Radial vs. Bias-Ply Tires, (Taken from Peterson 4wheel & off road, Feb 03)

Most tires are built from multiple layers of rubber-coated nylon cord and steel belts tied into the two bead wires that anchor the tire to the wheel’s rim. These layers if reinforced rubber are known as plies. The differences between a radial and bias-ply tire is in how the plies are arranged o form the carcass of the tire.

Radial tires use a two-piece construction where the sidewall plies are separate from the tread plies. The sidewall plies form the foundation of the tire and act like a spring to support the vehicle’s weight. The steel-belted tread plies run perpendicularly over the sidewall plies to resists tire punctures and hold the tread pattern of the tire in position. Because there are two different groups of plies in a radial tire, they can be individually maximized for the best tire performance. The pros of a radial tire are that they will have a more even contact patch with the terrain. Radials will ride smoother, dissipate heat better, and keep the tread flatter on the road when turning corners. Radials should also last longer than bias-ply tires when driven on the street. The downside to radial tires is that they tend to have weaker sidewalls than bias-ply tires, because most tire manufactures design all of the strength into the tread plies and leave the sidewalls thin for a good ride and to dissipate heat.

Bias-ply tires, on the other hand, use a one design to form the tread surface and the sidewall from a single poly. Multiple plies are layered over each other at a 30-degree angle to build strength in the tread and sidewall.  The benefits of this design are that a bias-ply tire’s sidewall plies are usually just as strong as the tread plies. Bias-ply tires are also better at conforming to and squirming over-trail obstacles when aired down, which are great for off road. Unfortunately it’s this same tire squirm that causes bias-ply tires to not feel as stable in highway turns when compared to radials.