Nick Katsaras, age 14, of Kallispell, Mont. for his question:
WHAT IS A RADIAL TIRE?
Radial tires for automobiles are built with the cord fabric running straight across the tire from one rim to the other. All radial tires are also belted. The combination of radial ply and belting produces a tire that has longer tread life than most tires.
There are three types of automobile tires: bias, belted bias and radial.
Bias tires are built with the cord fabric running diagonally ¬on the "bias" from one rim to the other. Each ply is added so that its cords run at an angle opposite to the angle of the cords below it.
As a vehicle moves, the plies of its tires rub against each other and against the tread in an action called "flexing and squirming." This action produces inner heat, one of the major causes of tire wear. Extreme heat can separate the tread or split the plies.
Belted bias tires are used on most new cars these days. They are made in the same way as bias tires, but a belt of fabric is placed between plies and the tread. The belt is made of fiberglass, rayon, steel or some other material that does not stretch. It helps prevent punctures and also helps to reduce inner heat.
Radial tires, as we have said, are built with the cord fabric running straight across the tire from one rim to the other.
Radial tires give longer wear because they have less flex and squirm than bias ply tires.
But radial tires do not provide as comfortable a ride, and they also cost more than belted bias tires.
A tire is made by hand on a slowly rotating roller called a drum. The drum has the same diameter as the wheel on which the tire will be used. As the drum turns, a workman wraps an inner liner around it. The inner liner is a band of soft rubber that makes the casing airtight.
The tire builder then wraps the rubberized cord fabric around the drum, ply by ply. Most automobiles use two ply or four ply tires.
After putting on the plies, the tire builder adds two beads. Each bead consists of two or more steel wire strands that have been twisted together into a hoop and covered with hard rubber. A bead is put on the outside of the tire at each side.
Next, the builder adds the side walls and the tread. The various parts of the tire are then united by a set of rollers in a process called "stitching."
The uncured tires are now ready to be vulcanized. The vulcanization process makes a rubber product strong, hard and elastic.
The tire is put into a mold that operates much like a giant waffle iron. Heat is applied and an inner air bag is filled with steam. The steam presses the tire against the mold. The air bag and the mold squeeze and press the tire into its final shape, complete with tread.