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Archive for February 15th, 2009
numbers on sidewall
Posted by Richard from Madera, PA, US on February 15, 2009
Just what do the new numbers on the sidewall of the new tire sizes mean & what does each number stand for? What is the relation to the old size numbers & the new numbers?
I assume your are refering to the metric size designaton (such as 295/75R22.5) compared to the older size designations (like 11R22.5). New, is a relative term since the metric size designations have been around for over 25 years in North America.
For the metric size desigination, the first number (295) refers to the section width of the tire in millimeters. The second number (75) is the aspect ratio, the tires section height divided by its section width. In this case the tires is 75% as tall as it is wide. The R means that the tire is a radial. Finally, the last number (22.5) is the nominal diameter of the wheel (in inches) for this tire. The older size designations were somewhat more simple. The first number (11) is the section width in inches, the R again means radial and the 22.5 again refers to the nominal wheel diameter for the tire.