As illustrated below, a tire is made up
of several different components.
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.
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
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.