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The sidewall of your tires is filled with important information that tells you everything about your tire regarding the dimensions, construction, operating characteristics and manufacturer.  The easiest way to understand tire markings is to take an example and break it down.

For our example, these numbers are: P225/60R16

(P) Tire Type

The “P” stand for passenger so these tires are often called P-Metric.  Other letters you might see include “LT” stands for Light Truck, “ST” stands for “Special Trailer” and “T” for temporary. The absence of a letter at the beginning of the size description indicates that the tire is Euro-Metric. The main difference is that Euro-Metric tires may have different load carrying capacities than their P-Metric counterparts.

(225) Tire Width

The 225 represents the approximate section width or width of the tire from sidewall to sidewall.  The larger the number, the wider the tire.

(60) Aspect Ratio

The 60 refers to the aspect ratio which is the nominal sidewall height reflected as a percentage of section width. So the sidewall height on this tire is 60% of 225 or approximately 135 millimeters.

(R) Construction

The “R” stands for radial construction, which is the industry standard for passenger car and light truck tires.  A “B”, “X”, or “-“ in place of the “R” would indicate that the tire has bias ply construction.

(16) Rim or Bead Diameter

The “16” represents (in inches) diameter of the beads, which means that this tire is designed to fit on a rim with a 16-inch diameter.

(97V) Service Description

The final component of the size designation is called the Service Description, which indicates the Load Index and the Speed Symbol for the tire.  Load Index, or 97 in this example, is a two or three digit code that represents the maximum load that can be carried at the speed indicated by the speed symbol.  In order to determine the actual maximum load for the tire, you must consult the Load Index Chart below.  The Speed Symbol, or V in this example, indicates the maximum speed for the tire, but it is more like a performance rating that reflects the handling characteristics after it is installed on the vehicle. To find the maximum speed for your tire, refer to the Speed Rating Chart below.

DOT Code

Another important piece of information on your tire’s sidewall is often referred to as the Department of Transportation, or DOT, code and the Tire Identification Number, or TIN.

The three letters, “DOT,” indicate that the tire has passed all of the tests required by the Department of Transportation (DOT) for motor vehicle safety standards.

After the DOT insignia is your tire’s identification number (TIN). The first grouping of two to three letters or numbers represents the assigned identification mark for the manufacturer.

The second group can be no more than two symbols and identifies the tire size. The third grouping can be no more than four symbols and may be used at the option of the manufacturer to indicate the tire type or other significant characteristics of the tire. The final four numbers in the TIN represent date of manufacturer. The first two numbers reflect the week and the last two indicate the year. So a tire stamped 2910 was manufactured in the 29th week of 2010.

UTQG Code

The Uniform Tire Quality Grading (UTQG) was established by the National Highway Traffic Safety Administration (NHTSA) to test tires following government prescribed test methods and then grade each tire on three main components:

  • Treadwear:  Treadwear is a comparative figure that attempts to project the longevity of the tire in the form of a three-digit number.  This is the wear rate of the tire, comparable only to other tires within a tire manufacturer’s line. It is based on a control tire that is tested under controlled conditions at a specified government test track.  The control tire is rated 100. Therefore a tire with 200 would theoretically wear twice as long on the government’s course compared to a tire with 100. Likewise, a tire rated 60 would be projected to wear about 60% as well as the control tire rated 100. Since it is does not take application, driving style or tire maintenance into account, the Treadwear rating cannot project the actual tread mileage of a tire nor can it be accurately used to compare the projected tread life of one brand against another.
  • Traction: Traction grades are AA, A, B and C (with AA being the highest grade). They represent the tire’s ability to stop straight in a straight line on wet pavement. Any tire rated under C is considered unacceptable for road travel.
  • Temperature: The Temperature grade indicates the resistance to heat and the ratings range from A to C with A being the most resistant to heat.

Additional Information on Your Tires

Some tires have unique benefits, such as winter tires.  These tires have special tread designs and rubber compounds that are engineered to perform better in temperatures below 40 degrees F with or without snow and/or ice.  If a tire passes the test requirements for a winter tire, the manufacturer will usually mold a mountain and snowflake icon on the sidewall of the tire to indicate it has been tested to perform in winter conditions.

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Using a P195/60R15 87S tire size as our example, the 87S at the end of the size represents the tire's service description. A service description identifies the tire's load index and speed rating. Service descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since 1991.

The first two digits (87S) represent the tire's load index and are followed by a single letter (87S) identifying the tire's speed rating.

Load Index

P195/60R15 87S - The load index (87) is the tire size's assigned numerical value used to compare relative load carrying capabilities. In the case of our example, the 87 identifies the tire's ability to carry approximately 1,201 pounds.

The higher the tire's load index number, the greater its load carrying capacity.

89 = 1,279 pounds
88 = 1,235 pounds
87 = 1,201 pounds
86 = 1,168 pounds
85 = 1,135 pounds

A tire with a higher load index than that of the Original Equipment tire indicates an increase in load capacity. A tire with a load index equal to that of the Original Equipment tire indicates an equivalent load capacity. A tire with a lower load index than the Original Equipment tire indicates the tire does not equal the load capacity of the original.

Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to 126.

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Load Index Pounds Kilograms
70 739 335
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

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Load Index Pounds Kilograms
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

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Load Index Pounds Kilograms
108 2205 1000
109 2271 1030
110 2337 1060
111 2403 1090
112 2469 1120
113 2535 1150
114 2601 1180
115 2679 1215
116 2756 1250
117 2833 1285
118 2910 1320
119 2998 1360
120 3086 1400
121 3197 1450
122 3307 1500
123 3417 1550
124 3527 1600
125 3638 1650
126 3748 1700

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When looking at light truck (LT) or newer Special Trailer Service (ST) tires, there are two load indexes branded on the sidewall, separated by a forward slash. Using an LT235/75R15 104/101S Load Range C tire as an example, the load index is 104/101. 104 corresponds to 1,984 pounds, and 101 corresponds to 1,819 pounds. So what is the true load carrying capacity of the tire? The answer changes depending on the situation in which the tire is being used.

Since LT tires are commonly used on trucks with dual rear wheels, they are branded with two load indexes. The first number indicates the load carrying capacity if the tire is installed on a truck with a single-wheel rear axle, and the second number applies when the tire is used in a dual rear application.

Though it may seem counterintuitive that a tire is rated to carry less weight when working in tandem with another tire in the dual pair, the purpose is to build in additional reserve capacity should one of the two tires fail, leaving the sole remaining tire to carry the load normally handled by two tires.

Speed Rating

In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturers' ability to manufacture tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.

Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.

It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.

Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:

225/50SR16

225/50SR16 89S

or 225/50R16 89S

 

Each of these was an acceptable method of identifying speed ratings.

Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.

225/50SR16 112 mph, 180 km/h
225/50HR16 130, 210 km/h
225/50VR16 in excess of 130 mph, 210 km/h

 

Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below:

L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h Temporary Spare Tires
N 87 mph 140km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars

 

When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of vehicles that have extremely high top-speed capabilities.

W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars

 

While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.

225/50ZR16 in excess of 149 mph, 240 km/h
205/45ZR17 88W 168 mph, 270 km/h
285/35ZR19 99Y 186 mph, 300 km/h

 

When the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:

285/35ZR19 99Y 186 mph, 300 km/h
285/35ZR19 (99Y) in excess of 186 mph, 300 km/h

 

As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tire's capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.

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The tires are the only thing between the vehicle and the road. When they are properly inflated and in good condition, the handling, stability and safety of the vehicle will be maximized. Conversely, when the tires are under inflated, worn out or damaged, all of the safety systems on the vehicle cannot overcome the loss of control that comes with a blow-out or hydroplaning situation. Air pressure in a tire is like oil in an engine; when it is low, the resulting internal damage is unseen until it is too late. Tires naturally lose 1-2 psi per month, so ongoing neglect will eventually result in a tire that cannot support the weight of the vehicle and the occupants. When this happens, the resulting blow-out can result in the loss of control and an accident.

It’s also important to rotate the tires on the vehicle every 5-7,000 miles. Today’s front-wheel-drive vehicles cause the steer tires to wear at a much faster rate than the tires on the rear axle. By periodically rotating the front tires to the back and the back tires to the front, motorists can achieve even treadwear on all four tires and increase the mileage and performance. Failing to rotate the tires often results in the front tires wearing out faster while the rear tires develop irregular treadwear patterns that cause vibrations. The same can be said for alignments. When the vehicle is not properly aligned, the tires will wear out faster which leads to increased operating costs.

Finally, drivers should perform a visual inspection of their tires on a regular basis, especially after hitting a pothole, curb or any type of road debris. Bulges, cuts and other visible damage weaken the internal components of the tire, which can lead to a blow-out. Regular visual inspections will often identify any potential problems before they result in an accident. It’s also a good idea to have the tires inspected by a professional before any long road trips to ensure there are no obvious out-of-service conditions that must be addressed.

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Tire naturally lose 1-2 psi per month, so check tire pressure when filling up gas for safety & improved gas mileage.

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Rotate the tires on your vehicle every 5-7,000 miles. By periodically rotating the front tires to the back and back tires to the front, you can achieve even treadwear on all four tires and increase the mileage and performance.

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Perform a visual inspection of your tires on a regular basis, especially after hitting a pothole, curb or any type of road debris. Bulges, cuts and other visible damage weaken the internal components of the tire, which can lead to a blow-out.

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