Tire Shop Talk

There are two basic types of tire construction that mud, all terrain and street tires use as their foundation.  They are bias-ply and radial designs.  Each type of tire construction has its own unique set of characteristics that are the key to its performance, whether on road or off road and these characteristics can help to define the purpose of the tire.  The following information will explain what identifies the difference between a bias ply tire and a radial type tire.

The bias ply tire construction utilizes rubber-coated layers known as plies composed of textile cords, usually nylon and sometimes Kevlar.  The plies are layered diagonal from one bead to the other bead at about a 30 degree angle. One ply is set on a bias in one direction as succeeding plies are set alternately in opposing directions as they cross each other and the ends are wrapped around the bead wires, anchoring them to the rim of the wheel.  The layers of plies are them covered with more rubber to form the tread of the tire.  Bias ply tires are sometimes called cross-ply tires.

Performance and Purpose of a Bias Ply

Bias ply tires have a limited purpose in life and are only used for specific purposes or jobs.  The reason for this is because of its performance characteristics.  However for some jobs the bias ply tire is an idea tire for the purpose such as for the tires of a towed trailer, farm equipment tires, some purpose built tires like extreme terrain tires and some forms of racing still use bias ply tires.  The reasons for this limited use are:

The bias-ply tire casing is constructed to form one working unit. When the sidewalls deflect or bend under load, the tread squeezes in and distorts. The distortion affects the tires footprint and can decrease traction and increases wear depending on the terrain.  The tread distortion also causes abrasion from the ground surface, which reduces the life of the tire. These factors are why bias ply tires are not idea for passenger car tires or as tires that my see highway use unless used as tires for a towed trailer.
Bias Ply Strength - The way to increase the strength of bias-ply tires is by increasing the number of plies and bead wires. More plies means more mass which increases heat retention and reduces tire life.
Because of the bias ply inherent construction, sidewall strength is less than that of a radial tire's construction and cornering is significantly less effective.  This is probably one of the main reasons bias ply tires are not used for passenger cars and trucks.
However because of the bias ply construction and inherent strength of a properly inflated tire, the bias ply is ideal for straight line towing.
The radial is a type of tire that is constructed with rubber coated, reinforcing steel cable belts that are assembled parallel and run from side to side, bead to bead at an angle of 90 degrees to the circumferential centerline of the tire.   (As opposed to the 30 degree alternating application lengthwise as in bias ply tires).  This makes the tire more flexible which reduces rolling resistance to improve fuel economy.  Then numerous rubber coated steel belts are constructed into the "crown" of the tire under the tread to form a strong stable two-stage unit.

Performance and purpose of Radial tires

Radial tires are the preferred tire of choice in most applications for several key reasons.  

The combination of steel stabilizing belts in the single-layer radial casing allows the tread and sidewall to act independently. The sidewall flexes more easily under the weight of the vehicle and its cargo, while the tank-track type tread provides even contact with the ground. Greater vertical deflection is achieved with radial tires. This is desirable because extreme flexing greatly increases resistance to punctures.
To increase a radial tire's strength, larger diameter steel cables are used. Larger steel cables can help reduce punctures, tears and flats. Larger steel cables also help distribute heat, resulting in a cooler running tire and improving fuel economy.  Unlike bias ply tires larger steel cables have little negative affect on performance.
The parallel stabilizing steel belts of the radial minimize tread distortion. As the sidewalls flexes under load, the belts hold the tread firmly and evenly on the ground or object and thus minimizing tread scrub and greatly increasing tread life.
When cornering the independent action of the tread and sidewalls keeps the tread flat on the road. This allows the tire to hold to its path.
When offroad, the radial tire's stabilizing steel belt design aids in greater traction by holding the tread evenly over obstacles allowing the tread of the tire to have a better chance of finding traction. 
Sipes are the small slots that are cut or molded into a tire tread surface.  These slots are meant to aid in increasing traction in snow, ice, mud, and wet road surfaces.  The name of the concept of siping a tire comes from a man named John Sipe, who received a patent in the 1920's, after realizing that an array of small transverse cuts in the heels of his shoes gave him better traction. Later Goodyear received a US patent claiming that the "sipes" improved traction characteristics in tires.

Tire tread is a series of block shapes, groove configurations, and sipes, all of which have an affect on the tires traction and noise level.  Typically, wide, straight grooves running in the direction that the tire travels will have a lower noise level and good water removal. More lateral grooves running from side to side will usually increase traction while increasing noise levels. Sipes are the small grooves or slits that are cut across larger tread elements. Up to a point, more sipes give more traction in snow and mud as well as over various terrains found offroad.

All tires are required to have certain information molded into the side of the tire in a location known as the sidewall.  Some of the information is self explanatory while other information requires a little knowledge to decipher.  The following will help you understand what this information means.