Why are the majority of cars able to drive nearly double the maximum speed limit of most countries?

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Why are the majority of cars able to drive nearly double the maximum speed limit of most countries?

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18 Answers

Anonymous 0 Comments

Cars need to be capable of low gear, high RPM operation for driving up gradients. They also need to do low RPM, high gear operation for efficient fuel use at higher speeds.

Therefore, they can also do high RPM, high gear driving, which means the top speed is well above their designed optimum efficiency speed range.

Edit: Due to a number of similar replies, I’m talking here purely in terms of the mechanical reason that road cars *can* achieve such high speeds, not whether they *should* or not.

Edit 2: A [simpler version](https://www.reddit.com/r/explainlikeimfive/comments/vqdqwh/eli5_why_are_the_majority_of_cars_able_to_drive/ieqw5xq?utm_medium=android_app&utm_source=share&context=3) for those that need it. I’ve tried to remove any big words.

Anonymous 0 Comments

To my understanding the main reason is the gearing. If they topped out at highway speeds, they would be redlined and have horrible gas mileage. They also need a bit of extra power/speed to pass others as well

Also just because a car registers 140 or so on the dash, doesn’t mean that it has anywhere near enough power to do it. And on top of that, alot of cars have a fuel pump cutoff switch that activates and cuts off the fuel lines or stops you from going any faster when you go over 100+ or so MPH

Anonymous 0 Comments

Imagine computers are designed that way. Cpu always max out 100% just to browse websites, Cpu fan spinning at max speed every minute, everyday. That’s not efficient. So computers are designed to be way faster than standard everyday use, and on rare occasion when you need the power (playing triple A games) you get the power.

Cars engine are designed that way too, in a sense. Thus they can be efficient to consume less gas for more mileage. That doesn’t mean they should go full power every minute, every time they are on the highway.

Speed limits are in place also due to how fast we humans react and respond ON AVERAGE to prevent avoidable accidents. So don’t tailgate people.

Anonymous 0 Comments

Top speed of a fully loaded semi truck on level ground is like 80mph. Top speed of the same thing going up a steep hill is like 30mph.

Unless you want the same thing to happen in your car, it needs to be more powerful.

A 4000lb car going up a 10% incline at 60mph requires 63 horsepower at the wheels… probably a 90 horsepower engine.

And then why the engine in a modern car is probably 3x more powerful even than that, is to increase fuel efficiency (slower RPM = slower combustion cycle) and to prolong engine life.

Edit: as a point of comparison, cars had 90HP engines around 1940, when most people drove around 45–50mph on open roads. Once interstate driving became common, overdrive and more powerful engines became the norm.

For example, starting in 1955, even Chevy’s started coming with a 160HP V8 instead of a 120HP straight-6.

Anonymous 0 Comments

This won’t compare to the other answers, but my thoughts:

Why is my shower capable of putting out water that is too hot or too cold?

Because accounting for taste, circumstance and the privilege of control are all important elements of a satisfying product.

This is why, in computers, I hate Apple and now also Microsoft compared to the old days. If I can’t ruin my own experience then I’m not truly free.

Anonymous 0 Comments

People touched on gearing, but this is also one of those things that is easily cracked in even modern computer ECUs.

Pretty much every car where there is a sports enthusiast market has super cheap chips to unlock artificially restricted power, remove rev limiters, and alter things that annoy owners like seatbelt chimes.

This kind of regulation would be beat by any consumer spending $200 and plugging a device in an OBD port.

Anonymous 0 Comments

Why don’t you run everywhere at max speed? It’s not efficient so you get tired soon. Topathletes in high impact sports are know to wear out their joints sooner. Just because you can do something at maximum level doesn’t mean it is good to do so. Maximum is maximum because you are pushing something to its absolute limits.

Anonymous 0 Comments

The technology exists to limit the top speed of a vehicle regardless of its drivetrain. You see this in some upper tier vehicles in the form of unlocking said restrictions with a special key and in some cases even confirming via GPS that the vehicle is in a particular place, like a race track. It isn’t widely used due to cost. Cost the manufacturer & cost to the consumer.

Anonymous 0 Comments

Speed limits can and do change. Would stuck to buy a car back when the national speed limit was 55 MPH then not be able to safely drive on modern freeways. You’d have to buy a whole new car!

Anonymous 0 Comments

Cars would not sell well with speed limiters. Speed limiters have been present in a few cars in the US that did not sell well, for example the smart fortwo. As to why people would not buy cars that can go at illegal speeds, I won’t publicly speculate here.