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Tire guide

Read thesidewall

Decode a size, look up load and speed ratings, and check the basics that keep a tire safe: tread depth, inflation pressure, rotation, and storage.

Open the decoder
Straight-on view of a tire tread with circumferential grooves and zigzag sipes
Fig. 01Tread grooves and sipes, straight on

01 / Sidewall decoder

Type a size. See what every part means.

The decoder checks each part of the size and service description, explains it, and turns the sidewall so the part you pick sits at the top.

Type the size and service description as they appear on the sidewall, or pick an example.

Nominal dimensions

Overall diameter
25.0 in 634 mm
Section width
8.9 in 225 mm
Circumference
78.5 in 1993 mm
Revolutions per mile
808 about

Estimates from the size: diameter = rim + 2 × (width × aspect ratio), and revolutions per mile = 63,360 in / circumference. Real dimensions vary with tire design, rim width, and load.

02 / Load index

The most a tire can carry.

The load index is the maximum load a tire can carry at the inflation pressure specified for that load. Kilograms are the table values; pounds are conversions as printed on U.S. charts.

Indexkglb
50 190 419
51 195 430
52 200 441
53 206 454
54 212 467
55 218 481
56 224 494
57 230 507
58 236 520
59 243 536
60 250 551
61 257 567
62 265 584
63 272 600
64 280 617
65 290 639
66 300 661
67 307 677
68 315 694
69 325 716
70 335 739
71 345 761
72 355 783
73 365 805
74 375 827
75 387 853
76 400 882
77 412 908
Indexkglb
78 425 937
79 437 963
80 450 992
81 462 1,019
82 475 1,047
83 487 1,074
84 500 1,102
85 515 1,135
86 530 1,168
87 545 1,201
88 560 1,235
89 580 1,279
90 600 1,323
91 615 1,356
92 630 1,389
93 650 1,433
94 670 1,477
95 690 1,521
96 710 1,565
97 730 1,609
98 750 1,653
99 775 1,709
100 800 1,764
101 825 1,819
102 850 1,874
103 875 1,929
104 900 1,984
105 925 2,039
Indexkglb
106 950 2,094
107 975 2,149
108 1,000 2,205
109 1,030 2,271
110 1,060 2,337
111 1,090 2,403
112 1,120 2,469
113 1,150 2,535
114 1,180 2,601
115 1,215 2,679
116 1,250 2,756
117 1,285 2,833
118 1,320 2,910
119 1,360 2,998
120 1,400 3,086
121 1,450 3,197
122 1,500 3,307
123 1,550 3,417
124 1,600 3,527
125 1,650 3,638
126 1,700 3,748
127 1,750 3,858
128 1,800 3,968
129 1,850 4,079
130 1,900 4,189
131 1,950 4,299
132 2,000 4,409
133 2,060 4,541
Indexkglb
134 2,120 4,674
135 2,180 4,806
136 2,240 4,938
137 2,300 5,071
138 2,360 5,203
139 2,430 5,357
140 2,500 5,512
141 2,575 5,677
142 2,650 5,842
143 2,725 6,008
144 2,800 6,173
145 2,900 6,393
146 3,000 6,614
147 3,075 6,779
148 3,150 6,944
149 3,250 7,165
150 3,350 7,385
151 3,450 7,606
152 3,550 7,826
153 3,650 8,047
154 3,750 8,267
155 3,875 8,543
156 4,000 8,818
157 4,125 9,094
158 4,250 9,370
159 4,375 9,645
160 4,500 9,921

On LT tires, the load range letter (C, D, E, F) is a separate strength rating. A pair such as 121/118 gives the load per tire for single and dual mounting.

03 / Speed symbols

A test rating, not a target.

The speed symbol is the highest speed a tire is rated for in a standardized laboratory test at a specified load and inflation pressure. It is not a recommended driving speed.

The letters run in order, with one exception: H sits between U and V. The letters I, O, and X are not used.

ZR in the size, as in 245/40ZR18, marks a tire for speeds above 240 km/h (149 mph). With a service description such as 97Y, the speed symbol sets the limit. Y in brackets, written (Y), means above 300 km/h (186 mph).

Symbolkm/hmph
L 120 km/h 75 mph
M 130 km/h 81 mph
N 140 km/h 87 mph
P 150 km/h 93 mph
Q 160 km/h 99 mph
R 170 km/h 106 mph
S 180 km/h 112 mph
T 190 km/h 118 mph
U 200 km/h 124 mph
H 210 km/h 130 mph
V 240 km/h 149 mph
W 270 km/h 168 mph
Y 300 km/h 186 mph
(Y) over 300 km/h over 186 mph
Lower symbols, A1 to K
Symbolkm/hmph
A1 5 km/h 3 mph
A2 10 km/h 6 mph
A3 15 km/h 9 mph
A4 20 km/h 12 mph
A5 25 km/h 16 mph
A6 30 km/h 19 mph
A7 35 km/h 22 mph
A8 40 km/h 25 mph
B 50 km/h 31 mph
C 60 km/h 37 mph
D 65 km/h 40 mph
E 70 km/h 43 mph
F 80 km/h 50 mph
G 90 km/h 56 mph
J 100 km/h 62 mph
K 110 km/h 68 mph
Tread depth gauge pressed into a groove of a tire
Fig. 02Measuring tread depth with a gauge

04 / Tread depth

Replace at 2/32 inch.

NHTSA's guidance is direct: tires are not safe and should be replaced when the tread is worn down to 2/32 of an inch. Passenger tires have tread wear indicator bars molded into the grooves; when the tread is flush with them, it has reached that depth.

The penny test. Place a penny in the tread with Lincoln's head upside down and facing you. If you can see the top of Lincoln's head, replace your tires. Check several grooves across the tread.

Penny test: on the left the top of Lincoln's head is hidden in the tread; on the right it is visible, so the tire should be replaced Head hidden Tread left Head visible Replace

Trucks and buses. Federal rules (49 CFR 393.75) require at least 4/32 inch of tread on the front tires of a bus, truck, or truck tractor, and 2/32 inch on all other tires, measured in a major tread groove.

Checking tire pressure with a pencil gauge pressed onto the valve stem
Fig. 03Checking pressure at the valve stem

05 / Inflation pressure

Use the number on the door, not the sidewall.

The recommended cold pressure is on the Tire and Loading Information label on the driver's side door edge or door frame, and in the owner's manual. The pressure molded on the sidewall is the tire's maximum, not the pressure your vehicle needs.

Check all tires, including the spare, at least once a month when they are cold, meaning the vehicle has not been driven for at least three hours.

Simplified tire and loading information label, with the cold tire pressure column highlighted TIRE AND LOADING INFORMATION TIRESIZECOLD TIRE PRESSURE FRONTREARSPARE SEE OWNER'S MANUAL FOR MORE INFORMATION

06 / Rotation

Move the tires before the wear shows.

Follow the owner's manual for the interval and pattern. NHTSA's guidance: if the vehicle maker recommends it, rotate every 5,000 to 8,000 miles, or sooner if uneven wear appears.

Forward cross

Front tires move straight back; rear tires cross to the front. The most common pattern for front-wheel drive.

Rearward cross

Rear tires move straight forward; front tires cross to the rear. Used for rear-wheel drive.

X-pattern

Every tire crosses to the opposite corner. Used for four-wheel and all-wheel drive.

Front to rear

Directional tires stay on the same side and swap front and rear.

Side to side

For different sizes front and rear: swap left and right on each axle, with non-directional tires.

Patterns as described by tire makers, based on Tire and Rim Association guidance. Your vehicle's manual comes first.

Storage: tires off their wheels stand upright; tires on wheels can be stacked or hung OFF THE WHEELON THE WHEEL Stand uprightStack or hangDo not stack or hangDo not stand upright

07 / Storage and age

Cool, dry, dark, and away from motors.

  • Store tires, on wheels or not, in a clean, dry, cool, well-ventilated place.
  • Keep them out of direct sunlight and away from heat, and away from electric motors, battery chargers, generators, welding equipment, and other sources of ozone.
  • Tires off their wheels: stand them upright; do not stack or hang them.
  • Tires on wheels: hang or stack them; do not stand them upright.

Age. NHTSA notes that some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of tread wear. The four-digit date code tells you when a tire was made: read a DOT code.

Storage guidance follows the U.S. Tire Manufacturers Association and tire maker recommendations.

Questions about a size

Ask usby email.

Sizes, load ranges, and speed ratings for a program: send us what you are working with and we will reply by email.

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