Some tires rated for use at high speed (up to 149 m.p.h) carry a "ZR" rating following the aspect ratio. Other speed ratings are contained in the service description code.
WHEEL DIAMETER
Following the "R" radial indicator is a number that states the wheel "rim size" in inches.
Wheels measured in inches are typically whole numbers with exception of some heavy duty wheels which are stated in half inches (16.5 for example). European tires may list wheel size in millimeters (190/65R390) and may also be followed by the letter "A" indicating an asymmetrical measurement of inner and outer rim size.
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