Tyre Terminology – What Does It All Mean

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Sometimes tyre 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 tyres.

The outer perimeter of the tyre 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 tyre where it is mounted on the rim of the wheel. The inner edge where the tyre meets a wheel is called the bead.

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 tyre is mounted directly on a wheel and forms an airtight chamber which holds the air that is used to inflate the tyre.

The original tube type tyre 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 tyre. This kind of tyre 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.

While certain uses may make one or the other type of tyre 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.

Tyres can be either bias-ply construction or radial. Radial tyres are the most commonly used today for cars. These tyres have reinforcing threads or cords which are embedded in the rubber compound which run across the width of the tyre 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 tyres 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 tyre results. This can be an advantage where strength in a tyre is more important than handling characteristics. For this reason automobiles tend to use radial tyres as their standard while trucks and trailers show a continued use for the bias-ply construction.