Tyre Categories

Tyres have two categories RADIAL and BIAS (or CROSS PLY). The radial tyres are a newer introduction while bias is old technology. The difference between the two lies in their construction.

In Radial tyres between the carcass and the tread are a number of belts, usually of steel which are perpendicular to the centre line. The belts provide stability at high speeds. In some good brands the belts are covered by full cap ply that provides additional stability, protection and longer life. All radial passenger car or light truck tyres, manufactured by General Tyre have the cap ply as standard.

In bias tyres the carcass is just covered by a tread. There are no belts in between. Furthermore, the sidewalls of a radial tyre are flexible unlike bias tyres while the radial tyre tread is rigid unlike bias tyres.

Tyre Size Markings.

A typical Toyota Corolla or Honda Civic tyre will have the following size markings

195/65R15 91 H

195 is the nominal section width in mm. (shoulder to shoulder width)
65 is the nominal aspect ratio ie the ratio between the width of the tread and the height of the sidewall
R stands for radial
15 is the rim size
91 is the load index
H is the speed symbol ie good for speeds up to 210 kms

185/60R15 84 H

185 is the nominal section width in mm.(shoulder to shoulder width)
60 is the nominal aspect ratio
R stands for Radial
15 is the rim size
84 is the load index
H is the speed

SPEED RATINGS (Symbol.Ratings.)

S 180 kph
T 190 kph
U 200 kph
H 210 kph
V 240 kph
ZR Above 240 kph

Point to note. Lower the aspect ratio the harder will be the tyre. It is preferable to stick to original size as specified by the vehicle manufacturers.