 The parts of a tire |
The Bead Bundle
The
bead is a loop of high-strength steel cable coated with
rubber. It gives the tire the strength it needs to stay seated
on the wheel rim and to handle the forces applied by tire
mounting machines when the tires are installed on rims.
The Body
The
body is made up of several layers of different fabrics,
called plies. The most common ply fabric is
polyester cord. The cords in a radial tire run
perpendicular to the tread. Some older tires used diagonal
bias tires, tires in which the fabric ran at an angle to
the tread. The plies are coated with rubber to help them bond
with the other components and to seal in the air.
A tire's strength is often described by the number of plies it has. Most car tires have two body plies. By comparison, large commercial jetliners often have tires with 30 or more plies.
The Belts
In
steel-belted radial tires, belts made from steel are
used to reinforce the area under the tread. These belts
provide puncture resistance and help the tire stay flat so
that it makes the best contact with the road.
Cap Plies
Some tires
have cap plies, an extra layer or two of polyester
fabric to help hold everything in place. These cap plies are
not found on all tires; they are mostly used on tires with
higher speed ratings to help all the components stay in place
at high speeds.
The Sidewall
The
sidewall provides lateral stability for the tire, protects the
body plies and helps keep the air from escaping. It may
contain additional components to help increase the lateral
stability.
The Tread
The
tread is made from a mixture
of many different kinds of natural and synthetic rubbers. The
tread and the sidewalls are extruded and cut to length. The
tread is just smooth rubber at this point; it does not have
the tread patterns that give the tire traction.
Assembly
All of these
components are assembled in the tire-building machine. This
machine ensures that all of the components are in the correct
location and then forms the tire into a shape and size fairly
close to its finished dimensions.
At this point the tire has all of its pieces, but it's not held together very tightly, and it doesn't have any markings or tread patterns. This is called a green tire. The next step is to run the tire into a curing machine, which functions something like a waffle iron, molding in all of the markings and traction patterns. The heat also bonds all of the tire's components together. This is called vulcanizing. After a few finishing and inspection procedures, the tire is finished.
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