Whats the difference between Torque and Horsepower

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Slick Rick

Slick Rick

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Guys im a bit confused and need some help.
Before, i used to think that Horsepower was all you needed for a powerful,fast car but now ive found out what torque is, i dont know what Horsepower is.

My state of thinking right now is that Horsepower is now irrelevant compared to Torque because if you have a huge twisting force all you need is the correct gearing and you can go really fast. Faster than a car with a lot of Horsepower and small torque. Is this true?
 
Basically, bare basics, HP is what helps you go fast, torque is what gets you off the line.

Trucks have lots of torque, but they lack the horsepower to go really fast.

It's like an elephant will start pulling a heavy cart quicker than a few horses. But while the Elephant is still plodding along quite comfortably the horses will be galoping at speed.
 
There was an old saying. I forgot what it was.

I know one was Horsepower sells cars, torque wins races.


Oh yeah. Torque is a stocky, muscular man. He is great on steep uphills but he just can't cut it on long flats. Meet horsepower, he isn't to great on hills, but he really womps torque on flats.

Or something to that effect. :D



Torque is a measurment of force, usually in foot-pounds.

Power is (Force divided by Time). This can be measured in Foot-pounds per second, but is commonly measured in Horsepower; 1 HP = 550 ft-lb/sec. In the context of car engines, power is the product of both torque and RPM. A handy equation:

HP = ( Torque * RPM ) / 5252

Despite advertising to the contrary, torque is what REALLY allows trucks to haul heavy loads and cars to accelerate quickly. However, more torque at the same speed equals more power, and power is what everyone wants. There is an old saying that goes, "People buy horsepower, but they drive torque." Torque is force, and force causes acceleration. Power is marketing, and marketing causes poverty.

The easiest way to think about torque is to imagine a long lever attached to the engine output. The amount of effort that the engine produces to turn this lever is the torque.If you imagine a lever about a foot long and hang a weight of about 1 pound then the equalivent torque would be described as 1ft lb If you have ever used a torque wrench then you can see how much effort you are putting into the wrench with the settings.

Torque is not affected really by time though whereas power is..
When he refer to power we usually talk about horsepower and this is measured over time. 1 horsepower can move 33000 pounds 1 foot in a minute (or 550 pounds a second)

brake horsepower is measured usually at the crank and a brake is applied to the engine the more braking required shows the engine is developing more torque. Due to friction and other forces though the power output at the drive wheels will be less than the reading at the crank.
 
It's not a car example but here's another example of mine.

I was using a fan to cool myself down the other day, and it spins really fast. When I touched it, it stops easily and it didn't push against my finger very much.

I got another fan out, it spun at the same speed as the other one, but it was much harder to stop it.

In car terms, the first fan has the same horsepower as the the second because they spun at the same speed, but the second one was harder to stop because it has more torque.

This means the more torque, the harder the car is to stop, so really heavy cars need lots of torque to get them moving. If they don't have much torque, all that horsepower will be less usefull.

Get it?
 
If thats the case, then like i said earlier, why doesnt someone create an engine with loads of torque and little HP and then create speed using a gearbox containing very high gears because the engine will be capable of turning them. The acceleration would be better and the top speed could also be much higher due to the gear ratio.
 
This is info I posted in the ***New Corvette Z06*** thread
Skicrush
Why does torque matter as much (or more) than hp? Hp makes you go fast--torque makes your tires spin. I don't think this relationship is exactly correct, but the general idea I believe goes something like this. Torque x rpm=hp. So, torque can actually be declining, but as long as the rpms go up faster than your torque drops off, your hp continues to go up. Race cars have close gearing that keeps the rpms in the ideal range, and they shift so fast that it doesn't matter if they have 4 gear changes instead of just one or 2. But road cars are different, since most of them you still shift yourself. On top of that, torque is really what drives acceleration.
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(incidentally, that formula is exactly correct. Torque x rpm=hp. But you have to convert to metric, and measure the right units at the right distance correctly). There's also this:

https://www.gtplanet.net/forum/showthread.php?t=13110 Thats right--there's good info right there in the car physics thread right above this one, stickied at the top for good reason. Saleen and Duke give good examples a few posts down.

So, you can see how a car like the Carrera GT can have peak torque of 381 ft lbs, but put out 604 hp--high RPMs. And a car like the Ford GT can put out 500 lb ft. (or 525--I keep seeing disagreements) of torque, and only put out 550 hp. Or worse in a diesel truck that redlines at 3000 rpm. High torque is really nice in a road going car because it offers tractability and flexibility with gearing and such. Gearing can equal out differences in torque, but an engine with half the torque of another, coupled with a gear that is created half as tall to equal out acceleration, is going to run out of room to run (will redline) twice as fast, too. The Ford GT and Z06 both have lower redlines than the Ferrari F430 by over 1000 rpm, but they have higher torque that allows them to have gears that are taller, allowing them to pass 60 mph in first gear. Also, gear selection doesn't have to be as precise. From an article in Car and Driver found here http://www.caranddriver.com/article.asp?section_id=15&article_id=7565&page_number=4
The Ferrari and the Porsche both require an upshift before 60 mph, but the Ford does not, which accounts for some of the huge sprint-time advantage.

But Ford can use a tall first gear because the engine has an enormously wide power band. In this comparo, it had the crispest throttle response. In the rolling-start test to 60 mph, where the gas pedal is floored at 5 mph, the GT hooked up and simply bolted, reaching 60 in 3.7 seconds, a full second quicker than the GT3 and 0.7 second faster than the Ferrari.

The rear tires do a fantastic job of turning the engine's mighty 500 pound-feet of torque (besting both the others by more than 200 pound-feet) into forward motion without losing traction.
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Horsepower doesn't exist... It's merely a function of torque.

1hp = 550ftlb/s (that's 550ftlb of torque per second). If you want to go fast, torque is irrelevant since, if you've got lots of power, you're converting lots of torque.

Assuming identical gearing, 190hp/140ftlb will be quicker than 140hp/190ftlb, since 190hp is 104,500ftlb/s and 140hp is 77,000ftlb/s. The actual torque rating is of no consequence.
 
Famine
Horsepower doesn't exist... It's merely a function of torque.

1hp = 550ftlb/s (that's 550ftlb of torque per second). If you want to go fast, torque is irrelevant since, if you've got lots of power, you're converting lots of torque.

Assuming identical gearing, 190hp/140ftlb will be quicker than 140hp/190ftlb, since 190hp is 104,500ftlb/s and 140hp is 77,000ftlb/s. The actual torque rating is of no consequence.
Click to expand...

So HP is a function of torque?? so when you convert torque to HP you kinda get more product than just having pure torque?

(dont destroy me if this seems stupid, im trying to understand)
 
Yes.

100,000ftlb isn't much use with 5hp, as only 2,750ftlb of torque is turned into useful end-product per second.

Interestingly, dynomometers measure torque. So, on a rolling road, the rollers measure wheel torque, convert it to wheel power, then use a guesstimate on transmission losses to "calculate" engine power. An engine dyno measures engine torque and converts it to engine power, which is toss anyway since you don't know your transmission losses and it's wheel power that counts.
 
standard235
Torque is a measurment of force, usually in foot-pounds.

Power is (Force divided by Time). This can be measured in Foot-pounds per second, but is commonly measured in Horsepower; 1 HP = 550 ft-lb/sec.
Click to expand...

Actually power is work divided by time, meaning it's the rate at which work is being done. The reason why you might have thought that it was force divided by time was because of torque. Torque is a force, but it's unit is in foot pounds because you multiply the applied force by the radius. Normally a force is measured in pounds or newtons, work would be measured in newton-metres. Work is force applied upon a mass through a certain distance.
 
This really does not explian what it is but more what it does.
Tourque can be seen as low end power, while horse power is high end power. You have more HP when your are close to red linning and much less when you are almost idle. Tourque however maxes at a lower R.P.M and therfore gives you power earlier.
Genrally big low reving American V8s have a lot of tourgue while the Itialan V-10 and V-12 that rev high have less tourque and more HP.
In racing tourgue is more important for almost every type of racing since the driver is opperating at diffrent R.P.M.s and shiffting throught gears. Drag Racing is where Horse Power is important since the car is always at high end of the R.P.M. gauge.
 
Slick Rick
If thats the case, then like i said earlier, why doesnt someone create an engine with loads of torque and little HP and then create speed using a gearbox containing very high gears because the engine will be capable of turning them. The acceleration would be better and the top speed could also be much higher due to the gear ratio.
Click to expand...

Because when you have less [horse]power you have to shift more to keep the car into it's powerband. Horsepower usually depends on top speed of teh car because it is the amount of work an engine can produce.

Famine

Assuming identical gearing, 190hp/140ftlb will be quicker than 140hp/190ftlb, since 190hp is 104,500ftlb/s and 140hp is 77,000ftlb/s. The actual torque rating is of no consequence.
Click to expand...

However 190 ft/lbs engine if produced at a higher RPM would be quicker than 140 ft/lbs engine because you wouldn't have to shift as often due to the engine pulling harder at higher revs...


Leet_Newb
This really does not explian what it is but more what it does.
Tourque can be seen as low end power, while horse power is high end power. You have more HP when your are close to red linning and much less when you are almost idle. Tourque however maxes at a lower R.P.M and therfore gives you power earlier.
Genrally big low reving American V8s have a lot of tourgue while the Itialan V-10 and V-12 that rev high have less tourque and more HP.
In racing tourgue is more important for almost every type of racing since the driver is opperating at diffrent R.P.M.s and shiffting throught gears. Drag Racing is where Horse Power is important since the car is always at high end of the R.P.M. gauge.
Click to expand...

Kind of irrelevant - F1 engines make barely 300Nm. However they have 800+bhp due to their very short stroke, which increases rpm hence more power.
 
Torque and horsepower are both related, and both can be interesting numbers if you understand what they mean.

Torque AT THE WHEELS is what accelerates your vehicle, however the torque at the wheels is different from the torque at the crank because the gearbox multiplies torque.

This is where horsepower is interesting, as its kinda a roundabout way of measuring torque at the wheels. If two cars are moving at the same speed, the one that puts out more power will be capable of putting more torque down to the wheels, regardless of how much torque each one is putting out at the crank.

Also, in a college level physics class, it'll usually take about a full term to get through all of the material that relates to torque and horsepower... and even then many of the people in the class won't have a great grasp of it. So I wouldn't expect to be able to read a paragraph off of a message board and then really understand what horsepower and torque are.
 
www.howstuffworks.com Im too lazy at work right now to direct link it, but search for both horsepower and torque on that site, it gives great definitions of both and uses nice pictures and illustations to show you how it all really works. It even tells you where the term Horse Power came from, and why.
 
Horsepower = Makes you go fast in the upper ranges of your tach
Torque = Makes you go fast in the lower ranges of your tach (or uphill), and do wheelspin

No doubt about it, horsepower is more important for racing, but neither one is "useless" or "pointless."
 
I have heard that horsepower is how quickly the engine can increase it's own speed(rpms) & I know torque is the ability to push against resistance
more torque will give a higher top speed along with quicker off the line acceleration....because the faster you go the more your eninge has to fight the air...& it becomes more of a pushing battle again
 
I've been trying to explain the differences to a friend of mine and I guess I'm not doing to well. I'm glad I've got a few new examples and ways of explaining things to him. Thanks guys.

Instead of searching all over the internet for this information, it's all in this one thread. Amazing.
 
Torque is very important when it comes to gearing.
Easiest way I guess in GT4 would be to take two similar powered cars, one with less torque.
Gear them exactly the same, make every gear as wide as it possibly can. It will help if both cars generate the torque at around the same RPM.

What I did was took a 300kw Vette Grand Sport, and a 300kW Mazda RX8.
about 250kg weight difference.

Then do a 1000m test and watch the car with more torque, despite the extra weight, finish first.

Wolfe2x7
Horsepower = Makes you go fast in the upper ranges of your tach
Torque = Makes you go fast in the lower ranges of your tach (or uphill), and do wheelspin

No doubt about it, horsepower is more important for racing, but neither one is "useless" or "pointless."
Click to expand...

Not entirely true. If tracks have alot of elevation changes and cars are ran with similar power, higher torque cars will have an advantage. Perfect example is the Spoon cars. They generate torque very high up in their rev ranges, it isn't much, however they can pull very hard, despite their horsepower rating. Also has to do with their very high redline.
 
Rzeractor
Not entirely true. If tracks have alot of elevation changes and cars are ran with similar power, higher torque cars will have an advantage. Perfect example is the Spoon cars. They generate torque very high up in their rev ranges, it isn't much, however they can pull very hard, despite their horsepower rating. Also has to do with their very high redline.
Click to expand...

I agree, and I think you may have missed that in my post ;) :

I
Horsepower = Makes you go fast in the upper ranges of your tach
Torque = Makes you go fast in the lower ranges of your tach (or uphill), and do wheelspin

No doubt about it, horsepower is more important for racing, but neither one is "useless" or "pointless."
Click to expand...

Or, you were embellishing a point that you felt I had not given enough attention to. If so, you're probably right. :)
 
I think something people very commonly overlook is that HP/WT ratio is somewhat pointless... what is far more relevant, is the torque to weight ratio... a 3500lb car with 300 hp and 320 lb-ft of torque will be equally as fast as a car with 2800LB car 300HP and 210 ft-lb of torque -- because the extra torque will move the extra weight along with it.
 
LeadSlead#2
I think something people very commonly overlook is that HP/WT ratio is somewhat pointless... what is far more relevant, is the torque to weight ratio... a 3500lb car with 300 hp and 320 lb-ft of torque will be equally as fast as a car with 2800LB car 300HP and 210 ft-lb of torque -- because the extra torque will move the extra weight along with it.
Click to expand...

Which is faster depends on the torque and power curves, those peak numbers don't really tell you a whole lot.

However, what accelerates your car is torque AT THE WHEELS... if two cars are moving the same speed, and are putting out the same power at that speed, then they will be putting identical torque to the ground. If both cars are constantly putting out 300hp then the lighter one will be faster.

Of course, both aren't putting out the same hp all the time, so you have to do a little calculus and look at the area under each cars horsepower curve.

unsanctified
Instead of searching all over the internet for this information, it's all in this one thread. Amazing.
Click to expand...

Except a lot of it is wrong :)
 
you couldnt be more incorrect -- just because two cars have the same hp, does NOT mean they have the same torque, and extra torque WILL overcome an equal portion of extra weight
 
If two cars are moving at the same speed, and both of their engines are putting out the same power, they will be putting out the same torque AT THE WHEELS, not at the crank. This is pretty basic physics, power at the wheels = power at the crank. If they are both making the same power at the crank, they are making the same power at the wheels, which means they are making the same torque at the wheels.

The transmission will multiply torque, but will not multiply power. The engine with less torque gets more torque multiplication, because it's spinning faster. That's kinda why you even consider power numbers.
 
retsmah
If two cars are moving at the same speed, and both of their engines are putting out the same power, they will be putting out the same torque AT THE WHEELS, not at the crank. This is pretty basic physics, power at the wheels = power at the crank. If they are both making the same power at the crank, they are making the same power at the wheels, which means they are making the same torque at the wheels.
Click to expand...

That's not strictly true though, is it? Movement requires power (or torque... :D ) at the wheels, but thanks to variances in drivetrain efficiencies the two cars may not be producing the same crank power. If the two cars are FWD and 4WD, then the 4WD car may be producing 20% MORE power at the crank than the FWD one.

But I digress.
 
when you say power, I take it you mean Horsepower? if not, you need to clarify -
If you do, that is absolutly wrong - two vehicles that have the same HP at the wheels do NOT have to have the same torque at the wheels - in some instances they might, (perhaps vehicles with very similar torque ratings) but in most they don't -- I sincerly hope that is not what you are saying
 

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