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Comment by aliswe | Hacker News Reader

8l / 100km? thats in the ballpark of my prius 2006, that consumes around 7l/100km. but this was 1939 ... have we come so non-far?

whats in play here? weight? fuel quality? engine? ...

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Most of the innovation in engine design over the decades has been in increasing "dynamic range". That is, the ability to produce high power when required without being super inefficient in the other 99% of the time when you're just cruising or coasting.

A small, simple old-tech engine will have similar fuel economy to a modern engine when cruising but will have much less peak power and refinement, and produce more noxious fumes from the tailpipe.

You don't even need to go to this crazy extreme to find relatively modern levels of fuel efficiency. The classic 60s-era Mini could get ~40mpg with a plain old carburetor.

As ICEs became more fuel efficient, the vehicles became both larger and heavier, negating the gains. Modern ICE vehicles have become so overweight they've managed to make EVs look somewhat average in the weight department.

Your Prius is in another galaxy regarding safety and infotainment, that’s why.

Also likely cruise speed in 1939 was much slower, and drag is a function of velocity^2

> drag is a function of velocity^2

i have to explain that to (fellow but new) EV drivers, that blasting down a highway at high speed for a fixed distance seems to drain the battery, because of drag, far more than travelling the exact same distance at slow speed.

I still feel like i've not sorted out the equations involved.

I did an experiment on the interstate and drove at highway speeds to see if the mpg was comparable. It wasn't, so there's definitely another factor there. Here they cut groves in the concrete pavement on the interstate where as the highways are smooth asphalt. I've wondered if maybe rolling resistance is also a factor here. It was a pretty huge difference. Like more than 10% IIRC.

I don't have reliable numbers on this, but rolling resistance appears to be the main factor up to about 60-80km/h, above which drag takes its place.

Looking at the fuel consumption in my hybrid it's around 50-60% higher at an average speed of 100km/h than at 70km/h.

The difference would have been 2x if was just due to drag.

For EVs it's pretty simple, the faster you go, the more power you use, and the more air resistance, and the less miles / kWh. The more power you use, the more power is lost in wiring, the hotter the batteries get and less efficient they are, etc. There's probably some minimum efficient speed, but as you go faster, everything works against you to make things less efficient.

For gas engines it's quite a bit trickier, because a hotter engine gets more complete combustion and more power out the driveshaft per gallon (also more NOx, see VW) and there's a small range of RPMs where power output is best, combined with a transmission gear where efficiency is best, combined that gets you a target speed for best fuel to power at the wheels. But air resistance does get worse as you go faster. So you've got some things pushing you to go faster (sometimes much faster), and other things pushing you to go slower.

You can get the same effect with a "gas" engine by having a smaller engine and going at a slower speed.

> there's a small range of RPMs where power output is best

The so called 'power band'.

My point was that at the same speed, the freeway uses more energy than the highway. There's more to it than just wind resistance in my area at least.

Does the car have a power usage estimator? Or would that perhaps be dangerous if one misses traffic changes due to following the dial

7+ years old BMW i3 so yes it does.

The equations of motion and power usage due to drag and rolling resistance for vehicles are well understood:

see: http://thecartech.com/subjects/auto_eng/car_performance_form...

thanks as i had not known proper terminology to search for that

this one topped 139km/h ... my prius is capped 180 :')

Weight, that is mostly coming from safety requirements (NCAP starts come with heavy weight and increased fuel consumption). That car with a modern engine can go as low as 3 liters/100 km, I did drive regular cars with 3.5l/100km over a 200km trip.

No doubt this car would have weighed a fraction of what a modern Prius weighs.

Yes… manual everything… brakes, steering, transmission and a suspension system that would barely be passable for a trailer now

Your Prius is more reliable, needs less maintenance, is easier to drive, has much more grippier tires, is safer if you crash, has more storage and passenger space, and is infinitely more comfortable.

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