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Tire terminology, or "What the heck are they talking about"?

Sometimes tire people use terms which seem like they're talking their own language.  Here's a brief guide of some of the terms you'll most likely need if you're discussing tires ...

Want to know about tire terminology?

tire partsThe outer perimeter of the tire which many people think of as the tread is technically called the crown. The tread is actually the grooves or depressions which are visible on the crown. Sometimes this is also referred to as the "design" of the tire.

The tread has several functions to perform, mostly related to providing traction and handling characteristics for different kinds of tire applications such as racing, winter driving conditions, mud and off-road use, rainy or wet road driving, etc.

Sidewall  refers to the area of the tire which is between the crown and the inner edges of the tire where it is mounted on the rim of the wheel. The inner edge where the tire meets a wheel is called the bead. The bead is reinforced with concentric steel wires embedded in the rubber to provide strength and prevent damage when the tires are being installed (mounted) or removed (dismounted) from a wheel.

There are two basic types of air-filled tires: tube type and tubeless. The tubeless variety is most commonly used today on passenger cars. In this variety the tire is mounted directly on a wheel and forms an airtight chamber which holds the air that is used to inflate the tire.

The original tube type tire has a sealed rubber tube with a valve which controls the entry and exit of air. This tube is placed within the hollow opening of the tire. This kind of tire is still widely used on wheels with spokes such as bicycles and motorcycles since it is difficult to make the wheel impermeable to air and even a small distortion of the wheel might break the seal allowing air to escape.

Tubeless tires have an inner coating which tends to be self healing if a minor puncture occurs, whereas inner tubes used in tube type tires, if they suffer even a pin prick, will begin to lose pressure.

While certain uses may make one or the other type of tire more suitable, for passenger car use the tubeless variety has become almost universal because it is simpler and more reliable under they kinds of conditions which they are generally used. In certain cases, where a vehicle is going to be used in a way which is not "normal" it might be advisable to consider the alternative.

Tires can be either bias-ply construction or radial. Radial tires are the most commonly used today for cars. These tires have reinforcing threads or cords which are embedded in the rubber compound which run across the width of the tire from bead to bead and provide a degree of flexibility in the lateral movement of the tire which improves its handling characteristics.

Bias or cross-ply tires have their reinforcing cords which run from one side to the other at an angle. Because the angles cross between the different layers of cord, a stronger, less flexible tire results. This can be an advantage where strength in a tire is more important than handling characteristics. For this reason automobiles tend to use radial tires as their standard while trucks and trailers show a continued use for the bias-ply construction.

Double-click the tire construction images to enlarge them
and click once to make them thumbnail size again.

radial tire from tire information world
bias ply or cross ply tire from tire information world
Bias Ply

It is extremely important to note that these two types of tires have different handling characteristics and it could be dangerous to mix radial and bias-ply tires on the same vehicle, especially on the same axle (front or rear).

Most of the characteristics of tires which we've discussed here are marked on the sidewall of the tire which we describe at tire markings.


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