HOW ARE TYRES MADE?
In order to understand what makes a tyre do what it does, let’s go back to basics and look at how one is actually put together. Almost all radial road tyres are constructed in more or less the same way, with the only major differences being the exact compounds of rubbers used and the final tread pattern design.
The process of building a tyre starts with the steel beads. These are then encapsulated in rubber and form the tyre bead as we know it, and provides the starting point for the rest of the tyre to be built upon. The next step is the tyre liner, which is a non-porous nylonreinforced rubber used to form the basic shape of the tyre. This creates an airtight seal between the steel beads so the tyres can be inflated – hence needing to be made from a non-porous material to prevent moisture in the air escaping and deflating the tyre.
On top of the liner the tyre body plies are added. These are made from nylon-reinforced rubber and help give the tyre its shape. The number of body plies depends on the application of the tyre, but a typical road tyre will feature two or three of these nylon plies.
Next come the steel belts. These are steel reinforced sheets of rubber that are added to give the tyre strength and durability. The number and type of steel belts used will help determine the finished tyre’s load and speed ratings. Again the number of steel belts used depends on the application, but typically you will find two or three layers in most road tyres.
The blend of plies and steel belts is then capped of with a final layer of nylon-reinforced rubber, before the tread cap is applied. The tread cap is the final, thicker layer of rubber that eventually forms the tread pattern of finished the tyre. The compounds of the rubbers used in the tread cap will alter depending on the intended purpose (ultimate grip race tyre or long-lasting road tyre, for example) and manufacturer’s specifications.
At this stage the tyre is still ‘green’, and the layers of soft, sticky, pliable rubber need to be cured before they can be used on the road. The curing process involves applying both heat and pressure to the tyres in a specific tyre curing press. This causes all the layers to bind together to create what is effectively a rubber laminate, and cures and hardens the rubber to give the desired characteristics. The curing press also indents the tread pattern design into the outer tread cap layer, as well as all the required sidewall markings and tyre information.
There’s a lot more to a tyre than just the outer tread cap layer