At no point was it ever illegal do display the old units. There were no martyrs; there were only idiots.
(Quite normally for my age in the UK I think, I'm familiar with both metric & Imperial measurements, but generally fairly bad at converting. Except I know 568ml = 1 (UK! Not US!) pint - for which I can thank my alma mater Imperial and its student bars: Metric, and FiveSixEight. I could probably guess effectively at lbs and kg from butter/flour. Of course I know 2.54cm = 1". A yard is 'a bit' less than 1m. It's the bigger ones that seem more obscure/are harder to work out from familiarity I suppose.)
1. I think with liters, people typically reverse the relationship so it's liters/100km. Which is a much more intuitive unit.
2. If you're buying gas in liters, I think it'd be a lot easier to switch over to using liters for efficiency. You may not be able to compare easily to other vehicles, but you'd be able to estimate your personal fuel more easily.
I think it's the other way around. Distance per quantity of fuel is the intuitive measurement that humans understand and can relate directly to how much fuel they purchase. It could be argued that it is less intuitive when comparing two cars, however. Although better MPG is still strictly better, which is about the level of detail most non-nerds care about.
Only since the 1958 International Yard and Pound Agreement tho. Before then the US used what is now known as the Survey Mile, which is why the survey mile exists (and survived until this year).
In the United States and some other countries, a gallon is equal to 128 fluid ounces or 3.785 liters. Meanwhile, in the United Kingdom and some Commonwealth countries, a gallon is equal to 160 fluid ounces or 4.546 liters.
But wait there’s more! The US also has the “food labelling” fluid ounce which is not the customary one, instead it’s exactly 30mL.
I mean, there are a million things, that do not need universal standards, but standards are imposed anyway.
But where one standard would be really helpful, like scientific values, we have many. And some people would rather go to prison, than adopt. (I think that happened in the UK, after they force switched to metric)
1 ft = exactly 30.48 cm; One pound is exactly 0.45359237 kilograms as in 0.453592370000000000… kilograms.
My diesel 3 series (2.9 litre, late 90s design) would get 8.83 L/100 km (32 mpg UK, 26 mpg US) driving round town, stopping at traffic lights and averaging <20 mph and never getting past 3rd gear. This didn't require much care, just a question of not trying to accelerate too hard at low RPMs or doing a 0-60 run from every stop.
Engine technology will presumably have moved on in the past 25 years, and efficiency will have improved, but you'll still get crappy fuel economy for stopping and starting all the time.
https://www.advantagebmwhouston.com/2022-bmw-3-series-fuel-e...
Well, my 12 years old (gas) Honda Fit does +40MPG being very "pedal happy" and near 50 driving normally, and my dad's 20 years old (diesel) Citroen Xsara Picasso does around 60MPG
https://www.fueleconomy.gov/feg/PowerSearch.do?action=noform...
3.9l/100km in a Xsara, really?
Very few people check the facts, and the only reliable way to know yourself is to take notes at the pump: gas pumped vs km travelled. I did check for a while and the numbers were quite different :-)
On a related note, for the VW ID.4, the manufacturer states 17kWh/100km which is actually achievable (much to my surprise) in city driving when it isn't cold. My real numbers are closer to 21kWh/100km. This goes up really quickly if you exceed 130km/h.