Anatomy Class: what a car tyre's made of and how they’re produced

Your car tyres are all that keep you on the road and in dealing with heat, cold, wet and dry conditions and various surfaces, they have a hard life. Knowing what tyres are made of and how they’re built will help you understand how they cope.

Car tyres are built round an inner liner of halobutyl rubber sheet with additives that help keep air inside the tyre. The next part out is the body ply, which consists of three layers, one of rubber, one of reinforcing fabric and a second layer of rubber. Rayon, nylon, polyester or Kevlar have replaced cotton as the reinforcing fabric and it is the tyre’s one or two body plies that give it structural strength while making it flexible.

Externally, the car tyre’s sidewalls make it resistant to abrasion and chemical attack. Sidewall material includes antioxidants and antiozonants to help maintain strength and flexibility. This goes on in and behind the sidewalls on which you can see the tyre maker’s name and the various code digits that the confirm tyre’s size and rating.

The tyre beads lie at the edges of the sidewalls. They are bands of high tensile steel wire, coated with an alloy of copper or brass to prevent corrosion. The beads, inside their rubber casings, are strong points in tyres. They are what holds it firmly to the wheel and help seal in the air. The apex is the section that joins the bead and sidewall. Triangular in section, it is the cushion between the two.

Now for the belt package, the part that lies beneath the tread. This consists of a two rubber layers sandwiching a layer of steel cords. Here’s where ‘radial’ tyres gets their name; the cords run radially in the package. This steelwork gives the tyre the strength to resist dents from road impacts.

Like the sidewalls, the tread is a visible part of a car tyre. The tread compound is as important as the tread pattern. Tyres made of hard compounds wear well, while softer ones grip the road better. ‘Compromise’ is the watchword.

How are car tyres built? This process starts by wrapping the inner liner, body plies, sidewalls and beads around a special drum. The belt package and tread are then added. During this process, the components are ‘spliced’ together, before the ‘green’ (uncured) tyre is blown up and shaped. These tasks are generally automated.

Now comes the curing process. Though spliced, the various parts of the tyre have yet to be bonded together. This involves applying heat in a mould, to speed the chemical reactions between the different materials. During this stage, a rubber bladder, the equivalent of an inner tube, is used to force the tyre into the mould. Unlike an inner tube, the bladder is filled with steam, hot water or an inert gas. Tyre curing is done at very high pressure – about 350 psi – and at around 350 degrees farenheit. A passenger car tyre can be cured in around 15 minutes. Finally, the tyre is run on a mock road surface, to test for imbalance and local inflexibility. All tyres are visually inspected, some are even X-rayed.

So as this shows, there is more to a car tyre than meets the eye. It’s no wonder car tyres are tough enough for the tough job they have.

Merityre are a leading UK independent supplier of car tyres. Why not visit their website at www.merityre.co.uk and see where you can buy your next set of tyres.