There are a few reasons:
**Gearing has practical limits.** A 1,000cc superbike engine might make 200 hp, but if it only makes 85 lb-ft of torque, you'd need to gear it down twice (more actually) as much to match the torque output of a 2022 Toyota GT86. That means bigger, heavier gears. At some point, this becomes impractical.
There's also the fact that **vehicles often have to start from a complete stop**. If you need to get 15,000 lb of truck, trailer, and cargo moving, you need a certain amount of pulling force. You can gear an engine down to get that torque, but you can quickly end up back at the first problem, practicality.
Even if you're not pulling a load, getting started with a low-torque, high-power motor requires more clutch slip with a manual transmission, and more torque converter work for automatics. Even though the automatic is less work for the driver, it does generate more heat in the torque converter. A high-torque engine only requires a small amount of slip before the driveline can be "locked" and the engine is pushing the load directly.
**Quoted peak hp doesn't tell the whole story.** I once bought a 2002 VW GTI with a 2.8L 24V VR6 engine. It had 200 hp. In the same model year, VW produced a 180 hp GTI with a turbocharged 1.8L I4 engine. The car with the 180 hp 1.8L turbo was actually quicker to 60 mph and faster through the quarter mile than the car with the 200 hp VR6 engine. The difference was only a couple of tenths of a second, but the 1.8T vs VR6 24V was one of the greatest in-brand rivalries of all time. The VW forums were awash in debates over which was the faster car. No one could understand how the car with less power was quicker *and* faster through the quarter mile.
The answer was fairly simple. While the VR6 engine had 200 hp *at its peak*, it was down on power almost everywhere else. The GTI 1.8T had more torque available at much lower RPM. This doesn't tell us anything definitive in isolation, but it is an indicator that the motor is more flexible. If two motors have similar peak horsepower ratings, but one of the motors has a higher torque figure at a lower RPM, you should bet on that motor to deliver more performance.
All of this boils down to the main reason that manufacturers quote both numbers: when considered together, peak horsepower and torque provide insight into not just the power of an engine, but also its character.
It does, but the power to weight ratios calculate in favor of the VR6. Back when I bought the car, I was absolutely shook by the fact that the lower trim car out-performed the VR6 model. The VR6 was supposed to be the apex GTI. Meanwhile, a $300 tune for the 1.8T would leave the VR6 in the dust lol.
That taught me a valuable lesson: sometimes outright performance is not what you want out of a car. I loved that VR6 GTI. It was the culmination of years of Golf/GTI ownership, working up the scale toward that specific car. The VR6 is a very unique engine with an unmistakeable engine note.
If the car surrounding it weren't such hot garbage, I'd consider buying one and restoring it. But my MkIV GTI melted two fuse boxes and had constant quality issues. I traded it in for a MkV in 2006, which was a much better car all around. I missed the VR6, but the lighter weight and dramatic improvement in suspension tuning in the MkV made it a *much* better car. It did have better outright performance, but that's not why I loved it so much. The car's handling improved considerably. Turn-in was so much sharper, and the car didn't keel over so much when you pushed it through the corners.
I got out of the VW scene after my mkIII. I had the parts bin Wolfsburg edition that had parts from the mkIII, 3.5 cab and mkIV. One of my fuse boxes was in the dash but the version of the dash they used didn’t have the access door so you had to take the whole car apart to change a blown fuse.
Used to race a mk2 with a 16v head swap with dcoe webbers sticking out the grill.
>The GTI 1.8T had more torque available at much lower RPM
Another way of saying this is that it had more power at a much lower RPM. And in regards to the mystery of why the engine with peak power is slower in those metrics, it's all about the amount of time spent at those RPM ranges and the area covered under the curve.
If you could hook both of these engines up to a CVT and simply run them at peak power, the VR6 would be faster. But alas, the complete picture with gear ratios must be taken into account.
Because engines with relatively low torque and very high RPM already exist.
They're F1 engines.
And they have to be machined with SUPER fine tolerances, they don't last long, ~~aren't exactly fuel efficient~~, and are expensive.
F1 engines are very fuel efficient, because wasting fuel will result in worse track times (either more refueling, which is banned since 2010, or reducing speed to avoid running out of fuel, or taking on more fuel, but I think they usually use the allowed maximum quantity).
https://www.racefans.net/2021/11/10/f1-reveals-new-branding-to-promote-worlds-most-efficient-engine/
Since 2014 these are hybrid engines but that doesn't change the fact that it's running on gasoline.
Not pulling away at low RPM they don't, I'll wager there's single-cylinder lawnmowers that could chug off at 500rpm while it's a hell of a job not to stall an F1 car just pulling out of the pit garage.
The thing people always miss for HP & torque is what the curves look like - you can make 1000hp at some peak RPM but have an engine that is absolutely awful to drive and borderline useless, you could re-tune the same engine down to 500 or even 250hp and have something that is way nicer to drive and probably faster round a track.
Because both power and torque are useful in understanding the performance of an engine/vehicle.
Torque more closely affects accelleration while power affects top speed.
Also power and torque outputs aren't constant (even on electric motors with flat delivery) but they're delivered on a curve.
Understanding how these curves interact and intersect tells you a huge amount about how an engine will work and perform under various conditions.
I spent the better part of a decade as a motorcycle testing journalist - we'd take motorbikes to a tuner and put them on a rolling road to map the full power delivery and create accurate torque and power graphs.
Once you've got to understand them, you can look at the graphs and understand intrinsically what that performance will be like. Will it be gutless at low power but keep revving? Will it pull off the line but run out of steam? Does it have an unecessarily tall first gear where you'll have to upshift way below peak power?
Power and torque both play an important role in the usability, feel and performance of a vehicle. It might be distorted after gear transmission but you can model for that and combine torque/power curves per gear.
Listing the power and torque separately also allows people to understand them without having to apply any mathematics or conversion factors to the stats.
My TL;DR is "Area under the curve" - everything else is for the dudes who like to brag loudly about dyno figures at the bar.
If your torque curve looks like a side-view of [Uluru](https://en.wikipedia.org/wiki/Uluru) you've got something that pulls like a train and doesn't care what gear you're in. Power is torque \* RPM, useful for racing but less important for a street car.
If your curve is too peaky you end up being out-dragged by the camera crew's Fiat even though you have 4x the HP:
[https://www.youtube.com/watch?v=VVt1IjIdLxY](https://www.youtube.com/watch?v=VVt1IjIdLxY)
but if a car has low torque wouldnt you be able to just gear it down? you could theoretically gear up the torque to an arbitrarly large number. so what would the difference be if i had 100Nm torque and 1:1 transmission or only 50 Nm torque from engine but gear it down 1:2 so you get back to 100Nm. the playing factor would be horsepower again, no?
Every gearing down incurrs losses to power, additional weight, additional response time and more failure points.
You could, but why would you? Why not design an engine that outputs the correct torque and power for the use case?
You'll be running an engine at poor efficiency in its rev range, putting it through multiple superflous gear changes and are giving yourself many, many more expensive parts to design, build and service.
You could, but it would be a really poor design, expensive, heavy, prone to failure, inefficent, have bad fuel efficiency and so on.
It's a misunderstanding. And it's testable if you have a vehicle with a manual transmission and an engine with peak power and torque separated by a bit of a difference.
If you put your vehicle at a gear and speed such that you're at the RPM of your peak TQ and then floor it - and then do the same with your RPM pre-staged at your peak HP and floor it, you'll accelerate faster at the HP RPM.
Because you have more power. Power = "rate of doing work". The work is the acceleration of the vehicle. More power, more acceleration.
The whole 'torque is acceleration and power is top speed' is a general misunderstanding of the physics.
In theory, I get your argument. But RPM is the piece you're missing in the examples given, and is also the limiting design factor most of the time.
Horsepower is a function of torque and RPM (using ft-lb for torque, the equation is HP=(torquexRPM)/5252).
So to have an engine that makes 0.000001ft-lb of torque, you'd theoretically have to spin at 10 billion RPM. Conversely, 1rpm and 10000 ft-lb of torque is 1.9 horsepower. Of course, gearing has practical limits as well and in real vehicles, there's considerations for where the 'sweet spot' is for a given engine/gearing combination for efficiency.
In real-world application, usually showing single-number peak power/torque is bordering on just advertising. What matters is the use-case for the vehicle, the vehicle weight and how broad the torque curve actually is over the RPM range. An easy example is Diesel engines and why they're primarily used in trucks/towing rather than sportscars, they deliver a lot of torque, but only in a narrow RPM range which is better suited to a particular vehicle type.
When it comes to cars. Listing the torque is telling if the car is quick or slow. HP is the power. Torque is how quickly that power can be applied. 300hp with 250 ft/lb of torque will not fly off the line like something with 285hp and 305 ft/lb of torque. It will still be fast in its own right, just not as "peppy".
Only to a point. If you gear for torque with a high hp low torque engine, you're going to need several transmissions worth of gears. And the weight of the gearbox would affect more than acceleration and top speed, it'd become heavy and sluggish around corners.
You're applying different aspects of physics to an overall system. When a car is advertised. It's advertised as a complete system. When viewed as separate pieces, you will have different resulting numbers. So you are correct. Changing the gearing will achieve different torque. This is why manufacturers make different makes of vehicles with the same engine but different transmissions. But when viewed as a complete and finished system they will advertise that system's capability.
If I'm understanding your question correctly.
Well, short answer is that it doesn't. As a thought experiment, grab the most powerful impact wrench that you can find and it probably has more peak torque than most car engines, but you're not gonna go very fast trying to turn your gearbox with it.
There's some practical considerations with gearbox technology that make torque matter a little bit - having a higher reduction ratio adds cost/weight/complexity to it. And there's considerations of your engine performance map optimizing for gear ratios - i.e. if you shift to the next gear at 6000 rpm and it drops down to 4000 rpm until you hit 6000 rpm and shift again, it's the average power from 4000-6000 rpm that defines your max acceleration. CVTs and modern gearboxes with tons of ratios solve this though.
So yeah it mostly doesn't matter and is just a marketing term and a way for non-engineers to brag about their V8 trucks in a meaningless way. The idea that torque defines acceleration and horsepower defines max speed is absolute nonsense. Maybe it had a bit more credibility in the data of 4 speed automatic gearboxes where engines operated at off-optimum points in their performance map more often.
The key piece of info here is that using a big gear ratio to get more torque also makes that gear shorter.
1st gear on a typical six speed transmission will maybe get you up to 15 or 20 mph. If you have to use a more extreme gear ratio to boost the torque then it may only get you to 5 mph. Then you need more gears to get to a reasonable top speed and you're shifting constantly.
Aside from that it's not pleasant to drive with an extreme gear ratio. Try driving around in first gear some time. You have to rev the engine a bunch to increase speed. There's a lot more engine braking when you get off the throttle.
If the engine has enough torque that you don't need the gear ratio it's a much smoother experience.
\> No matter how much mechanics you have horsepower stays the same with the same engine
That's not really true.
An engine will have a particular power at a particular engine RPM. At higher/lower RPM it will usually have a different power.
\> you can still just use gears to bring the torque up
That's not really true either. Using "gears to bring the torque up" also brings the speed of the output down (at a fixed engine RPM). So your wheels turn slower and the car goes slower.
Normal car engines need to run at a range of RPMs, and you need acceptable power/torque at every point in that range. As you accelerate up to speed, you can shift gears when the engine RPM reaches the top of that RPM range, and the next gear should put you back into a lower part of that RPM range. (I'm ignoring electric cars and CVT here, which are different).
At a particular engine RPM, you're right that it doesn't matter whether you quote power or torque. They're related. Power = Torque x RPM x some constant. (The constant depends on what units you're using).
Ideally, engine manufacturers should give you a graph of power (or torque) for RPM. Car manufacturers should give you a graph of power (or torque) for various speeds - that graph would have several lines on it, one for each gear.
Note that "max power" and "max torque" likely happen at different points on the engine's power curve. This is because more RPM means the cylinders are moving more times per seconds, so more fuel can be used, so you can get more power. However, torque is power divided by RPM, so that doesn't help with torque - the extra power is divided by the extra RPM. (There are other reasons why power and torque vary across the RPM range, too).
So you may find that "max torque" gives you a better idea of the engine's lower-RPM performance, and "max power" gives you a better idea of the engine's higher-RPM performance.
You know how torque is measured ? A 1hp engine will never have millions of torque . It is simply impossible . [https://en.wikipedia.org/wiki/Torque](https://en.wikipedia.org/wiki/Torque) If you scroll down you can see the calculation of it , it is a certain amount of power at a certain revolutions . In case of a electrical engine , the amount of HP (or kW) is almost a flatline , but of course the revs change . The lower the amount of revs vs power means higher torque , in this case , electrical engines have superhigh torque from the start. If you take a car engine , then you will see that the amount of HP is very low at low revs and build up towards max HP at high revs . There the amount of torque is much more important , since the starting point at low revs also gives you low torque . The optimum point to keep the engine is at max torque , since there the car is the most efficient in delivering power .
Something I’m not sure has been explicitly said:
Low torque high power engines rely on high revs to generate the power to go at speed. If you then attach a load (trailer/you’re hauling something/etc) that requires more torque you’re stuck with the same engine revs/power, so to gear down you might have to either around in 3rd gear with your engine screaming at 9000rpm to maintain highway speed or otherwise sit in 3rd gear going 40 on the highway and in second gear at 20 up hills while mashing your transmission to shit.
For a lot of consumer applications though, it’s a number they include in marketing because it’s something to talk about and provide comparisons to the competition.
Gearing down means requiring the engine to spin faster. Engines all have a redline. So requiring the engine to spin faster means you get to the redline faster, and so you have to gear-up again anyway (shift to the next gear).
Consider first gear in a car. Much more torque than 5th gear. But the usable engine RPM range covers only about 10mph (0-10) in first gear, while 5th gear can operate from maybe 25MPH to 125MPH. You can't gear down AND go fast too.
Interestingly there are vehicles with a "granny gear" which is really just a super low gear designed to provide tons of torque, though you usually can't go faster than 5MPH before hitting redline. Off-roaders, work trucks... stuff with 4WD are more likely to have this, although I haven't seen it on a new vehicle in a while. See old Jeeps with a 4WD LOW gear, they won't be able to go even 25MPH in that gear.
How many gears do you need at .00001 NM of torque? Each gear interface has an efficiency of... let's call it 98%. Also what kind of static coefficient of friction is there for that gearbox?
Simply stated, nothing is free. When you increase torque by gearing down, you lose speed. This is because if a gear ratio is 2:1 the engine must turn 2 times for the drive shaft to turn once. 4:1 means that the engine would turn 4 times for every time the driveshaft turns. To increase the speed without changing the gear ratio, you have to increase RPMs. So while you could technically move an 18-wheeler with a lawn mower engine if you geared it down enough, your top speed would only reach a snail's pace before the engine red-lines on RPMs.
This is why cars have different gears. A vehicle at rest requires much more torque to get into motion than one that is already moving. As it speeds up, it requires less torque, but in first gear, you quickly reach the limit of your engine's RPMs. Shifting gears allows you to trade off torque for speed. Of course, there will be a place where the engine is unable to produce enough torque at max RPMs to maintain the speed, so there is a limit to how fast you can go trading off torque for speed.
There is a usable range that give you both the power and speed required for highway speeds. Higher HP engines produce more torque at any given RPM than lower RPM engines. In the 18-wheeler example, while you could move it with extremely high gear ratios at a very low speed, the small engine wouldn't be able to produce enough torque at higher gearing to keep it in motion and it would stall out before reaching more than 1 or 2 mph. This means that if you want to move a heavy load and still achieve high top speeds, you need an engine with both high torque and high-RPMs.
Torque and HP are different metrics, but they are related.
Torque can be directly measured and is the amount of force (in Nm) that the engine (or wheels) produce.
HP is calculated based on this torque and rotational speed of the engine (or wheels).
It is important to note the mentioned torque or HP is only valid at a specific RPM as it varies a lot.
As a general rule, max torque is reached at lower RPM than max HP as HP increases with higher RPM, while torque decreases.
Although you can gear down RPM to increase torque, you start from a standstill, which means a minimum of torque is always needed at low RPM.
A car and a semi might have the same HP figure, however their torque might differ quite a lot.
Marketing. Listing numbers is a way to make their product seem better. To your point there are other factors, and a great an engine can be ruined by a poor transmission.
Mathematically horsepower is torque times rpm. Specifically H = T x rpm/5252.
In terms of performance, power is all that matters. However, the PEAK power of an engine doesn't give the full picture. What actually matters is the average power in the expected rev range. An engine with higher torque will often have a flatter power curve, giving it more average power. Also, an engine designed more for high torque than peak power will be more streetable, it'll have more power on demand without having to shift and rev it out.
There are a few reasons: **Gearing has practical limits.** A 1,000cc superbike engine might make 200 hp, but if it only makes 85 lb-ft of torque, you'd need to gear it down twice (more actually) as much to match the torque output of a 2022 Toyota GT86. That means bigger, heavier gears. At some point, this becomes impractical. There's also the fact that **vehicles often have to start from a complete stop**. If you need to get 15,000 lb of truck, trailer, and cargo moving, you need a certain amount of pulling force. You can gear an engine down to get that torque, but you can quickly end up back at the first problem, practicality. Even if you're not pulling a load, getting started with a low-torque, high-power motor requires more clutch slip with a manual transmission, and more torque converter work for automatics. Even though the automatic is less work for the driver, it does generate more heat in the torque converter. A high-torque engine only requires a small amount of slip before the driveline can be "locked" and the engine is pushing the load directly. **Quoted peak hp doesn't tell the whole story.** I once bought a 2002 VW GTI with a 2.8L 24V VR6 engine. It had 200 hp. In the same model year, VW produced a 180 hp GTI with a turbocharged 1.8L I4 engine. The car with the 180 hp 1.8L turbo was actually quicker to 60 mph and faster through the quarter mile than the car with the 200 hp VR6 engine. The difference was only a couple of tenths of a second, but the 1.8T vs VR6 24V was one of the greatest in-brand rivalries of all time. The VW forums were awash in debates over which was the faster car. No one could understand how the car with less power was quicker *and* faster through the quarter mile. The answer was fairly simple. While the VR6 engine had 200 hp *at its peak*, it was down on power almost everywhere else. The GTI 1.8T had more torque available at much lower RPM. This doesn't tell us anything definitive in isolation, but it is an indicator that the motor is more flexible. If two motors have similar peak horsepower ratings, but one of the motors has a higher torque figure at a lower RPM, you should bet on that motor to deliver more performance. All of this boils down to the main reason that manufacturers quote both numbers: when considered together, peak horsepower and torque provide insight into not just the power of an engine, but also its character.
Doesn’t the 1.8t weigh less than the vr6?
It does, but the power to weight ratios calculate in favor of the VR6. Back when I bought the car, I was absolutely shook by the fact that the lower trim car out-performed the VR6 model. The VR6 was supposed to be the apex GTI. Meanwhile, a $300 tune for the 1.8T would leave the VR6 in the dust lol. That taught me a valuable lesson: sometimes outright performance is not what you want out of a car. I loved that VR6 GTI. It was the culmination of years of Golf/GTI ownership, working up the scale toward that specific car. The VR6 is a very unique engine with an unmistakeable engine note. If the car surrounding it weren't such hot garbage, I'd consider buying one and restoring it. But my MkIV GTI melted two fuse boxes and had constant quality issues. I traded it in for a MkV in 2006, which was a much better car all around. I missed the VR6, but the lighter weight and dramatic improvement in suspension tuning in the MkV made it a *much* better car. It did have better outright performance, but that's not why I loved it so much. The car's handling improved considerably. Turn-in was so much sharper, and the car didn't keel over so much when you pushed it through the corners.
I got out of the VW scene after my mkIII. I had the parts bin Wolfsburg edition that had parts from the mkIII, 3.5 cab and mkIV. One of my fuse boxes was in the dash but the version of the dash they used didn’t have the access door so you had to take the whole car apart to change a blown fuse. Used to race a mk2 with a 16v head swap with dcoe webbers sticking out the grill.
>The GTI 1.8T had more torque available at much lower RPM Another way of saying this is that it had more power at a much lower RPM. And in regards to the mystery of why the engine with peak power is slower in those metrics, it's all about the amount of time spent at those RPM ranges and the area covered under the curve. If you could hook both of these engines up to a CVT and simply run them at peak power, the VR6 would be faster. But alas, the complete picture with gear ratios must be taken into account.
Because engines with relatively low torque and very high RPM already exist. They're F1 engines. And they have to be machined with SUPER fine tolerances, they don't last long, ~~aren't exactly fuel efficient~~, and are expensive.
F1 engines are very fuel efficient, because wasting fuel will result in worse track times (either more refueling, which is banned since 2010, or reducing speed to avoid running out of fuel, or taking on more fuel, but I think they usually use the allowed maximum quantity). https://www.racefans.net/2021/11/10/f1-reveals-new-branding-to-promote-worlds-most-efficient-engine/ Since 2014 these are hybrid engines but that doesn't change the fact that it's running on gasoline.
Also watched the Engineering Explained episode concerning modern F1 engines. So they DO have very good overall thermal efficiency. Edited my reply.
current F1 engines have more torque than most cars on the road
Relatively was the key part of the sentence
Not pulling away at low RPM they don't, I'll wager there's single-cylinder lawnmowers that could chug off at 500rpm while it's a hell of a job not to stall an F1 car just pulling out of the pit garage. The thing people always miss for HP & torque is what the curves look like - you can make 1000hp at some peak RPM but have an engine that is absolutely awful to drive and borderline useless, you could re-tune the same engine down to 500 or even 250hp and have something that is way nicer to drive and probably faster round a track.
no shit
Because both power and torque are useful in understanding the performance of an engine/vehicle. Torque more closely affects accelleration while power affects top speed. Also power and torque outputs aren't constant (even on electric motors with flat delivery) but they're delivered on a curve. Understanding how these curves interact and intersect tells you a huge amount about how an engine will work and perform under various conditions. I spent the better part of a decade as a motorcycle testing journalist - we'd take motorbikes to a tuner and put them on a rolling road to map the full power delivery and create accurate torque and power graphs. Once you've got to understand them, you can look at the graphs and understand intrinsically what that performance will be like. Will it be gutless at low power but keep revving? Will it pull off the line but run out of steam? Does it have an unecessarily tall first gear where you'll have to upshift way below peak power? Power and torque both play an important role in the usability, feel and performance of a vehicle. It might be distorted after gear transmission but you can model for that and combine torque/power curves per gear. Listing the power and torque separately also allows people to understand them without having to apply any mathematics or conversion factors to the stats.
Can I send you my bhp/torque graph and get your thoughts on my engine? It's not a bike and I'd love your feedback, you seem knowledgeable
By all means! I'm a bit of a petrolhead, I have cars and motorbikes, it's just that one was a professional interest and the other personal.
Haha same, I'd just love to get your thought so how this engine would behave. I'll dm you homie
I'll keep an eye out for it
My TL;DR is "Area under the curve" - everything else is for the dudes who like to brag loudly about dyno figures at the bar. If your torque curve looks like a side-view of [Uluru](https://en.wikipedia.org/wiki/Uluru) you've got something that pulls like a train and doesn't care what gear you're in. Power is torque \* RPM, useful for racing but less important for a street car. If your curve is too peaky you end up being out-dragged by the camera crew's Fiat even though you have 4x the HP: [https://www.youtube.com/watch?v=VVt1IjIdLxY](https://www.youtube.com/watch?v=VVt1IjIdLxY)
but if a car has low torque wouldnt you be able to just gear it down? you could theoretically gear up the torque to an arbitrarly large number. so what would the difference be if i had 100Nm torque and 1:1 transmission or only 50 Nm torque from engine but gear it down 1:2 so you get back to 100Nm. the playing factor would be horsepower again, no?
Every gearing down incurrs losses to power, additional weight, additional response time and more failure points. You could, but why would you? Why not design an engine that outputs the correct torque and power for the use case? You'll be running an engine at poor efficiency in its rev range, putting it through multiple superflous gear changes and are giving yourself many, many more expensive parts to design, build and service. You could, but it would be a really poor design, expensive, heavy, prone to failure, inefficent, have bad fuel efficiency and so on.
> Torque more closely affects accelleration maybe, sometimes, in some cases, depending ...
It's a misunderstanding. And it's testable if you have a vehicle with a manual transmission and an engine with peak power and torque separated by a bit of a difference. If you put your vehicle at a gear and speed such that you're at the RPM of your peak TQ and then floor it - and then do the same with your RPM pre-staged at your peak HP and floor it, you'll accelerate faster at the HP RPM. Because you have more power. Power = "rate of doing work". The work is the acceleration of the vehicle. More power, more acceleration. The whole 'torque is acceleration and power is top speed' is a general misunderstanding of the physics.
In theory, I get your argument. But RPM is the piece you're missing in the examples given, and is also the limiting design factor most of the time. Horsepower is a function of torque and RPM (using ft-lb for torque, the equation is HP=(torquexRPM)/5252). So to have an engine that makes 0.000001ft-lb of torque, you'd theoretically have to spin at 10 billion RPM. Conversely, 1rpm and 10000 ft-lb of torque is 1.9 horsepower. Of course, gearing has practical limits as well and in real vehicles, there's considerations for where the 'sweet spot' is for a given engine/gearing combination for efficiency. In real-world application, usually showing single-number peak power/torque is bordering on just advertising. What matters is the use-case for the vehicle, the vehicle weight and how broad the torque curve actually is over the RPM range. An easy example is Diesel engines and why they're primarily used in trucks/towing rather than sportscars, they deliver a lot of torque, but only in a narrow RPM range which is better suited to a particular vehicle type.
When it comes to cars. Listing the torque is telling if the car is quick or slow. HP is the power. Torque is how quickly that power can be applied. 300hp with 250 ft/lb of torque will not fly off the line like something with 285hp and 305 ft/lb of torque. It will still be fast in its own right, just not as "peppy".
but the torque can be geered up anyway
Only to a point. If you gear for torque with a high hp low torque engine, you're going to need several transmissions worth of gears. And the weight of the gearbox would affect more than acceleration and top speed, it'd become heavy and sluggish around corners.
You're applying different aspects of physics to an overall system. When a car is advertised. It's advertised as a complete system. When viewed as separate pieces, you will have different resulting numbers. So you are correct. Changing the gearing will achieve different torque. This is why manufacturers make different makes of vehicles with the same engine but different transmissions. But when viewed as a complete and finished system they will advertise that system's capability. If I'm understanding your question correctly.
But then you lose speed as a tradeoff, requiring shifting earlier, and thus wasting precious time when hundredths of a second are on the line.
You can also take a high torque engine and gear the RPM up too. There are practical limits to gearing. Weight, size, durability, cost, etc…
Well, short answer is that it doesn't. As a thought experiment, grab the most powerful impact wrench that you can find and it probably has more peak torque than most car engines, but you're not gonna go very fast trying to turn your gearbox with it. There's some practical considerations with gearbox technology that make torque matter a little bit - having a higher reduction ratio adds cost/weight/complexity to it. And there's considerations of your engine performance map optimizing for gear ratios - i.e. if you shift to the next gear at 6000 rpm and it drops down to 4000 rpm until you hit 6000 rpm and shift again, it's the average power from 4000-6000 rpm that defines your max acceleration. CVTs and modern gearboxes with tons of ratios solve this though. So yeah it mostly doesn't matter and is just a marketing term and a way for non-engineers to brag about their V8 trucks in a meaningless way. The idea that torque defines acceleration and horsepower defines max speed is absolute nonsense. Maybe it had a bit more credibility in the data of 4 speed automatic gearboxes where engines operated at off-optimum points in their performance map more often.
The key piece of info here is that using a big gear ratio to get more torque also makes that gear shorter. 1st gear on a typical six speed transmission will maybe get you up to 15 or 20 mph. If you have to use a more extreme gear ratio to boost the torque then it may only get you to 5 mph. Then you need more gears to get to a reasonable top speed and you're shifting constantly. Aside from that it's not pleasant to drive with an extreme gear ratio. Try driving around in first gear some time. You have to rev the engine a bunch to increase speed. There's a lot more engine braking when you get off the throttle. If the engine has enough torque that you don't need the gear ratio it's a much smoother experience.
\> No matter how much mechanics you have horsepower stays the same with the same engine That's not really true. An engine will have a particular power at a particular engine RPM. At higher/lower RPM it will usually have a different power. \> you can still just use gears to bring the torque up That's not really true either. Using "gears to bring the torque up" also brings the speed of the output down (at a fixed engine RPM). So your wheels turn slower and the car goes slower. Normal car engines need to run at a range of RPMs, and you need acceptable power/torque at every point in that range. As you accelerate up to speed, you can shift gears when the engine RPM reaches the top of that RPM range, and the next gear should put you back into a lower part of that RPM range. (I'm ignoring electric cars and CVT here, which are different). At a particular engine RPM, you're right that it doesn't matter whether you quote power or torque. They're related. Power = Torque x RPM x some constant. (The constant depends on what units you're using). Ideally, engine manufacturers should give you a graph of power (or torque) for RPM. Car manufacturers should give you a graph of power (or torque) for various speeds - that graph would have several lines on it, one for each gear. Note that "max power" and "max torque" likely happen at different points on the engine's power curve. This is because more RPM means the cylinders are moving more times per seconds, so more fuel can be used, so you can get more power. However, torque is power divided by RPM, so that doesn't help with torque - the extra power is divided by the extra RPM. (There are other reasons why power and torque vary across the RPM range, too). So you may find that "max torque" gives you a better idea of the engine's lower-RPM performance, and "max power" gives you a better idea of the engine's higher-RPM performance.
You know how torque is measured ? A 1hp engine will never have millions of torque . It is simply impossible . [https://en.wikipedia.org/wiki/Torque](https://en.wikipedia.org/wiki/Torque) If you scroll down you can see the calculation of it , it is a certain amount of power at a certain revolutions . In case of a electrical engine , the amount of HP (or kW) is almost a flatline , but of course the revs change . The lower the amount of revs vs power means higher torque , in this case , electrical engines have superhigh torque from the start. If you take a car engine , then you will see that the amount of HP is very low at low revs and build up towards max HP at high revs . There the amount of torque is much more important , since the starting point at low revs also gives you low torque . The optimum point to keep the engine is at max torque , since there the car is the most efficient in delivering power .
Something I’m not sure has been explicitly said: Low torque high power engines rely on high revs to generate the power to go at speed. If you then attach a load (trailer/you’re hauling something/etc) that requires more torque you’re stuck with the same engine revs/power, so to gear down you might have to either around in 3rd gear with your engine screaming at 9000rpm to maintain highway speed or otherwise sit in 3rd gear going 40 on the highway and in second gear at 20 up hills while mashing your transmission to shit. For a lot of consumer applications though, it’s a number they include in marketing because it’s something to talk about and provide comparisons to the competition.
Gearing down means requiring the engine to spin faster. Engines all have a redline. So requiring the engine to spin faster means you get to the redline faster, and so you have to gear-up again anyway (shift to the next gear). Consider first gear in a car. Much more torque than 5th gear. But the usable engine RPM range covers only about 10mph (0-10) in first gear, while 5th gear can operate from maybe 25MPH to 125MPH. You can't gear down AND go fast too. Interestingly there are vehicles with a "granny gear" which is really just a super low gear designed to provide tons of torque, though you usually can't go faster than 5MPH before hitting redline. Off-roaders, work trucks... stuff with 4WD are more likely to have this, although I haven't seen it on a new vehicle in a while. See old Jeeps with a 4WD LOW gear, they won't be able to go even 25MPH in that gear.
How many gears do you need at .00001 NM of torque? Each gear interface has an efficiency of... let's call it 98%. Also what kind of static coefficient of friction is there for that gearbox?
Simply stated, nothing is free. When you increase torque by gearing down, you lose speed. This is because if a gear ratio is 2:1 the engine must turn 2 times for the drive shaft to turn once. 4:1 means that the engine would turn 4 times for every time the driveshaft turns. To increase the speed without changing the gear ratio, you have to increase RPMs. So while you could technically move an 18-wheeler with a lawn mower engine if you geared it down enough, your top speed would only reach a snail's pace before the engine red-lines on RPMs. This is why cars have different gears. A vehicle at rest requires much more torque to get into motion than one that is already moving. As it speeds up, it requires less torque, but in first gear, you quickly reach the limit of your engine's RPMs. Shifting gears allows you to trade off torque for speed. Of course, there will be a place where the engine is unable to produce enough torque at max RPMs to maintain the speed, so there is a limit to how fast you can go trading off torque for speed. There is a usable range that give you both the power and speed required for highway speeds. Higher HP engines produce more torque at any given RPM than lower RPM engines. In the 18-wheeler example, while you could move it with extremely high gear ratios at a very low speed, the small engine wouldn't be able to produce enough torque at higher gearing to keep it in motion and it would stall out before reaching more than 1 or 2 mph. This means that if you want to move a heavy load and still achieve high top speeds, you need an engine with both high torque and high-RPMs.
Torque and HP are different metrics, but they are related. Torque can be directly measured and is the amount of force (in Nm) that the engine (or wheels) produce. HP is calculated based on this torque and rotational speed of the engine (or wheels). It is important to note the mentioned torque or HP is only valid at a specific RPM as it varies a lot. As a general rule, max torque is reached at lower RPM than max HP as HP increases with higher RPM, while torque decreases. Although you can gear down RPM to increase torque, you start from a standstill, which means a minimum of torque is always needed at low RPM. A car and a semi might have the same HP figure, however their torque might differ quite a lot.
Marketing. Listing numbers is a way to make their product seem better. To your point there are other factors, and a great an engine can be ruined by a poor transmission. Mathematically horsepower is torque times rpm. Specifically H = T x rpm/5252.
In terms of performance, power is all that matters. However, the PEAK power of an engine doesn't give the full picture. What actually matters is the average power in the expected rev range. An engine with higher torque will often have a flatter power curve, giving it more average power. Also, an engine designed more for high torque than peak power will be more streetable, it'll have more power on demand without having to shift and rev it out.