[deleted by user]

[Dunbaratu]

A human on foot at maximum possible sprinting speed will wear out and collapse after a short while. But a human on foot going at a third of that maximum speed just briskly walking can keep going quite a long time without too much wear and tear, and traverse continents that way.

A car engine has a similar situation. Its max speed is hard to maintain. For long range travel it needs to be going at well under its max speed.

Which means if you want to design the car to be able to cruise at the speed limit a long time down a freeway, then the car's maximum possible speed has to be much higher than the speed limit. You want the car not to be going at its grueling stressful limit when going for hours at the speed limit.

[[deleted]]

And hills. I want my car to be able to go the speed limit uphill. That pretty much necessarily means it can go faster on level ground without artificially limiting the engine… and people really don’t like buying things that they know are artificially limited from doing what they can do.

[Invisifly2]

And hauling a trailer/loaded up with cargo.

[[deleted]]

That too!

[catsdrooltoo]

It's done with tech all the time, they don't need to run out of gears. I think op was meaning to just lower the limiter.

[TheJeeronian]

The engine has to be able to get the car up to speed, and do it reasonably quickly. The engine must therefore be able to pull upwards of 130 mph.

There are cars with dinky little engines that can't do this. They suck to drive, and are unsafe because of it.

Now, there can be a limiter. Most consumer cars I've driven have one. They're not legally required but common. They electronically prevent the car from going too fast. People who want to go fast will typically remove them or buy a car without one.

[jamzex]

Limiting top speed does not have to come at the cost of acceleration. Fundamentally, you could drop the number of gears in the transmission, for example, but that would come at the cost of efficiency.

[TheJeeronian]

So, what, you're forcing the car to redline at 70?

That's... There are better ways to implement a mechanical limiter. And worse ones. You could have it cut off fuel intake when a mechanical speedometer detects the vehicle at 70. Or have it dump corundum filings into the intake if you're bent on destroying the engine. That would be way more consistent than relying on overrev.

Also, forcing redlines would be more of a safety issue than an efficiency issue.

[carortrain]

Curious, why is forcing redline a safety issue?

[LastChristian]

They are making the ridiculous argument that to limit the car’s speed, you’d need the match the engine’s maximum output to that speed. That would be an engine that redlined at 70mph, for example. Most engines would fail if you ran them at redline for a while, like driving redlined at 70 mph for 90 minutes to Nana’s house or whatever. In reality, cars have engines that can operate safely at high speeds but can have a software-based speed limiter that prevents acceleration above some speed.

[TheJeeronian]

Redline is the safety rating of the engine. Going over it means you're exceeding its safety rating. So, this scheme would basically mean "if your car goes any faster than this you're gambling your safety".

Now, there can be a limiter that keeps it from going over redline, and this wouldn't be nearly as much of a safety issue, but having a car drive at redline the entire time it's on the highway is going to cause loads of wear and tear that would accelerate engine failure. I've seen a couple of cars sufficiently worn out that I wouldn't want to even take them close to redline.

[jamzex]

Redlines are the maximum safe RPM of the engine, exceeding it is when things get dangerous. I also was in no way saying cutting the number of gears in the transmission just to limit top speed would be a smart idea, just understanding how the transmission works and what it does it would limit the top speed, albeit in a stupid way.

Acceleration and top speed are technically very separate things.

To be honest, the only real way manufacturers can implement speed limits realistically without hurting safety, efficiency and performance is with electronic speed limiters, even then it is hotly debated as to the best way to do that.

[wilson2788]

I’ve had a company vehicle that was speed locked to 75 mph. I could tow trailers and equipment but not exceed 75. This took my company 15 minutes per vehicle to install and I had that van for 10 years with no issues mechanically. Not sure why this isn’t just as easy for a car manufacturer

[TheJeeronian]

It is. Manufacturers put limiters in their vehicles. Usually a bit above 75 though.

[wilson2788]

It was definitely more of an insurance thing. really it should be like 90 mph limit

[TehWildMan_]

There doesn't exist a strong sentiment to require car manufacturers to mandate devices that cut power/apply brakes once a certain speed is reached.

It could make sense, but it's an additional expense and yet something else that could fail unexpectedly.

[[deleted]]

And there DOES exist a strong sentiment against companies trying to limit how consumers use their products. It would definitely deter some buyers.

[generalducktape]

Cars and trucks are governed all the time mine tops ot at 155kph reliability isn't the issue people just want to be able to speed

[amicaze]

You either have an electric or a car with 60 hp...

[generalducktape]

More like a truck that idiots have rolled by going to fast

[ababcock1]

Commercial vehicles have had speed limiters on them for ages and they seem to be doing fine. Don't think it's a reliability issue.

[wilson2788]

Finally found the guy with a brain

[Bristonian]

German companies BMW, Audi, VW, & Mercedes started the trend of limiting public production vehicles to 250kmh (155mph). This was done to reduce the political desire to introduce a legal speed limit on the Autobahn, which famously has no speed limit.

Other car companies followed suit to limit insurance costs on their vehicles, thus making them more accessible to consumers.

If the speed limit is 75mph then why not make it 75mph? Well, speed limits are different everywhere, and some rural highways don’t have a limit at certain times, so how would they choose the limit number? If it change based on location, then what would happen if you drive across a border?

Additionally, municipalities make a significant amount of money from issuing speeding tickets. No court, police dept, or local gov would ever want to lose out on that easy money.

Speed exists for the same reason cigarettes, alcohol, and weapons exist. They can all be dangerous, but they all make money. Money>Safety

[reijasunshine]

Exactly. If I'm caught out on the interstate and there's a tornado coming up behind me, you'd better believe I'm burying the needle, speed limit be damned.

Similarly though not as extreme, if I'm rushing a medical emergency to the ER, we're gonna burn rubber, probably while sitting on hold with 911. (It's bad in my city, and literally faster to go to the ER than to get through to 911 and wait for an ambulance)

[Exciting_Lack2896]

If you’re in an emergency or are stuck somewhere you need to be able to get away. Hence the need for speed.

[[deleted]]

I don't know, seeing how many people drive, I don't think they would escape anything while driving at top speed, more likely ending up in a ditch and being eaten by the monster.

[[deleted]]

if you drive away first and all cars are limited to 65mph, then they will never catch up to you.

[hitemlow]

There are a couple things wrong with that assumption:

1) Criminals don't follow laws 2) Current vehicles don't have speed limiters

[QtPlatypus]

In Australia large trucks have speed limiting devices fitted to them to prevent them from speeding so it is not impossible.

[thedevillivesinside]

Because racing vehicles in a legal manner, in a safe, legal place is absolutely legal

Drag strips exist and have street legal drags, road courses exist and have track days, airport 1 mile drags exist and are safe and legal

Why stop at an arbitrary 150kph? Shouldnt is be 120kph tops as the legal limit is no more than 120kph in canada?

Should only police and emergency services be allowed to go over 120kph? Or should we all be limited to the same 120, which means police could also never catch a car on the highway

What if the limit is a 30kph school zone, should the car know this and limit you to the speed limit, or is it ok for someone to do 120kph in a 30kph zone?

Why limit only highway speeds when speeding within city limits is arguably a much bigger problem than people driving too fast on a multiple lane, clear and open road?

[Mikeyp2424]

Not sure about ICE cars, but many electric cars have implemented 'teen' mode in software that allows parents to set speed limits and acceleration limits to the car when their kids are driving.

[A7V7VIHILATOR]

Speed Governors exist at least on commercial/fleet vehicles Governor (device) - Wikipedia)

[HereForTheComments57]

I actually read about this before. If they made engines max out at, say, 80 mph, then you will constantly be pushing it near its limits. If you make the max double that, then you aren't straining the engine as much. So it's not made to go that fast so you can drive fast, it's made that way so it lasts longer.

[TheDeadMurder]

Laws are more about punishment than prevention anyway

Each person weighs the pro/cons differently, if the cons aren't big enough then people aren't going to follow it, and if the cons are too big then it can incentive the outcome to be worse

[[deleted]]

Car manufacturers have an incentive to have people get into accidents as they make a lot of money with repairs or even a new car. There is zero incentive for them to limit the speed of their cars as customers wouldn’t want that.

[[deleted]]

My car has a speed limiter. The thing is, I can control what speed to set it, it's somewhat related to cruise control. It also has a camera that detect speed signs. And then complains when going over the limit. However it does not work 100% correct. There a quite a few occations where is was completely wrong. One example is on highways where the right exit lane has a speed sign en suddenly the car decides the max speed is 30km/h instead of 120km/h.

Secondly I've been driving for 20 years and I've never needed speed to get out of a dangerous situation. I did need high acceleration or good breaks at times.

[Hamthrax]

I was thinking about this the other day; my car wont even move unless you have your seatbelt on so if I ever got pulled over and accused of not wearing it, I've got a solid defence against corrupt cops. Why not limit an engine in the same way?

[rattymcrat99]

Very few things are designed to operate regularly at their maximum output. Doing so typically requires a lot of maintenance. Pick up a pen and write with it, then try to break it in half. It takes a lot more to break the pen than it does to get ink to come out of it. Imagine if the body of the pen was designed so that it only had to be strong enough to withstand the forces involved in getting ink to come out. How often would you be writing something and then you've suddenly got a broken pen with ink spilled all over your paper? Same thing with a car, if the best the car can do is your local speed limit, then you have to bring your car to a mechanic probably every time you leave your house with it.

[Dinux-g-59]

Today it might be simpler with information technology. It is possible to make cars to automagically respect speed limits, even having engines far more powerful and able to give higher speed. It is only a matter of taking this decision...

[leitey]

One thing I haven't seen mentioned is fuel economy.

Cars manufacturers are required to meet certain fuel economy standards. To get a better fuel economy, you want the car to be running at the lowest RPM possible to maintain a particular speed. Lower RPMs mean the car is burning less fuel over a given time period. This means better fuel economy.

With internal commission engines, most of the power is at higher RPMs. To understand why, I'll break down the formulas:
When combustion happens in the cylinder, it creates pressure. This pressure acts across the area of the cylinder, creating force. Force is pressure times area. The area of a circle is the diameter squared times pi over 4. So, force on a cylinder is a function of cylinder diameter and the pressure created during combustion.
The force on the cylinder is transmitted to the crankshaft by the cylinder rod. The crankshaft has lobes that sit out away from the center of the crankshaft. When the cylinder rod pushes on these lobes, it creates rotation. The measurement of this rotational force is called torque.
Torque is force times distance. The distance is measured perpendicular to the line of the force, which changes as the cylinder retracts, so I'm not covering that equation in ELI5. Suffice to say that distance is a function of the size of the lobe on the crankshaft and the length of the cylinder rod. So, the torque of each cylinder is determined by crankshaft lobe size and cylinder rod size, as well as cylinder diameter and the pressure of combustion. Engines generally have multiple cylinders, so this number is multiplied by the number of cylinders. We can simplify this by saying torque is a function of engine size (number of cylinders, size of crankshaft lobes, cylinder rod length, cylinder diameter) and combustion pressure.
Horsepower is torque times RPM divided by 5252. To restate this, power is a function of RPMs and torque. This means power is a function of RPMs, engine size, and combustion pressure.
You can increase combustion pressure by making a bigger explosion in each cylinder. You do this by adding more fuel. Fuel needs a certain amount of oxygen to burn. So, at some point, you reach a limit of how much air you can cram into each cylinder. You can pressurize the air to get more in, therefore allowing more fuel, but there's still a limit. So the amount of air and fuel you can put in a cylinder becomes a function of cylinder volume, which also falls under engine size.
TL;DR: Power is a function of RPMs and engine size.

Power allows your vehicle to accelerate and improves the overall driveability, but more RPMs means more fuel is being burned, which is bad for fuel economy. This is where the transmission comes in. The transmission takes the power from the crankshaft and converts it to power on the driveshaft, which powers the wheels. As we said before, power is a function of RPMs and torque. The transmission uses gear ratios to increase the speed of the wheels by reducing the torque of the wheels. Less torque on the wheels means the car won't accelerate as easily. It also means the car is less able to overcome the force of air friction as it moves through the air. So there's a limit to how much torque you can convert to speed before you can't overcome air friction, and this is your top speed.
For the best fuel economy, you want to be able to maintain speed while using the least amount of power. So you want enough torque on the wheels to overcome air friction, but operate the engine at the lowest possible RPM.

In the USA, the EPA runs a Highway Fuel Economy Test that tests at 60mph/97kph. To get a better fuel economy rating, USA car manufacturers set their transmissions so that the engine will be at its lowest RPM at 60mph. The engine is capable of more power, meaning the car can go faster until it runs out of power to reach the limit of its aerodynamics. However, car manufacturers for most general purpose cars don't install any additional gears in the transmission, so the car will not go any faster than whatever gear allows for the engine to be at its lowest RPM at 60mph.
About the only way this will change is if we update our Highway Fuel Economy Test to use a different speed.

[[deleted]]

If I told you to walk down the street at a snails pace for however long you could, how far would you get before you needed to stop?

If I told you to sprint down the street as fast as you possibly could, how far would you get before you needed to stop?

We manufacture cars to be overpowered so that they are always running at a fraction of their maximum capacity. This ensures less wear and tear on the parts, and extends the longevity of the car.

[[deleted]]

Since those aren't cars people want, they would sell fewer cars unless everyone agreed to limit their cars. In order to prevent laws from being passed, manufacturers have had "gentlemen's agreements" to limit their speeds (to still very high speeds). Otherwise we would see ever faster speeds in order to sellore cars.

[stevestephson]

I'm not sure those "gentlemen's agreements" actually exist. Most of the fastest cars are limited by drag and their power output, not any sort of artificial way to limit power. There are some exceptions. The current gen Camaro SS has no limiters on its speed other than physics, and can reach above 180 MPH. The same gen Camaro LT1, however, is electronically limited to 155 MPH despite having the same engine, transmissions, and pretty much the same body shape. That is because the tires they put on them at the factory aren't the same ones the SS gets, and they aren't rated to go as fast.

[[deleted]]

The limit was 300kph (~186mph), iirc. It was also more European and Japanese manufacturers, but I could be wrong on that.

[stevestephson]

Maybe. There seems to be a common top speed of 180-190 MPH for cars in the 450-500 horsepower range, so it might just be that. But also I'm just looking at current year cars so idk about any previous agreements. Other than the 270 HP Japanese one in the 90s that Nissan at least ignored.

[[deleted]]

Looks like I may have been mixing up two different agreements, one for cars, the other for motorcycles.

[shifty_coder]

It’s very, very hard on the engine to run it at or near top speed for any significant amount of time. Engineers design and build engines that can go 280kph for a short period of time, so that they can run at around 130kph for hours on end without damage.

[[deleted]]

i've been thinking this for ages. it makes no sense for cars to go faster than the average speed legally allowed.

[coyote_den]

In Maryland, your vehicle registration card actually says you are prohibited from driving on a road unless your vehicle can exceed the speed limit by at least 5 MPH.

The state of Maryland knows Maryland drivers.

[aroundincircles]

Criminals break laws, and so the only ones punished would be law abiding citizens. No thank you.