Have you ever wondered what all those numbers and letters on your tires mean? Well, so have most people. So, here is a breakdown of what the Sidewall Outer Circle mean:

P: The ‘P’ tells you that your tire is for passenger vehicles.

Nominal Width: This 3-digit number tells the width (in millimeters) of the tire from sidewall edge to sidewall edge. Generally speaking, the larger the number, the wider the tire.

Aspect Ratio: This two-digit number tells you the tire’s ratio of height to width. Numbers of 70 or lower indicate a short sidewall for better steering and handling on dry pavement.

R: The ‘R’ stands for radial. Radial ply construction of tires has been the industry standard for at least 20 years.

Rim Diameter Code: This two-digit number is the wheel or rim diameter (in inches). If you change your wheel size, you will have to buy new tires to match the new wheel diameter.

Load Index: This 2 or 3 digit number is a measurement of how much weight each tire can support. If you can not find this on your tires, check your owner’s manual.

Severe Snow Conditions: The ‘M+S’ or ‘M/S’ indicates that your tires have some amount of mud and snow capability. Most radial tires do.

Speed Rating: The speed rating shows the speed at which a tire is meant to be driven for extended periods of time. The ratings range from 99 mph to 186 mph. These ratings are listed below.

Note: You may not find this information on all tires because it is not required by law.

Q = 99 mph
R = 106 mph
S = 112 mph
T = 118 mph
U = 124 mph
H = 130 mph
V = 149 mph
W = 168 mph*
Y = 186 mph*

* For tires with a maximum speed capability over 149 mph, tire makers sometimes use the letters ZR. For those with a maximum speed capability over 186 mph, tire manufacturers always use the letters ZR.

Happy tire reading …

Tags: aspect ratio, load index, M+S, nominal width, radial, rim diameter code, severe snow conditions, speed rating, tire sidewall outer circle
Filed under: Cars