach a high speed (also helps acceleration if the machine has more power). Thats what I got out of what sombo said. Although maybe I just gleaned over it to quickly.

In any case Torque and horsepower really go hand in hand throughout the rev range because they are related quantities.

[CC Cowboy]

For anyone who answered this question;

Don't ever talk to me you eggheaded nerds!

[Flashmonkey]

Originally Posted by CC Cowboy

For anyone who answered this question;

Don't ever talk to me you eggheaded nerds!

For the meat heads:

Torque = how much weight you can lift once (instantaneously)

Horsepower = how much effort you exert lifting a certain amount of weight for a given period of time

The time variable depends on the kind of unit you're using.

If you don't lift weights regularly you may or may not know what the hell I'm talking about.

[Alex]

What if you lift weights irregularly?

[JMcDonald]

LOL!
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[Flashmonkey]

Originally Posted by Alex

What if you lift weights irregularly?

Then you're a Ducati and you need your valves serviced.

[tiggen]

Originally Posted by Sungfooo

Can someone please answer this question in the MOST BASIC form. What is Horsepower and Torque? And how do both of them affect Speed , acceleration , rpms , or whatever else they affect.

I've been looking around and every forum i've come across , people just explain it using scientific mumbo jumbo that I cannot understand.

like seriously try to explain it like you would to a 10 year old girl , then maybe I'd understand.

thankyouuuuuuuu

Torque is the size of your hammer. HP is the number of times you can swing it in a given period of time.

[FrugalNinja250]

Many confuse work with force. Pushing on something is force. Moving it is work. The more/faster you move it, the more work you do. Horsepower is a measure of work, not force. Torque is a measurement of force, not work. Since work requires force and time, torque has to be part of the equation to calculate horsepower. This isn't necessarily the most accurate way to understand it, but it gets pretty darned close, just like Newtonian physics gets pretty close but Einsteinian physics is actually more accurate. We use Newtonian physics in day to day life.

[gfloyd2002]

What this thread needs is pics.

Torque:



Horsepower:

[wvninja]

Torque:


hp:

[WindMeUp]

Torque is measured as pressure applied to the top of the piston, regardless of weather the piston moves are not.

[FrugalNinja250]

Originally Posted by WindMeUp

Torque is measured as pressure applied to the top of the piston, regardless of weather the piston moves are not.

Technically speaking, torque is a measure of rotational force. The piston is constrained to linear motion so the word torque doesn't apply. Torque on an internal combustion engine is typically measured at the crank, in turns of rotational force per distance from centerline. So, if the engine had a 24" diameter flywheel and at the edge of that flywheel the rotational force was measured as 50 lbs, the engine's torque would be 50 ft/lbs. If the flywheel was 12" in diameter and the force was still 50 lbs then the torque would be 25 ft/lbs, and so on.