Radial tires differ from traditional diagonal bias-ply tires in their construction, which minimizes tread wear and improves flexibility of the sidewall for better handling.
While tires may look simple they are actually made up of a series of layers of different materials. If we peeled back the tread in bias-ply tire one would see a nylon weave (these are the plies) beneath, running in a diagonal pattern meeting in the centerline of the face of the tire. The weave runs at an angle down the sidewalls to the bead – the part of the tire that fits on the wheel’s rim. Nylon ply is stronger than polyester but compresses and sets when under load especially when left for periods of time, resulting in “flat areas” on the tire. Due to the direction the ply runs on these tires, the sidewalls don’t bulge even if the tire is low. This design allows tread to wrap down over the sidewall because there is no transition point from the circumferential face to the sidewall.
A radial tire is constructed differently. Rather than diagonal nylon plies that meet in the centerline it’s made with polyester cords that run perpendicular from bead to bead, up over the face of the tire and down each sidewall. In other words it’s “wrapped” at a right-angle to the direction of the tread. On the face of the tire over this polyester wrap, is a belt that runs below the tread. The belt is nearly the width of the tire and runs the circumference. This gives the tire a “squared” look. Though belts used to be made of rubber-coated fibers nearly all belts today are made from steel fibers. Hence the steel-belted radial. This belt helps stabilize the tread, reducing wear. Because of the construction of a radial tire, the sidewall will always have a bulge at the point of contact. Because of this bulge, when radial tires were still fairly new to the market many people assumed they were under inflated.
The average steel-belted radial gets about 100,000 miles (161,000 km) of wear, while the bias-ply tires are generally rated at about 30,000 miles (48,280 km).
By reading the model number on the sidewall of any tire, you can quickly see what type of tire you have, though most radial tires include the word “radial” in the model name. To decode a common tire such as the P205/65R15:
* P - Stands for passenger. (LT would mean Light Truck.)
* 205 - Indicates width in millimeters.
* 65 - Refers to the aspect ratio, or how tall the tire is compared to how wide it is. In this example the tire height is 65% of its width.
* R - Radial. (“D” here would indicate diagonal bias ply)
* 15 - The diameter of the tire in inches.
The tire might also have other designations like XL or RF which indicates Extra Load or Reinforced respectively. It might also have tread type or other codes included
Good write-up man, this is the first time I noticed it. I work at a tire plant and it's pretty cool to watch all those layers go together. I'm pressed for time now but I'll try to think if there's anything helpful I might be able to add.
tire construction
