Tyre (or tire) is a circular and ring like part of a vehicle which comes in contact with ground. Tyres are fitted on rims and are filled with compressed air. Since their invention, natural rubber is the most widely used material in manufacturing of tyres. However, modern tyres also employ materials like synthetic rubber, fabric, steel wires, carbon black and some more compounds. Tyres find place in wide range of locomotives, from bicycles to aeroplanes.
In general, there are two major classes of tyres, according to the presence or absence of tubes in them. Thus, they are called 'tubed tyres' and 'tubeless tyres' respectively. Furthermore, based on the construction or skeleton of tyres known as carcass, tyres are classified into the following main types:
1. Cross ply or bias ply: In these tyres, ply cords are at an angle of 30°-40° to the tire axis.
2. Radial ply: In these tyres, ply cords run in the radial direction.
3. Belted-bias ply: This is a combination of the above mentioned types.
However, majority of the tyres used nowadays belong to the class of radial tubeless tyres.
1. To maintain contact between vehicle and ground by providing desired traction.
2. To support the load of vehicle.
3. Dealing with various forces acting on vehicle during its motion.
4. Providing cushion against shocks and damping them.
There is a specific method of denoting size of tyres. Manufacturers often call it the 'tyre-nomenclature' or 'tyre-code' and mark it on the side wall of tyre. Every term of this specification has some meaning associated with it. Selecting a proper tyre for a vehicle would be impossible unless one understands these terms perfectly. A typical tyre nomenclature of a passenger car tyre is as below:
175/65 R 14
In the above mentioned specification,
175: Nominal section width in mm
65: Aspect ratio. This means section height of tire is that many percent of its section width i.e. 65 % of 175 =114 mm(Approx.)
R: Denotes the construction of tire which is Radial in this case
14: Rim code or rim diameter in inches