Comments
hedoeswhathewants t1_ja577sm wrote
Your last paragraph also explains why cars can go 120+ when speed limits generally max out around 70. They have that power so they can accelerate quickly when they need to. The top speed is just a byproduct.
KarmaticIrony t1_ja5i1fu wrote
It's also (in fact mostly) because having the engine only use a portion of its maximum potential, so going around sixty when it could do over a hundred, is good for long-term reliability.
koalasarentferfuckin t1_ja61w95 wrote
I'm just sayin' that it's fuckin' dangerous to have a race car in the fuckin' red. That's all. I could blow.
rvgoingtohavefun t1_ja67www wrote
Oh, you ready to blow?
Well I'm a mushroom cloud layin' motherfucker, motherfucker.
malenkylizards t1_ja9em6u wrote
Man, I don't EVEN have an opi--
Polar76_ t1_ja65oqq wrote
r/unexpectedPulpFiction
akodo1 t1_ja8lfno wrote
Not nearly as dangerous as a farm tractor in the red. If/when it fails, all the chains, cables, equipment it's pulling against is going to go flying
delebojr t1_ja60tq3 wrote
That and you don't want to be sitting at 8,000 rpm on the highway
SerenadeNox t1_ja6jjw0 wrote
Wankel enters the chat
Dysan27 t1_ja6r3y7 wrote
Have you seen the custom 4 rotor Rob Dahm is building? Well built, currently tuning it.
rtfcandlearntherules t1_ja751db wrote
That's not the whole truth though, a lot of cars also need the speed, e.g. police and emergency vehicles.
The maximum speed limit is also higher than in the US in basically every country.
In Most European countries it's around 80 mph (130 km/h) and then there's Germany of course. For me as a German it is pure hell to go only 130 km/h on a straight road with no obstacles and low traffic. Feels super dangerous because you will get bored and "fall asleep" very fast. I guess that's how Americans manage to produce so many accidents on their highways despite the low speed.
it_might_be_a_tuba t1_ja79aty wrote
Australia has speed limits of 110km/h on the highways and far fewer deaths per capita than the USA. But we don't drive as many American cars and we're less drunk on the road.
LeftToaster t1_ja7merq wrote
>and we're less drunk on the road.
You sure about that?
Osiris_Dervan t1_ja8r30y wrote
They all drive drunk, so while there's more drunks driving the average amount of drunk is less.
it_might_be_a_tuba t1_ja9bpm5 wrote
Blood alcohol limits are .05 in Aus, .08 in most of the USA.
rvgoingtohavefun t1_ja9gs2j wrote
You could set it at 0.02 or 0.20 and it's the same don't-give-a-shit group of idiots that are going to drive drunk. Generally you aren't taking a breathalyzer before you get behind the wheel, and 0.05 is still plenty dangerous.
Something like 1/3 are repeat offenders and it's full of motherfuckers driving really fucking drunk, like 0.2 or higher.
rtfcandlearntherules t1_ja7f9qm wrote
Sleeping in the driver's seat also seems to be spreading around the US lately
Dont____Panic t1_ja9aso2 wrote
Is that the one video of the Tesla driver? I’m pretty sure that was in Toronto.
rtfcandlearntherules t1_ja9ply8 wrote
there are like 10 different cases that i can think of out of my head. Most are in the US but not all, i believe one even was in Germany.
balukabalu t1_ja7wshg wrote
I used to drive at 150 km/h because in my country the tolerance is 23 km/h at 130. But with the increasing fuel prices now I travel at 110 (13L/100km vs 8) and I like it, it has a very chill vibe
beyondusername t1_ja7gcz1 wrote
Emergency vehicles have the budget to do regular maintenance. Pushing the engines harder is less of an issue when you get regular check ups and maintenance to ensure reliable operation.
gobblox38 t1_ja8rlup wrote
The requirements for getting a license in the US are a joke. It's much more strict in Germany. One of the reasons why there are so many traffic collisions in the US is because there are so many terrible drivers on the road. Add to this that there isn't an alternative way of getting around in most of the US. This even includes sidewalks in some places. If there were interconnected and well funded mass transit systems in the US and walkable infrastructure, the driving standards could be higher.
rtfcandlearntherules t1_ja8yvyh wrote
yeah makes sense.
PharmaBrooo t1_ja6ojbt wrote
The top speed has become a selling point.
Snoo-76025 t1_ja75k5r wrote
speed limits generally max out around 70 screaming in German
AliMcGraw t1_ja6f7jd wrote
It is also, incidentally, pretty bad for the soil to drive fast on top of it -- going faster than 5 mph increases "washboarding" (or "corrugation"). Tires (and the weight of the vehicles on top of them) are TERRIBLE for soil, and a huuuuuuuge amount of research is put into ensuring that tractor tires compact the soil as little as possible. And even with those beautiful soil-protecting tires, if you're going faster than 5 mph, you're damaging the soil no matter what. Even if your tractor COULD go fast, you don't WANT it to.
rtfcandlearntherules t1_ja757v5 wrote
How is washboarding a concern on a field that's being plowed?
tanandblack t1_ja7l5xa wrote
You drive on it after plowing...
rtfcandlearntherules t1_ja7nke0 wrote
I mean the plow is behind the tractor ..?
Sure you might drive on it afterwards but from my experience a field is not a dry granular road surface like a gravel road. There's also way less traffic, the fields gets plowed frequently and sees almost no traffic. It also turns wet from rain and water and "moves" naturally.Completly different from a gravel road. On top of that the wiki article even recommends "plowing" the road to remove washboarding.
I am not saying that you are wrong because I am geniuenly interested to learn about this, i never thought about it before. But the arguments presented still have me sceptical. That being said the general idea you presented makes perfect sense, of course you'd want to "squish" the ground as little as possible with the tractor. I can understand that without any science.
gobblox38 t1_ja8v15o wrote
I've come across quite a few farmers that do no plow.
That's not to say the majority of your post is wrong though, just adding a little bit of extra information.
Naive_Composer2808 t1_ja98ov9 wrote
It more about soil compaction and disruption beyond what is really necessary to plant fertilize cultivate and harvest, any more than that and you are harming the productivity of the plants and soil.
freefrogs t1_ja9ib55 wrote
A few things to consider here. One is that not every field is a nice soft soil like you might think of in your garden - there are clays and sands and different compositions, some of which are susceptible and others aren't. Another is that not every farm still does plowing, and especially not deep plowing, and even that won't totally break up compaction especially farms that have to plow when it's still wet.
Also, even on farms that do plow, there are still a lot of operations that happen after plowing. There can still be tillage and fertilizing and top-dressing etc etc etc that happen after initial soil prep.
rtfcandlearntherules t1_ja9pgqz wrote
thanks, it makes sense.
jaa101 t1_ja5plcr wrote
If pulling a plow requires 1 ton of force at 10 mph then the same plow in the same ground is going to need around 4 tons of force at 20 mph. This means that doubling the speed requires eight times the power.
purplepatch t1_ja73mnu wrote
Surely you mean doubling the speed requires four times the power, not eight.
jaa101 t1_ja7845f wrote
If the speed doubles and the force required quadruples, then the power goes up by a factor of eight. This is because power is proportional to force times speed.
The above is true for air resistance and water resistance, where drag is proportional to speed squared. I found a publication linked in this thread that says the same is true of plowing, but another commenter found a paper with experimental results showing the force required increasing much more slowly with speed. If so, plowing is not like fluid resistance and the power required increases even less than the square of the speed.
InsidiousTechnique t1_ja66r9u wrote
Can you source this? I doubt it's true
CollegeAnarchy t1_ja6a1ay wrote
Here is a link to an explanation:
https://www.quora.com/Why-is-air-resistance-roughly-proportional-to-the-cube-of-speed
I understand that link is for air, but the concept Is true for any “fluid”. For all purposes of farm equipment, the soil is a fluid because it flows around the implement.
Actually, a lot of solids can be modeled as fluids when in small pieces. Fluidizing flour, sugar, and sand is how it handled on an industrial scale.
InsidiousTechnique t1_ja6b1qj wrote
I understand the concept, I doubt it applies to dirt in the same way. There's probably some affect there, but surely not in the same cubic relation.
As an example, you can plow dirt and if you were to go over the same dirt right after and it would take much less force at a constant speed.
It's more about the mechanical bonding and friction than fluid losses in this instance. I'm calling in to question your assertion that dirt acts similarly as a fluid in this specific instance.
How much force does it take to pull a plow through dirt at zero speed? Meaning, if you put a plow in to the dirt, does it take greater than zero force to move it?
MortalTwit t1_ja6iwq0 wrote
Force = mass times acceleration squared. If you double your speed, you need x4 the force.
ViridisWolf t1_ja6nnza wrote
No, f=ma. No squared term.
jaa101 t1_ja6fja6 wrote
Note that air resistance is only proportional to the square of the speed, so the heading of the linked article is incorrect. Resistance is a force. It's power that goes with the cube, because it's proportional to force multiplied by speed.
Travianer t1_ja6pfq0 wrote
The whole truck isn't moving through the medium of dirt though so it's apples to oranges in this case.
kyrsjo t1_ja6vq2w wrote
That doesn't really matter tough. The force would be the sum of two terms that both goes like v^2, the plow drag and the body air resistance drag. So the total drag force still goes like v^2, and the power (force x velocity) like v^3.
jaa101 t1_ja6ej8o wrote
InsidiousTechnique t1_ja6gtqn wrote
So I read the paper, and saw it did assert that. But here's another paper (that looks more researched) that has draft force compared to speed, and there's definitely not a squared relation there although it does show an increase on draft force compared to speed it appears more linear.
jaa101 t1_ja6iqeq wrote
Looks like you're right, in fact it shows closer to a power of 0.33 than 1, and far from 2. Neither document goes into the physics involved.
twelveparsnips t1_ja6jgp2 wrote
Resistance increases exponentially in relation to speed. Kinetic energy is 1/2 M*V^2
InsidiousTechnique t1_ja7cwhb wrote
Check the paper I linked.
SpaceAngel2001 t1_ja8o60m wrote
As an illustration of how power and speed relate. My neighbor buried a truck and trailer down to the axles in a mud bog. His truck was 300+ hp. My 70 hp tractor easily pulled them out but at a speed of about 2mph. Another example we've seen lately is Ukrainian 200 - 300 hp tractors towing 800 hp Russian tanks.
Any_Werewolf_3691 t1_ja6i4l4 wrote
Power is not linear with velocity. It's the cube of velocity.
DerCatzefragger t1_ja6re81 wrote
Torque is the difference between 500hp sending a 1.5 ton Mustang from 0-60 in 3 seconds, vs a 40,000 lb Freightliner doing the same in 2 and a half minutes. It's slow. . . but it does move.
mdchaney t1_ja876q8 wrote
To add to this - the old Volkswagen 4 cylinder engines put out around 55HP. Your normal modern car is 200HP and up. That engine was in the Beetle as well as the microbus. Neither vehicle was a barn burner, but could eventually get up to 60MPH. But after you got to that speed it would be fine. I used to also drive a 1980 Ford Mustang with a 6 cylinder engine that put out around 90HP. The post-muscle-car era had some pretty anemic engines, but we got around.
Dont____Panic t1_ja9ajwk wrote
Frankly, if people didn’t enjoy driving quick cars, more people would drive cars with 50 hp. That’s all you really need to go on the freeway.
I mean, I can’t talk, my car goes 0 to 60 in under four seconds, but practically, there isn’t a great mood for this.
Dr_Sigmund_Fried t1_ja4mn81 wrote
Because farming equipment requires more torque than horsepower. This torque is usually provided from diesel engines and special gear ratios.
quadmasta t1_ja5d8cz wrote
The gearing is the biggest thing. My granddad's 70 year old John Deere was a 2 cylinder and only made 50 horsepower but it could pull a house off of it's foundation and had enough torque to flip itself over if the tires were held stationary.
PM_ME_GLUTE_SPREAD t1_ja65zbb wrote
Yup. This is one of the big dangers of tractors. They have enough torque and the tires are built to get traction on dirt that they can be very easy to flip over backwards and crush the driver.
Dr_Sigmund_Fried t1_ja6b26y wrote
One of the other reasons why counterweights are put on the front of many farm tractors. When pulling a multi-plow ground breaking implement it is very easy for the resistance from it digging into the ground causing the high torque tractor to pop a wheelie and flip over backwards.
showard01 t1_ja70v8m wrote
Really? I thought the “Homer flipping the tractor” gag was meant to say he’s so inept he could screw something up in a really difficult way 😂
life_like_weeds t1_ja6fsoe wrote
It’s really about the gear ratios. Plenty of very good tractors run on gas engines. The diesel torque thing is a bit of a misnomer
KaareKanin t1_ja4tb9o wrote
I don't quite agree, and I would say the premise for the question is false. Cars don't require much power, unless you're going very fast or hauling something heavy up a hill (fast). Farming equipment don't need the same kind of speed. A tractor probably actually needs more power than a car to do what it needs to do
platypuswill t1_ja4ydsc wrote
u/Dr_Sigmund_Fried is correct and you sort of are too. Cars don't NEED all the horsepower they have, they do need some to get up ramps (think freeway) and such but they could go with a lot less. As far as the original question Dr.SigmundFried is right about the torque to horsepower ratio in farm equipment. and u/mmmmmmBacon12345 nails it with their response and u/PckMan explains the difference in what those two measurements of force actually are. hope you learned something new today, please check for yourself though it's good practice. Learning something new is always a cool thing to do.
Daelan3 t1_ja5mc9j wrote
The formula hp = torque x rpm applies both at the engine crank and at the wheels. This means the faster the wheels are turning (the faster you're going) the less torque they will have at a given power level.
If the engine is putting 100hp to the wheels, at low speeds that's enough torque to spin them. At highway speeds, the wheel torque is so low that you can barely accelerate. It doesn't matter whether the engine is achieving 100hp with low torque and high rpm or vice versa.
A tractor has a high torque low hp engine because such engines have good fuel economy and reliability, and the large size and heavy weight are not a problem for a tractor. It's not that a tractor needs more torque. A 100hp car engine can get double the torque as a 50hp tractor engine through gearing.
You can put an F1 engine in a fully loaded semi truck, lower the final drive ratio, and it will move it no problem. It just won't good fuel economy or reliability.
KaareKanin t1_ja6v2a5 wrote
The only thing is, I'm fully aware of this. With his answer Fried validated the initial question, and I still maintain that for normal people using cars normally, they don't require much power at all. They may use it in short bursts because it's there, but I've had rentals with only double digit horsepower figures, and I was never a hindrance to normal flow of traffic.
A tractor probably comes close to using what their engines can output frequently, and if they were to do ploughing a lot faster, power requirements would go up. It's almost all about speed.
platypuswill t1_ja6xxfr wrote
Yes and speed translation comes down to the difference between the original answer of what's more important for each piece of equipment,. Horsepower or torque? For farm equipment it's torque, for cars horsepower. If it's heavy and you need torque for moving heavy loads slowly but with power. taking a hatchback up a hill and onto the freeway horsepower, there have been some awesome answers so far in the responses that nailed it. This was a great question to ask and I hope a lot of others got their answers as well!
[deleted] t1_ja5b1yq wrote
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platypuswill t1_ja5cemq wrote
Thank you I hope you have a great day
IveGotDMunchies t1_ja50pon wrote
Torque vs horsepower is what you need to google
KaareKanin t1_ja6u1a0 wrote
I don't really need to. Horsepower is the measure of work that can be done. An engine with more horsepower will be able to do more work, hence most car engines could easily do the work a tractor does. And with regards to torque, that's just a question of gearing.
Speed up stuff = do more work.
IveGotDMunchies t1_ja6zt9r wrote
Legend has it that every time you reply, an angel loses a brain cell.
quadmasta t1_ja5cww8 wrote
Horsepower is the product of torque and rotational speed divided by 5252. If you're not spinning quickly, and diesels can't, you gotta have way more torque to produce higher horsepower.
Ever see a dyno graph for a combustion engine?
KaareKanin t1_ja6ucmc wrote
But on the flip side, gear down a normal car engine to output the same rpm, and the torque would be higher (with the premise that a car engine has more power).
Cars don't require much power, only the drivers do. Power is king, torque is just a matter of gearing
quadmasta t1_ja7h7mc wrote
No it wouldn't. Gasoline vehicle engines are designed for higher RPMs and don't make peak power until higher up in their operating range. Tractor engines are designed for low RPM operation and have their peak power waaaaay down in the RPM range.
KaareKanin t1_ja7krne wrote
A given power figure on a shaft rotating at given speed will give the same torque. This is how it works. You can't really argue with this. So I say again, gear both drivetrains to the same output speed, and the one with more power has more torque
Egineeering t1_ja6d085 wrote
An important thing to also keep in mind is a vehicle engine is only called to produce maximum power for short intervals. While farm and industrial equipment may be asked to output rated power continuously for hours. This means for any given displacement you'd expect the farm and industrial engine to produce less power to increase service life and reliability.
mechapoitier t1_ja840jx wrote
Yep, and if you looked at a curve of power output to engine size it follows reliability pretty closely, except for some badly designed outliers. The more hp you ask of an engine of the same size, generally the less longevity it’ll have.
There are 10+ liter turbodiesel engines in semi trucks putting out only 300-400hp that’ll go a million miles easily. On the other end when’s the last time you saw a 120hp 600cc sportbike with even 100,000 miles on the engine?
JetsetCat t1_ja4no7j wrote
Because speed is not needed as it is in a car for example, gearing between turns of the engine and rotation of the wheels or equipment can be very low.
turniphat t1_ja57uex wrote
Modern cars are ridiculously overpowered. Every year, the new models need to be better than the old models and better than the competition.
Farm equipment just needs to get the job done. A tractor rarely needs to work at more than 5 mph. So no reason to spend money on a larger engine.
Most commercial equipment has a lot less hp than you'd expect. When whoever is buying equipment is looking at operating costs, purchase price, expected profit, they buy just what they need, not what is most fun.
Most consumers on the other hand think, I may tow a trailer in the mountains one day, so I'd better get the bigger engine just in case. Commercial operators say put it in 2nd gear and go slow.
shuvool t1_ja5nvfk wrote
This question seems to miss the understanding that horsepower is a measure of work done- that is, some amount of mass multiplied by some amount of distance all divided by some amount of time. (Horsepower a a unit is kinda weird like most US customary units, so you would have to pay around with the numbers a bunch to get mass, distance, and time out of the force, rotational speed, and constant that make up this particular unit)
In an application where your work gets done at a slow speed and doesn't need to change that speed significantly or quickly like towing or farming, a better unit of measurement to use would be in units of force. How much force can this machine apply to this load. For things that rotate, the force is torque.
Horsepower is calculated from torque and rpm. The equation is (torque × rpm)/5252. If all the torque needed is generated at a very low rpm, as is the case with large diesel engines, the horsepower is going to come out small.
jaa101 t1_ja5q753 wrote
> horsepower is a measure of work done
Horsepower is a unit of power. You need to multiply it by time to get a unit of work (AKA energy).
shuvool t1_ja5qqgt wrote
I was being overly simplistic. It's a measurement of the rate at which work is done, not the measurement of work itself
thetravelingsong OP t1_ja5oe1q wrote
Thank you!
neo1piv014 t1_ja6dcj7 wrote
Horsepower is derrived from a mathematical function where torque is multiplied by RPM and divided by some constant. It's why a Harley Davidson can make a ton of torque down low, but have much lower HP numbers than you would expect - they just don't rev very high. A tractor is going to be similar. You want a boat load of low down torque off idle so you can plough through dirt and mud, but you don't need it to go very fast, so there's no point in making it rev as high as a car. If those engines could spin as fast as car engines, they'd make substantially more power, but they don't spin very fast, so the HP number is low
PckMan t1_ja4s2th wrote
Torque is the actual power of the engine. Horsepower is the rate at which it is produced. Farm equipment is slow, so with a relatively "weak", low Horsepower, high torque engine, you can get a lot of work done. Heavy flywheel, low revs, almost always diesel, which are big heavy engines with a lot of torque. The right gearbox and the job's done. Nobody's winning any races in a tractor but it can certainly pull a load.
CoralPilkington t1_ja4us1d wrote
>Nobody's winning any races in a tractor....
PckMan t1_ja4w7to wrote
I knew the moment I posted that someone would come along with a tractor drag race.
Interrophish t1_ja5c83e wrote
A tractor lost in every single race in that video...
jaa101 t1_ja5qjm3 wrote
Horsepower is the actual power of the engine. Torque is the twisting force. Multiply torque by RPM then by a conversion constant and you get horsepower.
quadmasta t1_ja5ddtd wrote
therealdilbert t1_ja5yutb wrote
> Torque is the actual power of the engine.
no torque is torque, power is the torque times rpm
Steveesq t1_ja5p09f wrote
First thing is the premise of the question. cars don't require that much horsepower. We like and want that much horsepower.
But horsepower is only one part of the equation when it comes to any vehicle, or piece of equipment. The engine usually drives a transmission of some kind, or a pump for hydraulics, etc.
My daily driver has an excess of 300 horsepower. I have a military truck that weighs 8,500 pounds, that has a whopping 92 horsepower. I also have a tractor with a front end loader, that's 38 horsepower, And it'll drag both of them around the yard. It's all about application.
therealdilbert t1_ja5yzuq wrote
> My daily driver has an excess of 300 horsepower
and it takes maybe 20hp to drive at high way speeds on a flat road
Steveesq t1_ja66e87 wrote
EXACTLY! But it sure is fun to drive!
koolaidman89 t1_ja6cgsa wrote
Yeah but it’s pretty handy to be able to get to highway speeds in a reasonable amount of time/distance when you find yourself on a short ramp going into dense high speed highway traffic.
lellololes t1_ja7htt2 wrote
You can take an engine that makes 50lbft of torque and make it output astonishing amounts of power at the wheels.
All it takes is gearing.
A lot of people don't realize this. If your car with 300lbft of torque at 2000RPM is geared so that it can go 20 miles per hour at that speed, it's going to output the same power to the wheels as an engine that makes 50lbft of torque that is geared to go ~3.3mph at that speed.
It just won't go nearly as fast.
twats_upp t1_ja5yozx wrote
Ive been operating the new cat 982(loader) lately and those things have balls.. to get that much weight, loaded or not, moving so quickly, is impressive.
Naive_Composer2808 t1_ja636lx wrote
If you take the LeTourneau L-1850 and do a per unit calculation, it accelerates quicker than a late ninety’s Top Fuel Dragster.
GilltheHokie t1_ja8wpb0 wrote
Horsepower is how fast you hit the wall, torque is how far you take the wall with you. Tractors need torque more than horsepower so they go at slower rpm’s and thus lower HP, but prioritize higher torque to pull big things like a wall.
Naive_Composer2808 t1_ja63vcw wrote
Id like to know what equipment you’re looking at, a John Deere S 980 has like a 900hp MTU engine. The new Nexat has an 1100 hp engine. Some silage choppers have 11-1200 hp engines. A typical 4wd modern tractor is 380-600 hp with 900-2000 lb-ft of torque.
showard01 t1_ja70xks wrote
Oh yeah totally. The ol S980. Or the 981, you know, whatever it takes
Imaginary_Fennel6772 t1_ja77rv7 wrote
I came here looking for this comment. Thank you sir.
thetravelingsong OP t1_ja8yds3 wrote
You can plough a field with a 15HP Tractor. My 150hp Civic could not plow a field.
Naive_Composer2808 t1_ja99tpf wrote
That statement has less to do with the power of the engine and more to do with what the overall design of the vehicle. If one so desires they could take the civic engine and put it in a more suitable vehicle to do the task. The engine doesn’t care what you hook it up to, only that it is not overloaded with resistance to its force exerted.
delebojr t1_ja60m0e wrote
Horsepower is a function of torque and speed. Since farming equipment generally requires higher torque & lower speeds, horsepower won't be high. I could go in more depth, but other people already covered it fairly well.
xdert t1_ja79rvk wrote
If you want to move something from A to B you do work: https://en.m.wikipedia.org/wiki/Work_(physics)
Now the question is how fast you want to do this, so work over time, this is power: https://en.m.wikipedia.org/wiki/Power_(physics)
So even though a car and a tractor might do the same work (going from A to B), a car does it much faster thus requiring more power.
So in simple terms: Going up 100 stairs slow and steady is not very exhausting but sprinting them as quick as you can leaves you exhausted and panting for air even though you ended up reaching the exact same goal.
fiftybucks t1_ja8wz5d wrote
Farming equipment is designed to do a lot of work but over a long period of time. It's not racing where time is of the essence. Horsepower is torque over time or how much work you do over time.
Farming equipment needs a lot of torque to move and carry tons of material but it doesn't need it to be delivered quick. So it's incredibly strong but slow paced. Which is also good, slow turning engines don't wear down as fast and are much more reliable.
That's why you can see most workhorse engines are low revving, low horsepower, but have high torque at the low end and usually are coupled with gearboxes that multiply that torque much higher still.
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sjwt t1_ja6blk8 wrote
Don't forget wind resistance, that's a bitch.
Im sure i saw something a few years ago about a superlightweight aerodynamic frame allowing people to get up to highway speeds
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cbeebout t1_ja7p6iw wrote
I remember learning in Classical Physics in college that the horsepower to drive a car on a flat surface was directly proportional to the drag of the vehicle as well as the cube of the speed.
Therefore, if it took say 30hp to drive a minivan down the interstate at 50mph to then triple the speed to 150mph would require (150mph/50mph) * * 3 times more horsepower or… 3 * * 3. 3 cubed is (3 * 3 * 3=)27 times more horsepower. 30 x 27 = 810hp. No stock minivan has 810 hp so no stock minivan can reach 150mph.
A Ferrari, however, might have half the drag of the minivan and would require only 15hp to drive down the interstate at 50mph. 15 x 27 = 405hp, so only 405hp would be required for the Ferrari to maintain 150mph, which many Ferraris can produce.
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andcal t1_ja7ryt5 wrote
You can do a lot with less horsepower if your gearing is low enough.
But
All the gearing in the world won’t make you go faster once air resistance eats up all your power once you start moving over X mph (X being whatever speed all your engine’s power is used up just fighting the air resistance).
Vast-Combination4046 t1_ja7vak1 wrote
Horsepower is a fictional number. It's an equation using Torque and RPM to determine horsepower. People have said "horsepower is how fast the car hits the wall torque is how far you move the wall" because torque is the actual force you apply to the work you are doing. Since it doesn't matter how fast you move your goal is the most amount of torque at a low rpm.
Jmazoso t1_ja862ob wrote
The other nuance is it’s not just torque it’s a idea called “tractive effort”. Which is a measurement of what it can pull. The same way a trains “power” is measured.
[deleted] t1_ja8gh1s wrote
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[deleted] t1_ja8lqyf wrote
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errolbert t1_ja6hwlv wrote
Plowing through the dirt at 5MPH takes considerably less effort than plowing through the atmosphere at 70MPH.
ryneches t1_ja73ce1 wrote
Because cars are ridiculously overpowered. As anyone who's owned an old VW can tell you, 40-50 horsepower is enough to get you anywhere you need to go at highway speeds. Old VWs are not particularly lightweight, either.
Horsepower beyond about 50 exists for entertainment purposes.
Dan-z-man t1_ja7f7lc wrote
Eh. I get your point but a 50hp minivan or a pickup with a family of four would slow as crap and sorta dangerous. I remember driving an old vw a few times and they would certainly get from point a to point b but they were pretty anemic. Part of this is just the enormous mass of modern vehicles. Let’s say more than 200hp is probably not necessary? But 400 is perfect
mmmmmmBacon12345 t1_ja4ofm9 wrote
They go at pretty slow speeds so the engines are built around high torque and long term reliability
At low speeds, power scales linearly with speed so pulling a plow that takes 1 ton of force at 10 mph requires half as much power as pulling the same plow at 20 mph. If you're only ever going to pull that plow at 10 mph you don't need a huge amount of power, lots of farming equipment doesn't work if you pull it too fast.
Cars and trucks need to get up to highway speeds over a relatively short distance, this is really why we put 100+ horse power in everything these days. You only need about 30 hp to cruise on the highway but doing 30-70 on a short onramp to get up to a safe speed requires quite a lot more power.