Quick update and summary

tyre sizes... width is in mm and diameter is still in inches. my car tyres are 205/50-16 205mm wide with a 16 inch diameter...lol
I'm not sure it can be quite as complicated as it is with bicycle tyres. See the table here, noting that 27 inch wheels are apparently bigger than 29 inch wheels, and that 700B/C/D are all different sizes.
Our Unimog have 365/80/R20 and i plowd 3,5 bar in my Bycicle Wheels last Thursday

More Confusing is that some Bycicles have these "Frenche Valve" and some have the same Valve Type like your car, , my Bycicle per Exemple, is a Mountainbike but have thees Frenche Valves
These are usaly for Racing Bycicle (Tour de France)
You don't have to worry about confusing people from other countries, you can confuse people within the same country with conflicting units...
Nothing conflicting about it. Just still as cumbersome as not having the metric system. ;)
There are reasons for both systems, lots of imperial is meant to be simple, so an inch is about the length from your thumb joint to the end of your thumb, a foot being around the length of a human foot. Having 12 inches in a foot is useful for the same reason as having 60 minutes in an hour: it is highly divisible without a remainder (1, 2, 3, 4, 6, all go into 12 a whole number of times) which is useful for when you need to describe a 12th, or a 6th, or a quarter, or a third, or half of a foot (vs if you have a 'nice whole' cm length, and you want a third of it, you then have 3.333333cm). It makes describing things using fractions a lot easier on the whole. If instead the clock didn't go 0 -> 12 and went 0 -> 10, when it is quarter past the hour, the clock hand would be half way between 2 and 3.

Of course the decimal system has lots of benefits, and has been adopted by a lot of the world, and having the same units everywhere of course has its merits, but, if you didn't already know, it is worth knowing that the old system has got it's own merits. It also helps explain why some people prefer it. There is also the fact lots of things have been standardized on imperial units, so perhaps door sizes for interior doors may typically be 24”, 28”, 30”, 32” and 36”, so if you builder who buys and fits a lot of doors, these numbers of quite some meaning, and they don't particularly want to switch to 60.96cm, 71.12cm, 76.2cm, 81.28cm and 91.44cm etc.

People can adapt, sizes can be updated, the world can keep spinning, but at the same time, for a lot of people, they are happy for things to keep running how they are.
If you want to be precise, the imperial system looses that first advantage. For the second advantage, try dividing by 3 two times in a row.
And, if a country goes full metric system, carpenters could still know inches. ;)
I allways try to hit the middle of the bound, if it dosnt sound that terrible, its ok..
i teached me to play guitar mostly autodidaktik, and i got a bit from a Scout Friend,.., so my Guitar Play is usable, but not the best..
@levi It's1.5875. It'd be 1.6, if inch/mm was 25.6, or what you said, if it was 2.4 - inch/mm is 25.4. The imperials could have done that better. :D
If you want to be precise, the imperial system looses that first advantage. For the second advantage, try dividing by 3 two times in a row.
And, if a country goes full metric system, carpenters could still know inches. ;)
Also carpenters could still use imperial as a trade specific measurement system!
Here is a fun one from my travels last year.

The Republic of Ireland uses the metric system. Speed limit signs are posted as a white circle with a red outer border and black numbers in the center. 50KPH is a fairly normal speed.
Northern Ireland uses British units. Speed limit signs are posted as a white circle with a red outer border and black numbers in the center. 30MPH is a fairly normal speed.

The border between the Republic of Ireland and Northern Ireland has no demarcation. The speed limit signs look pretty much the same - just the numbers change. There are no units presented on the signs. Driving North at 50KPH I encountered signs saying '30' and slowed down to a comparative crawl of 30KPH - wondering for a bit why everyone was passing me. It took about 30 seconds for me to figure out we had, 'crossed over' - about the same time the GPS figured it out too and flipped units.

I knew that there would not be a formal border checkpoint, but I had expected there to at least be a sign saying, "Welcome to ****!" But - there was nothing visual to indicate the border going in either direction. The part that the border 'is no big deal' was great. But - if you're going to switch units on a road on an island, would it hurt to put some units on the first couple of signs in each direction?

The US tried to go Metric in the 70s under Carter. The 'America First' conservatives used this (and other) 'Anti-American' change as a rallying point.

However, Carter's push on the Metric system gave a few of us a solid introduction to it in school. It is still the system used in science classrooms throughout the US. We also now have a 'mixture' of units. Gasoline and milk are sold by the gallon. Hard alcohol is sold by the portion of a liter, 750ml, 500ml. Soda & beer is sold in 12oz can or 2 liter bottles. For a while we had dual-limit speed signs showing both MPH and KPH (with units I might add). Since then the speed limits on many US roads has gone up substantially - from 55MPH (88KPH) to 80MPH (129KPH). The metric KPH portion of the signs were removed entirely.

For additional confusion, there are two differing definitions of 'Gallon'.
1 UK Imperial Gallon = 1.2 US Gallons. This means that the same car in the UK gets 20% 'better gas mileage' in MPG than the same car does in the US.
If you want to be precise, the imperial system looses that first advantage.

Well, this is clearly not true... you can measure just as accurately in either system... the fact you can convert between the two systems shows you can represent all the same data with both systems. The only thing I can possibly imagine you mean is if you using fractions only with imperial, but, you don't have to do that, the fraction side of it is useful for sure, but you aren't limited by it.

For the second advantage, try dividing by 3 two times in a row.

Sadly children these days, who never experienced the imperial system, probably consider this complicated, and can't fathom how imperial would make this easy. But 3/2 can be expressed simply as 3/2 if you like, so literally no work to do, and if you wish to divide by two again it just becomes 3/4 (double the bottom part of the fraction). You see, that was incredibly easy. Do the same in decial and you have 3/2 = 1.5 and 1.5/2 = 0.75 - which is, quite obviously, harder/more complicated. Just for a bit of fun, lets divide by two a couple more times: 3/2 -> 3/4 -> 3/8 -> 3/16 -> 3/32, let's do the same with decimal, 1.5 -> 0.75 -> 0.375 -> 0.1875 -> 0.09375. Hopefully that helps you.

Or if you want to divide by 3, so say we have 2 divided by 3 = 2/3, divided by 3 again = 2/9, divided by 3 again = 2/27. Let's do that with decimal, 2/3 = 0.6667, divided by 3 again = 0.222, divided by 3 again 0.07407. We are already at the point where I am guessing most people wouldn't be able to do this in their head... those who can then not particularly quickly... or those who can do it quickly, still, less quickly then just multiply a whole number by 3, which is what you do with fractions.

And, if a country goes full metric system, carpenters could still know inches. ;)

Well, as the rest of your post hasn't really proved anything, this final remark doesn't really mean anything either. Of course the country could change, of course life would go on. But you say carpenters coudl still know inches, the problem is, the carpenter goes to the store to buy a door, and it would be in metric instead (this literally happened when vegetables switched to being measured in metric, and some people, again mostly older, went to the grocers and struggled to work out how much to order). Does it mean people can no longer buy vegetables, no, they can adapt, it isn't the end of the world. But my post was simply highlighting some of the reasons why imerpial isn't all bad - and the lack of understanding (shown in your example of not seeing how easy it is to divide by two twice) just leads to people having a big opinion about something they don't really understand, which isn't ideal.
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@Rockthesmurf I should have phrased it better.

By the first advantage I was refering to the imperial units relating to biometrics, that are different from human to human. Plus one may learn hisher biometrics in cm or whatnot.

On the second point, I meant dividing by 9. By which you'd get a periodical fraction on the smaller imperial scale, too, in your example. Plus you could start of with an appropitly dividable measurement with metric untits, too, in case you have that degree of freedom in a given project.

Regarding the carpenters, I meant there would still be doors available fitting the x-inch-measurements - just for there would be the need for them, or out of tradition.