Tires Tire sizing, incorrectly...

Discussion in 'Bicycle Repair' started by DougC, Oct 29, 2009.

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  1. DougC

    DougC Guest

    We've had this topic come up a couple times before--that being, when it comes to bicycle tires, there's two different sizing systems. One uses a decimal point (such as 26 x 2.125) and the other is fractional (like, 26 x 2-1/8).
    Even though it would seem that these are the same, they're not. The two numbers represent the overall diameter and the width, but the bead diameters of the two systems is measured different.

    I happened to run across a pretty good example of this mix-up, including what happens when you to mount a 26" x 1-3/8" tire on a MTB rim-

  2. DougC

    DougC Guest

    The difference between these two systems is basically that the fractional system measures the diameter of the tire's bead, and the decimal system measures the maximum diameter of the tire when it's properly inflated.
  3. happycheapskate

    happycheapskate Active Member

    I know the differences by experience (I used to have a bike with the old gumwall tires, which rode pretty nicely but were heavy.) I also have modern bikes.

    But thanks for the explanation of how the standard was set for measuring.
    Last edited: Dec 4, 2009
  4. wheelbender6

    wheelbender6 Well-Known Member

    Sheldon Brown (God rest his soul) provides some very useful tire sizing data on his site.
  5. happycheapskate

    happycheapskate Active Member

    Yeah, Sheldon had a lot of fans. I learned a lot from his site but never met him.