Tire Construction

Bias Ply vs. Radial Ply Construction

BIAS PLY CONSTRUCTION

The body or casing of a tire is constructed in layers called plies. These plies are laid one on top of the other at an angle to each other; or bias, generally 45 degrees.
They are always laid on in pairs of plies. Most original passenger car plies were laid on in two pairs, or 4 plies.

Bias Ply construction strengthens the casing in the sidewall for increased load carrying capacity. Bias Ply construction stabilizes the tread area for contact patch, (footprint) stability.

Negative qualities: Bias ply construction tends to build up excessive heat and can accelerate wear. It can be very stiff and hard riding. Bias ply tires tend to flat spot after sitting in one spot and cooling down. This can cause a thumping sensation after taking off until the tire can warm up again and resume its original shape.

Example of Bias Ply Construction

Radial Ply Construction

The casing of a radial tire is constructed in layers or plies, also. But, not to the degree of angle of bias ply tires. The degree of angle is no more than 1 or 2 degrees in a radial tires versus the 45 degree angle of bias ply tires. So, the casing plies are laid out radially to the center of the tire. Unlike most bias ply passenger tires that are made up of 4 plies or more, most radial ply passenger tires are of 2 ply construction only in the casing.

Example of Radial Ply Construction

General

Sidewall

Construction

Sizing

D.O.T.

Summary