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


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

In: 8

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

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.

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.

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.

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.