this post was submitted on 17 Aug 2023
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The faster you go above 80 you use exponentially more energy. Invest in public transport you knobs.
You don't use exponentially more fuel, but cubically. Exponentially is not just a word for "quickly", but a function.
And anyways, that isn't only the case for speeds higher than 80, but for every higher speed. So it's not like there is an objective sweet spot.
The 80 kph rule of thumb is actually part of the design parameters of most regular cars. They are built to be most fuel efficient at 80 (or probably more accurately aerodynamic designed for 80).
I was using exponential colloquially (and fair cop given its usage during Covid), but I think you're just using cubic as a rough guide also due to air resistance. I'd note there are no extra gears at the higher speeds, so you're probably less efficient on the tyres etc.
I didn't know about that. Thanks, that's interesting! Sorry if I sounded a little condescending, I didn't intend to.
And cubic just means an exponent of 3, which is one kind of exponential relation.
No, exponential is N^x^, polynomial growth takes the form x^N^, and in the case of a cubic, N is 3. Exponential functions tend to grow much, much faster than polynomial ones.
Only if you're talking about air resistance exclusively. I don't know what number it is precisely, but at lower speeds other forces dominate (like efficiency in the gears), and at a certain point air resistance becomes the more dominant force, growing with the cube of velocity. It's certainly possible that the number is 80 km/h.
Car crash outcomes are also much worse.
Yep. Because kinetic energy increase at the square of the velocity.