Bike tires are composite
materials with an elastomer as the matrix and various fibers and fabrics
as the reinforcing components. An exploded view of a modern tire is shown
below. This tire is a tubeless design with the inner Butyl rubber air liner
replacing the inner tube. The sidewalls of the tire are reinforced with
a two ply nylon fabric, and a cotton tape is used to separate the tire from the
inside of the rim. Because it is a closed tubular structure, the tire does
not require the wire or kevlar bead that is needed in a tire/tube design.
The tread is stabilized with two layers of reinforcing belt. One of these
may run circumferentially and the other have radial fibers. The contact surface
with the road is an elastomeric tread with a pattern that is designed to
provide water removal on a wet road and a suitable friction coefficient to give
the traction forces required for acceleration, braking, and cornering.
The Z21 tire shown is designed to have the lowest possible rolling friction.