Originally Posted by
modelmartin
So what do the inch designations refer to anyway? 700 mm is about 27 1/2 inches. Does it refer to the OD of the tire? OD of the flange of the rim and the 700mm is the diameter of the bead?
Antique car tires (early 30s and older)are sized by OD. Modern car tires are sized by rim diameter.
Anyone have the knowledge?
As alan s referenced earlier (and just elaborated on), details can be found at
http://sheldonbrown.com/tire-sizing.html. To summarize, 700C was from French sizing, originally based on the nominal diameter in mm, including a specific size tire (C was a width designation, there were also A, B, and D). It also notes that 29" is just a marketing term for some wide 700C tires (mostly MTB, presumably based on the approximate outsize diameter of the tire). As most have mentioned, ISO is the most clear, it consists of two numbers, the inner rim width in mm, and the bead seat diameter of the rim. When in doubt, check ISO size.