What’s complex about a tire?

That’s just the trouble. If all you see is the outside, a tire looks pretty simple. In fact, you’d almost think you could make them like angel food cakes.

Unlike angel food cakes, though, tires are literally “built,” from parts.

Besides calendering, the other main way tire components are is by extrusion.

How many parts?

The average truck tire has at least 16 or more components, each of which may be made of several parts. Several different kinds of steel. Lots of different types and compounds of rubber.

And the tire is “built,” not “poured.”

What do you mean by built?

We’re going to take a separate article in this series to cover the tire building process, because right now, we want to focus on the many “parts” that go into a tire.

Think about your arm. There are several layers of skin on the outside, then muscles, fat, sinew and cartilage, together with blood vessels and nerves, all surrounding bones with marrow inside them.

In a tire, you have different rubber compounds surrounding other rubber compounds, surrounding steel wire and steel cable, with maybe a bit of polyester fabric as well.

Where do all these parts come from?

Each has to be made, then brought to the “tire builder.” In fact, when you look at a tire factory, it’s amazing how much space, how many machines and how many people it takes to make the parts that one person will assemble into a tire.

Most of the parts of a tire are made using either calendering (squeezing things between giant steel rollers), or by extrusion (squeezing rubber through dies that impart their shape to the components).Let’s take a look at a tire, and see how some of these parts are made.

Tread “Cap” Grips road, wears slowly for high traction and long tread life
(rubber, extruded together with Tread “Base”)

Tread “Base” Shields casing from tread heat for better retreadability
(rubber, extruded together with Tread “Cap”)

Undertread Additional protection for belts to improve retreadability
(rubber, extruded)

Belts Hold tread flat for superior traction and wear, resist penetration by road hazards
(rubber and steel cables, calendered)

Mini-sidewalls Join tread stock to sidewall stock while protecting tread base from exposure
(rubber, extruded)

Belt edge inserts and fillers Maintain optimum belt shape for long casing life
(rubber, extruded)

Sidewalls Transmit steering, driving and braking forces to tread
(rubber, extruded, plus casing ply)

Innerliner Seals air chamber to resist inflation pressure loss and prevent cord rusting
(multiple layers of rubber, calendered)

Casing ply “Foundation” framework for whole tire
(rubber and steel cables, calendered)

Soft bead filler Helps provide softer ride, smoother handling
(rubber, extruded)

Hard bead filler Stiffens bead area for better durability, retreadability
(rubber, extruded)

Chafer Shields bead against wheel flange and mounting abrasion
(rubber and steel cables, calendered)

Bead bundle Stiffens tire edge to seat and seal against wheel flange to prevent air loss
(steel wire, coated with rubber by extrusion)

That’s a lot of parts!

And we didn’t try to show every last one of them either. All of these have to be assembled. Next time, we’ll see how they get put together by the tire builder – into something that looks a lot like a tire.