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Why are cars designed to be capable of going much faster than the speed limit? (theguardian.com)
32 points by beardyw 9 months ago | hide | past | favorite | 89 comments



It's economical to have low engine RPM at cruising speed, which necessitates high gearing. This has the side effect of a higher top speed. The engine might be at 1500 RPM at 60 MPH for maximum economy (and low noise), but it might have a maximum of say 6000 RPM... so gearing would limit the speed to 240 MPH. (side note: engine power is almost always the limiting factor in top speed instead of RPM, as power requirement scales with the cube of speed... though most cars nowadays have electronic limiters below the 'physical' top speed)

Acceleration ability is needed and valued. Good acceleration is needed to safely execute a lot of manoeuvres: especially overtaking on a two-lane road with oncoming traffic (more acceleration means less time and distance facing oncoming traffic), and entering a highway (less risk of high speed differential when merging). Again, higher engine power is needed for good acceleration. Indeed at cruising speed, only a small fraction of "power capability" is utilized; short bursts of acceleration are the only time the engine is used to its full extent. Lots of engineering goes into making car engines capable of these short high-intensity sprints, but with low fuel consumption the other 99% of the time.


Why not electronically or mechanically govern them (except speeds > 250KM/h), then?

With today's electronics, you can use very smart feathering off acceleration curves, soft speed limit overrides for overtaking, etc.

Gearing doesn't make sense. I can keep higher RPM but turn cylinders off to reduce power and cap the consumption and speed if I'd like to, but it's not implemented.


>Gearing doesn't make sense. I can keep higher RPM but turn cylinders off to reduce power and cap the consumption and speed if I'd like to, but it's not implemented.

"Why doesn't trillion dollar industry with millions of engineering hours devoted to optimizing performance just do X, Y, Z?" is classic HN.


Why do we ask those questions? Because we want to know the answer, that's why. The OP didn't say that they should do X, Y, Z, they asked why they didn't. The OP likely knew there was a good reason, and wanted to know what it was.


There should be a 'rule' (in the style of Godwin's or similar) regarding people making overly reductive, grand statements in areas way outside of their expertise.


Sometimes knowledgeable people ask dumb questions on purpose. :D


That's not what I mean though -- what I mean is like saying 'just add more lanes and that will fix traffic', and not knowing how wrong you are since the reason it won't work is not intuitive.


The OP didn't break that rule. They asked a question, they didn't make a statement.


Actually he wrote “gearing does not make sense” - something based on every car having gearing makes me wonder this might make sense

Also he asked a question


"does not make sense" means "I do not understand", implying to me he wants to be enlightened.

If you're trying to be generous, which you should be.


> classic HN.

Thanks. Actually I know about cars more than I show for reasons I won't detail, but I wanted to people to voice their opinions on the matter.

Having prejudices about people without asking them proper questions is so classic HN, too.


> Why not electronically or mechanically govern them

Some vehicles do come with built in speed limiters.

Trucks, vehicles used by delivery companies etc will often have speed limiters; presumably it lowers their insurance?

And some production cars offer them as well. As I understand it, this allows them to scam the emissions/range tests, because no matter how easy to disable or how rarely used the speed limiter is, so long as it leaves the factory with the 60mph speed limiter enabled, then it goes through the emissions tests with it enabled.


I know. I'm asking why the hard limit is at 250KM/h for most cars, but not at 120.

I use cruise control and speed limiters regularly, otherwise.


Because many countries have speed limits higher than that? In the Netherlands 130 km/h is allowed (usually only at night), in Poland they have 140 km/h in some places, and in Germany there are many roads where a maximum speed of 130 km/h is recommended, but there is no limit (provided you drive responsibly).


Speed restrictors are often set to the maximum tyre speed minus a bit of margin.

eg. a "W" rated tyre is 270kmh max rated, so the manufacture might set the max vehicle speed to 250.

Tyres get exponentially more expensive as speed ratings go up.


Volvo has been doing this to all of its new vehicles for a while now, they're limited to 180km/h.


One of the ways to make an intractable problem seem easy is to underspecify it. Easy to do by accident.

In this case, try enumerating who would govern, and what each possible actor might do to govern, or suggest to govern. There's a tree of options.

For example, it might be a single car manufacturer, and might introduce the limit either globally or in some region. Or it might be a country, except not, because if it's a country it has to start with a department of the state or with a political party. If it's a political party, it can be in government or opposition. The tree is deep.

I'll do one of the leaf nodes: A political party that's currently in government, including the relevant minister if there's a coalition. Such a party has to put forward a concrete suggestion, perhaps a hard limit 120km/h with mandatory 100% responsibility for any accidents if the limited is modified, with supervision by forcing the navigation and mobile phone companies to report user locations. Or it chooses some other concrete proposal. It doesn't matter, because whatever it is it'll get a collection of shitstorms about the concrete details.

The people who think 120km/h is too high would flame it for having an obviously wrong speed limit, the ones who think it's too low would do the same, the data protection/privacy crowd would flame it for the big-brother-ish data collection (but without that, another crowd flames it for lack of enforcement), and so on and so forth.

That a particular change is generally desirable doesn't imply that there exists anyone that can put forward an actionable proposal. Making the change actionable means providing concrete details, and those attract shitstorms.

(On a semirelated note: a politician, a sometime finance minister of a large country, struggled for 10+ years to push through a worldwide reform that most people would consider good. The reform was put into force this year. I haven't seen that politician's name in any reporting in the past year.)


High rpm always equals more wear. More revolutions, less perfect oil film on lubricated surfaces, more parasitic losses, more oil burnt.


Well, again why not governing it at a modern 5th gear at 120 KM/h, with a soft bump at 90 KM/h?


>Well, again why not governing it at a modern 5th gear

Why not add a 6th, 7th, 8th, 9th or 10th gear? Wait, modern transmissions do.


Yeah, which depends on the torque band of the engine which drives the transmission.

Generally 8 gear systems are paired with ~1.5L force induction engines to keep them in a very narrow RPM band, similar to Diesel engine dynamics. However, speeds nearing 180 KM/h is a natural result of these mathematics.

What I was proposing to keep the same engine, reduce the gear count to 5-6 and keep engine RPM around 2-3K which maps to 90-120 KM/h band generally.

You'll either keep 8 gears with closer ratios for a smoother acceleration, or shave two gears from top, because 8th gear on 120KM/h results in RPMs too low for the engine (on the cars I have driven though).


Oh I can’t answer that. Was just pointing out advantages of lower RPM.


> Why are cars designed to be capable of going much faster than the speed limit?

German here. I don't understand the question.


"Don’t tell me they’re made with the Autobahn in mind."

A quote from the inquiry. Other than that the speed limit is not universal, and it's not 'the speed limit' as the limit is context based. There are many a situation where speeding up would help prevent an accident.


Thank you. Just wanted to find out if a little bit of joking is still allowed on HN.


That's a hit and miss there. Sometimes a humorous bunch makes a mundane thing giggle worthy, sometimes a joke is taken too serious and you get accused of being manipulative.

So, YMMV.


'joking' is always a bit manipulative anyway (I bet asperger people understand that better than me, I've heard that it's how therapists teach them white lies).

I guess the issue is when the joke isn't that funny and perceived as too manipulative, and anybody's threshold is different on both those.


I mean, I hate jokes belittling people or throwing them curveballs and hitting their self esteem. As a result, I never make these kinds of jokes. The jokes I labeled manipulative are about something else and built upon double meanings of words, in the context of the subject being discussed.


i see what you did there. and smiled :-)


Absolutely verboten. You have the choice of the manner of your excommunication today.


As the percentage of humorless PC drones rises, that's going steadily down.


You know that most german manufactures limit the max speed of their cars right?


What is that limit set to supposedly?

Last summer I topped out at 210 km/h in my Audi A3 which was bought in Spain, and it seemed to be limited by the engine rather than a hardcoded limit (slowly approached 210 km/h instead of reaching it and then getting stuck there)


> What is that limit set to supposedly?

Even on the autobahn, you'll very rarely see anyone exceeding 3×10⁸ m/s


It’s always drivers of red cars.


They always look blue to me... maybe it's relative


yeah but the real question is if they'll see you


250 km/h for most models that are limited.

But not all are.


Afaik those limits are there because the tires aren't rated for higher speeds


Not really - my Mercedes AMG came with tyres rated for 300km/h(ZR rated Contis), and it was still limited to 255km/h electronically. For me it's just a way to make more money - Mercedes will happily take that limiter off for an extra £1200 when buying the car.


Supposedly, the Bugatti Veyron tires last for 12-15 minutes at 400 km/h. Then you need a new set, for $42k.


That's safe though, as the fuel tank also only lasts 12 minutes.


The only information I can find about that is an article from 2005 about car makers dropping this informal limitation:

> Premium automakers are quietly abandoning their informal agreement limiting the top speed of production cars to 250km/h.

https://www.just-auto.com/news/germany-car-makers-dropping-2...

Maybe it's not a thing anymore?


It's 250 for Audi, BMW, Porsche, Mercedes-Benz and Volkswagen. It's a "voluntary self-restriction" because they feared regulations in the 90s.


Well played sir! Well played!


The question was:

> Why are cars designed to be capable of going much faster than the speed limit? (Don’t tell me they’re made with the Autobahn in mind.)

Since you didnt read the question, it was questioning whether the autobahn is a valid reason for the majority of cars and if there was a better reason.


Outside Germany, there are places with 140km/h in Europe. Outside Europe there are cases with 160km/h.

Even with 140km/h in mind, you'd not want to be the absolute upper limit as that would make it inefficient in different ways. If it's about having an artificial limit (say electronics) it could also be needed to temporary speed up over the max. Such a limit would stimulate over inflating the tyres to 'cheat' it.


I was merely pointing out that the question was whether there were any benefits of having such a high speed on a lot of road vehicles. The dismissive nature of the gpp of the question because they didn't read it, was irritating.

I would also show the relationship between top speed and engine power. I don't need to drive at 200mph, but I like that I can drive up a hill with 4 adults in the vehicle.

My wife's car has a smaller engine, lower top speed and struggles with more than 2 adults, and 2 children when dealing with hilly countryside.


Small electric scooters got people hysterical for "safety". They now have speed limiters, with different zones based on GPS.

But for cars, killing and maiming millions a year, no one wants the same. So weird.


Thought experiment: if bicycles were a new invention that came out this year, would they be allowed on the road? I'd say almost certainly not.


Counterpoint: if ̶b̶i̶c̶y̶c̶l̶e̶s̶ cars were a new invention that came out this year, would they be allowed on the road? I'd say almost certainly not


absolutely they would - not just on the road, but also on the pedestrian pavement, everywhere. Case in point - electric scooters.


Why not? We allow haven't even banned those electric one-wheel balancing things that if they lose power will face plant the person riding it.


It's like vape pens vs cigarettes, or Bitcoin vs block lattice. There's people who will lose money to a markedly better alternative, so they smear the opposition.

There's a whole playbook of strategies for this, developed by tobacco and oil companies.


Perhaps there should be a way to limit their speed from the user side at least. Maybe I don’t want my teen driving over 65 mph anywhere.

And then there’s courts. If courts can force drunk drivers to add ignition interlocks to their cars, they can throttle the engines of chronic speeders too.


Just TIL from side comment [1]

> Apart from the speed cap, every Volvo car will now also come with a Care Key, which allows Volvo drivers to set additional limitations on the car’s top speed, for example before lending their car to other family members or to younger and inexperienced drivers.

[1] https://www.media.volvocars.com/global/en-gb/media/pressrele...


Devils advocate here, if you limit the speed for your teen and then need to accelerate to get out of a dangerous situation, what will happen?

I’m not saying it happens often, but I’ve had times when driving on the motorway when I simply need to accelerate past the normal legal limit to get some distance or swap lanes safely to get away from some one behind me or next to me.


Devils advocate here. If you don't let your send your kid out in the fastest car you can afford, with the highest acceleration possible, then it's your fault if the kid gets rear-ended or sideswiped by another car.

You should start funeral planning if you buy the kid a Chevrolet Spark, with its 0-60 of 11 seconds and top speed of 90mph.


You should probably start funeral planning anyway if you can’t trust your kid in a vehicle without artificially limiting their speed.

I didn’t use any hyperbole about the fastest car, with highest acceleration, I was merely pointing out that a hard cap at 65mph is (imo) a silly idea as there’s many reasons you would need to accelerate beyond that to get out of an unsafe situation.

I could maybe advocate for a happy medium here, something like a black box given by your insurance company (they already do), insurance premiums for larger, more powerful vehicles being higher (they already are), traffic calming measures, or speed cameras (already exist) and punishments for speeding such as fines, points, bans or additional speed awareness courses (all already exist). If you’ve any additional input here, other than ‘plan a funeral if you don’t limit your kids speed’ then I’d appreciate the discussion as these things clearly don’t fix all the problems that we encounter on the road, but they certainly prevented me from being a dumb ass on the road when I was a teenager, and still manage to.


It seems like you were only pretending when you said you were playing devil's advocate, when you were actually expressing your true viewpoints.

I trust you weren't using "devil's advocate" as a way to say something while trying to avoid direct criticism.

If 65 mph is too low, then what maximum speed do you think is appropriate? 70? 90? 120? The local maximum speed limit + 15mph?

If you think any artificial limit is intrinsically less safe (bear in mind that high-end cars are already artificially limited to 155 mph), then the same logic says that, if price is not any issue, it's always safer for a kid to drive a faster car with good acceleration - the faster and more powerful, the safer it is.

If you think a maximum of 90mph is too slow to be safe, what do you say to parents who buy their kid a car with a max speed of 90mph? Do you tell them you think that care is unsafe and they should get a faster car if they can afford it?

(This reminds me of the Swedish A-Tractor, which lets 16+ year olds drive certain vehicles so long as they are limited to a max of 30km/h, including through electronic limiters. According to you, that's more unsafe than allowing faster speeds. Strange that the Swedish government feels otherwise.)

Your examples were all on the motorway. I presume a parent wanting the 65 mph speed limit will also want the teen driver to stay off the interstate, motorway, or other highway. If the kid is only supposed to drive on roads with a max 45 mph speed limit, then a car limit of 65 mph should be just fine, yes?

Many US states limit school buses carrying students to 55 mph, even on the interstate. Buses also have lower acceleration than a car. From what I can tell, the consensus by the relevant authorities is that raising the limit to better match the flow of traffic is more dangerous because of the increased deadliness of any crashes.

How is it that the driver of a 15-passenger school bus is able to handle restrictions you think are so unsafe that you couldn't handle them?

I don't understand the point of your last paragraph. Just because those things helped keep you from being a dumb-ass driver as a kid doesn't mean that another tool - a speed limiter - can't be an additional useful parental restriction on a beginning driver. For one, unlike everything you listed, it does not require third-party involvement.


I feel like my devils advocate argument was in good faith, however if it didn't come across that way, my apologies.

To answer your first question, I'd say 90mph is probably the most you'd need to use in pretty much all circumstances to safely overtake or maneuver out of a bad situation. If we need to enforce a limit, I'd be erring around that number, personally. The current 155mph limiter that we get in the EU is overkill for road cars outside of Germany, unless there's other places with unrestricted public roads.

I don't recall saying any artificial limit is less safe, I suggested a 65mph limit would be less safe.

I think parents buying a 90mph max car are doing nothing wrong, as that isn't artificially limited to 65mph and would still have the acceleration potential to move out of the way when going the speed limit, albeit slower than some higher spec'd cars would. My first car was a Mazda 2, with no limits on it. It's top speed is 106mph according to Google, and I probably saw 90 once or twice within 4 years of having it.

I'm not sure comparing what we're talking about to tractors is a fair argument - we can drive tractors on the road at 14 in the UK, they don't go on motorways, nor are they the same type of vehicle as a car. I think this goes for a bus as well, it's not only a professional vehicle, with a different class of licence, but they are significantly larger, bright colours, lots of signage stating their restrictions (at least in the UK).

Yes, if the car is only used on the 45/50mph roads then I'd agree 65mph would suffice. If the parent limited to 65, and requested their child didn't go on the highway should we start including GPS limiters as well just incase your kid thought they knew better? It seems like people can't trust their kids anyway in this discussion, as you're wanting to set a limiter on their car, so may as well include some measure to stop them even trying in the first place.

Not particularly sure of your focus on buses here, as I said they're a totally different class of vehicle and clearly don't accelerate the same as personal vehicles for many reasons. Public liability, efficiency, comfort, safety and longevity for starters, and I reckon physics probably comes into play somewhere.

The limiter can be another deterrent, or parental restriction, I just think it's a potentially dangerous one, personally.


> I don't recall saying any artificial limit is less safe

Your devil's advocate position was "if you limit the speed for your teen and then need to accelerate to get out of a dangerous situation, what will happen" further clarified as "You should probably start funeral planning anyway if you can’t trust your kid in a vehicle without artificially limiting their speed.".

Had the original limit been 70 mph, I assume you would have said the same thing, as your comment didn't suggest any artificial limit was reasonable.

Hence my devil's advocacy.

> we can drive tractors

While the name comes from farm tractor use some 50 years ago, a Swedish A-tractors is not farm tractor like what you are thinking of. See for examples https://www.curbsideclassic.com/automotive-histories/regiona... and https://www.archivish.com/epas-and-a-tractors-the-slow-swedi... for examples. They can be can be a regular car modified to limit the speed, take out the suspension, shorten the length, and have max two seats. See those links for some images.

> with a different class of licence ...

If you got the same training, does that mean there would be fewer situations where you need to exceed 65 mph on the motorway? Since you asked what could make things safer, it sounds you think additional mandatory training would help.

> should we start including GPS limiters as well just incase your kid thought they knew better?

No clue. That's a far more complicated question which I am ill-informed to answer.

I can make some obvious comments: Exposing the controls for an existing and well-tested speed limiter seems a lot easier than creating an entirely new geofence input system and adding GPS, to say nothing of the more complicated set of failure conditions. The geofence mapper needs to stay up-to-date because road change, so someone has to pay for that service. Most parents who want GPS tracking can already ask their teens to keep their phone on while the car is in use, for viewing aftewards, so the differential safety improvement of a built-in system - if it exists - seems rather low.

But I don't care to defend all conjectural possibilities, only to point out that electronic speed limits for teen drivers is not unreasonable, and already exists for some places, so if it were dangerous we should see that already.


Well, that they might die tragically. I mean, you are assuming a risk on a moving vehicle, why would that be different. The only meaningful question is “is it less risky to allow a teenager to speed than to limit the max velocity he can reach?”. I would bet the limiter is a net positive; and maybe data can prove me wrong, but definitely not a couple of anecdotes.


Any car can have a governor installed and some parents do it. I believe many modern cars have this integrated and can do things like notify the owner even if a limit is exceeded.



> Perhaps there should be a way to limit their speed from the user side at least. Maybe I don’t want my teen driving over 65 mph anywhere.

Standard Tesla feature.


We should legislate so car manufactures have to stop cars going past a certain speed. Like we do with limiting van speeds.

Excess speed causes a very large proportion of car crashes and traffic jams and injuries.


Wind speed is an other argument. Air resistance is big component at higher speed. And adding wind to that. So you need to some reserve power to overcome those sort of conditions.


On resistance, some cars are purchased to be able to tow a double axle caravan | trailer laden up a hill - on the flat with no towing it's going to be able to go fast.


You could make the argument that with strong headwind you should drive slower to optimize for efficiency.


Why is water designed to be capable of drowning people?


Unlike water, we can decide how fast a car ca go.


The question should be "has there been a speed limit before the cars are designed the way to be capable of going much faster then the speed limit by itself"?

You asking the question the wrong way:)

Just, we have a lot of different cars today. Some are for comfortable driving, some address the aggressive part of one's personality with capabilities to go very fast. And that: very fast.

Fact is, you can go on any street very fast. If your car allows, you also can conquer that one curve over there with sounding tires.. even the weakest car can be pushed to its limits. The law makers look at the street and decide what's the fastest speed you can go without being to dangerous for yourself and for others. For not having a jungle of different possible speeds for each road, law makers decided to have like three classes of speed 30/40 km/h for inner city - 50/60 km/h for the big streets and 80+130 km/h for the countryside and Autobahn highspeed roads.

So.. should the cars be designed to be slower than speed limit, when speed limit have been chosen deliberately? What's the problem of cars being faster than speed limit, of one's adhere to the limit?

Of course, the measurements of oneself with others in a competitive manner play a role, too. Because the men are like they are, we need rules of which speed limit is one of...


Why are knives designed to be capable of being used as a murder weapon?


Not sure where you're going with that analogy.

Where I live knives designed primarily for killing humans are illegal to sell, sometimes illegal to own and definitely illegal to carry in public.

That's stuff like commando, flick or spiral bladed knives.

Kitchen, pen or even bush-craft knives generally aren't designed for that but you still can't wave them about in public.

If your analogy holds then are suggesting that if you got caught speeding in a Ferrari or 911 then you'd receive an instant custodial sentence because it was obviously premeditated? That would be the case here if you got into a fight with a spiral knife in your pocket.


I do not think your comparison is valid. Unlike a knife, a car can implement a max speed limit without impacting its usefulness.


The driver’s ability to command a car’s speed gives effect to our rights to self defense, to unrestrained movement, to due process, to choose to break the letter of the law where there are extenuating circumstances, etc.


I don’t find these arguments compelling. You don’t have a right to the means to commit a crime. It’s illegal to shoot a gun on a plane but it’s also illegal to bring one in your carry on. Even if there could be a hypothetical self defense scenario where a gun is advantageous, that doesn’t outweigh the baseline risk.


And yet, you can probably count on one hand how often that has saved anyone's life. But need phone books of paper to count all the deaths it has caused..


My first thought has always been that they are able to go faster because the world is not perfectly flat (or, perfectly round to be precise) so we have hills that cars need to be able to climb, and that extra power ends up making us able to travel faster than necessary when on flat ground.

Since I'm no car expert (or expert in anything really), I'm eager to hear how wrong my intuition is.


An electronic governor wouldn't care about that. The important engineering issue for an ICE car would be the gear ratios of the upper gears but that's already pretty well handled.

Fundamentally there is limited consumer demand for a governor (but some from parents and also Volvo does it to support their zero deaths goal). In the end, governments should mandate this but the value is not incredibly high compared to many other safety features. Sometimes deadly accidents happen because a driver is going 100mph but for the most part it's people running red lights at 50mph in a 30mph zone (which should be 25mph) that cause the most carnage.


And thank the Lord for that - the speed limit where I live is 120 km/h, which in some highways is a snoozefest.


The simplest reason? My guess is capitalism.

If every car model available for a consumer to purchase has the same advertised speeds, the competition between manufacturers will slowly dry up. I'd guess this would result in less cars being sold.

Would manufacturers compensate by competing in other areas to attract buyers?

Why buy a Kawasaki Ninja H2SX when you could buy a Yamaha N Max...


People don't really buy cars based on top speed. Most higher-end cars are limited to the same 250 km/h (155 mph).


Reminds me of Japanese cars having rather high maximums listed on their speed dial, despite most never getting close

My ‘89 Mazda 626 had 240km/h, but similar era cars had 320km/h

Despite these usually being a ~2L inline-fours


The speedometer is a design choice, not an indication of potential performance.

And given F1 cars have a 1.6L displacement, the relationship between engine size and capability is weak.


That’s a bit disingenuous

The thread is about road cars

Road cars don’t run their engines at 20,000RPM

Displacement is one of the main predictor variables of road cars’ top speeds

You are completely right technically but it’s not an apt comparison given the thread’s topic


Looking at the top speedometer speed (and going ooo 320 or heh only 160) was our favorite hobby in the 90s as a preteenage boy


At 120mph, my car can only go about 35mph over the posted speed limit in some places around here so I wouldn’t call it ‘much’ faster.




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