Tyre Definition
 A tyre can
be defined as an envelope of rubbers and chemicals,
reinforced with fabric. The tyre is held to a
metal rim by the compressive forces of wire beads.
The primary function of the tyre is to contain
a volume of compressed air which in turn, creates
the pressure sufficient to carry the load of the
vehicle and move it at the desired speed.
The major characteristics of the tyre can be
summarized as follows:
- Load carrying capacity
- Cushioning ability
- Torque transmission
- Steering response
- Road holding ability
Tyre Terminology
The major components of a tyre are described
below:
 TREAD:
The rubber in contact with the road. This puts necessary
pull on the tyre to make the vehicle move.
SIDEWALL: The part of the tyre which keeps
the plies intact. It also provides some cushioning
effect by means of flexing when load is applied
on it.
PLY: The layer made up of steel and rubber
that takes up the load.
INNERLINER: A layer of special rubber compound
put on the inner side of the tubeless tyres to prevent
loss of air.
BEAD BUNDLE: A set of steel wires bundled
together and put with the rubber to make the tyre
sit on the rim properly and seal it.
CHAFER: A layer of hard rubber that resists
erosion of the bead area by the rim flange.
Tyre Dimension:
Tyre companies through out the world follow standard
norms for tyre dimensions, tolerances, load carrying
capacities and inflation pressures for the different
tyre categories and sizes. These are decided and
governed by tyre manufacturer's association. The
basic tyre and rim nomenclature is explained below:
 The
basic tyre and rim nomenclature is explained below:
OUTSIDE DIAMETER (OD): The diameter of
an unloaded tyre, mounted on its recommended rim
and inflated to recommended pressure.
SECTION WIDTH (SD): The width of the inflated
tyre section, excluding any lettering or decoration.
SECTION HEIGHT (SH): The radial distance
between where the bead sits on the rim to the
outer most point at centerline.
STATIC LOADED RADIUS (SLR): The radial
distance between the road surface to the axle
center under nominal tyre load /inflation conditions.
LOADED SECTION WIDTH: The width of the
loaded cross-section.
MINIMUM DUAL SPACING: The minimum recommended
distance between centerline of dual mounted tyres
to avoid the tyres rubbing against each other.
ASPECT RATIO: The ratio of section height
to section width expressed in percentage.
There's a lot of useful information molded into
the sidewall of a tyre. It shows the name of the
tyre, its size, whether it is tubeless or tube
type, the tyre grade, speed rating, the maximum
load, maximum inflation, an important safety warning
and more.
Passenger Tyre Sidewall Information
| 1. BIAS: |
5.90
|
15
|
| INFLATED SECTION WIDTH (INCHES) |
NOMINAL BEAD DIA (INCHES) |
| 2. Radial: |
P
|
215
|
65
|
R
|
15
|
89
|
H
|
|
Passenger Car
|
Section width
|
Aspect Ratio
|
Radial
|
Rim Diameter
|
Load Index
|
Speed Rating
|
"P" means this is a passenger car tyre (as opposed
to a tyre made for a truck or other vehicle).
P- metric is the U.S. version of a metric tyre-sizing
system.
"215" Section Width: The width of the tyre in
millimeters from sidewall to sidewall. This measurement
varies depending on the width of the rim to which
the tyre is fitted: larger on a wider rim, smaller
on a narrow rim. The number on the side of tyre
indicates the width measured with the tyre fitted
to the recommended rim width.
"65" Aspect Ratio: The ratio of height to width;
this tyre's height is 65% of its width.
“R" Construction: How the plies are constructed
in the tyre carcass. "R" means radial. "B" in
place of the "R" means the tyre is belted bias
construction. "D" in place of the "R" means diagonal
bias construction.
15" Rim Diameter: The diameter of the wheel in
inches.
"89" Load Index: This tyre has an industry-standard
maximum load of 580 kilogram. Different numbers
correspond to different maximum loads. The maximum
load is shown in lbs. (pounds) and in kg (kilograms),
and maximum pressure in PSI (pounds per square
inch) and in kPa (kilopascals). Kilograms and
kilopascals are metric units of measurement.
"H" Speed Rating: This tyre has an industry-standard
maximum service speed of 210 km per hour. tyres
using an older European system carry the speed
rating in the size description: 215/65HR15. Different
letters correspond to different maximum service
speeds.
The letters "DOT" certify compliance with all
applicable safety standards established by the
U.S. Department of Transportation (DOT). Adjacent
to this is a tyre identification or serial number;
a combination of numbers and letters with up to
11 digits.
The sidewall also shows the type of cord and
number of plies in the sidewall and under the
tread.
Tyre Grades: Uniform tyre Quality Grading
System or UTQG
Except for snow tyres, the DOT requires tyre
manufacturers to grade passenger car tyres based
on three performance factors: tread wear, traction
and temperature resistance.
Tread Wear
- More Than 100 - Better
- 100 - Baseline
- Less Than 100 - Poorer The tread wear grade
is a comparative rating based on the wear rate
of the tyre when tested under controlled conditions
on a specified government test track. A tyre
graded 200 would wear twice as long on the government
test track as one graded 100. Your actual tyre
mileage depends upon the conditions of their
use and may vary due to driving habits, service
practices, differences in road characteristics
and climate. Note: Tread wear grades are valid
only for comparisons within a manufacturer's
product line. They are not valid for comparisons
between manufacturers.
Traction
- A - Best
- B - Intermediate
- C - Acceptable
Traction grades represent the tyre's ability
to stop on wet pavement as measured under
controlled conditions on specified government
test surfaces of asphalt and concrete. The
Traction grade is based upon "straight ahead"
braking tests; it does not indicate cornering
ability
Temperature
- A - Best.
- B - Intermediate
- C - Acceptable
Load Index and Speed Rating
The speed rating is the maximum service speed
of a passenger car tyre. Truck tyres are not
speed rated. Here is a list of rating indicators
and their mile-per-hour equivalents. This
rating system applies to all tyre makers
| Rating |
Maximum Speed |
| Q |
99 mph |
| S |
112 mph |
| T |
118 mph |
| U |
124 mph |
| H |
130 mph |
| V |
Above 130 mph (without service description) |
| V |
149 mph (with service description) |
| Z |
Above 149 mph |
Light Truck Sidewall Information
"LT" stands for Light Truck
"LT235/85R16" is the size designation for
a metric light truck tyre
"LOAD RANGE D" identifies the load and inflation
limits
"RADIAL" indicates that the tyre has a radial
construction
"MAX. LOAD SINGLE 2623 lbs. AT 65 psi COLD"
indicates the maximum load rating of the tyre
and corresponding minimum cold inflation pressure
when used in a dual configuration. The other
markings on the sidewall have the same meaning
as described for the passenger car tyre.
|
