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 Modern
tires use a combination of materials to contain pressurized air.
The foundation of the tire is the plies (layers of nylon,
polyester, fiberglass or steel) just beneath the tread that
provides flexibility and strength. Regardless of size, cost or
brand, there are only three types of tires-bias, bias-belted,
and radial, now the standard on all passenger vehicles.
Bias tires, the old stand-by, are constructed with cords running
across the tread (from bead-to-bead) at an angle about 35° to
the tread centerline; alternate plies reverse direction.
Crisscrossing adds strength to the tire sidewalls and tread.
When properly inflated, these tires give a relatively soft,
comfortable ride.
Bias-belted tires are similar, but additional belts of
fiberglass or rayon encircle the tire under the tread. The belts
stabilize the tread, holding it flatter against the road with
less squirm (side movement). Belted tires offer a firmer ride,
better traction, improved puncture resistance and longer life
than bias ply tires. Bias tires are now found mainly on antique
vehicles to preserve their original appearance, and in some
commercial applications.
Radial tires now rule the road as they are original equipment
on virtually every passenger car and light truck. Radials are
constructed with steel or fabric carcass plies crossing the
tread at approximately a 90° angle, and two or more belts circle
the tire under the tread. The sidewalls flex while the tread
remains rigid, accounting for the characteristic sidewall bulge
of a radial. The tread runs flatter on the road with a better
grip and the inherently harsher ride is offset by superior
handling and mileage. |
