Jeepers, I totally left inflation pressure out of the width calculation. Now I have to reformulate my perfect world. I want to say that the tire pressure is used is maybe relatively unimportant, as long as it's an appropriate pressure for that tire width, but "appropriate" is inexact, and covers a wide range. So in my perfect world, width is stated at highest recommended tire pressure, which shall be molded into the tire.
So the size spec for a 700x28 tire, that is 28mm at highest recommended pressure (HRP) on a rim with xxmm internal width should read:
622-28-xx-HRP
A 622-28-19-95 size would tell me the tire should be 28mm on a 19mm internal width rim at a pressure of 95psi. That would let you know that it'd be a little narrower at lower pressures, a little wider on wider rims, a little narrower on narrower rims. If I knew my frame is too tight at 28mm actual width, but I'm running older rims w/14mm internal width, I'd know these 28s would be closer to 26mm actual and should fit.
I could envision an argument to standardize the internal rim width for all mfrs, just to save us doing a little less math.
Make it so.
Originally Posted by
Bad Lag
One thing very few people understand, even engineers, is that EVERYTHING has variation in its characteristics. Whether it is a dimension (size) or a mass or,... whatever. It is not a fixed value. Typically characteristics are given as "nominal" values (average/mean, median, typical, target, ...).
Even then, the actual tire width can be dependent upon the rims they are on or the pressure inside. How would you like to decide whether to use this tire or that one when the sizes are quoted at two different pressures mounted on two different rims?