At first glance, you look at the sidewall of your tire and think, “’Do I need a super secret decoder ring to read this?” In addition to the model name of the tire there is a series of numbers that at first, you don’t deem important. However, these numbers are extremely helpful, especially when it’s time to replace your tires. Here’s a quick breakdown to help you decipher one of the best kept secrets in the automotive world.
TIRE SIZE
Example: P225/60/R16 94V
P identifies your tire as a Passenger Tire. The P stands for PMetric. If your tire size starts with LT rather than a P then it identifies the tire as a Light Truck tire.
225 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which it is fitted.
(There are 25.4 millimeters per 1 inch.)
60 is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. For example, this aspect ratio of 60 means that the tire's section height is 60% of the tire's section width.
R indicates the construction used within the tires casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.
16 The last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.
If a tire size reads, LT235/75R15 104/101S, the LT indicates that this tire is meant for Light Truck use. These tires are made for light-duty and heavy-duty pickup trucks (typically ½ ton, ¾ ton, or 1-ton load capacity), SUVs and vans. These tires fall into one of three categories:
Numeric– designed to carry heavy cargo loads and/or tow trailers.
Wide Base – designed to carry heavy cargo loads and/or tow trailers on a wheel rim with a diameter of 16.5 inches.
Flotation – wider, oversized tires designed to carry heavy cargo loads and/or tow trailers on loose surfaces such as sand, gravel, or dirt.
Tires beginning with a ST (for example ST175/80R13) indicate a Special Trailer tire and should only be used on car, boat or utility trailers.
LOAD INDEX AND SPEED RATING
Example: P225/60/R16 94V
The load index and speed rating, or service description, are the numbers that follow the tire size. In the example above, the first two digits (94) represent the tire’s load index and the single letter (V) identifies the tire’s speed rating. But what does that mean?
94 - The load index tells you how much weight the tire can support when properly inflated. Load indexes typically range from 70 - 126, with each numeric value corresponding to a certain carrying capacity. The higher toe tire’s load index number, the greater its load carrying capacity. The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tire, the load limit is listed in pounds. European tires have the load limit listed in kilograms and sometimes pounds.
When it comes to Light Truck (LT) or Special Trailer (ST) tires, there are two load indexes branded (example - LT235/75R15 104/101S). In this example, the 104 corresponds to 1,984 pounds (see chart below), and the 101 corresponds to 1,819 pounds. So which number do you use? The answer is, it depends on the how the tire is being used…and it can change.
LT tires are commonly used on trucks with dual rear wheels and are branded with two load indexes. The first number indicates 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.
V - Speed ratings are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, V is equivalent to a maximum speed of 149 mph. Even though a tire can perform at this speed General Tire does not advocate exceeding legal speed limits. It is also important to note that speed ratings only apply to tires that have not been under-inflated, overloaded, damaged, or altered.
Rating Maximum Speed Use
L 75 MPH Off-Road & Light Truck tires
M 81 MPH Temporary Spare tires
N 87 MPH
P 93 MPH
Q 99 MPH Winter tires (w/or w/out studs)
R 106 MPH H.D. Light Truck tires
S 112 MPH Family Sedans & Vans
T 118 MPH Family Sedans & Vans
U 124 MPH
H 130 MPH Sport Sedans & Coupes
V 149 MPH Sports Cars, Sport Sedans & Coupes
Z Over 149 MPH Sports Cars
