Wheels and Tires
Tyres
A tire is a ring-shaped component that surrounds a wheel's rim to transfer a
vehicle's load from the axle through the wheel to the ground and to provide traction
on the surface traveled over. Most tires, such as those for automobiles and
bicycles, are pneumatically inflated structures, which also provide a flexible
cushion that absorbs shock as the tire rolls over rough features on the surface. Tires
provide a footprint that is designed to match the weight of the vehicle with the
bearing strength of the surface that it rolls over by providing a bearing pressure
that will not deform the surface excessively.
Fig. Tyre side wall numbers
Construction
A tire comprises several components: the tread, bead, sidewall, shoulder, and ply.
The tread is the part of the tire that comes in contact with the road surface.
The tire bead is the part of the tire that contacts the rim on the wheel.
The sidewall is that part of the tire, that bridges between the tread and bead.
The shoulder is that part of the tire at the edge of the tread as it makes transition to
the sidewall.
Plies are layers of relatively inextensible cords embedded in the rubber to hold its
shape by preventing the rubber from stretching in response to the internal pressure.
The orientations of the plies play a large role in the performance of the tire and is
one of the main ways that tires are categorized.
Fig. components of a tyre
Types of tyre
Radial tire construction utilizes body ply cords extending from the beads and
across the tread so that the cords are laid at approximately right angles to the
centerline of the tread, and parallel to each other, as well as stabilizer belts directly
beneath the tread. The belts may be cord or steel. The advantages of this
construction include longer tread life, better steering control, fewer blowouts,
improved fuel economy, and lower rolling resistance. Disadvantages of the radial
tire are a harder ride at low speeds on rough roads and in the context of off-
roading, decreased "self-cleaning" ability and lower grip ability at low speeds.
Bias tire construction utilizes body ply cords that extend diagonally from bead to
bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid
at opposing angles forming a crisscross pattern to which the tread is applied. The
design allows the entire tire body to flex easily, providing the main advantage of
this construction, a smooth ride on rough surfaces. This cushioning characteristic
also causes the major disadvantages of a bias tire: increased rolling resistance and
less control and traction at higher speeds.
Wheels
A wheel is a circular block of a hard and durable material at whose center has been
bored a circular hole through which is placed an axle bearing about which the
wheel rotates when a moment is applied by gravity or torque to the wheel about its
axis, thereby making together one of the six simple machines. Construction
Fig. components of wheels
Rim: The rim is the "outer edge of a wheel, holding the tire." It makes up the outer
circular design of the wheel on which the inside edge of the tire is mounted on
vehicles such as automobiles. For example, on a bicycle wheel the rim is a large
hoop attached to the outer ends of the spokes of the wheel that holds the tire and
tube.
Hub: The hub is the center of the wheel, and typically houses a bearing, and is
where the spokes meet.
Spokes: A spoke is one of some number of rods radiating from the center of a
wheel (the hub where the axle connects), connecting the hub with the round
traction surface.
Wire: The rims of wire wheels (or "wire spoked wheels") are connected to their
hubs by wire spokes.
Offset measures the distance from the centerline of the wheel to the mounting
surface. It is measured in millimeters. It can be a zero, positive, or negative offset.
With a 0 (zero) offset, the mounting surface is exactly in the center of the wheel.
With a positive offset, the mounting surface is to the front of the wheel. It is
expressed as the number of millimeters from the centerline. With a negative offset,
the mounting surface is to the back side of the wheel. It is expressed as the number
of millimeters from the centerline.
