@kritiper Maybe that would explain it then; some mechanics and tire salespeople are not familiar with how things have changed since the 1970’s. I wonder if they even know that most cars don’t use carburetors any more, and that Carter hasn’t been President for quite a while….
For any tire marked in accordance with internationally accepted ISO standards, the number before the slash is the nominal section width (in millimeters), and the number after the slash is the aspect ratio ( Sidewall height = Width / (Aspect ratio / 100) ) . But there is a difference between section width and tread width, and the treads on a truck’s 195/75-R14 tire may be narrower than they would be on a car’s 195/75-R14 simply because the weight of the truck makes the middle of the tires bulge out, making the middle wider than the tread.
However, some trucks (and older American cars) don’t use the ISO standard, and their ratings place the width second and the tire diameter first. Of course, none of them would start with numbers much above 40 as the first number is in inches. Try mounting tires over 17 feet in diameter on your car! But those tires are obvious as they don’t use a slash either; they use an X, as in 37×12.5R17LT.