The Key Parameters of the Tire Code

The Key Parameters of the Tire Code as Basis for Choosing AutoSock

We have all been in the situation of not knowing which tires are mounted on the car. In a certain situation, one knows even less about the dimensions of the according tire. A look at the tire’s sidewall is the only reliable solution. But what does that have to do with AutoSock?

In order to determine the correct AutoSock size for a certain vehicle, the tire dimensions must be known. With the help of three key parameters, the right AutoSock model can be found through our online size finder. The tire code elements of tire width, tire profile and wheel diameter are decisive for choosing the correct AutoSock size. Here our brief explanation:

In our example, we start with a 3-digit number that indicates the width of a tire in millimetres. It is measured at the widest point of the tire’s sidewall (technically named as "nominal section width"). But expect the width of the tire in contact with the road to be smaller than this value.

After the width of tire, the next sign is a forward-slash to separate the characters from each other. The following parameter is a 2- or 3-digit number representing the profile of tire. This number is the aspect ratio of the sidewall height to the tire's width, expressed as percentage.

Following the second character, you might see an optional letter indicating the type of tire construction. Radial (R) is now the most common and the standard design for car tires today, with over a 98% market share. Here is a summary of radial and some other constructions you may see:

R: radial - cords that make up the structure of the tire are at right angles to the travel direction.

ZR: The R stands for radial (see above). The Z in ZR corresponds to an old label used by manufacturers to indicate that the speed index is higher than V. It means a ZR tire is designed for speeds of 150 mph / 240 km/h or higher.

D: diagonal (or cross-ply) - cords are at an angle diagonal to the travel direction.

B: bias belt - same as diagonal, but with an extra layer of reinforcing belts under the tread.

No letter: a diagonal tire construction is assumed.

The wheel diameter is indicated by the final 1- or 2- digit number, measured in inches. You might also see the wheel (or rim) diameter given to an accuracy of half an inch. In some rare cases, the number is three digits long. In that case, it represents the wheel diameter in millimetres.

Key Paramaters of the Tire Code: with, profile ratio, radial and wheel diameter

If the tire’s sidewall shows 175 / 65 R15 (without the letter regarding intended use in the beginning), this means:

1) 175 (section width in mm): It’s the total width of the tire in millimetres.
2) 65 (aspect profile ratio in percentage) – It’s the aspect profile ratio of section height to the section width.
3) R (radial construction) – Denotes that the layers run radially across the tire.
4) 15 (rim diameter in inches) – The measurement of rim.

Tire measurements and distances of key parameters of the tire code explained

Enter the values for the tire's width, profile (aspect ratio), and wheel size diameter obtained from either the tire code or from measuring into the first three fields of the AutoSock size finder. Only with this dimension accuracy, we can guarantee the highest product functionality of AutoSock for your vehicle. Behind our online size finder is a continuously updated database with thousands of tire dimension combinations. We cover more than 98 percent of all tires in the market.


You want to know more about AutoSock? Read also our news blog articles about the principal function of AutoSock from a more scientific point of view and the AutoSock components and their functions

You have more questions about AutoSock? Please check out our frequently updated FAQ's.


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