How to read the tire sizes

How to read the tire sizes In all the tires there is a series of numbers and letters that show the features. It is important that these characteristics correspond to those indicated in the vehicle registration document. The tires that can be fitted are those that comply with the features provided in the registration book or with better features.

An exceptional case is for winter tires, but this topic is addressed in a special article.

What can be read on the tire is a type designation and How to read the tire sizes :

Brand Model P215 / 60R16 95H M + S

Brand and model of the tire do not require explanations, while the rest of the code can be divided as follows:

ABBB / CCDEE FFG where:

  • A = Type of tire
  • BBB = Width of the tire
  • CC = Ratio of shoulder height
  • D = Structure
  • EE = Diameter of the rim
  • FF = Allowable load
  • G = Maximum speed

Tire type

This inscription is not mandatory in Europe, so it is not normally seen in tires sold in Italy. However, some of the abbreviations that may exist are:

P = for passenger transport

LT = for Light Truck tyres

ST = for special trailers

T = temporary as for spare tires

Tire width

This number is typically expressed in millimeters and represents the maximum width of the tire with air pressure and load defined by the standards.

If a value like 205 is written, it means that the tire has a maximum width of 205 mm.

Shoulder height ratio

The second number that appears serves to determine the height of the shoulder. This number is meant as a percentage of the tire width.

For example for a tire with values 205/60 it means that the tire is 205 mm wide while the shoulder height will be 205 * 60/100 = 123 mm.

Structure

This letter is typically an R that indicates a radial structure. This is because this structure has given excellent results coming to monopolize car tires.

For some dated tires or for vehicles other than cars, such as trucks, you may find a B that indicates the cross-ply structure.

Circle diameter

This number indicates the diameter of the rim. By custom, it remained in inches. To convert it to mm, simply multiply it by 25.4.

For example, a 17 ″ rim is assembled, converting in millimeters to obtain the diameter of the rim equal to 17 * 25.4 = 431.8 mm

Allowable load

This number is an index used to determine the maximum load for each individual wheel. In your vehicle, it is necessary to mount a tire that has an index equal to or greater than that indicated in the booklet. If, for example, a value of 92 is indicated (equal to 630 kg) a tire with an index equal to 95 (equal to 690 kg) can also be mounted.

Full speed

This symbol indicates the maximum speed of the tire. Also here it is possible to mount also a tire that exceeds the level foreseen by the registration book. Some of the most used codes are:

  • M = Maximum speed 130 km / h
  • N = Maximum speed 140 km / h
  • P = Maximum speed 150 km / h
  • Q = Maximum speed 160 km / h
  • R = Maximum speed 170 km / h
  • S = Maximum speed 180 km / h
  • T = Maximum speed 190 km / h
  • U = Maximum speed 200 km / h
  • H = Maximum speed 210 km / h
  • V = Maximum speed 240 km / h
  • W = Maximum speed 270 km / h
  • Y = Maximum speed 300 km / h
  • VR = Speed over 210 km / h (maximum is not specified)
  • ZR = Speed over 240 km / h (maximum is not specified)
  • ZR + W = Speed over 240 km / h but less than 270 km / h
  • ZR + Y = Speed over 240 km / h but less than 300 km / h

Example

215/45 R17 87W

This tire is:

215 mm wide

  • the shoulder is 45%, so it is about 97 mm high
  • the structure is radial
  • the rim is 17 inches
  • the allowable load is 87, equal to 545 kg
  • the maximum speed is 270 km / h

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