Cross Section of Your Tyre
- 1 - The inner liner
A layer of airtight synthetic rubber.This is found inside the tyre and is the modern equivalent of the inner tube.
- 2 - The casing ply
This casing is composed of fine textile fibre cords, laid down in straight lines and sandwiched in rubber. These cords are a key element in the structure of a tyre and enable it to resist pressure. In each individual ply of a car tyre, there are about 1400 cords, each one of which can resist a force of 15 kg.
- 3 - The lower bead area
This is where the rubber tyre grips the metal rim and its role is to transmit the power from the engine and braking effort from the rim of the tyre through to the contact patch.
- 4 - The bead wires
The bead wires help to hold the tyre onto the rim. They can each take a load of up to 1800 kg without the risk of breakage and you have eight of them on your car, two per tyre. Thats a massive 14,400Kgs of strength where an average car weighs about 1,500kgs. The bead 'wire' is actually a cable but is made from a single piece of wire woven in a circle with the ends securely joined together for maximum strength.
- 5 - Supple rubber sidewalls
These help to protect the tyre from shocks that could damage the casing, eg minor shocks against pavements, potholes etc. There is hard, protection rubber where the tyre joins the rim.
- 6 - Bracing plies
Reinforced with very fine, very resistant steel cords in a rubber sandwich. These two, (occasionally more), plies are stuck together and cross the tread area at angles of around 60° to each other. When the tyre is cured (baked), their steel cords cross the casing cords to form triangles. This is known as triangulation, and it makes the top of the tyre (its crown) rigid.
The plies encircle the entire crown of the tyre, and perform a very complex role:
- They must be sufficiently rigid around the tyre's circumference that they aren't stretched by the rotation of the tyre so that the tyre doesn't stretch and become larger.
- They must also be rigid across the tyre, to resist the stresses and strains of cornering.
- They must ALSO be flexible enough, to "absorb" deformations caused by bumps and lumps in the road and other obstacles that may be found.
To make this work, steel has to be bonded with rubber which is very difficult to do in they way that we need it to be done, (it is not just 'glued') but Michelin has mastered the art of perfect bonding between these dissimilar materials, and which is absolutely essential to your safety.
- 7 - Safety ply
This cord allows the tyre to maintain a stable shape under the effect of speed and to reduce the effect of friction heating. It is reinforced with (generally) nylon based cords bedded in a layer of rubber and laid around the circumference of the tyre to prevent the effect of speed stretching the tyre. We sometimes refer to this as a 'zero degree belt'.
- 8 - The tread layer
The tread is laid over the bracing plies. It is the patterned part of the tyre that will be in contact with the road. The tread in the contact patch (the part of the tyre that touches the road) must be able to resist very significant stresses. The tread rubber compound must grip on all types of surfaces, resist wear and abrasion, and heat up as little as possible.
All that then remains is to mould in the tread pattern and vulcanize (bake) all these semi-finished products together to form what we know as a whole tyre.