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What Do You Know About Your Tyres? PDF Print E-mail


On the sidewall of a your tyre you will find various codes and markings.

The list below aims to simplify the coding system and allow you to understand the information imprinted on the sidewall.


Tyre Sizes

Tyre sizes are made up of a number of different numbers and letters. For example tyre size 175/70 R 13 82 T is made up of the following information:


175,   This is the tyre section width in millimetres

70 ,    This is the aspect ratio in % (the height of the sidewall divided by the tyre's width)

R ,      This denotes the tyre's construction type - in this case it's a radial

13 ,     This is the rim diameter in inches

82       This is the load index

T         This is the speed rating


Tyre Age

Tyres carry a three digit age code on the sidewall indicating the month and year of manufacture. For example 129 means the tyre was manufactured in December 1999


Other Markings

M&S - Identifies Mud and Snow tyres.


DOT Codes

Coding satisfying the requirements of the US Department of Transportation contain a mixture of letters and numbers such as DOT DVDE MTA 129



Tyres for sale in the European Community must carry an E -Mark in accordance with ECE Reg 30 - e.g. E4 027550


How a Tyre is Made

Tyre manufacturing is a complex technical process, which, for the sake of simplicity can be broken down into eight manufacturing stages:


1) Mixing

Various grades of natural and synthetic rubber are blended in an internal mixer (commonly known as a Banbury) and mixed with carbon black and other chemical products. This blend is called the "masterbatch" and its make-up is carefully constructed according to the desired performance parameters of the tyre


2) Calendering

Textile fabric or steel cord is coated with a film of rubber on both sides. Calendered textiles such as rayon, nylon and polyester are used for the casing and the cap plies. Steel cord is used for the belts.


3) Tread and Sidewall Extrusion

The tread and sidewalls are constructed by forming two different and specifically designed compounds into tread profiles by feeding the rubber through an extruder. Extruders produce continuous lengths of tread rubber which are then cooled and cut to specific lengths.


4) Bead Construction

The bead core is constructed by coating plated steel wires, which are wound on a bead former by a given number of turns to provide a specific diameter and strength for a particular tyre


5) Tyre Building

Tyre building is traditionally a two-stage process. Although modern tyre factories now use a certain number of single-stage building machines, two-stage building is still widely used, particularly for the more standard sizes. In the first stage, the inner liner, the body plies and the sidewalls are placed on a building drum. The beads are they positioned, the ply edges are turned around the bead core and the sidewalls are simultaneously moved into position. In the second tyre building stage, the tyre is shaped by inflation with two belts, a cap ply and the tread being added. At the end of this stage the tyre is now known as a "green tyre".


6) Curing

The green tyre is now placed in a mould inside a curing press and cured for a specific length of time at a specific pressure and temperature. The finished tyre is then ejected from the mould.


7) Trimming

Excess rubber is removed from the cured tyre on a trimming machine.


8) Inspection

Before the tyre is allowed to go to the despatch warehouse, it is inspected both visually and electronically for quality and uniformity.




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