How a tyre is constructed
Tyres. They're wonderful things, all black, round and pretty. Many people believe a tyre to be a simple rubber creation which pops out of a mould and onto your wheel but in reality, the modern radial tyre is a complex piece of engineering.
To help you understand just how many layers there are to the modern tyre, below is a cut away of our example tyre, a Goodyear Optigrip
. Currently this is one of the latest tyres to market and uses a unique dual compound construction to improve longevity and performance over the life cycle.
1. The inner tyre.
This is the tyre's version of an inner tube and stops air escaping. Usually constructed from a simple rubber.
2. The casing ply.
These are fine cords, usually made from aramid fibres such as Twaron and Kevlar. These are laid in straight lines and sandwiched in rubber. The cords are key to the tyres construction, providing shape and strength to the tyre.
3. Bracing ply.
The bracing ply is usually constructed of a very fine steel cord in a rubber sandwich. Two or more plies are stuck together across the tread, at opposing angles of around 60 degrees. When the tyre is cooked (cured) the opposing steel cords form triangles which keep the tyre rigid. The formation of this structure is key to the tyres characteristics as they have to be strong enough to resist the forces generated by driving but supple enough to absorb lumps and bumps in the road. To make this work, steel has to be bonded with rubber which is a very difficult process
4. Safety ply.
This cord keeps the tyre in shape at speed and reduces the effect of friction heating.
This is the top layer of the tyre we all know. Not only does the rubber have to be soft enough to generate grip by "keying" into the road and clearing water, but it also needs to ensure it doesn't heat up too much to avoid unnecessary wear. In the example tyre the blue layer is a softer compound rubber, designed to ensure the tyres grip stays constant as the tread wears away.
6. The shoulder / sidewall.
Moving round to the side of the tyres these further help absorb bumps and give the tyre it's turn in characteristics.
7. The bead.
The bead is where the tyre joins the rim.
Hopefully you can now appreciate just how complex the modern tyre is. If you'd like to ask any questions please leave a comment below.