wheel-bearing construction for both rear-wheel and
Most modern passenger vehicles and light trucks
use tubeless tires that do NOT have a separate inner
tube. The tire and wheel form an airtight unit. Many
commercial and construction vehicles use inner tubes
which are a soft. thin. leakproof rubber liner that fit
inside the tire and wheel assemblies. However. in the
last few years tubeless tires have been introduced to
commercial and construction vehicles. reducing the
need for tube type tires. Tires perform the following
two basic functions:
They must act as a soft CUSHION between the
road and the metal wheel.
They must provide adequate TRACTION
(friction) with the road surface.
Tires must transmit driving. braking. and
cornering forces to the road in all types of weather. At
the same time, they should resist puncture and wear.
Although there are several tire designs. the six major
parts of a tire are as follows:
TIRE BEADS (two steel rings encased in rubber
that holds the tire sidewalls against the wheel
BODY PLIES (rubberized fabric and cords
wrapped around beads. forming the carcass or
body of the tire).
TREAD (outer surface of the tire that contacts
the road surface).
SIDEWALL (outer surface of the tire extending
bead to tread; it contains tire information).
BELTS (used to stiffen the tread and strengthen
the plies; they lie between the tread and the inner
LINER (a thin layer of rubber bonded to the
inside of the plies: it provides a leakproof
membrane for tubeless tires).
There are many construction and design variations
in tires. A different number of plies may be used and
ran at different angles. Also, many different materials
may be used. The three types of tires, found on late
model vehicles, are bias-ply, belted bias. and radial.
A bias-ply tire is one of the oldest designs, and it
does NOT use belts. The position of the cords in a
bias-ply tire allows the body of the tire to flex easily.
This design improves the cushioning action, which
provides a smooth ride on rough roads.
A bias-ply tire (fig. 8-29) has the plies running at
an angle from bead to bead. The cord angle is also
reversed from ply to ply, forming a crisscross pattern.
The tread is bonded directly to the top ply.
A major disadvantage of a bias-ply tire is that the
weakness of the plies and tread reduce traction at high
speeds and increase rolling resistance.
Belted Bias Tire
A belted bias tire provides a smooth ride, good
traction, and offers some reduction in rolling
resistance over a bias-ply tire. The belted bias tire is a
bias-ply tire with stabilizer belts added to increase
tread stiffness. The belts and plies run at different
angles. The belts do NOT run around to the sidewalls
but lie only under the tread area. Two stabilizer belts
and two or more plies are used to increase tire
Radial Ply Tire
The radial ply tire (fig. 8-30) has very flexible
sidewall, but a stiff tread. This design provides for a
very stable footprint (shape and amount of tread
touching the road surface) which improves safety,
cornering, braking, and wear. The radial ply tire has
plies running straight across from bead to bead with
stabilizer belts directly beneath the tread. The belts can
be made of steel, flexten, fiber glass, or other materials.
Figures 8-29.Bias-ply tire construction.