what size tires should my mountain bike have
The industry responded by making middleweight tires, marked 26 x 1.75 to fit the same rims. Although they are still called 26 inch, these tires are actually 25 5/8, not 26. This same rim size was adopted by the early pioneers of west-coast klunkers, and became the standard for mountain bikes. Due to the appetite of the market, you can get tires as narrow as 25 mm to fit these rims, so you wind up with a 26 inch tire that is more like 24 7/8 in actual diameter! A second number or letter code would indicate the width of the tire. (26 x 1.75, 27 x 1 1/4...650B, 700C...)