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Archive for November 15th, 2006
US Measurement and Metric Tire Size comparison
Posted by E Patrick on November 15, 2006
I would like to get a list of tire sizes in US measurement vs metric in all tire sizes. ie I believe a 285 is the height, what is that size as far as us sizing is concerned? 33 inch, 245 height is 31 inch? also the 75 series tire is 8 inches wide, a 60 series tire is 12 inches wide? There must be a list some where showing the comparison.
Actually, there is not such a list. Like a lot of things in life, it is not that easy. I believe the history goes something like this. The US and our friends in Europe each developed separate tire sizing conventions many years ago. There was a move to standardize the size nomenclature but, tires using the old style (11R22.5, for example) are still around and very popular. The explanation for each element of the metric sizing system is as follows: The first three digits (like 285) is the nominal width of the tire in millimeters. After the / comes a two digit number (like 75) is the aspect ratio (height of the tire section divided by the width of the tire section). The R stands for radial and the final two digit number is, of course, the nominal rim or wheel diameter. There is no simple translation of a metric size to the older, US sizing system.