I see some 26” wheels, they are rated 26x1.5 or 26x1.75/2.125 etc, this is written on the rim. Measuring the internal width of the rim is usually less than the stated number and even putting on a tire the width can vary a lot, for example a 26x1.5 rim can take a 1.5” wide tire or wider or thinner (according to sheldon brown’s chart and my own experience too). So what is the reason for the second number in the 26 x X.XX when it is written on the rim? And why do some rims have two numbers after the x, for ex 26x1.75/2.125?