 |
  |
|
Casings - A Primer
Mechanical functions:
A casing is an element that allows the tire to guarantee its
principal task, i.e., to support the load. When the tire is
inflated, the air is injected at a pressure in relation to the
volume of the tire, which makes it possible to support the load
weighing on the tire. The purpose of the casing is to contain air
under pressure and consequently the load.
In addition, it ensures, vertically, the function of the
suspensions. When you're behind a truck, observe how the tires work:
it is the casing that absorbs and filters most of the irregularities
of the roadbed, even when the vehicle goes up onto a sidewalk!
Laterally, the casing resists drifting, resists the centrifugal
force around curves and resists important deformations notable at
low speeds: for proof, just look at tires of a semi-trailer on the
highway or while it maneuvers around a city square.
Finally, it's the casing that transmits the vehicle's torque
stresses to the tread, which is in contact with the ground,
resisting considerable longitudinal stresses to transmit the motive
torque and the braking torque, which tend to separate the cables
that compose it.
A composite material:
In the case of Michelin, about 30 different materials such as steel
and different qualities of rubber have to be made to co-exist. Steel
is also found in the bead wires: those two elements that allow the
tire to be locked onto the rim around which the ply of the casing is
fixed. In larger tires the bead wires have a rectangular section
that permits the perfect positioning of the bead into the housing of
the rim. This design has been patented by Michelin to ensure a much
longer life than that of the bead wires with a round section
normally used.
Steel cables composed of 12-27 wires "coated" in rubber form the
different plies making up the casing. The radial ply and the plies
of the crown, arranged with different angles, form an undeformable
triangular structure.
Last, the elastic cables of the protective ply situated underneath
the tread improve the resistance to cuts and perforation.
Different rubber compounds:
On the crown, sidewall or in the bead, the compounds of rubber used
have specific roles and require elasticity, rigidity, grip, and
resistance to high temperatures. Inside the tire, air-proof rubber,
100% butyl, guarantees the best pressure seal.
source credit : retread.org
|
|
|
|
Tire Tread
The tire tread provides the gripping action and traction that prevent
your vehicle from slipping or sliding, especially when the road is wet
or icy. In general, tires are not safe and should be replaced when the
tread is worn down to 1/16 of an inch. Tires have built-in treadwear
indicators that let you know when it is time to replace your tires.
These indicators are raised sections spaced intermittently in the
bottom of the tread grooves. When they appear "even" with the outside
of the tread, it is time to replace your tires.
Another method for checking tread depth is to place a penny in the
tread with Lincoln's head upside down and facing you. If you can see
the top of Lincoln's head, you are ready for new tires.
source credit : nhtsa.dot.gov
|
|
|
