Tires, if you have an automobile you have to have tires.  Little thought is given to their construction by the average driver as the tread pattern or the size is more of a concern.  There are two basic types of tire construction, Radial and Bias-Ply tires.  Tires are not just ballons that hold air, as without the built in chords or belts the tire would simply expand in a round fashion being unusable.  By adding constriction to the tire it is shaped, given tread, and given the ability to support weight by it's air pressure. 

Radial Tire - A radial tire has the plies running perpendicular to the bead and to the ground. This gives the chords, which make up the plies, a radiating look giving the tire it's name.  Radial tires generally are made out of softer materials than their Bias-ply cousins.  Normally the plies are made of polyester with steel belts over lapping on the tread section forming a damage resistant tread and very stable tire.  However, the side wall is generally weaker on Radial tires than on Bias tires when it comes to puncture resistance.  Part of this is due to less rubber being needed as the radial cords give the tire it's strength and low bearing ablity.  With a radial design there is better handling, mainly due to the tread being independent from the sidewall so side wall flexing does not alter tread pattern.  This leads to better traction with less heat build up resulting in greater tire wear with better fuel economy.

Bias-Ply Tire - A Bias-Ply tire has criss crossing layers that are generally 32 to 40 degrees from each other from the center line of the tread.  Each layer is only strong going one direction, so the criss crossing pattern gives the tire it's strength in both directions.  Bias tires are generally made from Nylon chords.  Nylon is very strong for load ratings but is also very stiff.  As the tire is loaded by the vehicle the chords are stretched and the entire body supports the weight.  Since there is no other layer to the plies for the tread the tread tends to be round.  If you look at military truck tires from the past they appear to be rounded.  This is due to their bias construction.   This creates a smaller tread pattern for contact to the road hindering handling.  The bias tire also creates more heat as the cords flex and stretch. This heat is retained and degrades the tire over time.  However, the bias design does have a very strong sidewall and can more easily withstand trail hazzards than a radial design.   Due to their weight and less ease in rolling Bias-Ply tires tend to be less fuel effeciant for highway use than Radial tires.