Whats the difference between Torque and Horsepower

[Denilson]

Everything put together.

You can make assumptions from a handful of bits of information - power, torque, weight, drivetrain - but without the whole dataset (including gearing, power/torque curves and losses, then local atmospheric conditions, CdA, surface grip coefficient, tyre grip coefficient) you can't get a decent picture.

This is why saying "an F1 car has no torque but is really fast, while a truck has loads of torque and is really slow" isn't really an argument against using torque as a metric of performance - you're missing weight and power, and that the F1 car has 1600hp/ton where the truck has 40hp/ton should be a clue - the fact that engine torque is a meaningless figure as a metric of performance should do that by itself.

You can defenetly get a decent picture by looking at the car and know how much effect (P) it have.
I know perfectly well that other factors play a part in a cars performance. But those are similar for all cars.
If 2 cars have the exact same engine, but apart from that are constructed in different ways, those details come in to play ofc.

This is why saying "an F1 car has no torque but is really fast, while a truck has loads of torque and is really slow"

Did I say that?
Perhaps you need to read my post again.

As far as I remember, I made an example of 2 equally powerful engines (despite it's torque differences) that are manufactored with different purposes in mind.
Still, they both are equally strong/powerful.

 

[Famine]

I distinctly recall responding to the person I quoted, but not to you. Perhaps I need to read my post again and work out where I said "Denilson said". I thought you said "tractor" rather than "truck" anyway. Boy is my eyesight bad today.

You're good with words, I'll give you that.
But putting it like you did, "The second most useless is peak engine power" implyes that the peak bhp number is irrelevant when it's not.

It's completely irrelevant. I mean, mind-blowingly irrelevant.

You're talking about the average bhp over a sertain rpm range. So if the average bhp output over the rpm range is 50 bhp, that's what you get in average acceleration, and therefore the peak bhp is'nt relevant..

Now you've added a modifier - range of rpm over which the power is delivered. That's not the peak power on its own.

But, we're duscussing cars here, and the manufactors don't develop cars with high peak bhp, and then fit a gearbox to that that don't allow the Engine to work in the best range.

They do it all the time. The same gearbox will be fitted to cars with the same essential block, but in 1.2, 1.4, 1.6 and 2.0 variants, despite the differences in power and torque curves. And what about where different manufacturers have the same basic car type, with the same basic engine power and torque but different gearboxes?

But now you have power and torque curves and gear ratios as modifiers to your peak power. That's not the peak power on its own.

Therefore, the peak bhp will give you a decent idea of how fast a car is.

Not on its own. On its own it is useless.

2 similar cars:

Now you've made yet another modifier - you've said the cars are similar. That's not the peak power on its own.


Let's remove all of the modifiers:

Car A: Peak power of 135hp
Car B: Peak power of 170hp

Which is faster? Which is quicker? This is why peak power is the second most useless number - it's just torque at one unspecified point of the rev range modified by time.

Here's the same thing for torque:

Car A: Peak torque of 115lbft
Car B: Peak torque of 170lbft

Which is faster? Which is quicker? This is why peak torque is the most useless number - it's just torque at one unspecified point of the rev range.

We're missing the power curve, the torque curve (though one can be derived from the other), the gearing (including the wheel assembly size), the weight (and distribution), the drivetrain and the CdA at a minimum to determine which of the two cars is quicker or faster, even if they're wearing the same tyre compounds on the same piece of road at the same time.

So I shall repeat, peak power on its own is a useless metric, but not quite as useless as peak torque on its own, of vehicle performance.

 

[Denilson]

You quoted something that I said in the wrong way (and you still have'nt appologized that you implyed that I said something I defenetly did'nt say.. Or anyone else have said either for that matter).. That's why I quoted you.

And I had to bring such things up, because you brought it up.
Don't try to make me look bad.
My initial post was only aimed at the actual engine alone.
No matter the loss in drivetrain, draftcooficients, tire grip etc. Such parameters are TOTALLY irrelevant for the bhp/torque debate.

Now that you've brought other factors in to the equation, I need to tweak my example so that you don't neglecte well known physics.
You're not doing that in fact, but the way you write won't help bringing any light on the actual subject.

You only try to stay on top of this.. But physics are physics. No matter what mighty Famine says. Sorry..


I did'nt once say that peak power will tell you everything. But the fact that manufactors don't put gearboxes in the cars that does'nt fit the powerband will help you to get a DECENT idea of what an engine is capable of performing.


Oh, and I have to add that you're right in what you say..
But you totally run away from the bhp/torque debate when bringing up all other details that are'nt relevant for the OP's question.
And I know that you know that I'm right.. But you can't for your life admit it.. It's not in the nature of you moderators... Sorry, Administrators..

 

[Famine]

You quoted something that I said in the wrong way (and you still have'nt appologized that you implyed that I said something I defenetly did'nt say.. Or anyone else have said either for that matter).. That's why I quoted you.

I in no way referred to you nor quoted you. You're imagining a slight.

You are not the originator of the "torque is a useless metric of performance because F1 cars have very little and trucks have loads" argument.

My initial post was only aimed at the actual engine alone.
No matter the loss in drivetrain, draftcooficients, tire grip etc. Such parameters are TOTALLY irrelevant for the bhp/torque debate.

There should be no debate.

Peak engine torque is irrelevant to performance - it needs modifying by a whole host of factors to work any function from it. Peak engine power is slightly less irrelevant to performance but still irrelevance - it's just torque modified by time.

Neither figure on its own is relevant.

Now that you've brought other factors in to the equation, I need to tweak my example so that you don't neglecte well known physics.

If I'm neglecting well known physics there must be some way to derive vehicle performance directly from either peak engine torque or peak engine power, since the only point I've made is that both are irrelevant on their own.

Please furnish me with what I have neglected and how to calculate these things with no other modifiers from peak engine torque or peak engine power on its own.

You only try to stay on top of this.. But physics are physics. No matter what mighty Famine says. Sorry..

Then please go through the physics from peak engine power on its own to ultimate vehicle performance with no other modifiers.

I did'nt once say that peak power will tell you everything.

Then why, for the love of bees, are you arguing with me?

But the fact that manufactors don't put gearboxes in the cars that does'nt fit the powerband will help you to get a DECENT idea of what an engine is capable of performing.

They do it all the time. The same gearbox will be fitted to cars with the same essential block, but in 1.2, 1.4, 1.6 and 2.0 variants, despite the differences in power and torque curves.

It's called "saving millions in R&D".

Oh, and I have to add that you're right in what you say..

Then why, for the love of bees, are you arguing with me?

But you totally run away from the bhp/torque debate when bringing up all other details that are'nt relevant for the OP's question.

Luckily, I answered it 7 years ago and he's long since stopped caring.

Peak power and peak torque on their own tell you nothing. You need lots of modifiers. In the answer I modified the peaks by gearing and vehicle (identical).

 

[CSLACR]

Peak power all by itself is useless, yes.

- BUT -
If you leave every element in the equation, you know the gearing, the cd, the mass, every detail about a vehicle except HP, you have absolutely no clue how fast it will go.
If you do the same but leave the torque rating out, you'll actually have a pretty good idea how fast it will go.

Excuse yourselves(whomever all said it) saying "high rpm motors don't last".

 

[Denilson]

Famine.. Sorry mate.. You still run away from what my first post in here was all about.
Namely that: Effect (P) moves an object. Nothing else.
Only reason I took sertain examples are to demonstrate that torque is irrelevant, but effect is not when trying to guess how a car will perform.
It's simple..

And if you read my post again, I did'nt say that you neglect physics.
But what you do do, is to throw in parameters that's not relevant for the power/torque debate, and therefore people will not pay attention to what this is all about.
You're correct (once again) in what you say have an impact on a cars performance, bit that's still irrelevant to the actual subject.

 

[Luminis]

If you want an engine that you don't need to rev much at all, and don't need to change gears at all because you don't want to do that either..
Perhaps you want to pull a mobile home behind it as well..

It's still the effect that makes your car move.

Er, what?

You've been comparing an engine with lots of low end torque to one with high peak RPM and the resulting high HP, implying that there was no difference between the too. While, in fact, you do get the same HP, or rather, effect out of the two, you'll have to put a lot more stress on the engine, if you're going with the F1-style one.

Dunno about you, but I would consider that a downside - especially if the effect is constantly needed, for example if you're driving a huge, heavy truck.

I know that, in the end, it's the effect that makkes the car move, and I don't dispute that. All I'm saying is that lots of low end torque have their benefit, obviously. Whether you want to call it irrelevant that you've got to put much more stress on a low-torque engine to do certain things, that's for you to decide. I for one don't think it's in any way irrelevent.

 

[homeforsummer]

Excuse yourselves(whomever all said it) saying "high rpm motors don't last".

Not the best example. Sports bikes aren't designed to last for hundreds of thousands of miles like car engines. They also need much more frequent servicing and even rebuilds.

So although whoever said "high rpm motors don't last" wasn't entirely correct, your rebuttal isn't a particularly good example of a high rpm motor that *does* last.

 

[CSLACR]

Er, what?

You've been comparing an engine with lots of low end torque to one with high peak RPM and the resulting high HP, implying that there was no difference between the too. While, in fact, you do get the same HP, or rather, effect out of the two, you'll have to put a lot more stress on the engine, if you're going with the F1-style one.

Dunno about you, but I would consider that a downside - especially if the effect is constantly needed, for example if you're driving a huge, heavy truck.

I know that, in the end, it's the effect that makkes the car move, and I don't dispute that. All I'm saying is that lots of low end torque have their benefit, obviously. Whether you want to call it irrelevant that you've got to put much more stress on a low-torque engine to do certain things, that's for you to decide. I for one don't think it's in any way irrelevent.

Single stroke power is 100% unusable. That's his entire point, and it's 100% fact.
Idle speed is at minimum 500 hit per minute, or roughly 8.5 per second. So at the lowest idle, a single stroked is come and gone 8+ times in a single second.
So no, when you're doing tens or hundreds of revolutions per second, the power of just one of those isn't significant at all.
You multiply the single stroke power by how many times it is delivered to get total force. My car makes over 1 million ft-lbs of torque per minute at it's peak. 200 X 5252 = 1,050,400
500 ft-lbs? Gonna need more than that to tow anything.

He never said an F1 car is a good tool for towing, but with the right chassis and gearing, it could tow as well as a much larger motor, yes.
Because HP = Power per minute.

HP is the mathematical calculation we use to determine how much power an engine makes while it runs.
Torque + RPM's = True power.

Not the best example. Sports bikes aren't designed to last for hundreds of thousands of miles like car engines. They also need much more frequent servicing and even rebuilds.

So although whoever said "high rpm motors don't last" wasn't entirely correct, your rebuttal isn't a particularly good example of a high rpm motor that *does* last.

Hard to find the sport bike with a blown motor.

And if we're talking longevity, people have to start driving the cars we're comparing in the same manner as the bike.
The simple fact bikes can reach 100,000 miles with the way they're generally used is outstanding, and your common car engine would be long dead.

 

[Luminis]

He never said an F1 car is a good tool for towing, but with the right chassis and gearing, it could tow as well as a much larger motor, yes.

I get the initial point. The only thing that is bothering me is that example. Whith a small, F1 style engine, you'll have to rev way higher to get the same effect - and that's not going to make the engine last any longer or make it consume less fuel.

That's all I, for one, am saying.

Hard to find the sport bike with a blown motor.

And if we're talking longevity, people have to start driving the cars we're comparing in the same manner as the bike.
The simple fact bikes can reach 100,000 miles with the way they're generally used is outstanding, and your common car engine would be long dead.

And the fact that a bike engine has to move considerably less weight (a 440lbs bike + driver compared to a 3400 lbs car + driver) doesn't matter at all, right?

 

[CSLACR]

I get the initial point. The only thing that is bothering me is that example. Whith a small, F1 style engine, you'll have to rev way higher to get the same effect - and that's not going to make the engine last any longer or make it consume less fuel.

That's all I, for one, am saying.

So change the example to a Dodge Viper engine vs a diesel.
Same result.

And the fact that a bike engine has to move considerably less weight (a 440lbs bike + driver compared to a 3400 lbs car + driver) doesn't matter at all, right?

Full power is full power, no?
I guess if you like we'll change that example too.

Honda Civics last longer than Chevy Luminas. Despite running 2-3K more RPM and constantly running higher RPM in daily driving.



I'll never understand why people have the need to pick at an example even while they know the meaning behind it is true.
Seems argumentative to say the least really. Didn't get anywhere with it either.

 

[Denilson]

I get the initial point. The only thing that is bothering me is that example. Whith a small, F1 style engine, you'll have to rev way higher to get the same effect - and that's not going to make the engine last any longer or make it consume less fuel.

That's all I, for one, am saying.

I'm perfectly aware of the practical issues with an F1 engine towing heavy loads.

But, with the proper gearing, it actually can.

Yes, it's likely the maintenace bill would take a step up
Yes, it will consume much more fule
Yes, it is not practical at all
But that does'nt have anything to do with the subject.

So what you can see when compring the 2 equally strong engines is that on the other hand, the purpose is
* Towing heavy loads
* Low maintenance costs
* Low fule costs
* Durability

And on the other hand
* Really fast acceleration and top speed
* High maintenance bills
* Enormous fuel costs
* Low durability

But both engines are still equally strong at it's peak bhp. It's just that the purposes are different.

And I only wanted to discuss bhp/torque as far as the engine goes.
If we're going to discuss how and why this or that happens in this or that car/truck/F1 or whatever, we need to start a totally new subject.

Many things can determine how fast a car accelerates, much more than the engine alone. But if we're going to discuss the engine alone, we need to leave the discussion regarding practicallity issues, tire grip etc behind, cause that has nothing to do with what the engine is doing.

If 2 identical cars engines produce 500 bhp, and my tires are made of hard plastic, I won't accelerate as fast as your car with proper rubber tires, cause it have much better grip.
But hey, the engines are still equally strong, right? 👍

 

[homeforsummer]

Yes, it's likely the maintenace bill would take a step up
Yes, it will consume much more fule
Yes, it is not practical at all
But that does'nt have anything to do with the subject.

...

And I only wanted to discuss bhp/torque as far as the engine goes.
If we're going to discuss how and why this or that happens in this or that car/truck/F1 or whatever, we need to start a totally new subject.

That being the case, why make a massive deal over it?

In my previous post I already explained why journalists use the term "torque" outside of its mechanical term - it's a useful indication of how little effort you need to use to extract a car's performance. A relatively* high torque figure at relatively* low revs suggests to the reader/viewer you can bomb along with reasonable haste without much effort.

*I'm deliberately using the word relatively here. Magazines don't compare tractors and F1 cars so the rate of work each can do is irrelevant. They do compare groups of hot hatchbacks or groups of convertibles, and assuming that each car has a similar peak horsepower output (usually the case in group tests) then one car having a strong, wide torque band at low revs (something with a turbocharged engine, for example) suggests you don't need to thrash it down the road in the same way you might with a very peaky engine, where a smaller torque figure is delivered at higher revs (say, something with a "VTEC" badge).

If you're wanting to discuss only the mechanical properties of torque, then why bring the subjective field of journalism into it?

And if we're talking longevity, people have to start driving the cars we're comparing in the same manner as the bike.
The simple fact bikes can reach 100,000 miles with the way they're generally used is outstanding, and your common car engine would be long dead.

And the reason bikes can do those high revs and take lots of punishment in the first place is because they need far more regular servicing and maintenance than a car. They're much closer in character to race car engines... which are also more highly-strung than road car engines.

If you can find me a 100k-mile CBR that isn't an absolute shed, you're a better man than I. The internet is full of forum threads asking if a CBR with half that mileage is too high. Bike engines simply aren't designed to last as long as car engines.

That's not a bad thing because as you say, they develop higher performance. But you can't use it as an example that high-revs engines go on and on, because it's too extreme an example and high-performance bike engines simply don't go on and on without a hell of a lot of attention.

 

[Denilson]

That being the case, why make a massive deal over it?

In my previous post I already explained why journalists use the term "torque" outside of its mechanical term - it's a useful indication of how little effort you need to use to extract a car's performance. A relatively* high torque figure at relatively* low revs suggests to the reader/viewer you can bomb along with reasonable haste without much effort.

*I'm deliberately using the word relatively here. Magazines don't compare tractors and F1 cars so the rate of work each can do is irrelevant. They do compare groups of hot hatchbacks or groups of convertibles, and assuming that each car has a similar peak horsepower output (usually the case in group tests) then one car having a strong, wide torque band at low revs (something with a turbocharged engine, for example) suggests you don't need to thrash it down the road in the same way you might with a very peaky engine, where a smaller torque figure is delivered at higher revs (say, something with a "VTEC" badge).

If you're wanting to discuss only the mechanical properties of torque, then why bring the subjective field of journalism into it?



And the reason bikes can do those high revs and take lots of punishment in the first place is because they need far more regular servicing and maintenance than a car. They're much closer in character to race car engines... which are also more highly-strung than road car engines.

If you can find me a 100k-mile CBR that isn't an absolute shed, you're a better man than I. The internet is full of forum threads asking if a CBR with half that mileage is too high. Bike engines simply aren't designed to last as long as car engines.

That's not a bad thing because as you say, they develop higher performance. But you can't use it as an example that high-revs engines go on and on, because it's too extreme an example and high-performance bike engines simply don't go on and on without a hell of a lot of attention.

1st: The F1 vs Diesel example is to illustrate how much bhp is a good indication of performance, and torque is'nt.

2. What you, or any journalist feel in the back when accelerating at *relatively low rpm's, what you or he feel in your back, thru the seats pushing forward is nothing but effect (P). It's not torque.
Just because torque in this case happen to somehow make sense in this perticular example does'nt meen it's correct.

I.e
Bike
Lbft: 500
Rpm: 60
[(500 * 20) / 5,252) = 1,9 BHP

Car:
Lbft: 250
Rpm: 2500
[(250 * 2500) / 5,252) = 119 BHP

The bike does'nt stand a chance despite it's much lower weight and twice the higher torque.
Why is that?
Can you find an example that shows the opposite?

P.S: When journalist refere to the torque as an alternative magical force when testing cars is nothing but non sense.
If you will, "effect", or for that matter "Low rpm effect" would be much better words.

And the reason why I don't bring up practicallity issues is that it's completely irrelevant for the point I'm trying to make, namely, the effect (P) is the force that accelerates your car. Absolutely nothing else.

 

[homeforsummer]

And the reason why I don't bring up practicallity issues is that it's completely irrelevant for the point I'm trying to make, namely, the effect (P) is the force that accelerates your car. Absolutely nothing else.

I'll say again: It's not worth making a big deal over. Very, very few people care about the mechanics of it and whether you like it or not, a torque number is still a good indication of how much work an engine can do.

Whether you like it or not, or whether it's technically inaccurate or not is largely irrelevant, since in like-for-like cars, that "irrelevant" torque number happens to nicely correspond to the shove you get at a particular point in the rev range.

It's nary but the rantings of a pedant.

 

[PAPPACLART]

Torque of an engine is THE primary measuring force. Any other measurement outside of torque whether it be thrust or Power is simply torque and the inclusion of other variables.

In vehicle terms yes torque on its own will not make you go fast, you need that torque to be applied with movement over time. 10,000lbs of force moving at 1mph may push through a house but it will only do it at 1mph.

Again in vehicle terms the repetition of a torque value over time (plus gear ratios, etc) now gives torque it's ability to accelerate a vehicle over a speed range which is determined by the peak rpm and gear ratios. (And forgetting roiling resistance aeor and other variable etc)

Once we give torque motion/repetition (RPM), just calling it or quoting max torque figures fails to really show the potential of the motor/vehicle. The introduction of the repetition of torque over time creates something we know as power.

An F1 engine has around 230ft/lb while your average Turbo diesel road car makes around the same figure.

The F1 engine is far more capable simply because it can apply its torque over a wider and higher rpm range/peak. simply being able to deliver the same peak/average torque as the diesel car but at higher engine rotations vs time makes it faster.

Add gear ratios into the equation of which are a multiplier of torque. Then factor in more revs allowing for ever lower gear ratios equaling more acceleration in each gear over the speed range determined by the rpm and ratio.

To the journo thing, when they refer to "torque", what they actually mean but do not realize it, is that they are actually talking about the wheel "Thrust". Thrust is often measured in pounds and is the result of 3 things - Torque rpm and gear ratios.

An illusion of having more "torque" can be achieved by having lower gear ratios with higher rpm vehicles being able to create an even bigger allusion of having "torque" which is in fact like I said is thrust, which is the by product of torque, rpm and gear ratios. When you accelerate in your car you do not feel torque you experience the thrust in a curve that follows the same peaks and drops as your torque curve.



Torques curve

Power curve

Thrust curve

look closely at the torque curves and compare each bike, then compare the thrust curves and see what clever gearing can do.

Also notice that all of the dips and peak of the power and thrust curve are exactly the same as the peaks of the torque curve. That's because power IS torque multiplied by revs and thrust is torque rpm and gear ratios. In this case torque has 2 children! lol

 

[Denilson]

PAPPACLART: Can you evaluate on thrust?
If you mean torque at the wheels, I hear you.
But I'm talking about the torque in the engine (which is what journalists refere to in most cases imo)..
Let's say I'm in 2nd gear at 2000 rpm, doing 25 mph.
The car produce 200 lbft and 76 bhp at this point.
From here, the power goes thru the gearbox with a ratio of 1:2.5, now, still 76 bhp but 500 lbft on the crank.
Then, thru the Diff, which have let's say a 1:3 ratio.. Suddenly, the torque on the axle is 1500 lbft.. But the effect is the same all the way from the engine to the wheels.

Am I reading your post correct?
English is'nt my primary language I might add if it was'nt obvious.

 

[homeforsummer]

If you mean torque at the wheels, I hear you.

I suspect that's what he's referring to.

But I'm talking about the torque in the engine (which is what journalists refere to in most cases imo)..

Not unsurprisingly, because torque at the flywheel is the only measurement most of us can come by without a dyno handy.

To the journo thing, when they refer to "torque", what they actually mean but do not realize it, is that they are actually talking about the wheel "Thrust". Thrust is often measured in pounds and is the result of 3 things - Torque rpm and gear ratios.

Essentially, yeah.

Though as I've been trying to stress to Denilson, it doesn't actually matter that much. As long as the reader understands the message being relayed, it doesn't really matter what you call it. You could pluck a word from mid-air as long as it means the same thing to everyone!

 

[Denilson]

I suspect that's what he's referring to.

Not unsurprisingly, because torque at the flywheel is the only measurement most of us can come by without a dyno handy.

But you just (your first sentance in the quote above) said that PAPPACLART is refering to torque at the wheels.. Then you drop your next sentence like a bomb..

I'll say again: It's not worth making a big deal over. Very, very few people care about the mechanics of it and whether you like it or not, a torque number is still a good indication of how much work an engine can do.

You got to be kidding me?
How fast will this engine be?

Torque: 500 lbft?



Well, it might sound like it's mighty fast to you..
But the engine I have in mind looks like this:
Lbft: 500
Rpm's: 20
[(500 * 20) / 5,252] = 1,9 bhp
Yes, as you suspected, it's a bike.

You'd say that 500 lbft sounds like something strong, right..
And despite it's high torque and low weight it does'nt do perticulary well in a race against this car:
Lbft: 250
Rpm's: 4000
[(250 * 4000) / 5,252] = 190 bhp

Or, against another biker who's pedals are closer to the center, but he can pedal faster..
Lbft: 400
Rpm's: 40
[(400 * 40) / 5,252) = 3 Bhp

If you still think that torque alone would tell you about an egines performance, you better give me an example of one.
I doubt you'll find one though..

 

[CSLACR]

And the reason bikes can do those high revs and take lots of punishment in the first place is because they need far more regular servicing and maintenance than a car. They're much closer in character to race car engines... which are also more highly-strung than road car engines.

If you can find me a 100k-mile CBR that isn't an absolute shed, you're a better man than I. The internet is full of forum threads asking if a CBR with half that mileage is too high. Bike engines simply aren't designed to last as long as car engines.

That's not a bad thing because as you say, they develop higher performance. But you can't use it as an example that high-revs engines go on and on, because it's too extreme an example and high-performance bike engines simply don't go on and on without a hell of a lot of attention.

Well, a couple things... 1st, the CBR is just pretty, I don't own one or even know anyone with one, I hope to own one soon enough though.

Now, I'll admit before I say this, I hate it when people say this, but it's actually what brought me to bring the bikes up.
I do know someone with a 1200CC race motor shoved into their '95 FZR 1000, and he's personally ridden it over 100K miles in the past 8 years since he got it, without a single rebuild or major engine servicing of any kind. (not even valve adjustments)
And it makes an R1 seem like a dog sled.

As for how long a common bike can last? Not a clue, it's hard to say with the people riding them.
As for maintenance, there isn't that much and it isn't very expensive. Unless you're racing it, of course. Of course that's also bike dependent.

Look closely at the torque curves and compare each bike, then compare the thrust curves and see what clever gearing can do.

Also notice that all of the dips and peak of the power and thrust curve are exactly the same as the peaks of the torque curve. That's because power IS torque multiplied by revs and thrust is torque rpm and gear ratios. In this case torque has 2 children! lol

You are correct.(well, mostly)
Torque is not multiplied by both rpm's and gearing. Gearing multiplies RPM's, RPM's multiply torque. We call this horsepower.
And if you don't multiply that torque, what information do you have?

 

[PAPPACLART]

PAPPACLART: Can you evaluate on thrust?
If you mean torque at the wheels, I hear you.
But I'm talking about the torque in the engine (which is what journalists refere to in most cases imo)..
Let's say I'm in 2nd gear at 2000 rpm, doing 25 mph.
The car produce 200 lbft and 76 bhp at this point.
From here, the power goes thru the gearbox with a ratio of 1:2.5, now, still 76 bhp but 500 lbft on the crank.
Then, thru the Diff, which have let's say a 1:3 ratio.. Suddenly, the torque on the axle is 1500 lbft.. But the effect is the same all the way from the engine to the wheels.

Am I reading your post correct?
English is'nt my primary language I might add if it was'nt obvious.

Thrust is how you describe though I have not checked your math

Yes the effect is the same from engine to wheels, but lower the ratios and you have exaggerated the effect by increasing thrust. How silly you can go with your gears is determined by how high your motor can rev. The higher the rpm the lower you can take the gearing while still having a usable motor on the road/track.


When Journalist commonly refer and rave about the "torque" of a motor or the low/mid range "torque" what they are feeling and describing is the thrust at the wheels which is a product primarily of the torque the engine produces across a given RPM curve of which is then multiplied by the gear ratios. So to go from raw engine torque to physically accelerating, we need torque RPM and gear ratios. These 3 variables combined is what journalist are describing when they are talking about how great the torque of an engine is as well as the actual shape of the torque curve which is followed by both the power and Thrust curves.

It seems that your are putting way too much emphasis on how a journalist describes the wheel thrust in any given gear/rpm/speed of an engine. He says torque but he means torque plus gears plus rpm = thrust but either does not know the prior himself because he is not technically knowledgeable enough or he is using the word "torque"as that is the term/description of a flexible motor his audience will collectively understand.

Although none can really work without the other, however you look at it, torque is the most important factor, then how fast the engine can spin (RPM) followed by the gear ratios which multiply that torque and give thrust.

Words take on new meanings all of the time and the description of torque from the perspective of your Bum dyno is perhaps not the correct way to describe but is a way we all understand.

 

[Pako]

One could say,

Maximum acceleration at any speed occurs at the peak HP.
Maximum acceleration in any single gear occurs at the torque peak (but switching gears to one at any given speed with the most power gives you more acceleration).

 

[PAPPACLART]

You are correct.(well, mostly)
Torque is not multiplied by both rpm's and gearing. Gearing multiplies RPM's, RPM's multiply torque. We call this horsepower.
And if you don't multiply that torque, what information do you have?

Read my post you quoted I did not say that .

Power is torque x 5252

Thrust is worked out from torque rpm and gear ratios.


You say gearing multiplies rpms, rpms of what the the engine or the wheels? How does a gear multiply engine rpm's? I think you may be confused? The peak rpm capability of an engine is determined by the engine design, nothing increases the rpms other then giving the motor more throttle. RPM is how many Revolutions Per Second the crank/flywheel of an engine spins. excluding the obvious variables, any gear ratio theoretically can spin infinitely and in car/bike terms a gears length in terms of mph achieved is only limited by the engines rev limiter that stops a gear from spinning any faster, hence why you hook another gear. Once you hook top, it's drag/rolling resistance/lack of power that may stop you from hitting the limiter in top etc.

You also say RPM's multiply torque, not entirely correct . Rpm's spin gears which then multiply torque which give us thrust at the wheels. RPM can not multiply torque without gears as the ratio without gears would be 1:1. In engine terms, RPM without gears simply is a point of rotation measured over time where a figure of torque is produced. On the other hand RPM and Torque give us Power.





@ pako

caramall2
Maximum acceleration at any speed occurs at the peak HP.
Maximum acceleration in any single gear occurs at the torque peak (but switching gears to one at any given speed with the most power gives you more acceleration).

The above is wrong and does not make sense and contradicts itself.

How can maximum acceleration at any speed occur at peak power when according to the very same quote maximum acceleration in any gear occurs at peak torque?

So car A has peak torque at 5000rpm in 1st gear at 50mph. The car produces its peak power at 7000rpm which is 70mph. How can maximum acceleration occur at both points which the above quote suggests? It can't! for the above to be true an engine would have to have a completely (ruler level) flat torque curves which does not exist in a combustion engine.

Look at my earlier thrust curves. The peak of every thrust curve occurs at exactly the same rpm point in each gear which happens to be the same rpm point as where peak torque is produced. Peak thrust as well as peak torque is where a vehicle engine is at its most efficient and most accelerative.

 

[CSLACR]

Read my post you quoted I did not say that .

Power is torque x 5252

Thrust is worked out from torque rpm and gear ratios.


You say gearing multiplies rpms, rpms of what the the engine or the wheels? How does a gear multiply engine rpm's? I think you may be confused? The peak rpm capability of an engine is determined by the engine design, nothing increases the rpms other then giving the motor more throttle. RPM is how many Revolutions Per Second the crank/flywheel of an engine spins. excluding the obvious variables, any gear ratio theoretically can spin infinitely and in car/bike terms a gears length in terms of mph achieved is only limited by the engines rev limiter that stops a gear from spinning any faster, hence why you hook another gear. Once you hook top, it's drag/rolling resistance/lack of power that may stop you from hitting the limiter in top etc.

You also say RPM's multiply torque, not entirely correct . Rpm's spin gears which then multiply torque which give us thrust at the wheels. RPM can not multiply torque without gears as the ratio without gears would be 1:1. In engine terms, RPM without gears simply is a point of rotation measured over time where a figure of torque is produced. On the other hand RPM and Torque give us Power.

You are correct.(Sort of again)
In clearer terms, what I was saying is that gearing multiplies RPM's at a given speed, and RPM's multiply torque.
Gearing does not multiply torque, other than by raising RPM's at a given speed.(a similar effect, but not the same)

With a 1:1 gear, my car will still multiply torque as RPM's increase.
With a 2:1 gear, my car will still multiply torque as RPM's increase.
Gears cannot stop this.

@ pako

The above is wrong and does not make sense and contradicts itself.

How can maximum acceleration at any speed occur at peak power when according to the very same quote maximum acceleration in any gear occurs at peak torque?

Look at my earlier thrust curves. The peak of every thrust curve occurs at exactly the same rpm point in each gear which happens to be the same rpm point as where peak torque is produced. Peak thrust as well as peak torque is where a vehicle engine is at its most efficient and most accelerative.

Agreed 100% that the post contradicted itself.

Disagree that it's "the torque" that causes peak acceleration in gears.
If you look at this closely

You'll see it is in fact, the air/speed/rolling resistance that is slowing the Bike down. The reason it appears to peak at the torque peak is because the HP stop increasing as quickly as it once was, now that peak torque is past the HP is flatlining.
A flat line of HP will always result in steadily decreasing acceleration as speed rises, peak single-stroke torque has nothing to do with it.

Take note to the right side of the gears, and you'll see at the end of the gears forms a steadily declining amount of acceleration. This will happen regardless of torque/power, because of resistance.

Torque starts dropping at 8K, HP at 9400. That in itself makes this a terrible engine to use this analogy for, because the peak of each are so close together it's harder to see, but I'll work with what is here.

And now we show how much lower the acceleration rate would be if we kept it in the "Peak torque" range.

It's an optical illusion that's been deceiving many for quite some time.
The single-stroke torque isn't doing anything, the HP is, as always, because engines can't turn just one RPM, especially at the speed of 8,000RPM's.
The resistance is enough that as power levels off, so does acceleration, but again, not because you're past the peak torque, but because you have resistance increasing at a higher rate than power.

So car A has peak torque at 5000rpm in 1st gear at 50mph. The car produces its peak power at 7000rpm which is 70mph. How can maximum acceleration occur at both points which the above quote suggests? It can't! for the above to be true an engine would have to have a completely (ruler level) flat torque curves which does not exist in a combustion engine.

Ahem.
If an engine has a ruler flat torque curve, HP must be higher at 7,000RPM. This is how HP works.
All HP are created equal, 300 is 300 is 300.
300 ft-lbs could mean anything, without additional information (RPM, which is used to translate into hp) it is absolutely useless.

 

[Exorcet]

I wrote this for another website.

Power is a technical term. It does more than sells cars and, in fact, can aid in winning races. Unfortunately its true nature is sometimes poorly understood, even by car enthusiasts. Power is also often put in an unnecessary rivalry with another engine output metric - maximum torque.

There are a lot of explanations on the Internet and elsewhere that try to explain what's what. Some of them are right, some not. Many aren't very clear. What is clear, is the physics behind cars, and I hope that, by providing an explanation based in physics, I can clear up misunderstandings that anyone might have on what horsepower is and what it really says about a car or engine.

In physics, power is the rate of change of energy. A car in motion has a particular kind of energy known as kinetic energy (KE). KE is related to motion, the faster something goes, the more KE it has. The exact relation is KE = .5 * mass * velocity2.

Velocity is something that most people understand, and it's something that a driver wants to maximize when racing. Using the equation above, it's possible to determine the amount of KE carried by a car at a certain speed if we know its mass.

A 1000 kg car traveling at 50 m/s possesses 1,250,000 joules of energy. Note that units are important. Mass is in kilograms (kg), you can't use Newtons or pound-force (as they are weight) unless you use their mass equivalents - the Newton-mass and pound-mass, as long as you include the proper correction factor.

The KE is important and can provide a lot of information. When a car tries to stop, the brakes need to remove all the KE from the car by converting it into heat. The more KE, the more the brakes have to work. It's pretty clear that having a lighter car is better for your brakes. But none of this has to do with horsepower...

Let's imagine the same 1000 kg car from before traveling at 50 m/s as it starts to accelerate. It would be useful to calculate how fast it can accelerate. This can be determined from torque if the gear ratios and tire sizes are known, but goog-ling this information might take minutes!

Instead of using torque, it's possible to use power, and this makes things much easier. Now the gearing and the wheels don't matter at all. Power provides a method to determine the acceleration of a car, whether it has mile wide gear spacing and bicycle tires, or a gear limited speed of 5 mph and monster truck tires.

For simplicity's sake, assume that the engine makes a constant 500,000 Watts (units are important) of power at every RPM. The engine will simply add 500,000 joules of energy to the car every second since a Watt is equivalent to a joule per second.

So the car starts at 1,250,000 Joules or 50 m/s. One second later it will have 1,750,000 joules and its speed will be 59 m/s. At 2 seconds from starting, KE is 2,250,000 and speed is 67 m/s. It's clear that even though power is constant, the acceleration is not. 500,000 W averaged 9 m/s2 acceleration from time zero to one, but only 8 m/s2 from time one to two. This is because 500,000 joules becomes a smaller and smaller percentage of the total KE. The faster the car goes, the harder it is to make it accelerate.

Thinking in terms of energy might seem a little abstract however. Force is a more familiar term, and fortunately, power and force are related. To see this relationship, requires a deeper understanding on energy.

Energy, in general, is the ability to do Work, and Work is force exerted over a distance. 1 Newton of force exerted for 1 meter of distance is 1 joule of work, or 1 joule of energy. Power is the rate of change of energy. For those familiar with calculus, {Power is the derivative of energy. Don't worry, I won't mention calculus again...

Displacement (Distance), Velocity, and Acceleration are related in the same way that energy and power are. Acceleration is the rate of change of velocity, which is the rate of change of distance. Going back to the Work/Force relationship (Energy = Work = Force * Distance), let's turn energy into power by using rate of change (RoC).

Power = RoC of Energy
Power = RoC of Force * Distance
Velocity = RoC of Distance
RoC of Force * Distance = Force * RoC of Distance
RoC of Force * Distance = Force * Velocity
Power = Force * Velocity

Now if the engine's power is known, so is the force pushing the car. Force and Acceleration are already known.

F = ma
Acceleration = Force / mass
Acceleration = Power /(Velocity * mass)

Unlike the KE method used before, this new equation can calculate the acceleration at any point in time. Going back to the example car at 1000 kg with the 500,000 W engine, acceleration is 10 m/s2 at time zero, 8.5 m/s2 at time one, and 7.5 m/s2 at time two.

Horsepower tells you everything you need to know about how the car will accelerate. Power and torque are really the same thing as far as the car in concerned, but horsepower is far easier to use, and this is why it is such a popular metric.

The power and force relationship also allows for other helpful calculations, like those involving drag. Drag is a force, but using the equation relating power to force, it's possible to convert drag force into drag power.

Drag power can be thought of as the opposite of an engine. Instead of creating power, it absorbs it and slows the car down. To see the effect of drag on a car's acceleration, add the drag power to the engine power. Remember that drag power will be negative in this case. Since drag gets bigger with speed, at some point the engine power + drag power will equal zero. At that point, the car would be at its maximum speed.

All of this still leaves one question, where did the horsepower vs torque argument come from? It's actually a result of poor terminology. The heart of the argument lies with the engine's power-band, and not the peak values of horsepower and torque or the individual properties of those two quantities.

Peak refers to the maximum values of power and torque. These numbers can be misleading because they only occur in a narrow RPM range. As long as an engine does not have continuously variable transmission (CVT) with no distinct gear ratios, the power and torque over a range of RPM is more important than the peak values.

For example, a 500 hp car can easily be quicker than a 1000 hp car. If the 500 hp car produces at least 90% of peak power within 2000 RPM of the peak power RPM, it will easily outrun the 1000 hp car that only produces 125 hp of power everywhere that is off peak RPM, and doesn't have a CVT.

Going back to the horsepower vs torque debate, a torque-rich engine is one that produces torque over a wide range of RPM, or one that produces large amount of torque (and thus horsepower) at low RPM. This gives the car good acceleration from a low speed even if the engine is not spinning very fast. This is great for road cars where the RPM is usually low and there is a lot of stop and go driving.

Conversely, a horsepower-rich engine is one that forgoes torque at low RPM in order to produce more torque (and thus horsepower) at high RPM. This is actually preferred for race cars, and the reason should be obvious once the relationship between power and torque is understood. Power is proportional to torque multiplied by RPM. In other words, 500 units of torque produces more power at 6000 RPM than it does at 5000 RPM. The "horsepower" engine produces more power overall, and this makes it faster.

This isn't to say that low end torque isn't important for race cars though. Depending on the track, a wide, torque-rich power-band can prove advantageous. A torque-ish engine requires less downshifting then a peaky engine, and it also allows the gears to be spaced further apart or for unneeded gears to be dropped completely to save weight.

In the end, power isn't all that complicated and it's not some superfluous number. It's a very helpful performance metric and should be seriously considered in any comparison between sports cars.

 

[Blackbird.]

In order to calculate hp you have to use your peak torque to plug into the formula no?

 

[Denilson]

CSLACR and Exorcet! 👍 👍 👍

"Amen" to both of you!!

Excoret: Your post is one of the best and most educational post I've ever read.
And since you mentioned that the 500 bhp car can be the faster one compared to a 1000 bhp car as long as it's average bhp is higher over the rpm's allowed by the gearbox, I'd like to post an example.

I.e, let's say for the sake of the example that car A produce a totally flat effect (P) curve
over the entire rpm range allowed by the gearbox in let's say 4th gear. And this car got an enormous effect at low revs compared to "normal" cars (remember that this is just for the example to be clear and easy to understand)
[(500 bhp / 2000) * 5252] = 1313 Lbft @ 2000 rpm's
[(500 bhp / 3000) * 5252] = 875 Lbft @ 3000 rpm's
[(500 bhp / 4000) * 5252] = 656 Lbft @ 4000 rpm's
[(500 bhp / 5000) * 5252] = 525 Lbft @ 5000 rpm's
[(500 bhp / 6000) * 5252] = 437 Lbft @ 6000 rpm's
[(500 bhp / 7000) * 5252] = 375 Lbft @ 7000 rpm's

So, the above car have, in average 500 bhp at disposal all the way from 2000-7000 rpm's.
Then, we take a look at the 1000 bhp car, Car B, which in this case have a somewhat flat torque curve (compared to Car A's), and a pointy effect curve in contradiction to the 500 bhp car..
[(325 Lbft * 2000) / 5252) = 123 Bhp
[(400 Lbft * 3000) / 5252) = 228 Bhp
[(475 Lbft * 4000) / 5252) = 361 Bhp
[(550 Lbft * 5000) / 5252) = 523 Bhp
[(625 Lbft * 6000) / 5252) = 714 Bhp
[(750 Lbft * 7000) / 5252) = 1000 Bhp
Now, given that both cars gearboxes force the amount of rpm's to stay within 2000-7000 rpm (yes, these engines are extreme ), we can see that Car A can produce 500 Bhp in average over the rpm's allowed.
Car B:
123 + 228 + 361 + 523 + 714 + 1000 = 2949
2949 / 6 = 491

We can see that Car A produce 500 bhp in average over the rpm range allowed by the gearbox, and that Car B produce 491 bhp in average over the rpm range allowed by the gearbox.
So, given that both cars are equal in terms such as tire grip, draftcooficients, loss in drivetrain etc, Car A will accelerate better in average from 2000-7000 rpm's.

These examples are extreme, but it demonstrates perfectly what Exorcet said:

For example, a 500 hp car can easily be quicker than a 1000 hp car. If the 500 hp car produces at least 90% of peak power within 2000 RPM of the peak power RPM, it will easily outrun the 1000 hp car that only produces 125 hp of power everywhere that is off peak RPM, and doesn't have a CVT.

 

[niky]

Unfortunately, given the reading level of the general public, it's very difficult to explain to them why a sub-500 hp Nissan GT-R can match a 600 hp Supercar in a drag race. Using the shortcut of saying:

"Man, this GT-R has :censored:loads of torque."

Gets the point across, quite nicely without having to post a dynochart and trying to explain to readers what a power curve is and how short-gearing, low drivetrain losses, an ultra-quick transmission and turbo-boost can make a car without headline horsepower figures faster than they think it should be.

 

[Rotary Junkie]

CSL, you're somewhat wrong with saying that peak torque isn't peak thrust.

It absolutely is. In fact, if we had a Magical Engine Of Alien Magicality that made the same amount of torque (say, 500 ft-lb) for an infinite RPM range, the thrust curve would be absolutely flat for every gear, just more for lower gears. Same story applies when we've got a flat curve from, say, 2000 to 7000rpm (stealing the range from Denilson). If we can't rev the engine any higher than said 7000rpm, we'd have a thrust curve of flat lines for each gear. If we had, say, a 500hp constant from n (where n = anything above zero) RPM onward with an infinite rev range, thrust would be a parabolic curve downwards, never quite hitting zero nor quite infinity (but could get infinitely close in either direction) regardless of gear ratio.

Point being, average horsepower over the usable operating range = outright speed. Torque is irrelevant. It doesn't actually matter if it's 500 ft-lb at 5252rpm or 250 at 10504 because we've got the ability to multiply torque (at least when speaking from theory, in practice due to drivetrain losses and such it isn't completely true, as losses aren't entirely percentage based).

If CVTs were to become practical for high-output usage, there'd be a field day about being able to tune for a very narrow operating range... Oh and the thrust curve would be a downwards parabola again, seeing as horsepower would be a constant and output torque would be constantly decreasing as gear multiplication decreased, though it'd be stopped at both ends by the possible multiplication of the transmission.

I'll just close with saying... The best transmission keeps the engine as close to peak horsepower as possible as long as possible. The "best" engine would have no torque peak, and power would be linear with RPM. In GT5, however, mainly thanks to how certain things work, the best engine depends on the use of the car.

If racing power limited, it's whatever holds peak power as long as possible. So, as much power limiting as possible.
If racing PP limited, it's whatever has peak power for as narrow of a range as the gearbox can be tuned to hold and very little in any other region of the rev range.

Edit: @niky: That shortcut makes me want to kill people. One would think the easy way of explaining it would be to just say that it uses what power it has extremely efficiently (which is true).

 

[niky]

Reminds me.

A friend once remarked: WRC cars may be limited to around 300-400 hp... but nobody's saying over how much of the rev range they hold it.