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Tire Specifications

Sidewall Markings

The largest marking on the side of the tire is the size, load, and speed rating.  For the 2.5 RS and WRX, it looks like this:

205/55 R16 89V

The 205/55 and 16 are the size (see below).  The 89 is the load index (how much weight that individual tire can support), and the V is the speed rating.

In smaller print, you'll also find the recommended air pressure in PSI, U.S. DOT Compliance code, UTQG marking (see below), and various other manufacturer's codes.

Size

This often comes up on the forums as a topic of discussion because of the amount of misinformation floating around.  This should help to explain what everything's about.

Tire sizes are normally listed in 3 numbers, such as 205/55/16.

The first number is simply the width of the tire in mm (205 mm).

The second number is sidewall height as a percentage of the width.  For instance, in this case, the sidewall is 55% of 205 mm: 112.75 mm.

The third number is the diameter of the wheel (rim) in inches.

So to calculate the diameter of a tire:

(sidewall X 2) + wheel

Converting the wheel diameter to mm. gives:
(112.75 mm X 2) + 406.4 = 631.9 mm or 24.88 in.

To calculate the circumference of the tire (how far the tire travels in one revolution):
631.9 * pi = 1985.17 mm or 78.16 in.

Also be sure to check out the Speed/RPM Calculator to see how different tire sizes can affect a car's speed.

See Tire Rack's Tire Tech center for an explanation of different tire size designations used over the years.

Tire Size Calculator

Enter the three size numbers below and press Calculate.

/ /

Diameter: in.
Circumference: in.

UTQG (Uniform Tire Quality Grade)

A U.S. DOT labeling requirement for all tire manufacturers.  It has three parts: treadwear, traction, and temperature.

Treadwear is a relative designation that really has no individual meaning.  The number is only in relation to other treadwear ratings.  A rating of 150 has tread wear of 1.5 times as long as a rating of 100

Traction is a measurement of straight-ahead wet braking.  These included AA (the highest), A, B, and C.

Temperature resistance a rating that specifies the maximum temperature the tire can withstand.  A, B, and C are given, with A being the highest.

Speed Rating

Code MPH KM/H
N 87 140
P 93 150
Q 99 160
R 106 170
S 112 180
T 118 190
U 124 200
H 130 210
V 149 240
W 168 270
Y 186 300
Z 149+ 240+

 

Load Index

Code Pounds Kilograms
71 761 345
72 783 355
73 805 365
74 827 375
75 853 387
76 882 400
77 908 412
78 937 425
79 963 437
80 992 450
81 1019 462
82 1047 475
83 1074 487
84 1102 500
85 1135 515
86 1168 530
87 1201 545
88 1235 560
89 1279 580
90 1323 600
91 1356 615
92 1389 630
93 1433 650
94 1477 670
95 1521 690
96 1565 710
97 1609 730
98 1653 750
99 1709 775
100 1764 800
101 1819 825
102 1874 850
103 1929 875
104 1984 900
105 2039 925
106 2094 950
107 2149 975
108 2205 1000
109 2271 1030
110 2337 1060