12-4
1. OVERVIEW
A radial tire uses a cord angle of 90 degrees. That is, the cord material runs in a radial or direct
line from one bead to the other across the tread. In addition, a radial tire has a belt overwrap
under the tread surface to provide greater structural stability. The belt overwrap of a radial tire
distortion while the radial structure enables high speed driving.
Tire supports the weight of the vehicle, reduces the impact from the road and at the same time,
transmits the power to propel, brake and steer on the road. It also functions to maintain a
<009d008c008f0090008a0093008c02c5009a004700940096009d008c0094008c0095009b0055004700700095004700960099008b008c00990047009b00960047008a0096009400970093008c009b008c0047009a009c008a008f0047009b0088009a009200
9a0053004700880047009b00900099008c00470094009c009a>t be structured to be a resilient
vessel of air.
There is wear limit mark on the tire, which protrudes as a strip shape located approximately 1.6
mm from the groove bottom. This wear limit mark is not seen from the outside so there is
additional "▲" mark on the shoulder to let the driver find the wear mark easily. To measure the tire
groove depth, measure at any point other than the point which has a wear limit mark.
The tire is worn unevenly according to the driver's driving habit, improper servicing, low tire
inflation pressure, changed tire location, etc.
1) Structure of Tire
Tread
This thick layer of rubber provides the
interface between the tire and the road.
Wear-resistant rubber is used to protect the
carcass and belt against fractures and
impacts and to deliver a long driving life.
Shoulder
Located between the tread and sidewall, the
shoulder rubber is the thickest so that the
design must allow for the easy diffusion of
heat generated within the tire while driving.
Sidewall
The part between the shoulder and bead, the
flexible sidewall protects the carcass and
enhances the ride. A tire’s type, size,
structure, pattern, manufacturing company,
product name and various characters are
indicated here. Bead
The bead attaches the tire to the rim and
wraps the end of the cord fabric. Comprised
of the bead wire, core, flipper and other parts,
the bead is generally designed to be slightly
tight around the rim so that in the case of a
sudden drop in inflation pressure, the tire will
not fall off the rim.
Carcass
As the most important framework of a tire, the
entire inner layer of cord fabric is called the
carcass. The carcass acts to support air
pressure, vertical load and absorb shocks.
Valve
Belt
Bead core
12-8
If weight is not equally distributed around the wheel, unbalance centrifugal force by the wheel
rotation produces vibration. As the centrifugal force is produced proportional to the square of the
rotating speed, the wheel weight should be balanced even at high speed. There are two types of
the tire and wheel balancing: static and dynamic. Abnormal vibration may also occur due to
unbalanced rigidity or size of tires.
1) Static Balance
When the free rotation of the wheel is
allowed, the heavier part is stopped on the
bottom if the wheel weight is unbalanced
and this is called "Static Unbalance". Also,
the state at which tire's stop position is not
same is called "Static Balance" when the
wheel is rotated again. If the part A is
heavier as shown in the figure 1, add the
balance weight of a weight corresponding
to unbalanced weight from B to A to
maintain the static balance. If the static
balance is not maintained, tramping, up
and down vibration of the wheels, occurs.
2) Dynamic Balance
The static unbalance of the wheel
creates the vibration in the vertical
direction, but the dynamic unbalance
creates the vibration in the lateral
direction. As shown in the figure 2 (a), if
two parts, (2) and (3), are heavier when
the wheels are under the static balance
condition, dynamic unbalance is
created, resulting in shimmy, left and
right vibration of the wheels, and the
torque Fxa is applied in the axial
direction. To correct the dynamic
unbalance, add the balance weight of a
same weight for two points of the
circumference of the rim, A and B, as
shown in the figure 2 (b), and apply the
torque in the opposite direction to the
torque Fxa to offset in order to ensure
smooth rotation of the wheel.
Center
A
B
a
a
Fxa
Fxa F
F
A
B
(a)(b)
[Figure 1]
[Figure 2]
3. WHEEL BALANCE
