A few observations:

1) The miles/km or mph/kph conversion is trivial, i.e., a 5:8 ratio comes within about 1/2 percent, and a 3:5 ratio is within 5 percent.

2) As bicycle enthusiasts, we have inherited the most screwed-up SAE-metric hybrid system ever invented. My favorite example is Italian BB threading: 24 threads per inch on a 36-mm diameter. Go figure! The derailleurs, brakes, and axles are all metric, but the ball bearings are in fractional inches, as are the ISO BB and handlebar stem sizings. You have to respect the French for trying to build all-metric bicycles, although they occasionally gave in on freewheel and pedal threads for U.S. export.

Ben Franklin, a Francophile, wanted the U.S. to make the Revolution complete by adopting the metric system, and we would have avoided years of costs and grief if the other Founding Fathers had listened to him.

I remember when my high school built a new swimming pool in the mid 1960s -- it was 25 yards x 25 meters, so that either metric or English unit competitions could be held.