Question: Why are almost all tires today radial ply tires?
Answer: Because radial ply tires are better than bias
ply tires.
The belts are layers of woven reinforcing fiber inside the
tire under the tread. The belts give the tire strength, keep
the tread from squirming and help resist punctures. The belts
may be fiberglass, steel, nylon, rayon or aramid fiber.
In bias ply tires, which were common before radials were invented,
the innermost plies crisscross like an "X" as they run
from bead to bead (side to side), while the outermost plies run
lengthwise around the circumference of the tire. This makes
a relatively firm tread, but it also increases rolling resistance.
And anything that increases rolling resistance increases fuel
consumption.
The innermost plies in radial tires, by comparison, run sideways
between the beads. This makes the tire more flexible, which reduces
rolling resistance and improves fuel economy. Changing from bias
ply to radial ply tires can improve fuel economy 10 to 15%, so
that's the main reason why most tires today are radials.
The increased flexibility of radial tires also helps improve
traction and cornering. Because the tire is more flexible, it
is better able to maintain tread contact when cornering. This
also allows lower aspect ratio tires (shorter sidewalls) which
provide better handling performance.
