Tyre sizing

The generally accepted system for indicating car tyre dimensions is to quote the approximate cross-sectional width of the tyre, followed by the height to ­width ratio (Aspect ratio), type of construction and rim diameter. In addition both the load index and speed rating maybe inserted adjacent to the tyre size designation, or the speed rating maybe inserted before the type of construction in a Radial tyre, or before the rim diameter in the case of cross ply tyre.Different symbols and terms used to designate a tyre are as follows

PLY RATING:
It is an index of tyre casing strength. It means the equivalent strength of the carcass, in terms of the tyre been manufactured with rayon/cotton plies. It does not represent the number of plies in a tyre.

CODIFICATION
a) BIAS TYRES:
Bias Tyres may be codified as
6.4 D 13 82 S
Nominal cross sectional width (inches)
Bias construction
Rim Diameter
Load index i.e. tyre load carrying Capacity (TLCC) of 475 Kg
Speed rating (180 km/hr)

B. RADIAL TYRES
Radial tyre can be codified as
P 185/70 R 13 84 H
Passenger Tyres
Nominal cross sectional width (mm) Aspect ratio (%)
Radial Construction
Rim Diameter (inch)
Load index i.e. tyre load carrying capacity (TLCC) of 500 Kg.
Speed rating (210 Km/hr)

Note: - Rim Diameter is expressed for both cases in inches. Nominal cross sectional width is expressed in "mm" for passenger tyres and in "inches" for Light Commercial Vehicles (L C V).
Design procedures based on sound mechanical principles have become a necessity to meet the ever-increasing demands of performance placed upon the tyre of today.
In previous years there was a tendency to consider tyre design somewhat as a black art. Tyre development during the early years consisted principally of improving materials, developing methods of component assembly, shaping materials to form a tyre and improving vulcanization techniques. The increasing service demands through the years have led to increase analytical studies of the finely balance system of forces in a tyre for the sake of design improvements. The tyre engineer is in the unique and probably unenviable position of working with materials that are assembled and shaped in a form, quite different from the finished product.
The actual design process requires a combination of engineering skills and procedures as well as the influence of professional judgment based on experience. Engineering decisions fall into three areas, namely application or service demands to be made in the tyre.

Common marking on tyres
· Tyre size designation
· Manufactures name
· Brand name and extensions
· Ply rating /load range
· Single /dual Maximum load and corresponding inflation pressure
· Collaborators name
· Mould number
· Drawing number
· Serial number and date of production
· Tread wear indicator
· Radial
· Carcass ply material
· Tubeless /tube type
· Made in
· Use radial tube only
· Regroovable
· Visual alignment indicator
· Direction of rotation
· Standard marking(ISI,DOT,ECE)
· Number and types of plies
· Safety warning
· Quality grades