Check the sidewall for a code like P215/65R15 95H
P = tire type
215 = section width in millimeters
65 = aspect ratio, sidewall height as a percentage of width
R = radial construction
15 = wheel diameter in inches
95 = load index
H = speed rating
LT = light truck tire
T = temporary spare tire
C = commercial tire
M+S = mud and snow rating
DOT = meets U.S. Department of Transportation standards
The first number after the type letter is the width
The second number after the slash is the sidewall ratio
The number after the construction letter is the rim size
The last numbers and letters indicate load and speed capability
Match the tire size exactly to the vehicle manufacturer’s recommendation