A tyre is a complex combination of components made from numerous ingredients.  The materials in a truck tyre can be divided into two categories, structural components such as steel cord and core wire, plus the compounds. These include natural and synthetic rubber, butyl rubber and a multitude of other chemicals such as sulphur, accelerators, activators, inhibitors, and processing aids. 

All tyres contain a combination of natural and synthetic rubber.  Truck tyres have around 30% natural rubber and 5% synthetic.  Natural rubber is very strong.  Not only is it resistant to tearing and abrasion, it also dampens vibrations well and is good at gripping the road surface.  On the other hand, synthetic rubber is good at withstanding extreme temperatures, is resistant to chemical damage, sunlight, ozone and weather, and remains flexible at low temperatures. 

Anti ozone chemicals further slow the aging process of the compound and then, there are fillers.  Carbon black is one of the most important fillers as it acts as a reinforcing agent.  So not only is it why tyres are black, it adds to the rubber’s stiffness, hardness, and resistance to abrasion. Silica meanwhile improves the compounds wet grip, tear and cut resistance and reduces rolling resistance.  

So how do all these things end up being a tyre? Well let's start from the inside and work our way out. The inner liner is made from synthetic butyl rubber and is fundamental to ensuring the truck tyre retains its air pressure.  The radial body ply is made from steel carcass cords.  They run from bead to bead at approximately 90° to the tread centre line and provide structural strength.  Next is the bead core and the bead apex.  The bead is a continuous strand of copper coated high tensile steel wire.  It holds the tyre on the wheel rim and seals the air in and, it's very strong.  The bead apex is made from hard synthetic rubber.  It is fitted to the top of the bead and tapers down towards the mid wall of the tyre, blending the bead into the tyre sidewall.  

Then we come onto the steel belts.  A typical truck tyre has between four and five of them.  They provide a rigid base under the thread to allow the full tread width to be in contact with the road at all times, giving additional stability.  This cross section shows how the tyre’s sidewall is made from a blend of rubbers and covers the area from the tread to the beads.  It provides protection from physical, weather and ozone damage.  

Last but not least, is the tread. The rubber compounds are a blend of synthetic and natural rubbers.  The tread could consist of different compounds on the top, known as the cap, and at the bottom known as the base.  The cap compound grips the road surface so must be resistant to abrasion but must also provide good grip in all conditions. The base compound helps give the tyre better rolling resistance.  

So how does it all come together? Well, the chemicals and rubber we met earlier are combined in precise quantities into a compound.  This is finally honed and tested by the Rubber Technologist to have the ultimate desired performance, depending on what the tyre is used for.  The materials then go into the mixing machine, which produces a batch of compound.  Using what's called a Mill, the compound is processed into strips of uncured rubber tyre compound. 

These tyres are in the process of being retreaded, so the carcass or casing, which already features the cords, inner liner, belt and bead that we saw earlier, is already in one piece.  Around 20 kilogrammes of the new compound is, what's known as, extruded onto this existing carcass.  The result is a green tyre.  It's a tyre that has sidewalls and a tread area, but none of the lettering or tread patterns that we associate with the finished product.  These green tyres wouldn't last very long on the road in their current state.  Their durability, lettering and tread pattern all come from the final process, vulcanisation.  

The prepared tyre goes into a press which is like a giant oven.  This sees a chemical reaction take place involving three very important elements, time, temperature and pressure.  

By combining time; about an hour, pressure; roughly 15 bar and temperature; 150 to 200°c you will have a road-ready tyre.  The tyre is then inspected and given its unique serial number.  Only then do we have something that's capable of carrying thousands of tonnes over tens of thousands of miles.