How did tire sizes end up mixed English/metric?

Discussion in 'Archived Threads 2001-2004' started by Dennis Nicholls, Mar 12, 2003.

  1. Dennis Nicholls

    Dennis Nicholls Lead Actor

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    This puzzles me. Tires are not sold in the English (inch pound) system of measurements, nor in the metric (cm kg) system, but rather in some mixed system. For example, a typical tire may be sized as 185 - R60/14, where the 185 is the number of millimeters of carcass width, the 60 is a unitless ratio, and the 14 is the number of inches of rim diameter. What flaming genius decided to mix measurement systems like this? [​IMG]
     
  2. Jay H

    Jay H Producer

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    The same person who made bottom brackets on bikes English Threaded or French Threaded or Italian threaded :)

    And it's tyre for those folks [​IMG]

    Jay
     
  3. PaulT

    PaulT Supporting Actor

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    The P-Metric System was developed in 1976 and is the 'US version' of the Metric tire sizing system for passenger vehicles.

    It is a conversion of the alpha-numeric system of 1968 in which the width used to be specified in inches. The rim size, however, remains in inches (for some reason??).

    In Canada we typically use P-Metric and include the European Metric Service description at the end to specify the load index and speed rating.

    For example:
    P215-65R15 89H
    reads
    Passenger Car, 215mm Width, 65 Aspect Ratio, Radial, 15 inch rim, 1279lb load, 210kph/130mph max speed.
     

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