14212463:cyphers said:
Bearings and all similar hardware is just spec'd as [inner diameter] x [outer diameter] x [width] all in the same units
Super easy, maybe I'm missing something but I'm not sure why tire companies couldn't just do the same
At this point it's just a trade size. Same reason a 2x4 isn't actually 2" x 4". Or how 1" PVC pipe isn't actually 1" diameter.
Found a super interesting summary for the reasoning behind this system.
"One key fact is that the U.S. has traditionally been a dominant world market for tires. The U.S. Department of Transportation got to set the original nomenclature for tires. That's why, until the 1960s, the wheel size was in inches, the tread width was in inches and there was no sidewall height information (the percentage known as the "aspect ratio"). Back then all tires had the same aspect ratio, which was 90.
But then, technologically superior radial tires were invented in Europe, and the Europeans wanted to sell their tires in the huge U.S. market. And since the only legal requirement for selling tires in the U.S. was that the wheel size be stated in inches (because consumers didn't care back then how wide a tire was), the Europeans just had to change that one number on their tires, and bingo! They had access to the world's largest tire market at the time.
Radial technology also allowed for wider tires and shorter sidewalls. That's when you started seeing aspect ratios on tires. And I'm guessing that, at some point, the U.S. and the U.K. were such dominant car markets that the European manufacturers just said "OK, Uncle!" and started using inches for wheel size in Europe, too. Because if you check out tires sold in Europe, the vast majority have the same nomenclature that we use here."
TLDR: US decided rim size, Europe decided width and aspect ratio
