What Do The Numbers On My Tyre Represnt?

Taking a first glance at the sidewall of your tyre, you often asked yourself, “’Do I need a super secret decoder ring to read this?” In addition to the Brand name of the tyre, 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 replacing your tyres. 

Here is a quick breakdown that may unveil to you some of the best kept secrets in the automotive world.

TIRE SIZE

Example: P225/50/R17 98H

P identifies your tyre as a Passenger Tyre. The P stands for PMetric. If your tyre size starts with LT, it identifies the tyre as a Light Truck tyre.

225 identifies the tyre section width, which is the measurement of the tyre 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.)

50 is the two-figure aspect ratio. This percentage compares the tyre's section height with the tyre's section width. For example, this aspect ratio of 50 means that the tyre's section height is 50% of the tyre's section width.

R indicates the construction used within the tyres casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.

17 The last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.

LOAD INDEX AND SPEED RATING

Example: P225/50/R17 98H

The load index and speed rating, or service description, are the numbers that follow the tyre size.

The load index tells you how much weight the tyre can support when properly inflated. Load index range from 75 - 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tyre, the load limit is listed in pounds. European tyres have the load limit listed in kilograms and sometimes pounds.

H 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, S is equivalent to a maximum speed of 112 mph. Even though a tyre can perform at this speed, though we does not advocate exceeding legal speed limits.

Rating	Maximum Speed
Q	100 MPH
S	112 MPH
T	118 MPH
U	124 MPH
H	130 MPH
V	149 MPH
W	168 MPH
Y	186 MPH
Z	Over 149 MPH

 

DOT Serial Number

The "DOT" symbol certifies the tyre manufacturer's compliance with the U.S. Department of Transportation (DOT) tyre safety standards. Tyres made in the United States have the DOT serial number located on the inside sidewall near the rim.

Below is a description of the serial number. Starting with the year 2000, four numbers are used for the Date of Manufacture, first two numbers identify the week and the last two numbers identify the year of manufacture.

Prior to year 2000 three numbers are used for the date of manufacture, first two numbers identify the week and the last number identifies the year of manufacture. To identify tyres manufactured in the 90s, a decade symbol (a triangle on its side) is located at the end of the DOT serial number.