Torque for dummies

It's simple imagine a 21 speed bike: If you're in gearing 1:1 for every 1 pedal push you go forward a little but in gearing 1:7 you go forward more. it's simple, maybe to the more engineer put mind it is.
 
LeVeL said:
Here's the simplest explanation: Horsepower makes you go fast. Torque makes you feel like you are going fast; it gives you that kick in the back when you push the gas.

/thread
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No, horsepower lets you go fast, torque gets you going fast.
 
Vislami said:
Agreed, even though I know what torque is, metric system would be better..
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I like the metric system but in regard to speed over time MP/H > KP/H. Other than that the metric system makes much more sense then our stupid system, I mean the converting is a pain in the arse!
 
OK, one more question. If you have 500Nm of torque at the engine, and a drive ratio of for example 10:1, does that mean you now have 5000Nm of torque at the axles? It would seem to me like you should, or am I making a grave error here?
 
If I'm not mistaken, it should go like this:

Torque, being a force, is the power to make a certain mass accelerate, so varying it's speed form x to y in a certain amount of time.

The more torque, the more mass can be accelerated. But when acceleration start and ends? It starts when the engine raises its revs, thus making the wheels spin faster and the car accelerate. It ends when the engine is not able to raise its revs anymore.

Now imagine you have an engine producing massive torque, from zero revs to 500, constant torque: If you connect it directly to the wheels, the acceleration will stop when the wheels, and the engine, will reach the maximum revs. It doesn't that your engine can accelerate to that point even eight time the mass of the car it is accelerating now. Its speed won't go past the line marked by the engine revs.

Then you think: "hey, since I could move up to eight time the mass I am moving now, I will use two cogs of different sizes (one having a circumference double than the other). The bigger will go on the engine shaft, and the smaller will go on the wheel axis. So, when the engine will reach its limit the wheels will spin twice as fast. Both acceleration and speed will double. This means I will be able to move only up to four times the mass of the car instead of eight, but that's way too much anyway".

And it works!

So you think again: "I will double again the bigger wheel, so the car will accelerate twice as fast as before (four time faster than the first time) and also double its maximum speed! My engine will be able to move only two times the mass of the car, but who cares! i only need to move one car, not two!".

And it works again!

So you do this for the third time, and it works again. The engine accelerate your car eight time faster than the first time, making its final speed eight time higher.

Then you try again. But you fail. The engine stall, because you want it to accelerate even faster, but the mass your engine can accelerate that way is smaller than the mass of the car.

Again you have reached your maximum speed.

Then one of your friends arrives. He has an engine that can develop the same torque as your engine, but only at 5000 rpm. You laugh, because at low revs he is not even able to move the car.

But he is smart, and brings in a clutch (but no cogs). With a clutch (a very heavy one), he can make the car accelerate slower than your car, but when finally he makes his car running at full speed (the same as the maximum revs) his car is already faster than your is after the use of cogs: remember? You had 500 rpm, and managed to make the wheels spin eight time that fast, so it's 4000 rpm at the wheels, and only if your car has that mass and no more. But he is developing, in the end, 5000 rpm at the wheels, and then he would still be able to move, to that speed, a mass eight time the one of the car. (very heavy clutch indeed). it only takes him more time to accelerate, but the maximum speed is higher.

And this is not even the end. Your friends sees your cogs, and decide to put something similar to his car. He makes two different set of cogs and a system to shift between the two; One is the standard, the second is just like yours (bigger cog on engine shaft, smaller cog on wheel axis).

And off he goes: He makes the engine reach the 5000 rpm, and alreay has a maximum speed higher than yours, than changes gear, making his engine developing its maximum torque at 5000 rpm, but the wheels spin eight time faster, at 40000 rpm, which is the maximum speed. Ten time more than your low-rev-constant-torque engine. His acceleration wil surely be slower, but it will be faster in the end.

There is more. What saves you is that you have a constant-torque-developing monster from zero to 500 rpm. But if he manages to have a better torque curve, optimizing it to yours, it will have an engine developing the same torque as your engine is developing... but up to 5000 rpm instead of 500. the difference is staggering.

So torque is the effective force that the engine produces, is what makes the car accelerating, horsepower is the maximum speed it can reach and what gears and transmission and clutch it can use or not use.

So, high torque engines at low revs like diesels, accelerate faster than, for example, petrol engines, but petrol engines will accelerate for more time, and the car will eventually be faster.

Just like mine car. I have 320 Nm of peak torque, which is good, but only 130 hp. The same model can also have a 3.2l v6, developing exactly the same peak torque, 320, but has 250 hp.

In the moment of maximum acceleration, we have roughly the same acceleration. But then my engine goes too high with revs, and I have to change gear, while the 320 hp car can continue to accelerate, and has gears that can make it accelerate even when I am in top gear and top revs. So it will ever be faster than me every time a gear change is involved (0-100 kph, top speed, 0-60 kph...).

Sorry to everyone that understands physics for all the horrible simplifications I made.
 
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The transmission doesn't have anything to do with the hp an engine produces when understanding torque and horsepower.

Torque is the actual power produced by an engine, horsepower is how quickly an engine can utilize it's available torque. That's all you need to know to basically understand torque. After that you get into power-bands, and engine design, transmission and differential stuff, etc.
 
As long as we all agree that torque is better than HP I'm all for it!
Good explanation SirEdward


(hey, my car has the exact same hp/torque figures as you! go you!)
 
Twerp128

The transmission doesn't have anything to do with the hp an engine produces when understanding torque and horsepower.

Torque is the actual power produced by an engine, horsepower is how quickly an engine can utilize it's available torque. That's all you need to know to basically understand torque. After that you get into power-bands, and engine design, transmission and differential stuff, etc.
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True:

But I noticed that theoric physics (which I'm not very good at, actually) is truly complicated and quite abstract. I needed months to figure out the difference between the two concepts, and I was continually faced with ermetic walls of forumlas full of nonsensical (to me) x and y minus z per 0,67p, as if it was an unspeakable demon that could only be referred to through magical forumlas. Torque is not an equation, Torque is as physical as we are. It'is real. The equation comes after that, not before. So I've asked myself: how can I show the difference in our average world, made of people like me that panic when too much algebra is involved?

I hope that my example is correct (and if it is I hope it can be useful).

Noodle

hey, my car has the exact same hp/torque figures as you! go you!
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Good old German Cars!
 
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Torque is the effectiveness to turn an axis, or twisting force. It has NOTHING to do with acceleration.

This is something that has been a topic on every car forum on the entire internet, and it really isn't that complicated but many people have it wrong. Many people say "Torque is what wins races" but it doesn't necessarily. Semi trucks (same as a lorry) usually make about 1500 lb/ft of torque, but they're still slow, even if not pulling anything. Locomotive engines make upwards of 8000 lb/ft of torque, but they're slow as well. Rocket engines are very fast but have no measurable torque.

When figuring torque, there is no component of time. Horsepower is figured with time as a component, and is relevant to acceleration. The fact of the matter is that you need enough torque to effectively move the car, but horsepower is what makes you go fast.
 
satcomvato said:
Torque is the effectiveness to turn an axis, or twisting force. It has NOTHING to do with acceleration.

This is something that has been a topic on every car forum on the entire internet, and it really isn't that complicated but many people have it wrong. Many people say "Torque is what wins races" but it doesn't necessarily. Semi trucks (same as a lorry) usually make about 1500 lb/ft of torque, but they're still slow, even if not pulling anything. Locomotive engines make upwards of 8000 lb/ft of torque, but they're slow as well. Rocket engines are very fast but have no measurable torque.

When figuring torque, there is no component of time. Horsepower is figured with time as a component, and is relevant to acceleration. The fact of the matter is that you need enough torque to effectively move the car, but horsepower is what makes you go fast.
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First of all, yes it does. The harder you twist the axle, the harder the car will accelerate.

Second, you're correct, the "torque wins races" comment is something taken out of context from Carrol Shelby IIRC. As has already been discussed in this thread, a low torque, high revving engine can accelerate a car just as fast as a high torque low revving engine, because it can use lower ratio gearing. But its still the torque causing the car to accelerate. We've just made its job easier by using lower gears.


Thirdly, have you considered that trucks and locomotives accelerate slowly because they're freaking heavy? And noone has said torque is the only thing that can accelerate an object. Rocket engines have absolutely nothing to do with this discussion.
 
ed1911n said:
First of all, yes it does. The harder you twist the axle, the harder the car will accelerate.
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Just because it has more torque does not mean it will be faster. Torque is a measure of power. Horsepower is a measure of power/time.

Forget drivelines and gearing and take for instance two engines that both have 300 ft/lbs. of torque. One engine is of poor design and due to this the engine revs very slowly, however it still produces 300 ft/lbs. of torque. The second engine is sleeker and more efficient therefore it is able to reach it's maximum power very quickly even though it creates the same amount of power as the slower engine.
 
Twerp128 said:
Just because it has more torque does not mean it will be faster. Torque is a measure of power. Horsepower is a measure of power/time.

Forget drivelines and gearing and take for instance two engines that both have 300 ft/lbs. of torque. One engine is of poor design and due to this the engine revs very slowly, however it still produces 300 ft/lbs. of torque. The second engine is sleeker and more efficient therefore it is able to reach it's maximum power very quickly even though it creates the same amount of power as the slower engine.
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What do you mean revs slowly? If you mean two engines with the same torque but one can rev higher than the other, then, yes, that engine will be more effective, it will have more horsepower. This is covered in the example in my original post. That doesnt change the fact that torque is teh force that accelerates the car.

If you mean that the engine will use a long time to reach a certain rpm even if you floor it, then it doesnt sound to me like it produces the same torque as the other one at all, since the only thing I can think of that would make it rev slowly is that theres a lot of friction in the engine, so the torque it puts out will be reduced.
 
Stroke vs. Bore effects is most influential in how fast a given engine revs, along with weight (especially unsprung weight), and resistance.

For an extreme example I believe modern F1 engines only produce between 200 and 300 ft/lbs. of torque, however the engine is able to exert it's torque extremely quickly, thus they have double or triple the amount of horsepower as torque. A Porsche boxer engine may offer the exact same torque as an F1 car, but due to a less focused, engine design it can't exert it's torque as fast as a F1 car. Torque does not effect how fast an engine revs, it is the extreme basic measurement of how much work an engine is able to do.
 
Twerp128 said:
Stroke vs. Bore effects is most influential in how fast a given engine revs, along with weight (especially unsprung weight), and resistance.

For an extreme example I believe modern F1 engines only produce between 200 and 300 ft/lbs. of torque, however the engine is able to exert it's torque extremely quickly, thus they have double or triple the amount of horsepower as torque. A Porsche boxer engine may offer the exact same torque as an F1 car, but due to a less focused, engine design it can't exert it's torque as fast as a F1 car. Torque does not effect how fast an engine revs, it is the extreme basic measurement of how much work an engine is able to do.
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F1 engines may produce a relatively small amount of torque, but they can rev to like 20 000 rpm, resulting in high horsepower output, so again, through gearing achieve the same amount of acceleration that a lower revving but torquier engine will do. Are you sure we're not just talking circles around each other but really meaning the same thing here?
 
^Yeah I think we are.
 
Good point, twerp, in that drivelines and gears shouldn't be part of a discussion defining what torque is.

Of course trucks and locomotives are freakin heavy, but I mentioned their engines as extreme examples of high torque, low revving engines that illustrate that torque is not related to acceleration. I mentioned a rocket engine as an extreme example of an engine that has measurable horsepower (expressed as thrust) and no torque at all.

I mention applications other than cars because it helps to fully understand what torque is. If talked about only in the context of cars, it too often gets confused with horsepower.
 
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