Since this discussion happens so often, as it has, again, on the previous post, it’s about time we explain horsepower and torque and how they relate. There are a lot of misconceptions, but there doesn’t have to be because both are straightforward terms used everyday when motor vehicles (and a lot of other things) are discussed.
Please read this entire article carefully before commenting. You’ll see where that 5252 number comes from and you’ll see why you can’t talk about horsepower and disregard torque anymore than you can discuss an omelet and ignore the eggs.
You gotta start somewhere, this is a good place.
Every motorhead wants more horsepower, but what exactly IS horsepower? What does it measure? Horsepower is an arbitrary unit created from a common reference point that everyone can understand. In today’s world of advanced scientific instruments, horsepower hangs on, even though it is a little imprecise. Those keepers of the units and standards that quantify everything with precision would rather toss out this well known measure and substitute kilowatts. That Corvette has 298.28 kilowatts, hmm… 400hp just sounds better.
Where did horsepower come from?
James Watt, who did quite a bit of work on steam engines back in the 1700’s, needed a way to measure their output. Watt used a common reference, the horse, as the basis for his calculations (like the inch was based on the width of a man’s thumb). The exact process he followed to find out what a horse could do is open to speculation, everyone seems to have their own favorite story, but the end result was: 1 horsepower = 550 foot-pounds per second, which means, in Watt’s calculations, a horse can lift 550 pounds one foot in one second.
Horsepower conversion formulas
The neat thing about defining a reference point with numbers is how easy it is to convert that reference to some other unit of measure.
1 horsepower = 550 foot-pounds/second
1 horsepower = 33,000 foot-pounds/minute
1 horsepower = .7456999 * kilowatts
1 kilowatt = 1.34102 * horsepower
Horsepower is one measure of power
All of those formulas and conversions are different ways of saying how much work is being done, which is exactly what power is. Power is work done over time.
P = W / t
where P is power, W is the work done and t is time.
Watts are the more common term for measuring power which is why the conversion to and from horsepower is good to know. One watt is 1 joule/second. And that can be converted to … well, you’ll have to do the rest of that research yourself because we could go on forever.
Torque – what is it?
Now, remember that figure of 550 foot-pounds? We said that 1 horsepower was equal to 550 foot-pounds “per second.” It’s important to see that “per second” because horsepower is a calculation not a measurement. Think about that. It means you don’t actually measure horsepower, you measure that force exerted through a distance over a period of time and make a calculation that results in a number, the number is horsepower. That force being measured is torque.
Cars, motorcycles and most everything we are interested in here have engines that turn wheels. The twisting force necessary to turn them is torque. Torque can be measured in several different units but, because it’s more familiar here in the US, we’ll stick to foot-pounds . If you were to attach a one foot long wrench to a bolt and apply one pound of pressure to the end of the wrench, you would be applying one foot-pound of torque to the bolt. So,… torque is a twisting force measured (in our examples) in foot-pounds.
Torque to horsepower conversion
Now we need just a little math, it’s easy but you will have to pay attention. Suppose we attach that one foot wrench to the end of a crankshaft and the engine rotates one revolution against that one pound of resistance. The end of the wrench will move 6.2832 feet (Pi * a two foot diameter circle) against a one pound weight. The end result is 6.2832 foot-pounds of work done at one foot-pound of torque.
OK, here we go:
1 horsepower = 550 foot-pounds/second = 33,000 foot-pounds/minute
33,000 foot-pounds / 6.2832 foot-pounds = 5252Â (Here’s where 5252 comes from!)
So, if the engine rotates against the one pound resistance at 5252 rpm:
6.2832 X 5252 = 33,000 foot-pounds/minute = 1 horsepower
because the one pound of resistance was moved 33,000 feet in one minute
(1 foot-pound X 5252) / 5252 = 1
Therefore, to convert torque to horsepower:
(Torque X RPM) / 5252 = Horsepower
Example: 100 foot-pounds * 4000 rpm / 5252 = 76.16 horsepower
Example: 200 foot-pounds * 8000 rpm / 5252 = 304.65 horsepower
If you understand the above relationship, you’ll quickly see there is a lot of misunderstanding floating around. Both terms are important but they represent different things. Torque measures a force being applied while horsepower is a measure of how much work the force can do.
Most of this is taken directly from pages I wrote many years ago on HorsePowerSports:
Horsepower – Torque – Dynamometers
Adam says
Paul,
There is a minute, but significant error in your explanation:
“…you measure that force exerted over a period of time…”
It should read, “you measure that force exerted through a distance over a period of time.”
Paul Crowe says
Correct and corrected.
Tom Lyons says
I think you did a good job of getting the point across, Paul.
I see this issue as more of a tribal conflict between the “Pirates” and the “Power Rangers”.
The “Pirates” being mostly the Big Cruiser riders, represented mostly by the Harley contingent, have big engines which are quite rpm-limited by their stroke lengths in standard form. Since the torque curve by definition is always predominant over the hp curve up until 5252 rpm, the “Pirates” see their torque number being higher than their hp number, and try to emphasize how their “torque is strong”, and don’t care much about the hp number. And they are right to emphasize their torque curve, because that is going to be the defining factor in their power output, being that they are rpm limited to not much more than 5252 rpm, and probably almost never ride at rpms up there. So for them, torque is king, and they don’t care that the torque number is related to rpm and this gives the hp number at any given rpm. They just see that number and they hang their hats on it.
Conversely, the “Power Rangers” are the guys with the high-revving sport machines which soar to stratospheric rpms. And their engines are not nearly as rpm-limited by stroke, so they can take advantage of a high rpm powerband which is reached by elevating the most efficient rpm range for the torque curve(peak) to give high volumetric efficiency at a much higher rpm range in order to service the needs of high rpm running. This leaves their torque curve relatively lower in the low rpms, and so their attention is all paid to the high rpms where their hp numbers look the best. They “don’t care” about the low rpm torque because their riding is done at higher rpms nearer their torque peak location, and so they also are right to care about hp more than torque because they spend virtually all their time at rpms higher than 5252 rpm, and at those rpms the hp curve will always predominate over the torque curve, again by definition. And there is no doubt at all that a high revving engine which makes its torque at a high rpm will produce big hp numbers because they have both factors of high rpm along with their torque peak occurring at a relatively higher rpm, so they both work together to make big hp.
So, both of these groups, “Pirates” and “Power Rangers” are both “right” from their respective points of view.
From an engine developer’s point of view, there is only to do the modifications which are the main intent of the build.
If it’s a long-stroke low-revving cruiser, there will be efforts to improve the low rpm torque so that comfortable low-rpm cruising is attained, along with some rapid acceleration from even low rpms when needed for passing or highway entry ramps. That’s because those rpms are where the cruiser riders like to ride.
If it’s a high revving sportbike with a short stroke, of course the mods will be aimed at reaching the maximum rpm range with a torque curve that can hang on to produce increasing hp all the way up to max rpms. This means that the “meat” of the torque curve is going to also be way up high in the rpm band, and that low rpms will suffer in comparison, relatively.
That’s because those rpms are where the sport riders want to spend their time, doing high performance riding.
So, to me it’s just a social circle “conflict”, because the definitions are non-arguable. The argument comes in with the “my bike is better than your bike, and THIS is why….” kind of “discussions”. It’s not really a technical argument, but it often is “played” like a technical argument by some proponents of either POV.
In the end, the engine designer or modder makes the engine to produce the amount of power desired in the rpm range desired for the intended application.
Medicated Steve says
Which is exactly why Harley NEVER releases horsepower numbers and only torque values.
todd says
The constant is actually 5250.
What everyone here continues to forget is RPM. RPM is directly related to the speed at which you are traveling through any number of conversion (gear) ratios.
An engine spinning low RPM must utilize a higher gear to achieve the same speed as an engine spinning high RPM. That means the low RPM engine has less advantage, or leverage, to turn the rear wheel. In practical terms, at 40 mph say, one bike is already in fourth gear as another is still in first. It is best then to forget “horsepower” for a moment and calculate the forces (torque) that get translated to the rear wheel and, ultimately, to the road. This force is now called “thrust”.
Assuming zero transmission losses, take 100 ft-lb at the crank at 3000 RPM. With a 24″ diameter tire at 40 MPH you need a 5.4:1 gear reduction. The force at the rear wheel is now 100 x 5.4, or 540 LBF.
Now, take a 50 ft-lb engine at 8000 RPM with the same 24″ tire is also going 40 MPH with a 14.3:1 gear reduction. The force at the rear wheel is 50 x 14.3, or 715 LBF. There is 30% more torque or force at the rear wheel of a 50 ft-lb engine than a 100 ft-lb engine at speed. Now let’s look at that dirty “Horsepower” thing to see how it compares; 100 ft-lb @ 3000 = 57 HP. 50 ft-lb @ 8000 = 76 HP. Hmm, 76 HP is 30% more than 57. Why is it the same? It’s just math.
Horsepower is the result of a math equation and it represents all of the factors involved in propelling or accelerating a vehicle down the road. Horsepower is the apples-to-apples number that is used because it considers torque and RPM. Taking torque on its own for it’s face value does not tell the whole story. Horsepower does.
How many more ways do I need to illustrate this?
-todd
todd says
You are correct, both 5252 and 5250 are typically used in the calculation. Rounding, I imagine.
-todd
Nicolas says
The problem is that “Assuming zero transmission losses ” is not a real life assumption. Torque is what creates the thrust, HP is just a children of torque at best, a calculation at worst.
sfan says
For motorheads not interested in the math, here is the simple heuristic… if all other variables are kept constant:
– more horsepower means higher top speed
– more torque means quicker acceleration (especially if most of the torque band is available at low RPMs and sustained through normal operating speeds)
Most people say they want more horsepower, yet what they appreciate in 99.9+% of riding/driving is torque.
todd says
wrong. There are not two different types of power. According to you, you can have a vehicle with enough power to go 150 mph but not enough to accelerate up to that speed.
“For motorheads not interested in the math…” means I don’t want to take the time to understand something, I’ll just stick to what I “already know.”
-todd
Domino says
“For motorheads not interested in the math…†means I don’t want to take the time to understand something, I’ll just stick to what I “already know.â€
Nope… I see the guys come into the shop all the time and put their bike on the Dyno… I have taken the time to understand (Paul did a great job BTW), but am not interested. I have built my FXR “pirate bike” over time for torque & more torque. It is tuned/built by how it feels in the seat of my pants…feels like it could pull out tree stumps… turns me on. I understand what sfan is saying and agree.
Oh, then I get on my RD350 (power ranger bike) and hit that spot that trips my trigger… Tom, you are right (in my book)
I appreciate the discussion.. You guys are funny sometimes…
akaaccount says
Guess what cruiser guys. The torque and horsepower numbers we’re talking about are at the crank. A big twin turning 3k RPM makes more torque than an R6 turning 3k AT THE CRANK but once you run it through a much higher primary, transmission, and final ratio there’s not that big a difference. Peak HP and torque numbers aren’t aren’t all that are important but since it’s what everyone talks about: An R6 running at the redline (122 hp) makes more torque than a big twin (70 HP) running at the redline at the same wheel speed.
todd says
Another illustration:
What is more water; 100 gallons per minute or 50 gallons per second? If you say 100 then I know you’re really pulling my leg.
Yes, I know, “gallons” is really an antiquated metric of measurement. It no longer means much today but it’s a frame of reference that’s easy to grasp.
-todd
Jon says
Gallons isn’t antiquated at all. GPM is almost used exclusively in the US for sizing pumps, piping, etc in hydronic or plumbing systems.
Chad says
The thing that amuses me the most about these torque versus horsepower arguments at the local pub is that the motorcycle world is not split into high rpm power versus low rpm grunt. There are infinite shades of grey. Personally I step into the argument (foolishly) and state that my bike’s bore and stroke are square, it is mid capacity and has four cylinders to provide smooth operation. Yet it is optimized to produce sufficient low end torque, excellent mid rev torque and builds to 10,000RPM to take advantage of top end power. This means that you don’t get as much stump pulling grunt as a big twin and you don’t get the stratospheric high RPM power of a sportster, but you do get the best of both worlds for any given situation. Therin lies the sweetspot.
tortoise says
Todd, why do you say the constant is actually 5250?
33,000 / 2 pi = 5252.113 . . . or are you using a different value for pi than my calculator?
todd says
You are correct. The formula I remember probably was using rounded numbers. Thanks for catching that.
-todd
Sebastian Wiers says
5250 is accurate to three significant digits, which is as good as or better than you will get on most dyno measurements. Adding more little numbers at the end just creates artificial precision in your calculated values.
Adam says
Pull the math out of the argument and just think of the physical concepts.
Torque is a force (though the units for torque – lb-ft – can easily be confused with work or energy).
A force (torque) can be exerted on an object, but you cannot consider the object’s motion without considering the distance the object travels. This is called work (a force applied through a distance). Work is defined as a force applied through a distance. Work is not a force, it is a measurement.
Alright, so now we have work done. How quickly can the work be done? Power is a measure of this. Power is defined as work done over a period of time … or … power is defined as force exerted through a distance over a period of time. The shorter the time (quicker) or greater the force or distance, the greater the measure of power is.
The key point here is that you need more variables than just torque to describe an objects motion over a distance in a period of time. Without time and distance, the object is motionless, but may still experience a force (torque).
Sportster Mike says
@ Chad – was that Fifty Shades of Grey?
Have read all the above and still confused…
and why do ‘square’ engines feel more torqey??….
Medicated Steve says
It has always been said that square engines are “sweet” in that they have great torque and horsepower and seem to rev quite well also. I don’t know the science behind it but it is a popular belief.
Hawk says
Torque, eh? Yes, it’s long been misinterpreted for power. The Harley long stroke engine certainly gives that “off the line” oomph that equates to “power”, but it craps out as the engine runs out of revs.
I recall the old arguments about the “new” short stroke Manx Norton and if it was faster at the IOM.
Years ago, I drove semis with maybe 120 HP. Some of the hills through the Rocky Mountains were …. “tedious”, shall we say. About 10 years ago, being retired and bored, I decided to co-drive some trips with a buddy in his truck. 525 HP Detroit, 1950 ft-lbs of torque! (Just think about that figure for a moment …. BEFORE it goes through the gearbox!) Holy gee …. where did those hills go? Darn thing pulls like a locomotive! Oh yes, back in the day, we ran 1900 – 2100 rpm. Today, my buddy’s on my case if I’m over 1500 except maybe on a hard pull hill. Much happier at 1100 – 1300 …. fuel, you know.
But then, if we want to talk about torque …. http://www.vincelewis.net/bigengine.html
Tom Lyons says
Okay, so now that it appears to be coming clear that long stroke engines like Harley are most easily able to make their power and lower rpms, and short stroke screamers like MotoGP bikes are set to make their power at high rpms, and there are some in the middle.
Why is this?
It comes down to stroke length and piston speeds. For any given rpm, the longer the stroke is, the faster the piston speed is at that rpm. And the faster piston speed creates more depression(low pressure) in the cylinder than a slower piston speed will. It’s like pulling the plunger of a syringe down faster. It “sucks” in harder. Simple.
So, the long stroke engine like a Harley is getting faster piston speeds way down low in the rpm range. And that means that it can pull mixture into the cylinder better at those low rpms. And filling the cylinder better gives more combustion pressure, thus giving more Force on the piston crown, which turns the crank and gives more torque.
And for any given rpm, no matter what rpm that might be, whether 1700 rpm or 17000 rpm, the engine that makes more torque at that rpm will make more power at that rpm, because when you fix the rpm at one speed, then torque is the only variable left to increase the horsepower result. Increase torque at any given rpm, you also increase horsepower at that given rpm.
This is why the long stroke motors give more torque at the lower rpms, and hence they also give more horsepower at the lower rpms too.
But the long stroke is also why they cannot rev to high rpms too. Because the piston speeds from that long stroke get so high that the mechanical integrity of the engine can be jeopardized from parts going so fast that they might come apart or fail in some way.
Conversely, the high-revving bikes with the short stroke have very slow piston speeds at low rpms, so that they can reach the highest rpms without blowing up the engine. So, their piston speeds will not pull as hard on the inlet mixture until the rpms get considerably higher. Then they start making their best torque production up in that higher rpm range, and eventually they reach their piston speed limit too, except at a much higher rpm.
The torque curve is influenced by the stroke length in this way. And thus, the horsepower curve is influenced by the torque curve in this way.
There are other factors, of course. But the stroke and piston speeds are a good place to start to get a grasp on how an engine breathes and makes its power vs rpm.
tortoise says
“It comes down to stroke length and piston speeds. For any given rpm, the longer the stroke is, the faster the piston speed is at that rpm. And the faster piston speed creates more depression(low pressure) in the cylinder than a slower piston speed will. It’s like pulling the plunger of a syringe down faster. It “sucks†in harder. Simple.”
Well, no, unless it’s also larger in displacement. No matter what the bore/stroke ratio, equal displacement engines suck about the same amount of air each revolution at low revs. At higher rpm, the oversquare engine’s larger bore alllows bigger valves and ports, thus not choking off the breathing.
“There are other factors, of course.”
That’s for sure.
Tom Lyons says
I see what you’re saying.
.
Anyway, I would comment on the same displacement issue by saying that the smaller bore and longer stroke would likely have smaller valves and ports due to the smaller bore size having less room for valve size, and this would give more speed to the inlet charge at lower rpms.
Nicolas says
longer stroke means also a longer arm to which the force created by the descending piston applies to the crankshaft. So even in the case that you get a similar force created by the combustion on a short stroke or a long stroke engine, the long stroke engine will generate more torque.
It’s not the speed of the piston that’s problematic, but the acceleration of the piston reversing its course. Constant speed doesn’t generate any effort on a moving object, but acceleration does. Imagine when you fly a plane, when taking off you feel the acceleration that pushes you (gently) in your seat, while flying at cruise altitude and constant speed you don’t feel anything.
B50 Jim says
Jeeze,Paul — you should have stuck to wind-power turbines if you wanted to kick open a hornet’s nest. Everyone has an opinion on what is a simple concept, figured by simple arithmetic. Numbers don’t lie.
And let’s remember our grade-school science here — a descending piston in a normally-aspirated engine does not “suck” through the valves; it creates a partial vacuum, and atmospheric pressure pushes the air-fuel (or air in the case of direct-injection engines) through the valves. It’s a point of semantics but important.
Hawk says
Ok, so after I posted above, a buddy sends this …
http://www.liveleak.com/ll_embed?f=4a88a935f5f0
Adam says
That video demonstrates the advantages of a longer wheelbase, shorter gearing, and skill – take notice in the fact that the Fireblade rider is not holding the revs up off the line – he is not placing the engine near the peak horsepower range.
Paul Crowe says
Hawk, Excellent video! 🙂
Drive The Wheels Off says
That video is a good example of P = W / t
Stretch the t out more and things change. Comical video
Paulinator says
I spent an hour on a Ducati Multistrada 1200 a few weeks back. The dual purpose layout with a 33 inch seat height gave the bike a very high center of gravity. It made massive torque at low rpm (90 ft.lbs I believe) and is claimed to make 150 hp at 9200 rpm. The bike wasn’t set up with limits yet, so it was absolutely friggin’ dangerous!!! It felt like a 1/4 inch too much throttle at highway speeds would easily rub the numbers off the license plate and send me tomahawking into an awaiting ambulance.
I found it interesting that the Ducati L-twin engine is radically “over-square” at 4.17 inch bore / 2.67 inch stroke. I would say that stroke certainly governs maximum RPM, though swept volume determines maximum torque.
Hey Paul. You want to start another debate…the benefits of big-bores versus strokers… Discuss…
jurneyman says
A factor that seems to have been ignored relating to the higher piston speed of the longer stroke motors is the rod length to stroke ratio. The longer the rod in relation to the stroke the lower the piston speed will be.
Nicolas says
I’d need explanations on that point …
The stroke lenght is defined by the diameter of the rotation of the rod on the crankshaft. The speed of the piston is defined by the rpm and stroke. A longer or smaller rod will not change the stroke length not the rpm.
todd says
Here’s a good way to illustrate horsepower to yourself on your own bike, regardless or what kind of bike it is:
Find a nice stretch of open road and climb up to speed, say 40 mph (I like 40, it’s a good cruising speed) and snick your way into top gear. Now whack the throttle open. Result, hmm, OK. You feel the full benefit of your max torque (or thereabouts).
Now repeat the process, this time keep it in third gear at 40 mph. Now whack the throttle open. Result, wow, it’s pulling remarkably better. That’s funny, the engine is producing approximately the same amount of torque…
Try it again in second, then first. With each lower gear you get more and more acceleration even though your engine is producing the same, if not LESS, torque at these higher rpm. Why is this? It’s called leverage. The amount of force applied considering the leverage available (move more in the same time) can easily be quantified by “horsepower”. Yes, even a big, high-torque V-twin makes horsepower, more and more as you rev the engine.
Now, lower the overall ratios and spin the motor to 9k and you’ll understand why a little motor without much torque can accelerate harder than a big motor with big torque.
-todd
Adam says
Todd,
Your argument does illustrator horsepower, but it doesn’t eliminate the variable of leverage – torque/force at the wheel vs torque/force at the engine crank.
A much simpler version of your argument that eliminates the variable of leverage:
Rev your bike to half of the maximum RPMs in second gear (you’re most likely at the peak of the torque curve), drop the clutch and note the acceleration. Now repeat the process at 80-90% of the max RPMs in second gear (you’re still most likely near the peak of the torque curve, but now near the peak of power curve) and note the acceleration. Let’s hope you don’t loop the bike trying to do so…
Here’s the real question… Someone tells you an engine makes 50 lb-ft of torque, but they don’t tell you the RPMs at which that occurs. The engine makes 100 hp. Now, in the same vehicle, someone tells you the engine makes 200 hp, but still makes a peak of 50 lb-ft of torque. Which vehicle do you think will be faster?
todd says
Of course the 200 hp engine. It has twice as much power, it will accelerate twice as hard.
todd says
What’s even better to consider is that, if I told you one engine produces 50 ft-lbs of torque and another 100 ft-lbs there’s no way to know which one will accelerate harder without more information.
-todd
Marvin says
In drag racing we have a 1320 feet of test bed and there’s plenty of data to calculate HP & Torque figures by the vehicle weight, acceleration and speed along its length. The rule of thumb is-
Horsepower is how fast you hit the wall,
Torque is how far you take the wall with you.
http://www.wallaceracing.com/et-hp-mph.php
http://www.1728.org/mtrtrq.htm
Hope this data helps.
Qwerty1 says
Oh my goodness Paul, what have you done…………….??!!
Paul Crowe says
Wait until you see my post for the electric motorcycle crowd. I think I’ll define volts and amps. 😀
B50 Jim says
Volts are electrical horsepower, amps are electrical torque.
There, that oughtta start the argument… I mean, discussion.
todd says
Volts is more akin to RPM. Watts is the horsepower of electrical energy.
-todd
Eddy Current says
Volts = RPM
Amps = Torque
Volts X Amps = Watts = Horsepower ( X 746 and neglecting the motor efficiency curve)
Nicolas says
Now Paul hat you’ve explained the difference between Torque and Power, maybe it would be a good idea to explain what contributes to make an engine torquey and/or powerful …
Hooligan says
Torque is cheap.
Chris says
“Each unit can be determined by scientifically reproducible results”
For mass, this is actually untrue. All the other units are based off some physical constant (time is referenced to the vibrations of a cesium atom, length to how far light travels in a second, etc.), but for mass, the reference standard is a small ~1-Kg platinum cylinder stored in a vault in France that’s been gaining a few fractions of a gram for the past several decades.
cl
Paulinator says
…Its the cuisine.
Peter Miles says
This type of discussion has been going on in the sailing world for literally hundreds of years. The only difference was that the terms were “keel shape”, “Sail shape”, number of sails, incline angle, etc. The real issue is that any sailboat (or motorcycle) is a compromise of all the factors that go into the design. There is no best of everything, there’s only better for this purpose or worse for that purpose. You just have to think about what you want most from your sailboat or bike and find the design that suits the purpose the best. Then sit back and say “I’m happy!” and sup your brown ale while watching the aficionados try to out-brain each other with masterful arguments. Highly entertaining.
OMMAG says
I don’t know it looks like some of these wags are a bit like the Monty Python….
These came to mind:
“I came for an argument!” …. “No you didn’t.”
“What is the airspeed of an unladen swallow?” …. “An African or European swallow?”
“This parrot is dead!” … “No it’s not … it’s just sleeping!”
Cheers!
fast Eddie says
Spot on Peter, which leads me to open another can of worms . My [ ego for a reason ] 1997 Buell s3t . Was created with a vision .. Torque was top dog
for eric and company …. All of the other factors that were put into it were part of
the process. I would hope the discussion at hand would be to decide how this
all relates to a motorcycle and its rider …. I can tell you this . I had 30 or so M/c’s
over 40 years of riding . Torque is king when it comes to enjoying a m/c . Brown ale ?
na ,,,,,, I’ll take a 400 mi ride any day …… 106,435 mi now … ride safe FE
JanBros says
I coudln’t disagree more Eddie ! feel is what it’s all about, it’s not about horsepower or torgue. I’ve had many bikes, but I am still loving my current, even after almost 20 years of riding it, and after having ridden much more powerfull/torquier bikes. it’s only a 250 and needs to be kept higher up the rev-range, but it gives so much more back than any modern bike, and you have all the fun at much more reasonable speeds. btw : it only has about 65 BHP, has next to no torgue and …… it’s a 2-stroker 🙂
Drive The Wheels Off says
Good point Peter, This was illustrated in Austin last weekend between Honda & Yamaha and the COTA track
(although, some riders were saying Honda figured out some improvements while on the brakes. This improvement combined with Marquez’ increasing confidence could turn a highly anticipated year into a snooze)
roman says
Nice idea, but since you’re spending time on the definition of power and torque, why not talk about the official and most commonly used metric units such as NewtonMeters and Kilowatts instead of mixing it all up?
Also, there are different ways of measuring horsepower, the same word can be used as a reference to metric horsepower, mechanical horsepower, sometimes even brake horsepower.
I don’t want to sound annoying because I’m aware you guys are used to work with inches, feet and stuff but the explanation is really easier when using meters, Newton Meters and Watts the hole way through…
cheers!
Scotduke says
Yes, all this feet, inches and pounds stuff is plain confusing. Just how many feet are in a mile anyway? Metric units are a whole lot simpler. Back when I was still an engineer I remember being asked to rebuild an old piece of kit by my employer so as to save on costs. This involved cannibalising equipment made in the US and adding it onto base parts made in the UK some years previously, with new components made in the UK. The new bits were in metric sizes, the old British bits were in standard units but with Whitworth threads while the American parts had UNF threads and again with standard units. I tried to explain to my boss that maintaining the thing would be a nightmare (and trying to get it to fit together and work certainly was) but he said we needed to cut costs. And so I was proven right when the time came for servicing. Metrics please!
B50 Jim says
Anyone who works on on vintage English vehicles has sets of inch, metric and Whitworth wrenches. There are some situations when all three are needed, on the same vehicle. And a thread gauge is a necessity. All part of the fun. Why would anyone want to work on something with all the same kind of fasteners?
Sportster Mike says
Still confused ….
but would still like a square engine in my Sportster (Zippers 88ci kit) for more horse and more torque and more power and ……
Still my horse is happy (just the ONE horsepower) and is outstanding in its field!!….
Patrick Teng says
I think the point is… One rather have higher horsepower than torque because you can always get the more torque through gearing, but not the other way around.
MVista007 says
A horse is quite a strong animal.
Im sure one of those race horses, or the ones that used to pull heavy carts could do at least 25 HP.
Did anyone ever actually do the calculation of how many HP does a horse actually have?
B50 Jim says
It depends on how the horse feels that day, which points up the biggest drawback in using living creatures to set standards. But Watt based his calculations on his observations; that the average work horse of the time could lift 550 pounds/second reliably during the course of a workday. A good race horse probably could generate 25 hp, but only for a couple minutes, then it’s back to the stable for a week. It’s like a Top Fuel Dragster. A big draft horse can do far more work than the average nags used in Watt’s time, but it is bred for size and power, not much speed. It’s like a bulldozer.
Watt used a unit of measure everyone at the time understood. He could have given it another name, say, a watt, but English modesty forbade that. It’s ironic that the best international standard for rating engines now is the watt. Horsepower is outdated as work horses.
Scotty McScottish says
Scottish modesty!
Don Fraser says
horsepower measures how much work the engine will do, the engine with higher hp will win the race
tortoise says
An engine tuned for absolute maximum power, with big ports and long-duration cams, will produce this power over a very narrow range, requiring frequent shifting of a close-ratio transmission. A less radical tune, with a bit less power, may be more effective, and certainly easier to ride. This less-radically tuned engine would be commonly described, perhaps inaccurately, as “torquey”. In the era of dual-clutch, zillion-speed drivelines, the more extreme tune becomes more workable.
todd says
And it will also be described as slow.
Next time you’re on a highly tuned bike do a zero to sixty run. It’s likely you’ll be in first gear the whole three seconds to sixty. Now do the same test on a big “torquey” motor and notice that it takes all five or six gears to get to sixty in twice the time. And I ask you this, which bike has a narrower power band?
-todd
tortoise says
Not an apples-to-apples comparison. The racy job is going to be lighter. If the same power to weight, including rider, the machine with the broader torque curve will be at least as fast, all thing being equal, which they never are.
Don Fraser says
no one at a dyno brags about how much torque the engine made, it’s all about hp.
Doug says
have fun “riding” your Dyno
rohorn says
That’s why nobody races anymore. Just send in your dyno printout and get a trophy! Much more fun! Who cares how little power it makes either side of peak – that one single number means everything!
Tomorrow’s (or next week’s?) topic: Is that Made In America Motorcycle Company That Uses Non-American Sources Better For Americans Than The Non-American Motorcyle Company That Hires More Americans?
Followed by: How CARB Cleans California’s Air By Fining Violators Instead Of Requiring Them To Recall And Fix Offending Vehicles.
And In The Works: Is The Size Of A Motorcycle Market Proportional To The Profit They Make From It?
Hard issues we must finally address!: If Everyone Fixed Their Own Motorcycles Back In The Good Old Days, Then Where Did All Those Old Motorcycles Go?
And the hardest one of all to face: If Motorcycles Are So Much Fun, Then Why Am I Sitting At A Computer Wasting Time On The Internet???
todd says
Why do people care about peak power? I guess because its a good way to understand the maximum performance of a vehicle.
I guess most people don’t push a vehicle to its limits most of the time. In that case we can look at three quarters peak or maybe half peak. In that case a 100 peak HP bike will be able to put out 75 or 50 HP and a 50 peak horse bike will be putting out 38 or 25 HP. In fact I can’t think of any instances where a 50 peak HP bike will ever be more powerful than a 100 peak HP bike.
I know this for a fact, my BMW 750 will never, ever, accelerate as hard as a GSXR750.
-todd
rohorn says
I forgot that torque is constant and that power is always in proportion of peak power RPM. Yes, Always.
todd says
The effect of torque is also RPM dependent. 50 ft-lb will accelerate twice as hard at 8000 rpm as it will at 4000 at the same road speeds. Since torque doesn’t tell you how hard the motor will accelerate without knowing RPM that’s why we use the term “power”, or “horsepower” in these cases.
-todd
Gerry says
Before you head for electric nirvana, there are still some subjects that should also be explored in the context of power. How much fuel an hour are you burning? 1 US gal/hour = 15HP/Hr approximately. How much power is lost in the transmission on your bike? Chevy Turbo 400s suck up 14HP. Do you, like commercial pilots just carry enough fuel to get to the next city? unused fuel is dead weight. It also affects the C of G. Do you know what speed you can drive to get maximum efficiency or what sprocket you need to put that power on the road? Is all that torque/HP you see on the dyno optimized for your bike’s drive train? A 1o HP 1 cylinder engine hits the tranny with a 10HP impulse. A 20 HP 2 cylinder hits the tranny with the same 10HP impulse. If you are increasing the HP per cylinder perhaps you should consider more cylinders to protect the transmission.
Just some thoughts to consider….
todd says
There’s always cush drive.
-todd
Paulinator says
Good stuff 🙂
Nortley says
Two illustrations. I have two hydraulic machines, a shop press and a wood splitter. Both are rated at 20 tons of force. Remember, torque is a force. I can split wood with the splitter a lot faster than with the press. Why? The engine on the splitter has more power than my arm wanking the jack handle, so can maintain the hydraulic pressure to produce the 20 tons of force as ram extension tries to drop the pressure. A steam engine produces maximum torque at zero rpm – full steam pressure is exerted on the piston for maximum force on the crank, and pressure and torque actually drop off with rpm rise due to throttling and friction losses on the way to the cylinder. So we have a stopped locomotive, with a 28 ” cylinder and 34″ stroke, steam at 220 psi, and the throttle is yanked open. How much power is produced at that moment of maximum torque? None. No movement has occurred, so no work has been done, thus no power has been produced.
Mike T says
Despite the fact that the word “inch” is the same as the word for thumb in many languages, it isn’t derived from the width or length or whatever of a thumb. Its etymology is from the Latin word for “one twelfth part” i.e. of a foot, an ounce is similarly derived (for one twelfth of a Troy pound).
Kevin says
Great article and some interesting comments.
I want to bring up the horse. I too am interested in how much horsepower a horse actually “makes”.
I just don’t see a 1000lb motorcycle with a 1hp motor accelerating like a horse does.
Kyle T says
Some specific comments:
“In today’s world of advanced scientific instruments, horsepower hangs on, even though it is a little imprecise.”
Horsepower is not “imprecise.” Imprecise implies that it lacks precision; it does not. A horsepower is just as precise as a Watt or a joule/second. Perhaps you were looking for “arbitrary,” as the original James Watt definition is fairly arbitrary?
“horsepower is a calculation not a measurement. Think about that. It means you don’t actually measure horsepower, you measure that force exerted through a distance over a period of time and make a calculation that results in a number, the number is horsepower. That force being measured is torque.”
This is simply incorrect. Horsepower and torque, as you have mentioned, are mathematically related. As such, it’s silly to act as though one can be measured and one cannot. However, there are lots of examples of cases where you “measure horsepower” and not torque. For example, if you have an inertial dyno, and you measure the speed of that dyno, you are effectively measuring the kinetic energy of the roller. The change in kinetic energy over time is POWER. So, by measuring the speed of an inertial dyno, you can measure power just as directly as you can measure torque (which you’d measure by looking at the rotational acceleration of the dyno).
Any time two units are mathematically related, as torque and horsepower are, it’s silly to claim that only one of them can be “measured” and the other can only be “calculated.” With a little bit of high school algebra, you can swap out the units with ease.
Some additional commentary:
Torque (a measure of force in the rotational frame) is INCAPABLE OF DOING WORK by itself (ie without motion). In other words, torque, by itself, is not representative of the ability of an engine to accelerate a vehicle. You need to have information about torque AND speed (RPM) (or gearing, as the two are related), and we all know that torque and RPM just gives you horsepower, so what I’m saying is that you need horsepower. Horsepower, by itself, tells you what an engine is capable of doing, with regard to acceleration, top speed, etc.
In fact, you can easily work out a formula using simple algebra which shows that the amount of thrust (force accelerating a vehicle) available at any particular speed is purely a function of the amount of horsepower available; power is all that you need to know. On the other hand, if you just know the torque, it’s insufficient information to determine the thrust. Thrust is linearly proportional to horsepower for any speed.
Ellwood says
Hi Kevin, i read once, somewhere, that an average horse develops 50 hp. that sounds reasonable i think ???
Mike says
Seriously, torque vs horsepower is an issue that confuses even engineers. I’m one, I understand it well because I love the topic, but most of my colleagues are surprisingly ignorant about it, making for some heated discussions at the coffee breaks.
Torque is to power what area is to volume. It lacks one dimension – velocity – without wich you cannot make any prediction about performance. I can easily produce a dragracer-level torque with a socket wrench, but I cannot turn it at 10000 rpms. The wrench is for all intents and purposes static, making my power output zero.
Power is what propels your vehicle, assuming you want to move above 0 velocity. Power is torque times velocity. Twice the torque at the same revolutions per time unit equals twice the power. Half the torque at twice the revs equals same power. Twice the torque at half the revs equals same power. And acceleration is a function of power and weight.
A 100 BHP engine will accelerate you ten times quicker than a 10 BHP engine between velocity X and Y – regardless of torque, assuming no drag or difference in transmission losses.
One 100 BHP engine may have ten times more torque than another 100 BHP engine, it will still accelerate the same. Why? Because it will be ten times higher geared to reach the same vehicle speed. The torque on the wheel side of the gearbox will be the same.
There is however one interesting caveat: torque DISTRIBUTION over the velocity range. A 100 BHP high-torque engine may outperform a 100 BHP low-torque engine, for reasons you need to know what an integral is to comprehend. Over the revving range, the accumulated work may be higher.
This is not necessarily true, a badly built high-torque engine may have a worse torque distribution than a good low-torque engine, but it is mostly the case in the real world.
Thus, a 100 BHP large-displacement harley may well outperform a 120 BHP 600 cc bike at a dragrace.
Hamish Lamont says
Probably the most fascinating topic on the Kneeslider to date! I love it when really knowledgeable/smart people duke it out. So, what about every day applications? Speaking of Dukes, I’m building a 944SS which has had serious head work. It now has short manifolds, FCR41 carbs, ported heads, big headers; all the things which will make it a top-endy (hp biased) bike. BUT, its also got DP “Torque Cams” and I’m gonna stick 90mm bellmouths on it to make it super torquey! What will be the result I wonder???????
Also, I see Ferraris with high revving normally aspirated motors putting out pretty respectable (and reasonably flat) torque curves. So they have tractaable motors that rev to the heavens (surely the holy grail); what gives?
Mike says
I had a Camaro with similar configuration – good flowing parts for good high-revving aspiration, yet a mild cam.
Experts told me this was folly because I would get less fillrate at lower revs than optimal, yadda yadda, but the resulting character of the engine was very pleasant. It pulled like a truck from idle, very flat torque distribution most of the register, though it was obvious at “higher” revs (>4 krpm, hehe) that there was really no point in going further. It didn’t feel choked, it just sorta lost interest closer to the redline.
I could probably have gained a bunch of horsepower with a sportier cam, but I loved burbling around town at <1 krpm (manual tranny). Also, I would probably have gained torque with longer intake runners and whatever, but it didn't seem to suffer much in that department as it were.
So I think your Duke will be a blast.
Scott says
Wow, this must be one of the most detailed and accurate posts on the whole horsepower vs. torque topic I’ve seen so far. Good job! I found a similar article right here: http://www.unhaggle.com/blog/everything-need-know-torque-horsepower/
Basically, it does the same thing, describing the similarities and differences, but in a less detailed manner.